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Chris Lattner01d1ee32002-05-21 20:50:24 +00001//===- SimplifyCFG.cpp - Code to perform CFG simplification ---------------===//
Misha Brukmanfd939082005-04-21 23:48:37 +00002//
John Criswellb576c942003-10-20 19:43:21 +00003// The LLVM Compiler Infrastructure
4//
Chris Lattner4ee451d2007-12-29 20:36:04 +00005// This file is distributed under the University of Illinois Open Source
6// License. See LICENSE.TXT for details.
Misha Brukmanfd939082005-04-21 23:48:37 +00007//
John Criswellb576c942003-10-20 19:43:21 +00008//===----------------------------------------------------------------------===//
Chris Lattner01d1ee32002-05-21 20:50:24 +00009//
Chris Lattnerbb190ac2002-10-08 21:36:33 +000010// Peephole optimize the CFG.
Chris Lattner01d1ee32002-05-21 20:50:24 +000011//
12//===----------------------------------------------------------------------===//
13
Chris Lattner218a8222004-06-20 01:13:18 +000014#define DEBUG_TYPE "simplifycfg"
Chris Lattner01d1ee32002-05-21 20:50:24 +000015#include "llvm/Transforms/Utils/Local.h"
Chris Lattner723c66d2004-02-11 03:36:04 +000016#include "llvm/Constants.h"
Nick Lewycky9d523102011-12-26 20:37:40 +000017#include "llvm/DerivedTypes.h"
18#include "llvm/GlobalVariable.h"
Chris Lattner723c66d2004-02-11 03:36:04 +000019#include "llvm/Instructions.h"
Devang Patel383d7ed2009-02-03 22:12:02 +000020#include "llvm/IntrinsicInst.h"
Chris Lattner0d560082004-02-24 05:38:11 +000021#include "llvm/Type.h"
Chris Lattner302ba6f2010-12-14 06:17:25 +000022#include "llvm/Analysis/InstructionSimplify.h"
Benjamin Kramer10fcfb52011-05-14 15:57:25 +000023#include "llvm/Analysis/ValueTracking.h"
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +000024#include "llvm/Target/TargetData.h"
Chris Lattnereaba3a12005-09-19 23:49:37 +000025#include "llvm/Transforms/Utils/BasicBlockUtils.h"
Dan Gohman2c635662009-10-30 22:39:04 +000026#include "llvm/ADT/DenseMap.h"
Chris Lattner93e985f2007-02-13 02:10:56 +000027#include "llvm/ADT/SmallVector.h"
Chris Lattnerc9951232007-04-02 01:44:59 +000028#include "llvm/ADT/SmallPtrSet.h"
Evan Cheng502a4f52008-06-12 21:15:59 +000029#include "llvm/ADT/Statistic.h"
Chris Lattner6d4d21e2010-12-13 02:00:58 +000030#include "llvm/ADT/STLExtras.h"
Chris Lattner302ba6f2010-12-14 06:17:25 +000031#include "llvm/Support/CFG.h"
Evan Chengc3f507f2011-01-29 04:46:23 +000032#include "llvm/Support/CommandLine.h"
Chris Lattnere27db742010-12-17 06:20:15 +000033#include "llvm/Support/ConstantRange.h"
Chris Lattner302ba6f2010-12-14 06:17:25 +000034#include "llvm/Support/Debug.h"
Devang Patel3e410c62011-05-18 18:01:27 +000035#include "llvm/Support/IRBuilder.h"
Devang Pateld3a17882011-05-19 20:52:46 +000036#include "llvm/Support/NoFolder.h"
Chris Lattner302ba6f2010-12-14 06:17:25 +000037#include "llvm/Support/raw_ostream.h"
Chris Lattner01d1ee32002-05-21 20:50:24 +000038#include <algorithm>
Chris Lattnerd52c2612004-02-24 07:23:58 +000039#include <set>
Chris Lattner698f96f2004-10-18 04:07:22 +000040#include <map>
Chris Lattnerf7703df2004-01-09 06:12:26 +000041using namespace llvm;
Brian Gaeked0fde302003-11-11 22:41:34 +000042
Peter Collingbourne57808b32011-04-29 18:47:38 +000043static cl::opt<unsigned>
44PHINodeFoldingThreshold("phi-node-folding-threshold", cl::Hidden, cl::init(1),
45 cl::desc("Control the amount of phi node folding to perform (default = 1)"));
46
Evan Chengc3f507f2011-01-29 04:46:23 +000047static cl::opt<bool>
48DupRet("simplifycfg-dup-ret", cl::Hidden, cl::init(false),
49 cl::desc("Duplicate return instructions into unconditional branches"));
50
Evan Cheng502a4f52008-06-12 21:15:59 +000051STATISTIC(NumSpeculations, "Number of speculative executed instructions");
52
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +000053namespace {
54class SimplifyCFGOpt {
55 const TargetData *const TD;
56
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +000057 Value *isValueEqualityComparison(TerminatorInst *TI);
58 BasicBlock *GetValueEqualityComparisonCases(TerminatorInst *TI,
59 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases);
60 bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
Devang Patel007349d2011-05-18 20:35:38 +000061 BasicBlock *Pred,
62 IRBuilder<> &Builder);
Devang Patelb55d9242011-05-18 20:53:17 +000063 bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
64 IRBuilder<> &Builder);
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +000065
Duncan Sandsad99ef82011-09-05 12:57:57 +000066 bool SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder);
Devang Patel176ec402011-05-18 21:33:11 +000067 bool SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder);
Devang Pateld46ba262011-05-18 20:01:18 +000068 bool SimplifyUnwind(UnwindInst *UI, IRBuilder<> &Builder);
Chris Lattner3d512132010-12-13 06:25:44 +000069 bool SimplifyUnreachable(UnreachableInst *UI);
Devang Patel007349d2011-05-18 20:35:38 +000070 bool SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder);
Chris Lattner3d512132010-12-13 06:25:44 +000071 bool SimplifyIndirectBr(IndirectBrInst *IBI);
Devang Patela23812c2011-05-18 18:28:48 +000072 bool SimplifyUncondBranch(BranchInst *BI, IRBuilder <> &Builder);
Devang Patel007349d2011-05-18 20:35:38 +000073 bool SimplifyCondBranch(BranchInst *BI, IRBuilder <>&Builder);
Chris Lattner3d512132010-12-13 06:25:44 +000074
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +000075public:
76 explicit SimplifyCFGOpt(const TargetData *td) : TD(td) {}
77 bool run(BasicBlock *BB);
78};
79}
80
Chris Lattner2bdcb562005-08-03 00:19:45 +000081/// SafeToMergeTerminators - Return true if it is safe to merge these two
82/// terminator instructions together.
83///
84static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
85 if (SI1 == SI2) return false; // Can't merge with self!
86
87 // It is not safe to merge these two switch instructions if they have a common
88 // successor, and if that successor has a PHI node, and if *that* PHI node has
89 // conflicting incoming values from the two switch blocks.
90 BasicBlock *SI1BB = SI1->getParent();
91 BasicBlock *SI2BB = SI2->getParent();
Chris Lattnerc9951232007-04-02 01:44:59 +000092 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
Chris Lattner2bdcb562005-08-03 00:19:45 +000093
94 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
95 if (SI1Succs.count(*I))
96 for (BasicBlock::iterator BBI = (*I)->begin();
97 isa<PHINode>(BBI); ++BBI) {
98 PHINode *PN = cast<PHINode>(BBI);
99 if (PN->getIncomingValueForBlock(SI1BB) !=
100 PN->getIncomingValueForBlock(SI2BB))
101 return false;
102 }
103
104 return true;
105}
106
107/// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
108/// now be entries in it from the 'NewPred' block. The values that will be
109/// flowing into the PHI nodes will be the same as those coming in from
110/// ExistPred, an existing predecessor of Succ.
111static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
112 BasicBlock *ExistPred) {
Chris Lattner2bdcb562005-08-03 00:19:45 +0000113 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
114
Chris Lattner093a4382008-07-13 22:23:11 +0000115 PHINode *PN;
116 for (BasicBlock::iterator I = Succ->begin();
117 (PN = dyn_cast<PHINode>(I)); ++I)
118 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
Chris Lattner2bdcb562005-08-03 00:19:45 +0000119}
120
Chris Lattner7e663482005-08-03 00:11:16 +0000121
Chris Lattner73c50a62010-12-14 07:00:00 +0000122/// GetIfCondition - Given a basic block (BB) with two predecessors (and at
123/// least one PHI node in it), check to see if the merge at this block is due
Chris Lattner723c66d2004-02-11 03:36:04 +0000124/// to an "if condition". If so, return the boolean condition that determines
125/// which entry into BB will be taken. Also, return by references the block
126/// that will be entered from if the condition is true, and the block that will
127/// be entered if the condition is false.
Misha Brukmanfd939082005-04-21 23:48:37 +0000128///
Chris Lattner995ba1b2010-12-14 07:15:21 +0000129/// This does no checking to see if the true/false blocks have large or unsavory
130/// instructions in them.
Chris Lattner73c50a62010-12-14 07:00:00 +0000131static Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
132 BasicBlock *&IfFalse) {
133 PHINode *SomePHI = cast<PHINode>(BB->begin());
134 assert(SomePHI->getNumIncomingValues() == 2 &&
Chris Lattner723c66d2004-02-11 03:36:04 +0000135 "Function can only handle blocks with 2 predecessors!");
Chris Lattner73c50a62010-12-14 07:00:00 +0000136 BasicBlock *Pred1 = SomePHI->getIncomingBlock(0);
137 BasicBlock *Pred2 = SomePHI->getIncomingBlock(1);
Chris Lattner723c66d2004-02-11 03:36:04 +0000138
139 // We can only handle branches. Other control flow will be lowered to
140 // branches if possible anyway.
Chris Lattner995ba1b2010-12-14 07:15:21 +0000141 BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator());
142 BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator());
143 if (Pred1Br == 0 || Pred2Br == 0)
Chris Lattner723c66d2004-02-11 03:36:04 +0000144 return 0;
Chris Lattner723c66d2004-02-11 03:36:04 +0000145
146 // Eliminate code duplication by ensuring that Pred1Br is conditional if
147 // either are.
148 if (Pred2Br->isConditional()) {
149 // If both branches are conditional, we don't have an "if statement". In
150 // reality, we could transform this case, but since the condition will be
151 // required anyway, we stand no chance of eliminating it, so the xform is
152 // probably not profitable.
153 if (Pred1Br->isConditional())
154 return 0;
155
156 std::swap(Pred1, Pred2);
157 std::swap(Pred1Br, Pred2Br);
158 }
159
160 if (Pred1Br->isConditional()) {
Chris Lattner995ba1b2010-12-14 07:15:21 +0000161 // The only thing we have to watch out for here is to make sure that Pred2
162 // doesn't have incoming edges from other blocks. If it does, the condition
163 // doesn't dominate BB.
164 if (Pred2->getSinglePredecessor() == 0)
165 return 0;
166
Chris Lattner723c66d2004-02-11 03:36:04 +0000167 // If we found a conditional branch predecessor, make sure that it branches
168 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
169 if (Pred1Br->getSuccessor(0) == BB &&
170 Pred1Br->getSuccessor(1) == Pred2) {
171 IfTrue = Pred1;
172 IfFalse = Pred2;
173 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
174 Pred1Br->getSuccessor(1) == BB) {
175 IfTrue = Pred2;
176 IfFalse = Pred1;
177 } else {
178 // We know that one arm of the conditional goes to BB, so the other must
179 // go somewhere unrelated, and this must not be an "if statement".
180 return 0;
181 }
182
Chris Lattner723c66d2004-02-11 03:36:04 +0000183 return Pred1Br->getCondition();
184 }
185
186 // Ok, if we got here, both predecessors end with an unconditional branch to
187 // BB. Don't panic! If both blocks only have a single (identical)
188 // predecessor, and THAT is a conditional branch, then we're all ok!
Chris Lattner995ba1b2010-12-14 07:15:21 +0000189 BasicBlock *CommonPred = Pred1->getSinglePredecessor();
190 if (CommonPred == 0 || CommonPred != Pred2->getSinglePredecessor())
Chris Lattner723c66d2004-02-11 03:36:04 +0000191 return 0;
192
193 // Otherwise, if this is a conditional branch, then we can use it!
Chris Lattner995ba1b2010-12-14 07:15:21 +0000194 BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator());
195 if (BI == 0) return 0;
196
197 assert(BI->isConditional() && "Two successors but not conditional?");
198 if (BI->getSuccessor(0) == Pred1) {
199 IfTrue = Pred1;
200 IfFalse = Pred2;
201 } else {
202 IfTrue = Pred2;
203 IfFalse = Pred1;
Chris Lattner723c66d2004-02-11 03:36:04 +0000204 }
Chris Lattner995ba1b2010-12-14 07:15:21 +0000205 return BI->getCondition();
Chris Lattner723c66d2004-02-11 03:36:04 +0000206}
207
Bill Wendling5049fa62009-01-19 23:43:56 +0000208/// DominatesMergePoint - If we have a merge point of an "if condition" as
209/// accepted above, return true if the specified value dominates the block. We
210/// don't handle the true generality of domination here, just a special case
211/// which works well enough for us.
212///
213/// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
Peter Collingbournef15907f2011-04-29 18:47:31 +0000214/// see if V (which must be an instruction) and its recursive operands
215/// that do not dominate BB have a combined cost lower than CostRemaining and
216/// are non-trapping. If both are true, the instruction is inserted into the
217/// set and true is returned.
218///
219/// The cost for most non-trapping instructions is defined as 1 except for
220/// Select whose cost is 2.
221///
222/// After this function returns, CostRemaining is decreased by the cost of
223/// V plus its non-dominating operands. If that cost is greater than
224/// CostRemaining, false is returned and CostRemaining is undefined.
Chris Lattner9c078662004-10-14 05:13:36 +0000225static bool DominatesMergePoint(Value *V, BasicBlock *BB,
Peter Collingbournef15907f2011-04-29 18:47:31 +0000226 SmallPtrSet<Instruction*, 4> *AggressiveInsts,
227 unsigned &CostRemaining) {
Chris Lattner570751c2004-04-09 22:50:22 +0000228 Instruction *I = dyn_cast<Instruction>(V);
Chris Lattnerb74b1812006-10-20 00:42:07 +0000229 if (!I) {
230 // Non-instructions all dominate instructions, but not all constantexprs
231 // can be executed unconditionally.
232 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
233 if (C->canTrap())
234 return false;
235 return true;
236 }
Chris Lattner570751c2004-04-09 22:50:22 +0000237 BasicBlock *PBB = I->getParent();
Chris Lattner723c66d2004-02-11 03:36:04 +0000238
Chris Lattnerda895d62005-02-27 06:18:25 +0000239 // We don't want to allow weird loops that might have the "if condition" in
Chris Lattner570751c2004-04-09 22:50:22 +0000240 // the bottom of this block.
241 if (PBB == BB) return false;
Chris Lattner723c66d2004-02-11 03:36:04 +0000242
Chris Lattner570751c2004-04-09 22:50:22 +0000243 // If this instruction is defined in a block that contains an unconditional
244 // branch to BB, then it must be in the 'conditional' part of the "if
Chris Lattner44da7ca2010-12-14 07:41:39 +0000245 // statement". If not, it definitely dominates the region.
246 BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator());
247 if (BI == 0 || BI->isConditional() || BI->getSuccessor(0) != BB)
248 return true;
Eli Friedman0b79a772009-07-17 04:28:42 +0000249
Chris Lattner44da7ca2010-12-14 07:41:39 +0000250 // If we aren't allowing aggressive promotion anymore, then don't consider
251 // instructions in the 'if region'.
252 if (AggressiveInsts == 0) return false;
253
Peter Collingbournef15907f2011-04-29 18:47:31 +0000254 // If we have seen this instruction before, don't count it again.
255 if (AggressiveInsts->count(I)) return true;
256
Chris Lattner44da7ca2010-12-14 07:41:39 +0000257 // Okay, it looks like the instruction IS in the "condition". Check to
258 // see if it's a cheap instruction to unconditionally compute, and if it
259 // only uses stuff defined outside of the condition. If so, hoist it out.
Dan Gohmanf0426602011-12-14 23:49:11 +0000260 if (!isSafeToSpeculativelyExecute(I))
Chris Lattner44da7ca2010-12-14 07:41:39 +0000261 return false;
Misha Brukmanfd939082005-04-21 23:48:37 +0000262
Peter Collingbournef15907f2011-04-29 18:47:31 +0000263 unsigned Cost = 0;
264
Chris Lattner44da7ca2010-12-14 07:41:39 +0000265 switch (I->getOpcode()) {
266 default: return false; // Cannot hoist this out safely.
267 case Instruction::Load:
268 // We have to check to make sure there are no instructions before the
269 // load in its basic block, as we are going to hoist the load out to its
270 // predecessor.
271 if (PBB->getFirstNonPHIOrDbg() != I)
272 return false;
Peter Collingbournef15907f2011-04-29 18:47:31 +0000273 Cost = 1;
Chris Lattner44da7ca2010-12-14 07:41:39 +0000274 break;
Benjamin Kramer278be782011-02-25 10:33:33 +0000275 case Instruction::GetElementPtr:
276 // GEPs are cheap if all indices are constant.
277 if (!cast<GetElementPtrInst>(I)->hasAllConstantIndices())
Benjamin Kramer9b61c552011-02-24 22:46:11 +0000278 return false;
Peter Collingbournef15907f2011-04-29 18:47:31 +0000279 Cost = 1;
Benjamin Kramer9b61c552011-02-24 22:46:11 +0000280 break;
Chris Lattner44da7ca2010-12-14 07:41:39 +0000281 case Instruction::Add:
282 case Instruction::Sub:
283 case Instruction::And:
284 case Instruction::Or:
285 case Instruction::Xor:
286 case Instruction::Shl:
287 case Instruction::LShr:
288 case Instruction::AShr:
289 case Instruction::ICmp:
Peter Collingbourne8a701922011-04-29 18:47:25 +0000290 case Instruction::Trunc:
291 case Instruction::ZExt:
292 case Instruction::SExt:
Peter Collingbournef15907f2011-04-29 18:47:31 +0000293 Cost = 1;
Chris Lattner44da7ca2010-12-14 07:41:39 +0000294 break; // These are all cheap and non-trapping instructions.
Peter Collingbournef15907f2011-04-29 18:47:31 +0000295
Nick Lewycky83696872011-12-21 05:52:02 +0000296 case Instruction::Call:
Peter Collingbournef15907f2011-04-29 18:47:31 +0000297 case Instruction::Select:
298 Cost = 2;
299 break;
Chris Lattner44da7ca2010-12-14 07:41:39 +0000300 }
Chris Lattner570751c2004-04-09 22:50:22 +0000301
Peter Collingbournef15907f2011-04-29 18:47:31 +0000302 if (Cost > CostRemaining)
303 return false;
304
305 CostRemaining -= Cost;
306
307 // Okay, we can only really hoist these out if their operands do
308 // not take us over the cost threshold.
Chris Lattner44da7ca2010-12-14 07:41:39 +0000309 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
Peter Collingbournef15907f2011-04-29 18:47:31 +0000310 if (!DominatesMergePoint(*i, BB, AggressiveInsts, CostRemaining))
Chris Lattner44da7ca2010-12-14 07:41:39 +0000311 return false;
312 // Okay, it's safe to do this! Remember this instruction.
313 AggressiveInsts->insert(I);
Chris Lattner723c66d2004-02-11 03:36:04 +0000314 return true;
315}
Chris Lattner01d1ee32002-05-21 20:50:24 +0000316
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +0000317/// GetConstantInt - Extract ConstantInt from value, looking through IntToPtr
318/// and PointerNullValue. Return NULL if value is not a constant int.
Chris Lattner28acc132010-12-13 03:30:12 +0000319static ConstantInt *GetConstantInt(Value *V, const TargetData *TD) {
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +0000320 // Normal constant int.
321 ConstantInt *CI = dyn_cast<ConstantInt>(V);
Duncan Sands1df98592010-02-16 11:11:14 +0000322 if (CI || !TD || !isa<Constant>(V) || !V->getType()->isPointerTy())
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +0000323 return CI;
324
325 // This is some kind of pointer constant. Turn it into a pointer-sized
326 // ConstantInt if possible.
Chris Lattnerdb125cf2011-07-18 04:54:35 +0000327 IntegerType *PtrTy = TD->getIntPtrType(V->getContext());
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +0000328
329 // Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*).
330 if (isa<ConstantPointerNull>(V))
331 return ConstantInt::get(PtrTy, 0);
332
333 // IntToPtr const int.
334 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
335 if (CE->getOpcode() == Instruction::IntToPtr)
336 if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) {
337 // The constant is very likely to have the right type already.
338 if (CI->getType() == PtrTy)
339 return CI;
340 else
341 return cast<ConstantInt>
342 (ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false));
343 }
344 return 0;
345}
346
Chris Lattner0aa749b2010-12-13 04:26:26 +0000347/// GatherConstantCompares - Given a potentially 'or'd or 'and'd together
348/// collection of icmp eq/ne instructions that compare a value against a
349/// constant, return the value being compared, and stick the constant into the
350/// Values vector.
Chris Lattner28acc132010-12-13 03:30:12 +0000351static Value *
Chris Lattner0aa749b2010-12-13 04:26:26 +0000352GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra,
Benjamin Kramer33828bc2011-02-07 22:37:28 +0000353 const TargetData *TD, bool isEQ, unsigned &UsedICmps) {
Chris Lattner0aa749b2010-12-13 04:26:26 +0000354 Instruction *I = dyn_cast<Instruction>(V);
355 if (I == 0) return 0;
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000356
Chris Lattner7312a222010-12-13 04:50:38 +0000357 // If this is an icmp against a constant, handle this as one of the cases.
Chris Lattner0aa749b2010-12-13 04:26:26 +0000358 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) {
Chris Lattnere27db742010-12-17 06:20:15 +0000359 if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) {
360 if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ:ICmpInst::ICMP_NE)) {
Benjamin Kramer33828bc2011-02-07 22:37:28 +0000361 UsedICmps++;
Chris Lattner0aa749b2010-12-13 04:26:26 +0000362 Vals.push_back(C);
363 return I->getOperand(0);
364 }
Chris Lattnere27db742010-12-17 06:20:15 +0000365
366 // If we have "x ult 3" comparison, for example, then we can add 0,1,2 to
367 // the set.
368 ConstantRange Span =
Chris Lattnera37029c2010-12-18 20:22:49 +0000369 ConstantRange::makeICmpRegion(ICI->getPredicate(), C->getValue());
Chris Lattnere27db742010-12-17 06:20:15 +0000370
371 // If this is an and/!= check then we want to optimize "x ugt 2" into
372 // x != 0 && x != 1.
373 if (!isEQ)
374 Span = Span.inverse();
375
376 // If there are a ton of values, we don't want to make a ginormous switch.
Benjamin Kramer14c09872010-12-17 10:48:14 +0000377 if (Span.getSetSize().ugt(8) || Span.isEmptySet() ||
Chris Lattnere27db742010-12-17 06:20:15 +0000378 // We don't handle wrapped sets yet.
379 Span.isWrappedSet())
380 return 0;
381
382 for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp)
383 Vals.push_back(ConstantInt::get(V->getContext(), Tmp));
Benjamin Kramer33828bc2011-02-07 22:37:28 +0000384 UsedICmps++;
Chris Lattnere27db742010-12-17 06:20:15 +0000385 return I->getOperand(0);
386 }
Chris Lattner662269d2010-12-13 04:18:32 +0000387 return 0;
388 }
389
Chris Lattner7312a222010-12-13 04:50:38 +0000390 // Otherwise, we can only handle an | or &, depending on isEQ.
Chris Lattner0aa749b2010-12-13 04:26:26 +0000391 if (I->getOpcode() != (isEQ ? Instruction::Or : Instruction::And))
Chris Lattner662269d2010-12-13 04:18:32 +0000392 return 0;
Chris Lattner662269d2010-12-13 04:18:32 +0000393
Chris Lattner7312a222010-12-13 04:50:38 +0000394 unsigned NumValsBeforeLHS = Vals.size();
Benjamin Kramer33828bc2011-02-07 22:37:28 +0000395 unsigned UsedICmpsBeforeLHS = UsedICmps;
Chris Lattner0aa749b2010-12-13 04:26:26 +0000396 if (Value *LHS = GatherConstantCompares(I->getOperand(0), Vals, Extra, TD,
Benjamin Kramer33828bc2011-02-07 22:37:28 +0000397 isEQ, UsedICmps)) {
Chris Lattner7312a222010-12-13 04:50:38 +0000398 unsigned NumVals = Vals.size();
Benjamin Kramer33828bc2011-02-07 22:37:28 +0000399 unsigned UsedICmpsBeforeRHS = UsedICmps;
Chris Lattner0aa749b2010-12-13 04:26:26 +0000400 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
Benjamin Kramer33828bc2011-02-07 22:37:28 +0000401 isEQ, UsedICmps)) {
Chris Lattner0aa749b2010-12-13 04:26:26 +0000402 if (LHS == RHS)
403 return LHS;
Chris Lattner92407e52010-12-13 07:41:29 +0000404 Vals.resize(NumVals);
Benjamin Kramer33828bc2011-02-07 22:37:28 +0000405 UsedICmps = UsedICmpsBeforeRHS;
Chris Lattner0aa749b2010-12-13 04:26:26 +0000406 }
Chris Lattner7312a222010-12-13 04:50:38 +0000407
408 // The RHS of the or/and can't be folded in and we haven't used "Extra" yet,
409 // set it and return success.
410 if (Extra == 0 || Extra == I->getOperand(1)) {
411 Extra = I->getOperand(1);
412 return LHS;
413 }
414
415 Vals.resize(NumValsBeforeLHS);
Benjamin Kramer33828bc2011-02-07 22:37:28 +0000416 UsedICmps = UsedICmpsBeforeLHS;
Chris Lattner7312a222010-12-13 04:50:38 +0000417 return 0;
Anton Korobeynikov07e6e562008-02-20 11:26:25 +0000418 }
Chris Lattner7312a222010-12-13 04:50:38 +0000419
420 // If the LHS can't be folded in, but Extra is available and RHS can, try to
421 // use LHS as Extra.
422 if (Extra == 0 || Extra == I->getOperand(0)) {
Chris Lattner92407e52010-12-13 07:41:29 +0000423 Value *OldExtra = Extra;
Chris Lattner7312a222010-12-13 04:50:38 +0000424 Extra = I->getOperand(0);
425 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
Benjamin Kramer33828bc2011-02-07 22:37:28 +0000426 isEQ, UsedICmps))
Chris Lattner7312a222010-12-13 04:50:38 +0000427 return RHS;
Chris Lattner92407e52010-12-13 07:41:29 +0000428 assert(Vals.size() == NumValsBeforeLHS);
429 Extra = OldExtra;
Chris Lattner7312a222010-12-13 04:50:38 +0000430 }
431
Chris Lattner0d560082004-02-24 05:38:11 +0000432 return 0;
433}
Nick Lewycky9d523102011-12-26 20:37:40 +0000434
Eli Friedman080efb82008-12-16 20:54:32 +0000435static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
Nick Lewycky9d523102011-12-26 20:37:40 +0000436 Instruction *Cond = 0;
Eli Friedman080efb82008-12-16 20:54:32 +0000437 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
438 Cond = dyn_cast<Instruction>(SI->getCondition());
439 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
440 if (BI->isConditional())
441 Cond = dyn_cast<Instruction>(BI->getCondition());
Frits van Bommel7ac40c32010-12-05 18:29:03 +0000442 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) {
443 Cond = dyn_cast<Instruction>(IBI->getAddress());
Eli Friedman080efb82008-12-16 20:54:32 +0000444 }
445
446 TI->eraseFromParent();
447 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
448}
449
Chris Lattner9fd49552008-11-27 23:25:44 +0000450/// isValueEqualityComparison - Return true if the specified terminator checks
451/// to see if a value is equal to constant integer value.
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +0000452Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) {
453 Value *CV = 0;
Chris Lattner4bebf082004-03-16 19:45:22 +0000454 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
455 // Do not permit merging of large switch instructions into their
456 // predecessors unless there is only one predecessor.
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +0000457 if (SI->getNumSuccessors()*std::distance(pred_begin(SI->getParent()),
458 pred_end(SI->getParent())) <= 128)
459 CV = SI->getCondition();
460 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI))
Chris Lattner542f1492004-02-28 21:28:10 +0000461 if (BI->isConditional() && BI->getCondition()->hasOneUse())
Reid Spencere4d87aa2006-12-23 06:05:41 +0000462 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
463 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
464 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
Chris Lattner28acc132010-12-13 03:30:12 +0000465 GetConstantInt(ICI->getOperand(1), TD))
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +0000466 CV = ICI->getOperand(0);
467
468 // Unwrap any lossless ptrtoint cast.
469 if (TD && CV && CV->getType() == TD->getIntPtrType(CV->getContext()))
470 if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV))
471 CV = PTII->getOperand(0);
472 return CV;
Chris Lattner542f1492004-02-28 21:28:10 +0000473}
474
Bill Wendling5049fa62009-01-19 23:43:56 +0000475/// GetValueEqualityComparisonCases - Given a value comparison instruction,
476/// decode all of the 'cases' that it represents and return the 'default' block.
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +0000477BasicBlock *SimplifyCFGOpt::
Misha Brukmanfd939082005-04-21 23:48:37 +0000478GetValueEqualityComparisonCases(TerminatorInst *TI,
Chris Lattner542f1492004-02-28 21:28:10 +0000479 std::vector<std::pair<ConstantInt*,
480 BasicBlock*> > &Cases) {
481 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
482 Cases.reserve(SI->getNumCases());
483 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
Chris Lattnerbe54dcc2005-02-26 18:33:28 +0000484 Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i)));
Chris Lattner542f1492004-02-28 21:28:10 +0000485 return SI->getDefaultDest();
486 }
487
488 BranchInst *BI = cast<BranchInst>(TI);
Reid Spencere4d87aa2006-12-23 06:05:41 +0000489 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
Chris Lattner28acc132010-12-13 03:30:12 +0000490 Cases.push_back(std::make_pair(GetConstantInt(ICI->getOperand(1), TD),
Reid Spencere4d87aa2006-12-23 06:05:41 +0000491 BI->getSuccessor(ICI->getPredicate() ==
492 ICmpInst::ICMP_NE)));
493 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
Chris Lattner542f1492004-02-28 21:28:10 +0000494}
495
496
Bill Wendling5049fa62009-01-19 23:43:56 +0000497/// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
498/// in the list that match the specified block.
Misha Brukmanfd939082005-04-21 23:48:37 +0000499static void EliminateBlockCases(BasicBlock *BB,
Chris Lattner623369a2005-02-24 06:17:52 +0000500 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
501 for (unsigned i = 0, e = Cases.size(); i != e; ++i)
502 if (Cases[i].second == BB) {
503 Cases.erase(Cases.begin()+i);
504 --i; --e;
505 }
506}
507
Bill Wendling5049fa62009-01-19 23:43:56 +0000508/// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
509/// well.
Chris Lattner623369a2005-02-24 06:17:52 +0000510static bool
511ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
512 std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
513 std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2;
514
515 // Make V1 be smaller than V2.
516 if (V1->size() > V2->size())
517 std::swap(V1, V2);
518
519 if (V1->size() == 0) return false;
520 if (V1->size() == 1) {
521 // Just scan V2.
522 ConstantInt *TheVal = (*V1)[0].first;
523 for (unsigned i = 0, e = V2->size(); i != e; ++i)
524 if (TheVal == (*V2)[i].first)
525 return true;
526 }
527
528 // Otherwise, just sort both lists and compare element by element.
Chris Lattnerfca20f52010-12-13 03:24:30 +0000529 array_pod_sort(V1->begin(), V1->end());
530 array_pod_sort(V2->begin(), V2->end());
Chris Lattner623369a2005-02-24 06:17:52 +0000531 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
532 while (i1 != e1 && i2 != e2) {
533 if ((*V1)[i1].first == (*V2)[i2].first)
534 return true;
535 if ((*V1)[i1].first < (*V2)[i2].first)
536 ++i1;
537 else
538 ++i2;
539 }
540 return false;
541}
542
Bill Wendling5049fa62009-01-19 23:43:56 +0000543/// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
544/// terminator instruction and its block is known to only have a single
545/// predecessor block, check to see if that predecessor is also a value
546/// comparison with the same value, and if that comparison determines the
547/// outcome of this comparison. If so, simplify TI. This does a very limited
548/// form of jump threading.
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +0000549bool SimplifyCFGOpt::
550SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
Devang Patel007349d2011-05-18 20:35:38 +0000551 BasicBlock *Pred,
552 IRBuilder<> &Builder) {
Chris Lattner623369a2005-02-24 06:17:52 +0000553 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
554 if (!PredVal) return false; // Not a value comparison in predecessor.
555
556 Value *ThisVal = isValueEqualityComparison(TI);
557 assert(ThisVal && "This isn't a value comparison!!");
558 if (ThisVal != PredVal) return false; // Different predicates.
559
560 // Find out information about when control will move from Pred to TI's block.
561 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
562 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
563 PredCases);
564 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
Misha Brukmanfd939082005-04-21 23:48:37 +0000565
Chris Lattner623369a2005-02-24 06:17:52 +0000566 // Find information about how control leaves this block.
567 std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases;
568 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
569 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
570
571 // If TI's block is the default block from Pred's comparison, potentially
572 // simplify TI based on this knowledge.
573 if (PredDef == TI->getParent()) {
574 // If we are here, we know that the value is none of those cases listed in
575 // PredCases. If there are any cases in ThisCases that are in PredCases, we
576 // can simplify TI.
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000577 if (!ValuesOverlap(PredCases, ThisCases))
578 return false;
579
580 if (isa<BranchInst>(TI)) {
581 // Okay, one of the successors of this condbr is dead. Convert it to a
582 // uncond br.
583 assert(ThisCases.size() == 1 && "Branch can only have one case!");
584 // Insert the new branch.
Devang Patel007349d2011-05-18 20:35:38 +0000585 Instruction *NI = Builder.CreateBr(ThisDef);
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000586 (void) NI;
Chris Lattner623369a2005-02-24 06:17:52 +0000587
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000588 // Remove PHI node entries for the dead edge.
589 ThisCases[0].second->removePredecessor(TI->getParent());
Chris Lattner623369a2005-02-24 06:17:52 +0000590
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000591 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
592 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
Chris Lattner623369a2005-02-24 06:17:52 +0000593
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000594 EraseTerminatorInstAndDCECond(TI);
595 return true;
Chris Lattner623369a2005-02-24 06:17:52 +0000596 }
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000597
598 SwitchInst *SI = cast<SwitchInst>(TI);
599 // Okay, TI has cases that are statically dead, prune them away.
600 SmallPtrSet<Constant*, 16> DeadCases;
Chris Lattner623369a2005-02-24 06:17:52 +0000601 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000602 DeadCases.insert(PredCases[i].first);
Chris Lattner623369a2005-02-24 06:17:52 +0000603
David Greene89d6fd32010-01-05 01:26:52 +0000604 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000605 << "Through successor TI: " << *TI);
Chris Lattner623369a2005-02-24 06:17:52 +0000606
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000607 for (unsigned i = SI->getNumCases()-1; i != 0; --i)
608 if (DeadCases.count(SI->getCaseValue(i))) {
609 SI->getSuccessor(i)->removePredecessor(TI->getParent());
610 SI->removeCase(i);
611 }
612
613 DEBUG(dbgs() << "Leaving: " << *TI << "\n");
Chris Lattner623369a2005-02-24 06:17:52 +0000614 return true;
615 }
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000616
617 // Otherwise, TI's block must correspond to some matched value. Find out
618 // which value (or set of values) this is.
619 ConstantInt *TIV = 0;
620 BasicBlock *TIBB = TI->getParent();
621 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
622 if (PredCases[i].second == TIBB) {
623 if (TIV != 0)
624 return false; // Cannot handle multiple values coming to this block.
625 TIV = PredCases[i].first;
626 }
627 assert(TIV && "No edge from pred to succ?");
628
629 // Okay, we found the one constant that our value can be if we get into TI's
630 // BB. Find out which successor will unconditionally be branched to.
631 BasicBlock *TheRealDest = 0;
632 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
633 if (ThisCases[i].first == TIV) {
634 TheRealDest = ThisCases[i].second;
635 break;
636 }
637
638 // If not handled by any explicit cases, it is handled by the default case.
639 if (TheRealDest == 0) TheRealDest = ThisDef;
640
641 // Remove PHI node entries for dead edges.
642 BasicBlock *CheckEdge = TheRealDest;
643 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
644 if (*SI != CheckEdge)
645 (*SI)->removePredecessor(TIBB);
646 else
647 CheckEdge = 0;
648
649 // Insert the new branch.
Devang Patel007349d2011-05-18 20:35:38 +0000650 Instruction *NI = Builder.CreateBr(TheRealDest);
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000651 (void) NI;
652
653 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
654 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
655
656 EraseTerminatorInstAndDCECond(TI);
657 return true;
Chris Lattner623369a2005-02-24 06:17:52 +0000658}
659
Dale Johannesenc81f5442009-03-12 21:01:11 +0000660namespace {
661 /// ConstantIntOrdering - This class implements a stable ordering of constant
662 /// integers that does not depend on their address. This is important for
663 /// applications that sort ConstantInt's to ensure uniqueness.
664 struct ConstantIntOrdering {
665 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
666 return LHS->getValue().ult(RHS->getValue());
667 }
668 };
669}
Dale Johannesena9537cf2009-03-12 01:00:26 +0000670
Chris Lattner6d4d21e2010-12-13 02:00:58 +0000671static int ConstantIntSortPredicate(const void *P1, const void *P2) {
672 const ConstantInt *LHS = *(const ConstantInt**)P1;
673 const ConstantInt *RHS = *(const ConstantInt**)P2;
Chris Lattnerba3c8152010-12-15 04:52:41 +0000674 if (LHS->getValue().ult(RHS->getValue()))
675 return 1;
676 if (LHS->getValue() == RHS->getValue())
677 return 0;
678 return -1;
Chris Lattner6d4d21e2010-12-13 02:00:58 +0000679}
680
Bill Wendling5049fa62009-01-19 23:43:56 +0000681/// FoldValueComparisonIntoPredecessors - The specified terminator is a value
682/// equality comparison instruction (either a switch or a branch on "X == c").
683/// See if any of the predecessors of the terminator block are value comparisons
684/// on the same value. If so, and if safe to do so, fold them together.
Devang Patelb55d9242011-05-18 20:53:17 +0000685bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI,
686 IRBuilder<> &Builder) {
Chris Lattner542f1492004-02-28 21:28:10 +0000687 BasicBlock *BB = TI->getParent();
688 Value *CV = isValueEqualityComparison(TI); // CondVal
689 assert(CV && "Not a comparison?");
690 bool Changed = false;
691
Chris Lattner82442432008-02-18 07:42:56 +0000692 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
Chris Lattner542f1492004-02-28 21:28:10 +0000693 while (!Preds.empty()) {
Dan Gohmane9d87f42009-05-06 17:22:41 +0000694 BasicBlock *Pred = Preds.pop_back_val();
Misha Brukmanfd939082005-04-21 23:48:37 +0000695
Chris Lattner542f1492004-02-28 21:28:10 +0000696 // See if the predecessor is a comparison with the same value.
697 TerminatorInst *PTI = Pred->getTerminator();
698 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
699
700 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
701 // Figure out which 'cases' to copy from SI to PSI.
702 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
703 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
704
705 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
706 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
707
708 // Based on whether the default edge from PTI goes to BB or not, fill in
709 // PredCases and PredDefault with the new switch cases we would like to
710 // build.
Chris Lattner82442432008-02-18 07:42:56 +0000711 SmallVector<BasicBlock*, 8> NewSuccessors;
Chris Lattner542f1492004-02-28 21:28:10 +0000712
713 if (PredDefault == BB) {
714 // If this is the default destination from PTI, only the edges in TI
715 // that don't occur in PTI, or that branch to BB will be activated.
Dale Johannesenc81f5442009-03-12 21:01:11 +0000716 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
Chris Lattner542f1492004-02-28 21:28:10 +0000717 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
718 if (PredCases[i].second != BB)
719 PTIHandled.insert(PredCases[i].first);
720 else {
721 // The default destination is BB, we don't need explicit targets.
722 std::swap(PredCases[i], PredCases.back());
723 PredCases.pop_back();
724 --i; --e;
725 }
726
727 // Reconstruct the new switch statement we will be building.
728 if (PredDefault != BBDefault) {
729 PredDefault->removePredecessor(Pred);
730 PredDefault = BBDefault;
731 NewSuccessors.push_back(BBDefault);
732 }
733 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
734 if (!PTIHandled.count(BBCases[i].first) &&
735 BBCases[i].second != BBDefault) {
736 PredCases.push_back(BBCases[i]);
737 NewSuccessors.push_back(BBCases[i].second);
738 }
739
740 } else {
741 // If this is not the default destination from PSI, only the edges
742 // in SI that occur in PSI with a destination of BB will be
743 // activated.
Dale Johannesenc81f5442009-03-12 21:01:11 +0000744 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
Chris Lattner542f1492004-02-28 21:28:10 +0000745 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
746 if (PredCases[i].second == BB) {
747 PTIHandled.insert(PredCases[i].first);
748 std::swap(PredCases[i], PredCases.back());
749 PredCases.pop_back();
750 --i; --e;
751 }
752
753 // Okay, now we know which constants were sent to BB from the
754 // predecessor. Figure out where they will all go now.
755 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
756 if (PTIHandled.count(BBCases[i].first)) {
757 // If this is one we are capable of getting...
758 PredCases.push_back(BBCases[i]);
759 NewSuccessors.push_back(BBCases[i].second);
760 PTIHandled.erase(BBCases[i].first);// This constant is taken care of
761 }
762
763 // If there are any constants vectored to BB that TI doesn't handle,
764 // they must go to the default destination of TI.
Dale Johannesenc81f5442009-03-12 21:01:11 +0000765 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I =
766 PTIHandled.begin(),
Chris Lattner542f1492004-02-28 21:28:10 +0000767 E = PTIHandled.end(); I != E; ++I) {
768 PredCases.push_back(std::make_pair(*I, BBDefault));
769 NewSuccessors.push_back(BBDefault);
770 }
771 }
772
773 // Okay, at this point, we know which new successor Pred will get. Make
774 // sure we update the number of entries in the PHI nodes for these
775 // successors.
776 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
777 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
778
Devang Patelb55d9242011-05-18 20:53:17 +0000779 Builder.SetInsertPoint(PTI);
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +0000780 // Convert pointer to int before we switch.
Duncan Sands1df98592010-02-16 11:11:14 +0000781 if (CV->getType()->isPointerTy()) {
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +0000782 assert(TD && "Cannot switch on pointer without TargetData");
Devang Patelb55d9242011-05-18 20:53:17 +0000783 CV = Builder.CreatePtrToInt(CV, TD->getIntPtrType(CV->getContext()),
784 "magicptr");
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +0000785 }
786
Chris Lattner542f1492004-02-28 21:28:10 +0000787 // Now that the successors are updated, create the new Switch instruction.
Devang Patelb55d9242011-05-18 20:53:17 +0000788 SwitchInst *NewSI = Builder.CreateSwitch(CV, PredDefault,
789 PredCases.size());
Devang Pateld80e8ed2011-05-17 23:29:05 +0000790 NewSI->setDebugLoc(PTI->getDebugLoc());
Chris Lattner542f1492004-02-28 21:28:10 +0000791 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
792 NewSI->addCase(PredCases[i].first, PredCases[i].second);
Chris Lattner13b2f762005-01-01 16:02:12 +0000793
Eli Friedman080efb82008-12-16 20:54:32 +0000794 EraseTerminatorInstAndDCECond(PTI);
Chris Lattner13b2f762005-01-01 16:02:12 +0000795
Chris Lattner542f1492004-02-28 21:28:10 +0000796 // Okay, last check. If BB is still a successor of PSI, then we must
797 // have an infinite loop case. If so, add an infinitely looping block
798 // to handle the case to preserve the behavior of the code.
799 BasicBlock *InfLoopBlock = 0;
800 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
801 if (NewSI->getSuccessor(i) == BB) {
802 if (InfLoopBlock == 0) {
Chris Lattner093a4382008-07-13 22:23:11 +0000803 // Insert it at the end of the function, because it's either code,
Chris Lattner542f1492004-02-28 21:28:10 +0000804 // or it won't matter if it's hot. :)
Owen Anderson1d0be152009-08-13 21:58:54 +0000805 InfLoopBlock = BasicBlock::Create(BB->getContext(),
806 "infloop", BB->getParent());
Gabor Greif051a9502008-04-06 20:25:17 +0000807 BranchInst::Create(InfLoopBlock, InfLoopBlock);
Chris Lattner542f1492004-02-28 21:28:10 +0000808 }
809 NewSI->setSuccessor(i, InfLoopBlock);
810 }
Misha Brukmanfd939082005-04-21 23:48:37 +0000811
Chris Lattner542f1492004-02-28 21:28:10 +0000812 Changed = true;
813 }
814 }
815 return Changed;
816}
817
Dale Johannesenc1f10402009-06-15 20:59:27 +0000818// isSafeToHoistInvoke - If we would need to insert a select that uses the
819// value of this invoke (comments in HoistThenElseCodeToIf explain why we
820// would need to do this), we can't hoist the invoke, as there is nowhere
821// to put the select in this case.
822static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
823 Instruction *I1, Instruction *I2) {
824 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
825 PHINode *PN;
826 for (BasicBlock::iterator BBI = SI->begin();
827 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
828 Value *BB1V = PN->getIncomingValueForBlock(BB1);
829 Value *BB2V = PN->getIncomingValueForBlock(BB2);
830 if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) {
831 return false;
832 }
833 }
834 }
835 return true;
836}
837
Chris Lattner6306d072005-08-03 17:59:45 +0000838/// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
Chris Lattner37dc9382004-11-30 00:29:14 +0000839/// BB2, hoist any common code in the two blocks up into the branch block. The
840/// caller of this function guarantees that BI's block dominates BB1 and BB2.
Rafael Espindola216dde92011-05-19 02:26:30 +0000841static bool HoistThenElseCodeToIf(BranchInst *BI) {
Chris Lattner37dc9382004-11-30 00:29:14 +0000842 // This does very trivial matching, with limited scanning, to find identical
843 // instructions in the two blocks. In particular, we don't want to get into
844 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
845 // such, we currently just scan for obviously identical instructions in an
846 // identical order.
847 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
848 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
849
Devang Patel65085cf2009-02-04 00:03:08 +0000850 BasicBlock::iterator BB1_Itr = BB1->begin();
851 BasicBlock::iterator BB2_Itr = BB2->begin();
852
853 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++;
Devang Patel949666e2011-04-07 17:27:36 +0000854 // Skip debug info if it is not identical.
855 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
856 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
857 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
858 while (isa<DbgInfoIntrinsic>(I1))
859 I1 = BB1_Itr++;
860 while (isa<DbgInfoIntrinsic>(I2))
861 I2 = BB2_Itr++;
862 }
Devang Patelae6c95b2011-04-07 00:30:15 +0000863 if (isa<PHINode>(I1) || !I1->isIdenticalToWhenDefined(I2) ||
Dale Johannesenc1f10402009-06-15 20:59:27 +0000864 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
Chris Lattner37dc9382004-11-30 00:29:14 +0000865 return false;
866
867 // If we get here, we can hoist at least one instruction.
868 BasicBlock *BIParent = BI->getParent();
Chris Lattner37dc9382004-11-30 00:29:14 +0000869
870 do {
871 // If we are hoisting the terminator instruction, don't move one (making a
872 // broken BB), instead clone it, and remove BI.
873 if (isa<TerminatorInst>(I1))
874 goto HoistTerminator;
Misha Brukmanfd939082005-04-21 23:48:37 +0000875
Chris Lattner37dc9382004-11-30 00:29:14 +0000876 // For a normal instruction, we just move one to right before the branch,
877 // then replace all uses of the other with the first. Finally, we remove
878 // the now redundant second instruction.
879 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
880 if (!I2->use_empty())
881 I2->replaceAllUsesWith(I1);
Dan Gohman58cfa3b2009-08-25 22:11:20 +0000882 I1->intersectOptionalDataWith(I2);
Chris Lattner302ba6f2010-12-14 06:17:25 +0000883 I2->eraseFromParent();
Misha Brukmanfd939082005-04-21 23:48:37 +0000884
Devang Patel65085cf2009-02-04 00:03:08 +0000885 I1 = BB1_Itr++;
Devang Patel65085cf2009-02-04 00:03:08 +0000886 I2 = BB2_Itr++;
Devang Patel949666e2011-04-07 17:27:36 +0000887 // Skip debug info if it is not identical.
888 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
889 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
890 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
891 while (isa<DbgInfoIntrinsic>(I1))
892 I1 = BB1_Itr++;
893 while (isa<DbgInfoIntrinsic>(I2))
894 I2 = BB2_Itr++;
895 }
Devang Patelae6c95b2011-04-07 00:30:15 +0000896 } while (I1->isIdenticalToWhenDefined(I2));
Chris Lattner37dc9382004-11-30 00:29:14 +0000897
898 return true;
899
900HoistTerminator:
Dale Johannesenc1f10402009-06-15 20:59:27 +0000901 // It may not be possible to hoist an invoke.
902 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
903 return true;
904
Chris Lattner37dc9382004-11-30 00:29:14 +0000905 // Okay, it is safe to hoist the terminator.
Nick Lewycky67760642009-09-27 07:38:41 +0000906 Instruction *NT = I1->clone();
Chris Lattner37dc9382004-11-30 00:29:14 +0000907 BIParent->getInstList().insert(BI, NT);
Benjamin Kramerf0127052010-01-05 13:12:22 +0000908 if (!NT->getType()->isVoidTy()) {
Chris Lattner37dc9382004-11-30 00:29:14 +0000909 I1->replaceAllUsesWith(NT);
910 I2->replaceAllUsesWith(NT);
Chris Lattner86cc4232007-02-11 01:37:51 +0000911 NT->takeName(I1);
Chris Lattner37dc9382004-11-30 00:29:14 +0000912 }
913
Devang Pateld3a17882011-05-19 20:52:46 +0000914 IRBuilder<true, NoFolder> Builder(NT);
Chris Lattner37dc9382004-11-30 00:29:14 +0000915 // Hoisting one of the terminators from our successor is a great thing.
916 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
917 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
918 // nodes, so we insert select instruction to compute the final result.
919 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
920 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
921 PHINode *PN;
922 for (BasicBlock::iterator BBI = SI->begin();
Chris Lattner0f535c62004-11-30 07:47:34 +0000923 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
Chris Lattner37dc9382004-11-30 00:29:14 +0000924 Value *BB1V = PN->getIncomingValueForBlock(BB1);
925 Value *BB2V = PN->getIncomingValueForBlock(BB2);
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000926 if (BB1V == BB2V) continue;
927
928 // These values do not agree. Insert a select instruction before NT
929 // that determines the right value.
930 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
Devang Pateld3a17882011-05-19 20:52:46 +0000931 if (SI == 0)
932 SI = cast<SelectInst>
933 (Builder.CreateSelect(BI->getCondition(), BB1V, BB2V,
934 BB1V->getName()+"."+BB2V->getName()));
935
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000936 // Make the PHI node use the select for all incoming values for BB1/BB2
937 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
938 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
939 PN->setIncomingValue(i, SI);
Chris Lattner37dc9382004-11-30 00:29:14 +0000940 }
941 }
942
943 // Update any PHI nodes in our new successors.
944 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
945 AddPredecessorToBlock(*SI, BIParent, BB1);
Misha Brukmanfd939082005-04-21 23:48:37 +0000946
Eli Friedman080efb82008-12-16 20:54:32 +0000947 EraseTerminatorInstAndDCECond(BI);
Chris Lattner37dc9382004-11-30 00:29:14 +0000948 return true;
949}
950
Evan Cheng4d09efd2008-06-07 08:52:29 +0000951/// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
952/// and an BB2 and the only successor of BB1 is BB2, hoist simple code
953/// (for now, restricted to a single instruction that's side effect free) from
954/// the BB1 into the branch block to speculatively execute it.
Rafael Espindola216dde92011-05-19 02:26:30 +0000955static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
Evan Cheng4d09efd2008-06-07 08:52:29 +0000956 // Only speculatively execution a single instruction (not counting the
957 // terminator) for now.
Devang Patel06b1e672009-03-06 06:00:17 +0000958 Instruction *HInst = NULL;
959 Instruction *Term = BB1->getTerminator();
960 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end();
961 BBI != BBE; ++BBI) {
962 Instruction *I = BBI;
963 // Skip debug info.
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000964 if (isa<DbgInfoIntrinsic>(I)) continue;
965 if (I == Term) break;
Devang Patel06b1e672009-03-06 06:00:17 +0000966
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000967 if (HInst)
Devang Patel06b1e672009-03-06 06:00:17 +0000968 return false;
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000969 HInst = I;
Devang Patel06b1e672009-03-06 06:00:17 +0000970 }
971 if (!HInst)
972 return false;
Evan Cheng4d09efd2008-06-07 08:52:29 +0000973
Evan Cheng797d9512008-06-11 19:18:20 +0000974 // Be conservative for now. FP select instruction can often be expensive.
975 Value *BrCond = BI->getCondition();
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000976 if (isa<FCmpInst>(BrCond))
Evan Cheng797d9512008-06-11 19:18:20 +0000977 return false;
978
Evan Cheng4d09efd2008-06-07 08:52:29 +0000979 // If BB1 is actually on the false edge of the conditional branch, remember
980 // to swap the select operands later.
981 bool Invert = false;
982 if (BB1 != BI->getSuccessor(0)) {
983 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
984 Invert = true;
985 }
986
987 // Turn
988 // BB:
989 // %t1 = icmp
990 // br i1 %t1, label %BB1, label %BB2
991 // BB1:
992 // %t3 = add %t2, c
993 // br label BB2
994 // BB2:
995 // =>
996 // BB:
997 // %t1 = icmp
998 // %t4 = add %t2, c
999 // %t3 = select i1 %t1, %t2, %t3
Devang Patel06b1e672009-03-06 06:00:17 +00001000 switch (HInst->getOpcode()) {
Evan Cheng4d09efd2008-06-07 08:52:29 +00001001 default: return false; // Not safe / profitable to hoist.
1002 case Instruction::Add:
1003 case Instruction::Sub:
Dan Gohmanae3a0be2009-06-04 22:49:04 +00001004 // Not worth doing for vector ops.
Duncan Sands1df98592010-02-16 11:11:14 +00001005 if (HInst->getType()->isVectorTy())
Chris Lattner9dd3b612009-01-18 23:22:07 +00001006 return false;
1007 break;
Evan Cheng4d09efd2008-06-07 08:52:29 +00001008 case Instruction::And:
1009 case Instruction::Or:
1010 case Instruction::Xor:
1011 case Instruction::Shl:
1012 case Instruction::LShr:
1013 case Instruction::AShr:
Chris Lattner9dd3b612009-01-18 23:22:07 +00001014 // Don't mess with vector operations.
Duncan Sands1df98592010-02-16 11:11:14 +00001015 if (HInst->getType()->isVectorTy())
Evan Chenge5334ea2008-06-25 07:50:12 +00001016 return false;
Evan Cheng4d09efd2008-06-07 08:52:29 +00001017 break; // These are all cheap and non-trapping instructions.
1018 }
Chris Lattner6fe73bb2009-01-19 00:36:37 +00001019
1020 // If the instruction is obviously dead, don't try to predicate it.
Devang Patel06b1e672009-03-06 06:00:17 +00001021 if (HInst->use_empty()) {
1022 HInst->eraseFromParent();
Chris Lattner6fe73bb2009-01-19 00:36:37 +00001023 return true;
1024 }
Evan Cheng4d09efd2008-06-07 08:52:29 +00001025
1026 // Can we speculatively execute the instruction? And what is the value
1027 // if the condition is false? Consider the phi uses, if the incoming value
1028 // from the "if" block are all the same V, then V is the value of the
1029 // select if the condition is false.
1030 BasicBlock *BIParent = BI->getParent();
1031 SmallVector<PHINode*, 4> PHIUses;
1032 Value *FalseV = NULL;
Chris Lattner6fe73bb2009-01-19 00:36:37 +00001033
1034 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0);
Devang Patel06b1e672009-03-06 06:00:17 +00001035 for (Value::use_iterator UI = HInst->use_begin(), E = HInst->use_end();
Evan Cheng4d09efd2008-06-07 08:52:29 +00001036 UI != E; ++UI) {
Chris Lattner6fe73bb2009-01-19 00:36:37 +00001037 // Ignore any user that is not a PHI node in BB2. These can only occur in
1038 // unreachable blocks, because they would not be dominated by the instr.
Gabor Greif20361b92010-07-22 11:43:44 +00001039 PHINode *PN = dyn_cast<PHINode>(*UI);
Chris Lattner6fe73bb2009-01-19 00:36:37 +00001040 if (!PN || PN->getParent() != BB2)
1041 return false;
Evan Cheng4d09efd2008-06-07 08:52:29 +00001042 PHIUses.push_back(PN);
Chris Lattner6fe73bb2009-01-19 00:36:37 +00001043
Evan Cheng4d09efd2008-06-07 08:52:29 +00001044 Value *PHIV = PN->getIncomingValueForBlock(BIParent);
1045 if (!FalseV)
1046 FalseV = PHIV;
1047 else if (FalseV != PHIV)
Chris Lattner6fe73bb2009-01-19 00:36:37 +00001048 return false; // Inconsistent value when condition is false.
Evan Cheng4d09efd2008-06-07 08:52:29 +00001049 }
Chris Lattner6fe73bb2009-01-19 00:36:37 +00001050
1051 assert(FalseV && "Must have at least one user, and it must be a PHI");
Evan Cheng4d09efd2008-06-07 08:52:29 +00001052
Evan Cheng502a4f52008-06-12 21:15:59 +00001053 // Do not hoist the instruction if any of its operands are defined but not
1054 // used in this BB. The transformation will prevent the operand from
1055 // being sunk into the use block.
Devang Patel06b1e672009-03-06 06:00:17 +00001056 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end();
1057 i != e; ++i) {
Evan Cheng502a4f52008-06-12 21:15:59 +00001058 Instruction *OpI = dyn_cast<Instruction>(*i);
1059 if (OpI && OpI->getParent() == BIParent &&
1060 !OpI->isUsedInBasicBlock(BIParent))
1061 return false;
1062 }
1063
Devang Patel3d0a9a32008-09-18 22:50:42 +00001064 // If we get here, we can hoist the instruction. Try to place it
Dale Johannesen990afed2009-03-13 01:05:24 +00001065 // before the icmp instruction preceding the conditional branch.
Devang Patel3d0a9a32008-09-18 22:50:42 +00001066 BasicBlock::iterator InsertPos = BI;
Dale Johannesen990afed2009-03-13 01:05:24 +00001067 if (InsertPos != BIParent->begin())
1068 --InsertPos;
1069 // Skip debug info between condition and branch.
1070 while (InsertPos != BIParent->begin() && isa<DbgInfoIntrinsic>(InsertPos))
Devang Patel3d0a9a32008-09-18 22:50:42 +00001071 --InsertPos;
Devang Patel20da1f02008-10-03 18:57:37 +00001072 if (InsertPos == BrCond && !isa<PHINode>(BrCond)) {
Devang Patel3d0a9a32008-09-18 22:50:42 +00001073 SmallPtrSet<Instruction *, 4> BB1Insns;
1074 for(BasicBlock::iterator BB1I = BB1->begin(), BB1E = BB1->end();
1075 BB1I != BB1E; ++BB1I)
1076 BB1Insns.insert(BB1I);
1077 for(Value::use_iterator UI = BrCond->use_begin(), UE = BrCond->use_end();
1078 UI != UE; ++UI) {
1079 Instruction *Use = cast<Instruction>(*UI);
Chris Lattner9a2b72a2010-12-13 01:47:07 +00001080 if (!BB1Insns.count(Use)) continue;
1081
1082 // If BrCond uses the instruction that place it just before
1083 // branch instruction.
1084 InsertPos = BI;
1085 break;
Devang Patel3d0a9a32008-09-18 22:50:42 +00001086 }
1087 } else
1088 InsertPos = BI;
Devang Patel06b1e672009-03-06 06:00:17 +00001089 BIParent->getInstList().splice(InsertPos, BB1->getInstList(), HInst);
Evan Cheng4d09efd2008-06-07 08:52:29 +00001090
1091 // Create a select whose true value is the speculatively executed value and
1092 // false value is the previously determined FalseV.
Devang Pateld3a17882011-05-19 20:52:46 +00001093 IRBuilder<true, NoFolder> Builder(BI);
Evan Cheng4d09efd2008-06-07 08:52:29 +00001094 SelectInst *SI;
1095 if (Invert)
Devang Pateld3a17882011-05-19 20:52:46 +00001096 SI = cast<SelectInst>
1097 (Builder.CreateSelect(BrCond, FalseV, HInst,
1098 FalseV->getName() + "." + HInst->getName()));
Evan Cheng4d09efd2008-06-07 08:52:29 +00001099 else
Devang Pateld3a17882011-05-19 20:52:46 +00001100 SI = cast<SelectInst>
1101 (Builder.CreateSelect(BrCond, HInst, FalseV,
1102 HInst->getName() + "." + FalseV->getName()));
Evan Cheng4d09efd2008-06-07 08:52:29 +00001103
1104 // Make the PHI node use the select for all incoming values for "then" and
1105 // "if" blocks.
1106 for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) {
1107 PHINode *PN = PHIUses[i];
1108 for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j)
Chris Lattner9a2b72a2010-12-13 01:47:07 +00001109 if (PN->getIncomingBlock(j) == BB1 || PN->getIncomingBlock(j) == BIParent)
Evan Cheng4d09efd2008-06-07 08:52:29 +00001110 PN->setIncomingValue(j, SI);
1111 }
1112
Evan Cheng502a4f52008-06-12 21:15:59 +00001113 ++NumSpeculations;
Evan Cheng4d09efd2008-06-07 08:52:29 +00001114 return true;
1115}
1116
Chris Lattner2e42e362005-09-20 00:43:16 +00001117/// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1118/// across this block.
1119static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1120 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
Chris Lattnere9487f02005-09-20 01:48:40 +00001121 unsigned Size = 0;
1122
Devang Patel9200c892009-03-10 18:00:05 +00001123 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
Dale Johannesen8483e542009-03-12 23:18:09 +00001124 if (isa<DbgInfoIntrinsic>(BBI))
1125 continue;
Chris Lattnere9487f02005-09-20 01:48:40 +00001126 if (Size > 10) return false; // Don't clone large BB's.
Dale Johannesen8483e542009-03-12 23:18:09 +00001127 ++Size;
Chris Lattner2e42e362005-09-20 00:43:16 +00001128
Dale Johannesen8483e542009-03-12 23:18:09 +00001129 // We can only support instructions that do not define values that are
Chris Lattnere9487f02005-09-20 01:48:40 +00001130 // live outside of the current basic block.
1131 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1132 UI != E; ++UI) {
1133 Instruction *U = cast<Instruction>(*UI);
1134 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1135 }
Chris Lattner2e42e362005-09-20 00:43:16 +00001136
1137 // Looks ok, continue checking.
1138 }
Chris Lattnere9487f02005-09-20 01:48:40 +00001139
Chris Lattner2e42e362005-09-20 00:43:16 +00001140 return true;
1141}
1142
Chris Lattnereaba3a12005-09-19 23:49:37 +00001143/// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1144/// that is defined in the same block as the branch and if any PHI entries are
1145/// constants, thread edges corresponding to that entry to be branches to their
1146/// ultimate destination.
Chris Lattner302ba6f2010-12-14 06:17:25 +00001147static bool FoldCondBranchOnPHI(BranchInst *BI, const TargetData *TD) {
Chris Lattnereaba3a12005-09-19 23:49:37 +00001148 BasicBlock *BB = BI->getParent();
1149 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
Chris Lattner9c88d982005-09-19 23:57:04 +00001150 // NOTE: we currently cannot transform this case if the PHI node is used
1151 // outside of the block.
Chris Lattner2e42e362005-09-20 00:43:16 +00001152 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1153 return false;
Chris Lattnereaba3a12005-09-19 23:49:37 +00001154
1155 // Degenerate case of a single entry PHI.
1156 if (PN->getNumIncomingValues() == 1) {
Chris Lattner29874e02008-12-03 19:44:02 +00001157 FoldSingleEntryPHINodes(PN->getParent());
Chris Lattnereaba3a12005-09-19 23:49:37 +00001158 return true;
1159 }
1160
1161 // Now we know that this block has multiple preds and two succs.
Chris Lattner2e42e362005-09-20 00:43:16 +00001162 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
Chris Lattnereaba3a12005-09-19 23:49:37 +00001163
1164 // Okay, this is a simple enough basic block. See if any phi values are
1165 // constants.
Zhou Sheng6b6b6ef2007-01-11 12:24:14 +00001166 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
Chris Lattner9a2b72a2010-12-13 01:47:07 +00001167 ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i));
1168 if (CB == 0 || !CB->getType()->isIntegerTy(1)) continue;
1169
1170 // Okay, we now know that all edges from PredBB should be revectored to
1171 // branch to RealDest.
1172 BasicBlock *PredBB = PN->getIncomingBlock(i);
1173 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1174
1175 if (RealDest == BB) continue; // Skip self loops.
Bill Wendling6a648b82011-06-04 09:42:04 +00001176 // Skip if the predecessor's terminator is an indirect branch.
1177 if (isa<IndirectBrInst>(PredBB->getTerminator())) continue;
Chris Lattner9a2b72a2010-12-13 01:47:07 +00001178
1179 // The dest block might have PHI nodes, other predecessors and other
1180 // difficult cases. Instead of being smart about this, just insert a new
1181 // block that jumps to the destination block, effectively splitting
1182 // the edge we are about to create.
1183 BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(),
1184 RealDest->getName()+".critedge",
1185 RealDest->getParent(), RealDest);
1186 BranchInst::Create(RealDest, EdgeBB);
Chris Lattner6de0a282010-12-14 07:09:42 +00001187
1188 // Update PHI nodes.
1189 AddPredecessorToBlock(RealDest, EdgeBB, BB);
Chris Lattner9a2b72a2010-12-13 01:47:07 +00001190
1191 // BB may have instructions that are being threaded over. Clone these
1192 // instructions into EdgeBB. We know that there will be no uses of the
1193 // cloned instructions outside of EdgeBB.
1194 BasicBlock::iterator InsertPt = EdgeBB->begin();
1195 DenseMap<Value*, Value*> TranslateMap; // Track translated values.
1196 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1197 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1198 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1199 continue;
1200 }
1201 // Clone the instruction.
1202 Instruction *N = BBI->clone();
1203 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1204
1205 // Update operands due to translation.
1206 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1207 i != e; ++i) {
1208 DenseMap<Value*, Value*>::iterator PI = TranslateMap.find(*i);
1209 if (PI != TranslateMap.end())
1210 *i = PI->second;
1211 }
1212
1213 // Check for trivial simplification.
Chris Lattner302ba6f2010-12-14 06:17:25 +00001214 if (Value *V = SimplifyInstruction(N, TD)) {
1215 TranslateMap[BBI] = V;
1216 delete N; // Instruction folded away, don't need actual inst
Chris Lattner9a2b72a2010-12-13 01:47:07 +00001217 } else {
1218 // Insert the new instruction into its new home.
1219 EdgeBB->getInstList().insert(InsertPt, N);
1220 if (!BBI->use_empty())
1221 TranslateMap[BBI] = N;
1222 }
1223 }
1224
1225 // Loop over all of the edges from PredBB to BB, changing them to branch
1226 // to EdgeBB instead.
1227 TerminatorInst *PredBBTI = PredBB->getTerminator();
1228 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1229 if (PredBBTI->getSuccessor(i) == BB) {
1230 BB->removePredecessor(PredBB);
1231 PredBBTI->setSuccessor(i, EdgeBB);
1232 }
Bill Wendling6a648b82011-06-04 09:42:04 +00001233
Chris Lattner9a2b72a2010-12-13 01:47:07 +00001234 // Recurse, simplifying any other constants.
Chris Lattner302ba6f2010-12-14 06:17:25 +00001235 return FoldCondBranchOnPHI(BI, TD) | true;
Zhou Sheng6b6b6ef2007-01-11 12:24:14 +00001236 }
Chris Lattnereaba3a12005-09-19 23:49:37 +00001237
1238 return false;
1239}
1240
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001241/// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1242/// PHI node, see if we can eliminate it.
Devang Pateld3a17882011-05-19 20:52:46 +00001243static bool FoldTwoEntryPHINode(PHINode *PN, const TargetData *TD) {
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001244 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1245 // statement", which has a very simple dominance structure. Basically, we
1246 // are trying to find the condition that is being branched on, which
1247 // subsequently causes this merge to happen. We really want control
1248 // dependence information for this check, but simplifycfg can't keep it up
1249 // to date, and this catches most of the cases we care about anyway.
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001250 BasicBlock *BB = PN->getParent();
1251 BasicBlock *IfTrue, *IfFalse;
1252 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
Chris Lattner60d410d2010-12-14 08:01:53 +00001253 if (!IfCond ||
1254 // Don't bother if the branch will be constant folded trivially.
1255 isa<ConstantInt>(IfCond))
1256 return false;
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001257
Chris Lattner822a8792006-11-18 19:19:36 +00001258 // Okay, we found that we can merge this two-entry phi node into a select.
1259 // Doing so would require us to fold *all* two entry phi nodes in this block.
1260 // At some point this becomes non-profitable (particularly if the target
1261 // doesn't support cmov's). Only do this transformation if there are two or
1262 // fewer PHI nodes in this block.
1263 unsigned NumPhis = 0;
1264 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1265 if (NumPhis > 2)
1266 return false;
1267
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001268 // Loop over the PHI's seeing if we can promote them all to select
1269 // instructions. While we are at it, keep track of the instructions
1270 // that need to be moved to the dominating block.
Chris Lattner44da7ca2010-12-14 07:41:39 +00001271 SmallPtrSet<Instruction*, 4> AggressiveInsts;
Peter Collingbourne57808b32011-04-29 18:47:38 +00001272 unsigned MaxCostVal0 = PHINodeFoldingThreshold,
1273 MaxCostVal1 = PHINodeFoldingThreshold;
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001274
Chris Lattner3aff13b2010-12-14 08:46:09 +00001275 for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) {
1276 PHINode *PN = cast<PHINode>(II++);
Chris Lattner07ff3532010-12-14 07:20:29 +00001277 if (Value *V = SimplifyInstruction(PN, TD)) {
1278 PN->replaceAllUsesWith(V);
Chris Lattner3aff13b2010-12-14 08:46:09 +00001279 PN->eraseFromParent();
Chris Lattner07ff3532010-12-14 07:20:29 +00001280 continue;
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001281 }
Chris Lattner07ff3532010-12-14 07:20:29 +00001282
Peter Collingbournef15907f2011-04-29 18:47:31 +00001283 if (!DominatesMergePoint(PN->getIncomingValue(0), BB, &AggressiveInsts,
1284 MaxCostVal0) ||
1285 !DominatesMergePoint(PN->getIncomingValue(1), BB, &AggressiveInsts,
1286 MaxCostVal1))
Chris Lattner07ff3532010-12-14 07:20:29 +00001287 return false;
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001288 }
1289
Chris Lattner44da7ca2010-12-14 07:41:39 +00001290 // If we folded the the first phi, PN dangles at this point. Refresh it. If
1291 // we ran out of PHIs then we simplified them all.
1292 PN = dyn_cast<PHINode>(BB->begin());
1293 if (PN == 0) return true;
1294
Chris Lattner3aff13b2010-12-14 08:46:09 +00001295 // Don't fold i1 branches on PHIs which contain binary operators. These can
1296 // often be turned into switches and other things.
1297 if (PN->getType()->isIntegerTy(1) &&
1298 (isa<BinaryOperator>(PN->getIncomingValue(0)) ||
1299 isa<BinaryOperator>(PN->getIncomingValue(1)) ||
1300 isa<BinaryOperator>(IfCond)))
1301 return false;
1302
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001303 // If we all PHI nodes are promotable, check to make sure that all
1304 // instructions in the predecessor blocks can be promoted as well. If
1305 // not, we won't be able to get rid of the control flow, so it's not
1306 // worth promoting to select instructions.
Chris Lattner44da7ca2010-12-14 07:41:39 +00001307 BasicBlock *DomBlock = 0;
1308 BasicBlock *IfBlock1 = PN->getIncomingBlock(0);
1309 BasicBlock *IfBlock2 = PN->getIncomingBlock(1);
1310 if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) {
1311 IfBlock1 = 0;
1312 } else {
1313 DomBlock = *pred_begin(IfBlock1);
1314 for (BasicBlock::iterator I = IfBlock1->begin();!isa<TerminatorInst>(I);++I)
Devang Patel383d7ed2009-02-03 22:12:02 +00001315 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001316 // This is not an aggressive instruction that we can promote.
1317 // Because of this, we won't be able to get rid of the control
1318 // flow, so the xform is not worth it.
1319 return false;
1320 }
1321 }
1322
Chris Lattner44da7ca2010-12-14 07:41:39 +00001323 if (cast<BranchInst>(IfBlock2->getTerminator())->isConditional()) {
1324 IfBlock2 = 0;
1325 } else {
1326 DomBlock = *pred_begin(IfBlock2);
1327 for (BasicBlock::iterator I = IfBlock2->begin();!isa<TerminatorInst>(I);++I)
Devang Patel383d7ed2009-02-03 22:12:02 +00001328 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001329 // This is not an aggressive instruction that we can promote.
1330 // Because of this, we won't be able to get rid of the control
1331 // flow, so the xform is not worth it.
1332 return false;
1333 }
1334 }
Chris Lattnere0b18e52010-12-14 07:23:10 +00001335
1336 DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: "
Chris Lattner44da7ca2010-12-14 07:41:39 +00001337 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001338
1339 // If we can still promote the PHI nodes after this gauntlet of tests,
1340 // do all of the PHI's now.
Chris Lattner3aff13b2010-12-14 08:46:09 +00001341 Instruction *InsertPt = DomBlock->getTerminator();
Devang Pateld3a17882011-05-19 20:52:46 +00001342 IRBuilder<true, NoFolder> Builder(InsertPt);
Chris Lattner3aff13b2010-12-14 08:46:09 +00001343
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001344 // Move all 'aggressive' instructions, which are defined in the
1345 // conditional parts of the if's up to the dominating block.
Chris Lattner9a2b72a2010-12-13 01:47:07 +00001346 if (IfBlock1)
Chris Lattner3aff13b2010-12-14 08:46:09 +00001347 DomBlock->getInstList().splice(InsertPt,
Chris Lattner9a2b72a2010-12-13 01:47:07 +00001348 IfBlock1->getInstList(), IfBlock1->begin(),
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001349 IfBlock1->getTerminator());
Chris Lattner9a2b72a2010-12-13 01:47:07 +00001350 if (IfBlock2)
Chris Lattner3aff13b2010-12-14 08:46:09 +00001351 DomBlock->getInstList().splice(InsertPt,
Chris Lattner9a2b72a2010-12-13 01:47:07 +00001352 IfBlock2->getInstList(), IfBlock2->begin(),
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001353 IfBlock2->getTerminator());
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001354
1355 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1356 // Change the PHI node into a select instruction.
Chris Lattner9a2b72a2010-12-13 01:47:07 +00001357 Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1358 Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001359
Devang Patelf60364d2011-05-18 18:16:44 +00001360 SelectInst *NV =
1361 cast<SelectInst>(Builder.CreateSelect(IfCond, TrueVal, FalseVal, ""));
Chris Lattner86cc4232007-02-11 01:37:51 +00001362 PN->replaceAllUsesWith(NV);
1363 NV->takeName(PN);
Chris Lattner302ba6f2010-12-14 06:17:25 +00001364 PN->eraseFromParent();
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001365 }
Chris Lattner60d410d2010-12-14 08:01:53 +00001366
1367 // At this point, IfBlock1 and IfBlock2 are both empty, so our if statement
1368 // has been flattened. Change DomBlock to jump directly to our new block to
1369 // avoid other simplifycfg's kicking in on the diamond.
1370 TerminatorInst *OldTI = DomBlock->getTerminator();
Devang Patelf60364d2011-05-18 18:16:44 +00001371 Builder.SetInsertPoint(OldTI);
1372 Builder.CreateBr(BB);
Chris Lattner60d410d2010-12-14 08:01:53 +00001373 OldTI->eraseFromParent();
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001374 return true;
1375}
Chris Lattnereaba3a12005-09-19 23:49:37 +00001376
Chris Lattnerc9e495c2008-04-24 00:01:19 +00001377/// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1378/// to two returning blocks, try to merge them together into one return,
1379/// introducing a select if the return values disagree.
Devang Patel176ec402011-05-18 21:33:11 +00001380static bool SimplifyCondBranchToTwoReturns(BranchInst *BI,
1381 IRBuilder<> &Builder) {
Chris Lattnerc9e495c2008-04-24 00:01:19 +00001382 assert(BI->isConditional() && "Must be a conditional branch");
1383 BasicBlock *TrueSucc = BI->getSuccessor(0);
1384 BasicBlock *FalseSucc = BI->getSuccessor(1);
1385 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1386 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1387
1388 // Check to ensure both blocks are empty (just a return) or optionally empty
1389 // with PHI nodes. If there are other instructions, merging would cause extra
1390 // computation on one path or the other.
Chris Lattner9a2b72a2010-12-13 01:47:07 +00001391 if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator())
Devang Patel2cc86a12009-02-05 00:30:42 +00001392 return false;
Chris Lattner9a2b72a2010-12-13 01:47:07 +00001393 if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator())
Devang Patel2cc86a12009-02-05 00:30:42 +00001394 return false;
Chris Lattnerc9e495c2008-04-24 00:01:19 +00001395
Devang Patel176ec402011-05-18 21:33:11 +00001396 Builder.SetInsertPoint(BI);
Chris Lattnerc9e495c2008-04-24 00:01:19 +00001397 // Okay, we found a branch that is going to two return nodes. If
1398 // there is no return value for this function, just change the
1399 // branch into a return.
1400 if (FalseRet->getNumOperands() == 0) {
1401 TrueSucc->removePredecessor(BI->getParent());
1402 FalseSucc->removePredecessor(BI->getParent());
Devang Patel176ec402011-05-18 21:33:11 +00001403 Builder.CreateRetVoid();
Eli Friedman080efb82008-12-16 20:54:32 +00001404 EraseTerminatorInstAndDCECond(BI);
Chris Lattnerc9e495c2008-04-24 00:01:19 +00001405 return true;
1406 }
1407
Dan Gohmanfc74abf2008-07-23 00:34:11 +00001408 // Otherwise, figure out what the true and false return values are
1409 // so we can insert a new select instruction.
1410 Value *TrueValue = TrueRet->getReturnValue();
1411 Value *FalseValue = FalseRet->getReturnValue();
Chris Lattnerc9e495c2008-04-24 00:01:19 +00001412
Dan Gohmanfc74abf2008-07-23 00:34:11 +00001413 // Unwrap any PHI nodes in the return blocks.
1414 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1415 if (TVPN->getParent() == TrueSucc)
1416 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1417 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1418 if (FVPN->getParent() == FalseSucc)
1419 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1420
1421 // In order for this transformation to be safe, we must be able to
1422 // unconditionally execute both operands to the return. This is
1423 // normally the case, but we could have a potentially-trapping
1424 // constant expression that prevents this transformation from being
1425 // safe.
1426 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1427 if (TCV->canTrap())
1428 return false;
1429 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1430 if (FCV->canTrap())
1431 return false;
1432
Chris Lattnerc9e495c2008-04-24 00:01:19 +00001433 // Okay, we collected all the mapped values and checked them for sanity, and
1434 // defined to really do this transformation. First, update the CFG.
1435 TrueSucc->removePredecessor(BI->getParent());
1436 FalseSucc->removePredecessor(BI->getParent());
1437
1438 // Insert select instructions where needed.
1439 Value *BrCond = BI->getCondition();
Dan Gohmanfc74abf2008-07-23 00:34:11 +00001440 if (TrueValue) {
Chris Lattnerc9e495c2008-04-24 00:01:19 +00001441 // Insert a select if the results differ.
Dan Gohmanfc74abf2008-07-23 00:34:11 +00001442 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1443 } else if (isa<UndefValue>(TrueValue)) {
1444 TrueValue = FalseValue;
1445 } else {
Devang Patel176ec402011-05-18 21:33:11 +00001446 TrueValue = Builder.CreateSelect(BrCond, TrueValue,
1447 FalseValue, "retval");
Chris Lattnerc9e495c2008-04-24 00:01:19 +00001448 }
Chris Lattnerc9e495c2008-04-24 00:01:19 +00001449 }
1450
Devang Patel176ec402011-05-18 21:33:11 +00001451 Value *RI = !TrueValue ?
1452 Builder.CreateRetVoid() : Builder.CreateRet(TrueValue);
1453
Daniel Dunbare317bcc2009-08-23 10:29:55 +00001454 (void) RI;
Chris Lattnerc9e495c2008-04-24 00:01:19 +00001455
David Greene89d6fd32010-01-05 01:26:52 +00001456 DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
Chris Lattnerbdff5482009-08-23 04:37:46 +00001457 << "\n " << *BI << "NewRet = " << *RI
1458 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc);
Chris Lattnerc9e495c2008-04-24 00:01:19 +00001459
Eli Friedman080efb82008-12-16 20:54:32 +00001460 EraseTerminatorInstAndDCECond(BI);
1461
Chris Lattnerc9e495c2008-04-24 00:01:19 +00001462 return true;
1463}
1464
Chris Lattnerc8fbc342011-04-11 23:24:57 +00001465/// FoldBranchToCommonDest - If this basic block is simple enough, and if a
1466/// predecessor branches to us and one of our successors, fold the block into
1467/// the predecessor and use logical operations to pick the right destination.
Dan Gohman4b35f832009-06-27 21:30:38 +00001468bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
Chris Lattner093a4382008-07-13 22:23:11 +00001469 BasicBlock *BB = BI->getParent();
Devang Pateld3a17882011-05-19 20:52:46 +00001470
Chris Lattner1347e872008-07-13 21:12:01 +00001471 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
Owen Andersone84178a2010-07-14 19:52:16 +00001472 if (Cond == 0 || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1473 Cond->getParent() != BB || !Cond->hasOneUse())
1474 return false;
Devang Pateld4181942011-04-06 22:37:20 +00001475
Chris Lattner1347e872008-07-13 21:12:01 +00001476 // Only allow this if the condition is a simple instruction that can be
1477 // executed unconditionally. It must be in the same block as the branch, and
1478 // must be at the front of the block.
Devang Pateld0a203d2009-02-04 21:39:48 +00001479 BasicBlock::iterator FrontIt = BB->front();
Chris Lattner3c6e7462011-04-14 02:44:53 +00001480
Devang Pateld0a203d2009-02-04 21:39:48 +00001481 // Ignore dbg intrinsics.
Chris Lattner3c6e7462011-04-14 02:44:53 +00001482 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
Nick Lewycky9d523102011-12-26 20:37:40 +00001483
Owen Andersone84178a2010-07-14 19:52:16 +00001484 // Allow a single instruction to be hoisted in addition to the compare
1485 // that feeds the branch. We later ensure that any values that _it_ uses
1486 // were also live in the predecessor, so that we don't unnecessarily create
1487 // register pressure or inhibit out-of-order execution.
1488 Instruction *BonusInst = 0;
1489 if (&*FrontIt != Cond &&
Owen Anderson2722dfa2010-07-15 16:38:22 +00001490 FrontIt->hasOneUse() && *FrontIt->use_begin() == Cond &&
Dan Gohmanf0426602011-12-14 23:49:11 +00001491 isSafeToSpeculativelyExecute(FrontIt)) {
Owen Andersone84178a2010-07-14 19:52:16 +00001492 BonusInst = &*FrontIt;
1493 ++FrontIt;
Chris Lattner3c6e7462011-04-14 02:44:53 +00001494
1495 // Ignore dbg intrinsics.
1496 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
Devang Patel60d490c2011-04-07 23:11:25 +00001497 }
1498
Owen Andersone84178a2010-07-14 19:52:16 +00001499 // Only a single bonus inst is allowed.
1500 if (&*FrontIt != Cond)
1501 return false;
1502
Chris Lattner1347e872008-07-13 21:12:01 +00001503 // Make sure the instruction after the condition is the cond branch.
1504 BasicBlock::iterator CondIt = Cond; ++CondIt;
Chris Lattner3c6e7462011-04-14 02:44:53 +00001505
Devang Pateld0a203d2009-02-04 21:39:48 +00001506 // Ingore dbg intrinsics.
Chris Lattner3c6e7462011-04-14 02:44:53 +00001507 while (isa<DbgInfoIntrinsic>(CondIt)) ++CondIt;
1508
1509 if (&*CondIt != BI)
Chris Lattner1347e872008-07-13 21:12:01 +00001510 return false;
Chris Lattner6ff645b2009-01-19 23:03:13 +00001511
1512 // Cond is known to be a compare or binary operator. Check to make sure that
1513 // neither operand is a potentially-trapping constant expression.
1514 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
1515 if (CE->canTrap())
1516 return false;
1517 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
1518 if (CE->canTrap())
1519 return false;
1520
Chris Lattner1347e872008-07-13 21:12:01 +00001521 // Finally, don't infinitely unroll conditional loops.
1522 BasicBlock *TrueDest = BI->getSuccessor(0);
1523 BasicBlock *FalseDest = BI->getSuccessor(1);
1524 if (TrueDest == BB || FalseDest == BB)
1525 return false;
Devang Pateld4181942011-04-06 22:37:20 +00001526
Chris Lattner1347e872008-07-13 21:12:01 +00001527 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1528 BasicBlock *PredBlock = *PI;
1529 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
Chris Lattner6ff645b2009-01-19 23:03:13 +00001530
Chris Lattner093a4382008-07-13 22:23:11 +00001531 // Check that we have two conditional branches. If there is a PHI node in
1532 // the common successor, verify that the same value flows in from both
1533 // blocks.
Chris Lattner3c6e7462011-04-14 02:44:53 +00001534 if (PBI == 0 || PBI->isUnconditional() || !SafeToMergeTerminators(BI, PBI))
Chris Lattner1347e872008-07-13 21:12:01 +00001535 continue;
1536
Chris Lattner3c6e7462011-04-14 02:44:53 +00001537 // Determine if the two branches share a common destination.
1538 Instruction::BinaryOps Opc;
1539 bool InvertPredCond = false;
1540
1541 if (PBI->getSuccessor(0) == TrueDest)
1542 Opc = Instruction::Or;
1543 else if (PBI->getSuccessor(1) == FalseDest)
1544 Opc = Instruction::And;
1545 else if (PBI->getSuccessor(0) == FalseDest)
1546 Opc = Instruction::And, InvertPredCond = true;
1547 else if (PBI->getSuccessor(1) == TrueDest)
1548 Opc = Instruction::Or, InvertPredCond = true;
1549 else
1550 continue;
1551
Owen Andersone84178a2010-07-14 19:52:16 +00001552 // Ensure that any values used in the bonus instruction are also used
1553 // by the terminator of the predecessor. This means that those values
1554 // must already have been resolved, so we won't be inhibiting the
1555 // out-of-order core by speculating them earlier.
1556 if (BonusInst) {
1557 // Collect the values used by the bonus inst
1558 SmallPtrSet<Value*, 4> UsedValues;
1559 for (Instruction::op_iterator OI = BonusInst->op_begin(),
1560 OE = BonusInst->op_end(); OI != OE; ++OI) {
Nick Lewycky9d523102011-12-26 20:37:40 +00001561 Value *V = *OI;
Owen Andersone84178a2010-07-14 19:52:16 +00001562 if (!isa<Constant>(V))
1563 UsedValues.insert(V);
1564 }
1565
1566 SmallVector<std::pair<Value*, unsigned>, 4> Worklist;
1567 Worklist.push_back(std::make_pair(PBI->getOperand(0), 0));
1568
1569 // Walk up to four levels back up the use-def chain of the predecessor's
1570 // terminator to see if all those values were used. The choice of four
1571 // levels is arbitrary, to provide a compile-time-cost bound.
1572 while (!Worklist.empty()) {
1573 std::pair<Value*, unsigned> Pair = Worklist.back();
1574 Worklist.pop_back();
1575
1576 if (Pair.second >= 4) continue;
1577 UsedValues.erase(Pair.first);
1578 if (UsedValues.empty()) break;
1579
Chris Lattnerdaa02ab2010-12-13 07:00:06 +00001580 if (Instruction *I = dyn_cast<Instruction>(Pair.first)) {
Owen Andersone84178a2010-07-14 19:52:16 +00001581 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end();
1582 OI != OE; ++OI)
1583 Worklist.push_back(std::make_pair(OI->get(), Pair.second+1));
1584 }
1585 }
1586
1587 if (!UsedValues.empty()) return false;
1588 }
Chris Lattner36989092008-07-13 21:20:19 +00001589
David Greene89d6fd32010-01-05 01:26:52 +00001590 DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB);
Devang Pateld3a17882011-05-19 20:52:46 +00001591 IRBuilder<> Builder(PBI);
1592
Chris Lattner36989092008-07-13 21:20:19 +00001593 // If we need to invert the condition in the pred block to match, do so now.
1594 if (InvertPredCond) {
Chris Lattnerdaa02ab2010-12-13 07:00:06 +00001595 Value *NewCond = PBI->getCondition();
1596
1597 if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) {
1598 CmpInst *CI = cast<CmpInst>(NewCond);
1599 CI->setPredicate(CI->getInversePredicate());
1600 } else {
Devang Pateld3a17882011-05-19 20:52:46 +00001601 NewCond = Builder.CreateNot(NewCond,
1602 PBI->getCondition()->getName()+".not");
Chris Lattnerdaa02ab2010-12-13 07:00:06 +00001603 }
1604
Chris Lattner1347e872008-07-13 21:12:01 +00001605 PBI->setCondition(NewCond);
1606 BasicBlock *OldTrue = PBI->getSuccessor(0);
1607 BasicBlock *OldFalse = PBI->getSuccessor(1);
1608 PBI->setSuccessor(0, OldFalse);
1609 PBI->setSuccessor(1, OldTrue);
1610 }
Chris Lattner70087f32008-07-13 21:15:11 +00001611
Owen Andersone84178a2010-07-14 19:52:16 +00001612 // If we have a bonus inst, clone it into the predecessor block.
1613 Instruction *NewBonus = 0;
1614 if (BonusInst) {
1615 NewBonus = BonusInst->clone();
1616 PredBlock->getInstList().insert(PBI, NewBonus);
1617 NewBonus->takeName(BonusInst);
1618 BonusInst->setName(BonusInst->getName()+".old");
1619 }
1620
Chris Lattner36989092008-07-13 21:20:19 +00001621 // Clone Cond into the predecessor basic block, and or/and the
1622 // two conditions together.
Nick Lewycky67760642009-09-27 07:38:41 +00001623 Instruction *New = Cond->clone();
Owen Andersone84178a2010-07-14 19:52:16 +00001624 if (BonusInst) New->replaceUsesOfWith(BonusInst, NewBonus);
Chris Lattner36989092008-07-13 21:20:19 +00001625 PredBlock->getInstList().insert(PBI, New);
1626 New->takeName(Cond);
1627 Cond->setName(New->getName()+".old");
Chris Lattner70087f32008-07-13 21:15:11 +00001628
Devang Pateld3a17882011-05-19 20:52:46 +00001629 Instruction *NewCond =
1630 cast<Instruction>(Builder.CreateBinOp(Opc, PBI->getCondition(),
1631 New, "or.cond"));
Chris Lattner36989092008-07-13 21:20:19 +00001632 PBI->setCondition(NewCond);
1633 if (PBI->getSuccessor(0) == BB) {
1634 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1635 PBI->setSuccessor(0, TrueDest);
Chris Lattner1347e872008-07-13 21:12:01 +00001636 }
Chris Lattner36989092008-07-13 21:20:19 +00001637 if (PBI->getSuccessor(1) == BB) {
1638 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1639 PBI->setSuccessor(1, FalseDest);
1640 }
Devang Pateld4181942011-04-06 22:37:20 +00001641
Chris Lattner3c6e7462011-04-14 02:44:53 +00001642 // Copy any debug value intrinsics into the end of PredBlock.
1643 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
1644 if (isa<DbgInfoIntrinsic>(*I))
1645 I->clone()->insertBefore(PBI);
1646
Chris Lattner117f8cf2010-12-14 05:57:30 +00001647 return true;
Chris Lattner1347e872008-07-13 21:12:01 +00001648 }
1649 return false;
1650}
1651
Chris Lattner867661a2008-07-13 21:53:26 +00001652/// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
1653/// predecessor of another block, this function tries to simplify it. We know
1654/// that PBI and BI are both conditional branches, and BI is in one of the
1655/// successor blocks of PBI - PBI branches to BI.
1656static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
1657 assert(PBI->isConditional() && BI->isConditional());
1658 BasicBlock *BB = BI->getParent();
Dan Gohman4ae51262009-08-12 16:23:25 +00001659
Chris Lattner867661a2008-07-13 21:53:26 +00001660 // If this block ends with a branch instruction, and if there is a
1661 // predecessor that ends on a branch of the same condition, make
1662 // this conditional branch redundant.
1663 if (PBI->getCondition() == BI->getCondition() &&
1664 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1665 // Okay, the outcome of this conditional branch is statically
1666 // knowable. If this block had a single pred, handle specially.
1667 if (BB->getSinglePredecessor()) {
1668 // Turn this into a branch on constant.
1669 bool CondIsTrue = PBI->getSuccessor(0) == BB;
Owen Anderson1d0be152009-08-13 21:58:54 +00001670 BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1671 CondIsTrue));
Chris Lattner867661a2008-07-13 21:53:26 +00001672 return true; // Nuke the branch on constant.
1673 }
1674
1675 // Otherwise, if there are multiple predecessors, insert a PHI that merges
1676 // in the constant and simplify the block result. Subsequent passes of
1677 // simplifycfg will thread the block.
1678 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
Jay Foadd8b4fb42011-03-30 11:19:20 +00001679 pred_iterator PB = pred_begin(BB), PE = pred_end(BB);
Owen Anderson1d0be152009-08-13 21:58:54 +00001680 PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()),
Jay Foad3ecfc862011-03-30 11:28:46 +00001681 std::distance(PB, PE),
Chris Lattner867661a2008-07-13 21:53:26 +00001682 BI->getCondition()->getName() + ".pr",
1683 BB->begin());
Chris Lattnereb388af2008-07-13 21:55:46 +00001684 // Okay, we're going to insert the PHI node. Since PBI is not the only
1685 // predecessor, compute the PHI'd conditional value for all of the preds.
1686 // Any predecessor where the condition is not computable we keep symbolic.
Jay Foadd8b4fb42011-03-30 11:19:20 +00001687 for (pred_iterator PI = PB; PI != PE; ++PI) {
Gabor Greif62539832010-07-12 10:59:23 +00001688 BasicBlock *P = *PI;
1689 if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) &&
Chris Lattner867661a2008-07-13 21:53:26 +00001690 PBI != BI && PBI->isConditional() &&
1691 PBI->getCondition() == BI->getCondition() &&
1692 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1693 bool CondIsTrue = PBI->getSuccessor(0) == BB;
Owen Anderson1d0be152009-08-13 21:58:54 +00001694 NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
Gabor Greif62539832010-07-12 10:59:23 +00001695 CondIsTrue), P);
Chris Lattner867661a2008-07-13 21:53:26 +00001696 } else {
Gabor Greif62539832010-07-12 10:59:23 +00001697 NewPN->addIncoming(BI->getCondition(), P);
Chris Lattner867661a2008-07-13 21:53:26 +00001698 }
Gabor Greif62539832010-07-12 10:59:23 +00001699 }
Chris Lattner867661a2008-07-13 21:53:26 +00001700
1701 BI->setCondition(NewPN);
Chris Lattner867661a2008-07-13 21:53:26 +00001702 return true;
1703 }
1704 }
1705
1706 // If this is a conditional branch in an empty block, and if any
1707 // predecessors is a conditional branch to one of our destinations,
1708 // fold the conditions into logical ops and one cond br.
Zhou Shenga8d57fe2009-02-26 06:56:37 +00001709 BasicBlock::iterator BBI = BB->begin();
1710 // Ignore dbg intrinsics.
1711 while (isa<DbgInfoIntrinsic>(BBI))
1712 ++BBI;
1713 if (&*BBI != BI)
Chris Lattnerb8245122008-07-13 22:04:41 +00001714 return false;
Chris Lattner63bf29b2009-01-20 01:15:41 +00001715
1716
1717 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
1718 if (CE->canTrap())
1719 return false;
Chris Lattnerb8245122008-07-13 22:04:41 +00001720
1721 int PBIOp, BIOp;
1722 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
1723 PBIOp = BIOp = 0;
1724 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
1725 PBIOp = 0, BIOp = 1;
1726 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
1727 PBIOp = 1, BIOp = 0;
1728 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
1729 PBIOp = BIOp = 1;
1730 else
1731 return false;
Chris Lattner867661a2008-07-13 21:53:26 +00001732
Chris Lattnerb8245122008-07-13 22:04:41 +00001733 // Check to make sure that the other destination of this branch
1734 // isn't BB itself. If so, this is an infinite loop that will
1735 // keep getting unwound.
1736 if (PBI->getSuccessor(PBIOp) == BB)
1737 return false;
Chris Lattner867661a2008-07-13 21:53:26 +00001738
Chris Lattnerb8245122008-07-13 22:04:41 +00001739 // Do not perform this transformation if it would require
1740 // insertion of a large number of select instructions. For targets
1741 // without predication/cmovs, this is a big pessimization.
1742 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
Chris Lattner867661a2008-07-13 21:53:26 +00001743
Chris Lattnerb8245122008-07-13 22:04:41 +00001744 unsigned NumPhis = 0;
1745 for (BasicBlock::iterator II = CommonDest->begin();
1746 isa<PHINode>(II); ++II, ++NumPhis)
1747 if (NumPhis > 2) // Disable this xform.
1748 return false;
Chris Lattner867661a2008-07-13 21:53:26 +00001749
Chris Lattnerb8245122008-07-13 22:04:41 +00001750 // Finally, if everything is ok, fold the branches to logical ops.
1751 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1752
David Greene89d6fd32010-01-05 01:26:52 +00001753 DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent()
Chris Lattnerbdff5482009-08-23 04:37:46 +00001754 << "AND: " << *BI->getParent());
Chris Lattnerb8245122008-07-13 22:04:41 +00001755
Chris Lattner093a4382008-07-13 22:23:11 +00001756
1757 // If OtherDest *is* BB, then BB is a basic block with a single conditional
1758 // branch in it, where one edge (OtherDest) goes back to itself but the other
1759 // exits. We don't *know* that the program avoids the infinite loop
1760 // (even though that seems likely). If we do this xform naively, we'll end up
1761 // recursively unpeeling the loop. Since we know that (after the xform is
1762 // done) that the block *is* infinite if reached, we just make it an obviously
1763 // infinite loop with no cond branch.
1764 if (OtherDest == BB) {
1765 // Insert it at the end of the function, because it's either code,
1766 // or it won't matter if it's hot. :)
Owen Anderson1d0be152009-08-13 21:58:54 +00001767 BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(),
1768 "infloop", BB->getParent());
Chris Lattner093a4382008-07-13 22:23:11 +00001769 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1770 OtherDest = InfLoopBlock;
1771 }
1772
David Greene89d6fd32010-01-05 01:26:52 +00001773 DEBUG(dbgs() << *PBI->getParent()->getParent());
Devang Pateld3a17882011-05-19 20:52:46 +00001774
Chris Lattnerb8245122008-07-13 22:04:41 +00001775 // BI may have other predecessors. Because of this, we leave
1776 // it alone, but modify PBI.
1777
1778 // Make sure we get to CommonDest on True&True directions.
1779 Value *PBICond = PBI->getCondition();
Devang Pateld3a17882011-05-19 20:52:46 +00001780 IRBuilder<true, NoFolder> Builder(PBI);
Chris Lattnerb8245122008-07-13 22:04:41 +00001781 if (PBIOp)
Devang Pateld3a17882011-05-19 20:52:46 +00001782 PBICond = Builder.CreateNot(PBICond, PBICond->getName()+".not");
1783
Chris Lattnerb8245122008-07-13 22:04:41 +00001784 Value *BICond = BI->getCondition();
1785 if (BIOp)
Devang Pateld3a17882011-05-19 20:52:46 +00001786 BICond = Builder.CreateNot(BICond, BICond->getName()+".not");
1787
Chris Lattnerb8245122008-07-13 22:04:41 +00001788 // Merge the conditions.
Devang Pateld3a17882011-05-19 20:52:46 +00001789 Value *Cond = Builder.CreateOr(PBICond, BICond, "brmerge");
Chris Lattnerb8245122008-07-13 22:04:41 +00001790
1791 // Modify PBI to branch on the new condition to the new dests.
1792 PBI->setCondition(Cond);
1793 PBI->setSuccessor(0, CommonDest);
1794 PBI->setSuccessor(1, OtherDest);
1795
1796 // OtherDest may have phi nodes. If so, add an entry from PBI's
1797 // block that are identical to the entries for BI's block.
Chris Lattner6de0a282010-12-14 07:09:42 +00001798 AddPredecessorToBlock(OtherDest, PBI->getParent(), BB);
Chris Lattnerb8245122008-07-13 22:04:41 +00001799
1800 // We know that the CommonDest already had an edge from PBI to
1801 // it. If it has PHIs though, the PHIs may have different
1802 // entries for BB and PBI's BB. If so, insert a select to make
1803 // them agree.
Chris Lattner6de0a282010-12-14 07:09:42 +00001804 PHINode *PN;
Chris Lattnerb8245122008-07-13 22:04:41 +00001805 for (BasicBlock::iterator II = CommonDest->begin();
1806 (PN = dyn_cast<PHINode>(II)); ++II) {
1807 Value *BIV = PN->getIncomingValueForBlock(BB);
1808 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1809 Value *PBIV = PN->getIncomingValue(PBBIdx);
1810 if (BIV != PBIV) {
1811 // Insert a select in PBI to pick the right value.
Devang Pateld3a17882011-05-19 20:52:46 +00001812 Value *NV = cast<SelectInst>
1813 (Builder.CreateSelect(PBICond, PBIV, BIV, PBIV->getName()+".mux"));
Chris Lattnerb8245122008-07-13 22:04:41 +00001814 PN->setIncomingValue(PBBIdx, NV);
Chris Lattner867661a2008-07-13 21:53:26 +00001815 }
1816 }
Chris Lattnerb8245122008-07-13 22:04:41 +00001817
David Greene89d6fd32010-01-05 01:26:52 +00001818 DEBUG(dbgs() << "INTO: " << *PBI->getParent());
1819 DEBUG(dbgs() << *PBI->getParent()->getParent());
Chris Lattnerb8245122008-07-13 22:04:41 +00001820
1821 // This basic block is probably dead. We know it has at least
1822 // one fewer predecessor.
1823 return true;
Chris Lattner867661a2008-07-13 21:53:26 +00001824}
1825
Frits van Bommel65fdded2011-01-11 12:52:11 +00001826// SimplifyTerminatorOnSelect - Simplifies a terminator by replacing it with a
1827// branch to TrueBB if Cond is true or to FalseBB if Cond is false.
1828// Takes care of updating the successors and removing the old terminator.
1829// Also makes sure not to introduce new successors by assuming that edges to
1830// non-successor TrueBBs and FalseBBs aren't reachable.
1831static bool SimplifyTerminatorOnSelect(TerminatorInst *OldTerm, Value *Cond,
1832 BasicBlock *TrueBB, BasicBlock *FalseBB){
1833 // Remove any superfluous successor edges from the CFG.
1834 // First, figure out which successors to preserve.
1835 // If TrueBB and FalseBB are equal, only try to preserve one copy of that
1836 // successor.
1837 BasicBlock *KeepEdge1 = TrueBB;
1838 BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : 0;
1839
1840 // Then remove the rest.
1841 for (unsigned I = 0, E = OldTerm->getNumSuccessors(); I != E; ++I) {
1842 BasicBlock *Succ = OldTerm->getSuccessor(I);
1843 // Make sure only to keep exactly one copy of each edge.
1844 if (Succ == KeepEdge1)
1845 KeepEdge1 = 0;
1846 else if (Succ == KeepEdge2)
1847 KeepEdge2 = 0;
1848 else
1849 Succ->removePredecessor(OldTerm->getParent());
1850 }
1851
Devang Pateld3372b82011-05-18 18:43:31 +00001852 IRBuilder<> Builder(OldTerm);
1853 Builder.SetCurrentDebugLocation(OldTerm->getDebugLoc());
1854
Frits van Bommel65fdded2011-01-11 12:52:11 +00001855 // Insert an appropriate new terminator.
1856 if ((KeepEdge1 == 0) && (KeepEdge2 == 0)) {
1857 if (TrueBB == FalseBB)
1858 // We were only looking for one successor, and it was present.
1859 // Create an unconditional branch to it.
Devang Pateld3372b82011-05-18 18:43:31 +00001860 Builder.CreateBr(TrueBB);
Frits van Bommel65fdded2011-01-11 12:52:11 +00001861 else
1862 // We found both of the successors we were looking for.
1863 // Create a conditional branch sharing the condition of the select.
Devang Pateld3372b82011-05-18 18:43:31 +00001864 Builder.CreateCondBr(Cond, TrueBB, FalseBB);
Frits van Bommel65fdded2011-01-11 12:52:11 +00001865 } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) {
1866 // Neither of the selected blocks were successors, so this
1867 // terminator must be unreachable.
1868 new UnreachableInst(OldTerm->getContext(), OldTerm);
1869 } else {
1870 // One of the selected values was a successor, but the other wasn't.
1871 // Insert an unconditional branch to the one that was found;
1872 // the edge to the one that wasn't must be unreachable.
1873 if (KeepEdge1 == 0)
1874 // Only TrueBB was found.
Devang Pateld3372b82011-05-18 18:43:31 +00001875 Builder.CreateBr(TrueBB);
Frits van Bommel65fdded2011-01-11 12:52:11 +00001876 else
1877 // Only FalseBB was found.
Devang Pateld3372b82011-05-18 18:43:31 +00001878 Builder.CreateBr(FalseBB);
Frits van Bommel65fdded2011-01-11 12:52:11 +00001879 }
1880
1881 EraseTerminatorInstAndDCECond(OldTerm);
1882 return true;
1883}
1884
Frits van Bommelf7b2a9d2011-02-28 09:44:07 +00001885// SimplifySwitchOnSelect - Replaces
1886// (switch (select cond, X, Y)) on constant X, Y
1887// with a branch - conditional if X and Y lead to distinct BBs,
1888// unconditional otherwise.
1889static bool SimplifySwitchOnSelect(SwitchInst *SI, SelectInst *Select) {
1890 // Check for constant integer values in the select.
1891 ConstantInt *TrueVal = dyn_cast<ConstantInt>(Select->getTrueValue());
1892 ConstantInt *FalseVal = dyn_cast<ConstantInt>(Select->getFalseValue());
1893 if (!TrueVal || !FalseVal)
1894 return false;
1895
1896 // Find the relevant condition and destinations.
1897 Value *Condition = Select->getCondition();
1898 BasicBlock *TrueBB = SI->getSuccessor(SI->findCaseValue(TrueVal));
1899 BasicBlock *FalseBB = SI->getSuccessor(SI->findCaseValue(FalseVal));
1900
1901 // Perform the actual simplification.
1902 return SimplifyTerminatorOnSelect(SI, Condition, TrueBB, FalseBB);
1903}
1904
Frits van Bommel7ac40c32010-12-05 18:29:03 +00001905// SimplifyIndirectBrOnSelect - Replaces
1906// (indirectbr (select cond, blockaddress(@fn, BlockA),
1907// blockaddress(@fn, BlockB)))
1908// with
1909// (br cond, BlockA, BlockB).
1910static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) {
1911 // Check that both operands of the select are block addresses.
1912 BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
1913 BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
1914 if (!TBA || !FBA)
1915 return false;
1916
1917 // Extract the actual blocks.
1918 BasicBlock *TrueBB = TBA->getBasicBlock();
1919 BasicBlock *FalseBB = FBA->getBasicBlock();
1920
Frits van Bommel65fdded2011-01-11 12:52:11 +00001921 // Perform the actual simplification.
1922 return SimplifyTerminatorOnSelect(IBI, SI->getCondition(), TrueBB, FalseBB);
Frits van Bommel7ac40c32010-12-05 18:29:03 +00001923}
1924
Chris Lattner61c77442010-12-13 03:18:54 +00001925/// TryToSimplifyUncondBranchWithICmpInIt - This is called when we find an icmp
1926/// instruction (a seteq/setne with a constant) as the only instruction in a
1927/// block that ends with an uncond branch. We are looking for a very specific
1928/// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In
1929/// this case, we merge the first two "or's of icmp" into a switch, but then the
1930/// default value goes to an uncond block with a seteq in it, we get something
1931/// like:
1932///
1933/// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ]
1934/// DEFAULT:
1935/// %tmp = icmp eq i8 %A, 92
1936/// br label %end
1937/// end:
1938/// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ]
1939///
1940/// We prefer to split the edge to 'end' so that there is a true/false entry to
1941/// the PHI, merging the third icmp into the switch.
Chris Lattner302ba6f2010-12-14 06:17:25 +00001942static bool TryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI,
Devang Patela23812c2011-05-18 18:28:48 +00001943 const TargetData *TD,
1944 IRBuilder<> &Builder) {
Chris Lattner61c77442010-12-13 03:18:54 +00001945 BasicBlock *BB = ICI->getParent();
Devang Patela23812c2011-05-18 18:28:48 +00001946
Chris Lattner61c77442010-12-13 03:18:54 +00001947 // If the block has any PHIs in it or the icmp has multiple uses, it is too
1948 // complex.
1949 if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse()) return false;
1950
1951 Value *V = ICI->getOperand(0);
1952 ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1));
1953
1954 // The pattern we're looking for is where our only predecessor is a switch on
1955 // 'V' and this block is the default case for the switch. In this case we can
1956 // fold the compared value into the switch to simplify things.
1957 BasicBlock *Pred = BB->getSinglePredecessor();
1958 if (Pred == 0 || !isa<SwitchInst>(Pred->getTerminator())) return false;
1959
1960 SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator());
1961 if (SI->getCondition() != V)
1962 return false;
1963
1964 // If BB is reachable on a non-default case, then we simply know the value of
1965 // V in this block. Substitute it and constant fold the icmp instruction
1966 // away.
1967 if (SI->getDefaultDest() != BB) {
1968 ConstantInt *VVal = SI->findCaseDest(BB);
1969 assert(VVal && "Should have a unique destination value");
1970 ICI->setOperand(0, VVal);
1971
Chris Lattner302ba6f2010-12-14 06:17:25 +00001972 if (Value *V = SimplifyInstruction(ICI, TD)) {
1973 ICI->replaceAllUsesWith(V);
Chris Lattner61c77442010-12-13 03:18:54 +00001974 ICI->eraseFromParent();
1975 }
1976 // BB is now empty, so it is likely to simplify away.
1977 return SimplifyCFG(BB) | true;
1978 }
1979
Chris Lattnerabf70672010-12-13 03:43:57 +00001980 // Ok, the block is reachable from the default dest. If the constant we're
1981 // comparing exists in one of the other edges, then we can constant fold ICI
1982 // and zap it.
1983 if (SI->findCaseValue(Cst) != 0) {
1984 Value *V;
1985 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
1986 V = ConstantInt::getFalse(BB->getContext());
1987 else
1988 V = ConstantInt::getTrue(BB->getContext());
1989
1990 ICI->replaceAllUsesWith(V);
1991 ICI->eraseFromParent();
1992 // BB is now empty, so it is likely to simplify away.
1993 return SimplifyCFG(BB) | true;
1994 }
1995
Chris Lattner61c77442010-12-13 03:18:54 +00001996 // The use of the icmp has to be in the 'end' block, by the only PHI node in
1997 // the block.
1998 BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0);
1999 PHINode *PHIUse = dyn_cast<PHINode>(ICI->use_back());
2000 if (PHIUse == 0 || PHIUse != &SuccBlock->front() ||
2001 isa<PHINode>(++BasicBlock::iterator(PHIUse)))
2002 return false;
2003
2004 // If the icmp is a SETEQ, then the default dest gets false, the new edge gets
2005 // true in the PHI.
2006 Constant *DefaultCst = ConstantInt::getTrue(BB->getContext());
2007 Constant *NewCst = ConstantInt::getFalse(BB->getContext());
2008
2009 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
2010 std::swap(DefaultCst, NewCst);
2011
2012 // Replace ICI (which is used by the PHI for the default value) with true or
2013 // false depending on if it is EQ or NE.
2014 ICI->replaceAllUsesWith(DefaultCst);
2015 ICI->eraseFromParent();
2016
2017 // Okay, the switch goes to this block on a default value. Add an edge from
2018 // the switch to the merge point on the compared value.
2019 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge",
2020 BB->getParent(), BB);
2021 SI->addCase(Cst, NewBB);
2022
2023 // NewBB branches to the phi block, add the uncond branch and the phi entry.
Devang Patela23812c2011-05-18 18:28:48 +00002024 Builder.SetInsertPoint(NewBB);
2025 Builder.SetCurrentDebugLocation(SI->getDebugLoc());
2026 Builder.CreateBr(SuccBlock);
Chris Lattner61c77442010-12-13 03:18:54 +00002027 PHIUse->addIncoming(NewCst, NewBB);
2028 return true;
2029}
2030
Chris Lattner97fdb892010-12-13 05:03:41 +00002031/// SimplifyBranchOnICmpChain - The specified branch is a conditional branch.
2032/// Check to see if it is branching on an or/and chain of icmp instructions, and
2033/// fold it into a switch instruction if so.
Devang Patel02dd5412011-05-18 23:18:47 +00002034static bool SimplifyBranchOnICmpChain(BranchInst *BI, const TargetData *TD,
2035 IRBuilder<> &Builder) {
Chris Lattner97fdb892010-12-13 05:03:41 +00002036 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
2037 if (Cond == 0) return false;
2038
2039
2040 // Change br (X == 0 | X == 1), T, F into a switch instruction.
2041 // If this is a bunch of seteq's or'd together, or if it's a bunch of
2042 // 'setne's and'ed together, collect them.
2043 Value *CompVal = 0;
2044 std::vector<ConstantInt*> Values;
2045 bool TrueWhenEqual = true;
2046 Value *ExtraCase = 0;
Benjamin Kramer33828bc2011-02-07 22:37:28 +00002047 unsigned UsedICmps = 0;
Chris Lattner97fdb892010-12-13 05:03:41 +00002048
2049 if (Cond->getOpcode() == Instruction::Or) {
Benjamin Kramer33828bc2011-02-07 22:37:28 +00002050 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, true,
2051 UsedICmps);
Chris Lattner97fdb892010-12-13 05:03:41 +00002052 } else if (Cond->getOpcode() == Instruction::And) {
Benjamin Kramer33828bc2011-02-07 22:37:28 +00002053 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, false,
2054 UsedICmps);
Chris Lattner97fdb892010-12-13 05:03:41 +00002055 TrueWhenEqual = false;
2056 }
2057
2058 // If we didn't have a multiply compared value, fail.
2059 if (CompVal == 0) return false;
2060
Benjamin Kramer33828bc2011-02-07 22:37:28 +00002061 // Avoid turning single icmps into a switch.
2062 if (UsedICmps <= 1)
2063 return false;
2064
Chris Lattner97fdb892010-12-13 05:03:41 +00002065 // There might be duplicate constants in the list, which the switch
2066 // instruction can't handle, remove them now.
2067 array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate);
2068 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
2069
2070 // If Extra was used, we require at least two switch values to do the
2071 // transformation. A switch with one value is just an cond branch.
2072 if (ExtraCase && Values.size() < 2) return false;
2073
2074 // Figure out which block is which destination.
2075 BasicBlock *DefaultBB = BI->getSuccessor(1);
2076 BasicBlock *EdgeBB = BI->getSuccessor(0);
2077 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
2078
2079 BasicBlock *BB = BI->getParent();
2080
Chris Lattner302ba6f2010-12-14 06:17:25 +00002081 DEBUG(dbgs() << "Converting 'icmp' chain with " << Values.size()
Chris Lattner117f8cf2010-12-14 05:57:30 +00002082 << " cases into SWITCH. BB is:\n" << *BB);
2083
Chris Lattner97fdb892010-12-13 05:03:41 +00002084 // If there are any extra values that couldn't be folded into the switch
2085 // then we evaluate them with an explicit branch first. Split the block
2086 // right before the condbr to handle it.
2087 if (ExtraCase) {
2088 BasicBlock *NewBB = BB->splitBasicBlock(BI, "switch.early.test");
2089 // Remove the uncond branch added to the old block.
2090 TerminatorInst *OldTI = BB->getTerminator();
Devang Patel02dd5412011-05-18 23:18:47 +00002091 Builder.SetInsertPoint(OldTI);
2092
Chris Lattner117f8cf2010-12-14 05:57:30 +00002093 if (TrueWhenEqual)
Devang Patel02dd5412011-05-18 23:18:47 +00002094 Builder.CreateCondBr(ExtraCase, EdgeBB, NewBB);
Chris Lattner117f8cf2010-12-14 05:57:30 +00002095 else
Devang Patel02dd5412011-05-18 23:18:47 +00002096 Builder.CreateCondBr(ExtraCase, NewBB, EdgeBB);
Chris Lattner117f8cf2010-12-14 05:57:30 +00002097
Chris Lattner97fdb892010-12-13 05:03:41 +00002098 OldTI->eraseFromParent();
Chris Lattner97bd89e2010-12-13 05:34:18 +00002099
2100 // If there are PHI nodes in EdgeBB, then we need to add a new entry to them
2101 // for the edge we just added.
Chris Lattner6de0a282010-12-14 07:09:42 +00002102 AddPredecessorToBlock(EdgeBB, BB, NewBB);
Chris Lattner302ba6f2010-12-14 06:17:25 +00002103
2104 DEBUG(dbgs() << " ** 'icmp' chain unhandled condition: " << *ExtraCase
2105 << "\nEXTRABB = " << *BB);
Chris Lattner97fdb892010-12-13 05:03:41 +00002106 BB = NewBB;
2107 }
Devang Patel02dd5412011-05-18 23:18:47 +00002108
2109 Builder.SetInsertPoint(BI);
Chris Lattner97fdb892010-12-13 05:03:41 +00002110 // Convert pointer to int before we switch.
2111 if (CompVal->getType()->isPointerTy()) {
2112 assert(TD && "Cannot switch on pointer without TargetData");
Devang Patel02dd5412011-05-18 23:18:47 +00002113 CompVal = Builder.CreatePtrToInt(CompVal,
2114 TD->getIntPtrType(CompVal->getContext()),
2115 "magicptr");
Chris Lattner97fdb892010-12-13 05:03:41 +00002116 }
2117
2118 // Create the new switch instruction now.
Devang Patel02dd5412011-05-18 23:18:47 +00002119 SwitchInst *New = Builder.CreateSwitch(CompVal, DefaultBB, Values.size());
Devang Pateld80e8ed2011-05-17 23:29:05 +00002120
Chris Lattner97fdb892010-12-13 05:03:41 +00002121 // Add all of the 'cases' to the switch instruction.
2122 for (unsigned i = 0, e = Values.size(); i != e; ++i)
2123 New->addCase(Values[i], EdgeBB);
2124
2125 // We added edges from PI to the EdgeBB. As such, if there were any
2126 // PHI nodes in EdgeBB, they need entries to be added corresponding to
2127 // the number of edges added.
2128 for (BasicBlock::iterator BBI = EdgeBB->begin();
2129 isa<PHINode>(BBI); ++BBI) {
2130 PHINode *PN = cast<PHINode>(BBI);
2131 Value *InVal = PN->getIncomingValueForBlock(BB);
2132 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2133 PN->addIncoming(InVal, BB);
2134 }
2135
2136 // Erase the old branch instruction.
2137 EraseTerminatorInstAndDCECond(BI);
Chris Lattner117f8cf2010-12-14 05:57:30 +00002138
Chris Lattner302ba6f2010-12-14 06:17:25 +00002139 DEBUG(dbgs() << " ** 'icmp' chain result is:\n" << *BB << '\n');
Chris Lattner97fdb892010-12-13 05:03:41 +00002140 return true;
2141}
2142
Duncan Sandsad99ef82011-09-05 12:57:57 +00002143bool SimplifyCFGOpt::SimplifyResume(ResumeInst *RI, IRBuilder<> &Builder) {
2144 // If this is a trivial landing pad that just continues unwinding the caught
2145 // exception then zap the landing pad, turning its invokes into calls.
2146 BasicBlock *BB = RI->getParent();
2147 LandingPadInst *LPInst = dyn_cast<LandingPadInst>(BB->getFirstNonPHI());
2148 if (RI->getValue() != LPInst)
2149 // Not a landing pad, or the resume is not unwinding the exception that
2150 // caused control to branch here.
2151 return false;
2152
2153 // Check that there are no other instructions except for debug intrinsics.
2154 BasicBlock::iterator I = LPInst, E = RI;
2155 while (++I != E)
2156 if (!isa<DbgInfoIntrinsic>(I))
2157 return false;
2158
2159 // Turn all invokes that unwind here into calls and delete the basic block.
2160 for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE;) {
2161 InvokeInst *II = cast<InvokeInst>((*PI++)->getTerminator());
2162 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end() - 3);
2163 // Insert a call instruction before the invoke.
2164 CallInst *Call = CallInst::Create(II->getCalledValue(), Args, "", II);
2165 Call->takeName(II);
2166 Call->setCallingConv(II->getCallingConv());
2167 Call->setAttributes(II->getAttributes());
2168 Call->setDebugLoc(II->getDebugLoc());
2169
2170 // Anything that used the value produced by the invoke instruction now uses
2171 // the value produced by the call instruction. Note that we do this even
2172 // for void functions and calls with no uses so that the callgraph edge is
2173 // updated.
2174 II->replaceAllUsesWith(Call);
2175 BB->removePredecessor(II->getParent());
2176
2177 // Insert a branch to the normal destination right before the invoke.
2178 BranchInst::Create(II->getNormalDest(), II);
2179
2180 // Finally, delete the invoke instruction!
2181 II->eraseFromParent();
2182 }
2183
2184 // The landingpad is now unreachable. Zap it.
2185 BB->eraseFromParent();
2186 return true;
2187}
2188
Devang Patel176ec402011-05-18 21:33:11 +00002189bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI, IRBuilder<> &Builder) {
Chris Lattner3d512132010-12-13 06:25:44 +00002190 BasicBlock *BB = RI->getParent();
2191 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
2192
2193 // Find predecessors that end with branches.
2194 SmallVector<BasicBlock*, 8> UncondBranchPreds;
2195 SmallVector<BranchInst*, 8> CondBranchPreds;
2196 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
2197 BasicBlock *P = *PI;
2198 TerminatorInst *PTI = P->getTerminator();
2199 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
2200 if (BI->isUnconditional())
2201 UncondBranchPreds.push_back(P);
2202 else
2203 CondBranchPreds.push_back(BI);
2204 }
2205 }
2206
2207 // If we found some, do the transformation!
Evan Chengc3f507f2011-01-29 04:46:23 +00002208 if (!UncondBranchPreds.empty() && DupRet) {
Chris Lattner3d512132010-12-13 06:25:44 +00002209 while (!UncondBranchPreds.empty()) {
2210 BasicBlock *Pred = UncondBranchPreds.pop_back_val();
2211 DEBUG(dbgs() << "FOLDING: " << *BB
2212 << "INTO UNCOND BRANCH PRED: " << *Pred);
Evan Chengc3f507f2011-01-29 04:46:23 +00002213 (void)FoldReturnIntoUncondBranch(RI, BB, Pred);
Chris Lattner3d512132010-12-13 06:25:44 +00002214 }
2215
2216 // If we eliminated all predecessors of the block, delete the block now.
2217 if (pred_begin(BB) == pred_end(BB))
2218 // We know there are no successors, so just nuke the block.
2219 BB->eraseFromParent();
2220
2221 return true;
2222 }
2223
2224 // Check out all of the conditional branches going to this return
2225 // instruction. If any of them just select between returns, change the
2226 // branch itself into a select/return pair.
2227 while (!CondBranchPreds.empty()) {
2228 BranchInst *BI = CondBranchPreds.pop_back_val();
2229
2230 // Check to see if the non-BB successor is also a return block.
2231 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
2232 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
Devang Patel176ec402011-05-18 21:33:11 +00002233 SimplifyCondBranchToTwoReturns(BI, Builder))
Chris Lattner3d512132010-12-13 06:25:44 +00002234 return true;
2235 }
2236 return false;
2237}
2238
Devang Pateld46ba262011-05-18 20:01:18 +00002239bool SimplifyCFGOpt::SimplifyUnwind(UnwindInst *UI, IRBuilder<> &Builder) {
Chris Lattner3d512132010-12-13 06:25:44 +00002240 // Check to see if the first instruction in this block is just an unwind.
2241 // If so, replace any invoke instructions which use this as an exception
2242 // destination with call instructions.
2243 BasicBlock *BB = UI->getParent();
2244 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
2245
2246 bool Changed = false;
2247 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2248 while (!Preds.empty()) {
2249 BasicBlock *Pred = Preds.back();
2250 InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator());
2251 if (II && II->getUnwindDest() == BB) {
2252 // Insert a new branch instruction before the invoke, because this
2253 // is now a fall through.
Devang Pateld46ba262011-05-18 20:01:18 +00002254 Builder.SetInsertPoint(II);
2255 BranchInst *BI = Builder.CreateBr(II->getNormalDest());
Chris Lattner3d512132010-12-13 06:25:44 +00002256 Pred->getInstList().remove(II); // Take out of symbol table
2257
2258 // Insert the call now.
2259 SmallVector<Value*,8> Args(II->op_begin(), II->op_end()-3);
Devang Pateld46ba262011-05-18 20:01:18 +00002260 Builder.SetInsertPoint(BI);
2261 CallInst *CI = Builder.CreateCall(II->getCalledValue(),
Jay Foada3efbb12011-07-15 08:37:34 +00002262 Args, II->getName());
Chris Lattner3d512132010-12-13 06:25:44 +00002263 CI->setCallingConv(II->getCallingConv());
2264 CI->setAttributes(II->getAttributes());
2265 // If the invoke produced a value, the Call now does instead.
2266 II->replaceAllUsesWith(CI);
2267 delete II;
2268 Changed = true;
2269 }
2270
2271 Preds.pop_back();
2272 }
2273
2274 // If this block is now dead (and isn't the entry block), remove it.
2275 if (pred_begin(BB) == pred_end(BB) &&
2276 BB != &BB->getParent()->getEntryBlock()) {
2277 // We know there are no successors, so just nuke the block.
2278 BB->eraseFromParent();
2279 return true;
2280 }
2281
2282 return Changed;
2283}
2284
2285bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
2286 BasicBlock *BB = UI->getParent();
2287
2288 bool Changed = false;
2289
2290 // If there are any instructions immediately before the unreachable that can
2291 // be removed, do so.
2292 while (UI != BB->begin()) {
2293 BasicBlock::iterator BBI = UI;
2294 --BBI;
Eli Friedman81763882011-08-15 23:59:28 +00002295 // Do not delete instructions that can have side effects which might cause
2296 // the unreachable to not be reachable; specifically, calls and volatile
2297 // operations may have this effect.
Chris Lattner3d512132010-12-13 06:25:44 +00002298 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
Eli Friedman81763882011-08-15 23:59:28 +00002299
2300 if (BBI->mayHaveSideEffects()) {
2301 if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
2302 if (SI->isVolatile())
2303 break;
2304 } else if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) {
2305 if (LI->isVolatile())
2306 break;
2307 } else if (AtomicRMWInst *RMWI = dyn_cast<AtomicRMWInst>(BBI)) {
2308 if (RMWI->isVolatile())
2309 break;
2310 } else if (AtomicCmpXchgInst *CXI = dyn_cast<AtomicCmpXchgInst>(BBI)) {
2311 if (CXI->isVolatile())
2312 break;
2313 } else if (!isa<FenceInst>(BBI) && !isa<VAArgInst>(BBI) &&
2314 !isa<LandingPadInst>(BBI)) {
Chris Lattner3d512132010-12-13 06:25:44 +00002315 break;
Eli Friedman81763882011-08-15 23:59:28 +00002316 }
Bill Wendling23b49ba2011-08-16 20:41:17 +00002317 // Note that deleting LandingPad's here is in fact okay, although it
2318 // involves a bit of subtle reasoning. If this inst is a LandingPad,
2319 // all the predecessors of this block will be the unwind edges of Invokes,
2320 // and we can therefore guarantee this block will be erased.
Eli Friedman81763882011-08-15 23:59:28 +00002321 }
2322
Eli Friedman2adc5b62011-03-09 00:48:33 +00002323 // Delete this instruction (any uses are guaranteed to be dead)
2324 if (!BBI->use_empty())
2325 BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
Chris Lattner302ba6f2010-12-14 06:17:25 +00002326 BBI->eraseFromParent();
Chris Lattner3d512132010-12-13 06:25:44 +00002327 Changed = true;
2328 }
2329
2330 // If the unreachable instruction is the first in the block, take a gander
2331 // at all of the predecessors of this instruction, and simplify them.
2332 if (&BB->front() != UI) return Changed;
2333
2334 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2335 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
2336 TerminatorInst *TI = Preds[i]->getTerminator();
Devang Patel1aa89a22011-05-19 00:09:21 +00002337 IRBuilder<> Builder(TI);
Chris Lattner3d512132010-12-13 06:25:44 +00002338 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
2339 if (BI->isUnconditional()) {
2340 if (BI->getSuccessor(0) == BB) {
2341 new UnreachableInst(TI->getContext(), TI);
2342 TI->eraseFromParent();
2343 Changed = true;
2344 }
2345 } else {
2346 if (BI->getSuccessor(0) == BB) {
Devang Patel1aa89a22011-05-19 00:09:21 +00002347 Builder.CreateBr(BI->getSuccessor(1));
Chris Lattner3d512132010-12-13 06:25:44 +00002348 EraseTerminatorInstAndDCECond(BI);
2349 } else if (BI->getSuccessor(1) == BB) {
Devang Patel1aa89a22011-05-19 00:09:21 +00002350 Builder.CreateBr(BI->getSuccessor(0));
Chris Lattner3d512132010-12-13 06:25:44 +00002351 EraseTerminatorInstAndDCECond(BI);
2352 Changed = true;
2353 }
2354 }
2355 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
2356 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2357 if (SI->getSuccessor(i) == BB) {
2358 BB->removePredecessor(SI->getParent());
2359 SI->removeCase(i);
2360 --i; --e;
2361 Changed = true;
2362 }
2363 // If the default value is unreachable, figure out the most popular
2364 // destination and make it the default.
2365 if (SI->getSuccessor(0) == BB) {
Eli Friedmanb1a6eab2011-03-15 02:23:35 +00002366 std::map<BasicBlock*, std::pair<unsigned, unsigned> > Popularity;
2367 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) {
Nick Lewycky9d523102011-12-26 20:37:40 +00002368 std::pair<unsigned, unsigned> &entry =
Eli Friedmanb1a6eab2011-03-15 02:23:35 +00002369 Popularity[SI->getSuccessor(i)];
2370 if (entry.first == 0) {
2371 entry.first = 1;
2372 entry.second = i;
2373 } else {
2374 entry.first++;
2375 }
2376 }
2377
Chris Lattner3d512132010-12-13 06:25:44 +00002378 // Find the most popular block.
2379 unsigned MaxPop = 0;
Eli Friedmanb1a6eab2011-03-15 02:23:35 +00002380 unsigned MaxIndex = 0;
Chris Lattner3d512132010-12-13 06:25:44 +00002381 BasicBlock *MaxBlock = 0;
Eli Friedmanb1a6eab2011-03-15 02:23:35 +00002382 for (std::map<BasicBlock*, std::pair<unsigned, unsigned> >::iterator
Chris Lattner3d512132010-12-13 06:25:44 +00002383 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
Eli Friedmanb1a6eab2011-03-15 02:23:35 +00002384 if (I->second.first > MaxPop ||
2385 (I->second.first == MaxPop && MaxIndex > I->second.second)) {
2386 MaxPop = I->second.first;
2387 MaxIndex = I->second.second;
Chris Lattner3d512132010-12-13 06:25:44 +00002388 MaxBlock = I->first;
2389 }
2390 }
2391 if (MaxBlock) {
2392 // Make this the new default, allowing us to delete any explicit
2393 // edges to it.
2394 SI->setSuccessor(0, MaxBlock);
2395 Changed = true;
2396
2397 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
2398 // it.
2399 if (isa<PHINode>(MaxBlock->begin()))
2400 for (unsigned i = 0; i != MaxPop-1; ++i)
2401 MaxBlock->removePredecessor(SI->getParent());
2402
2403 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2404 if (SI->getSuccessor(i) == MaxBlock) {
2405 SI->removeCase(i);
2406 --i; --e;
2407 }
2408 }
2409 }
2410 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
2411 if (II->getUnwindDest() == BB) {
2412 // Convert the invoke to a call instruction. This would be a good
2413 // place to note that the call does not throw though.
Devang Patel1aa89a22011-05-19 00:09:21 +00002414 BranchInst *BI = Builder.CreateBr(II->getNormalDest());
Chris Lattner3d512132010-12-13 06:25:44 +00002415 II->removeFromParent(); // Take out of symbol table
2416
2417 // Insert the call now...
2418 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end()-3);
Devang Patel1aa89a22011-05-19 00:09:21 +00002419 Builder.SetInsertPoint(BI);
2420 CallInst *CI = Builder.CreateCall(II->getCalledValue(),
Jay Foada3efbb12011-07-15 08:37:34 +00002421 Args, II->getName());
Chris Lattner3d512132010-12-13 06:25:44 +00002422 CI->setCallingConv(II->getCallingConv());
2423 CI->setAttributes(II->getAttributes());
2424 // If the invoke produced a value, the call does now instead.
2425 II->replaceAllUsesWith(CI);
2426 delete II;
2427 Changed = true;
2428 }
2429 }
2430 }
2431
2432 // If this block is now dead, remove it.
2433 if (pred_begin(BB) == pred_end(BB) &&
2434 BB != &BB->getParent()->getEntryBlock()) {
2435 // We know there are no successors, so just nuke the block.
2436 BB->eraseFromParent();
2437 return true;
2438 }
2439
2440 return Changed;
2441}
2442
Benjamin Kramer56442df2011-02-02 15:56:22 +00002443/// TurnSwitchRangeIntoICmp - Turns a switch with that contains only a
2444/// integer range comparison into a sub, an icmp and a branch.
Devang Patel007349d2011-05-18 20:35:38 +00002445static bool TurnSwitchRangeIntoICmp(SwitchInst *SI, IRBuilder<> &Builder) {
Benjamin Kramer56442df2011-02-02 15:56:22 +00002446 assert(SI->getNumCases() > 2 && "Degenerate switch?");
Benjamin Kramer56442df2011-02-02 15:56:22 +00002447
Benjamin Kramer042b27f2011-02-03 22:51:41 +00002448 // Make sure all cases point to the same destination and gather the values.
2449 SmallVector<ConstantInt *, 16> Cases;
2450 Cases.push_back(SI->getCaseValue(1));
2451 for (unsigned I = 2, E = SI->getNumCases(); I != E; ++I) {
2452 if (SI->getSuccessor(I-1) != SI->getSuccessor(I))
2453 return false;
2454 Cases.push_back(SI->getCaseValue(I));
2455 }
2456 assert(Cases.size() == SI->getNumCases()-1 && "Not all cases gathered");
2457
2458 // Sort the case values, then check if they form a range we can transform.
2459 array_pod_sort(Cases.begin(), Cases.end(), ConstantIntSortPredicate);
2460 for (unsigned I = 1, E = Cases.size(); I != E; ++I) {
2461 if (Cases[I-1]->getValue() != Cases[I]->getValue()+1)
2462 return false;
2463 }
2464
2465 Constant *Offset = ConstantExpr::getNeg(Cases.back());
Benjamin Kramer56442df2011-02-02 15:56:22 +00002466 Constant *NumCases = ConstantInt::get(Offset->getType(), SI->getNumCases()-1);
2467
Benjamin Kramer33828bc2011-02-07 22:37:28 +00002468 Value *Sub = SI->getCondition();
2469 if (!Offset->isNullValue())
Devang Patel1f5812b2011-05-19 00:13:33 +00002470 Sub = Builder.CreateAdd(Sub, Offset, Sub->getName()+".off");
2471 Value *Cmp = Builder.CreateICmpULT(Sub, NumCases, "switch");
Devang Patel007349d2011-05-18 20:35:38 +00002472 Builder.CreateCondBr(Cmp, SI->getSuccessor(1), SI->getDefaultDest());
Benjamin Kramer56442df2011-02-02 15:56:22 +00002473
2474 // Prune obsolete incoming values off the successor's PHI nodes.
2475 for (BasicBlock::iterator BBI = SI->getSuccessor(1)->begin();
2476 isa<PHINode>(BBI); ++BBI) {
2477 for (unsigned I = 0, E = SI->getNumCases()-2; I != E; ++I)
2478 cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
2479 }
2480 SI->eraseFromParent();
2481
2482 return true;
2483}
Chris Lattner3d512132010-12-13 06:25:44 +00002484
Benjamin Kramer10fcfb52011-05-14 15:57:25 +00002485/// EliminateDeadSwitchCases - Compute masked bits for the condition of a switch
2486/// and use it to remove dead cases.
2487static bool EliminateDeadSwitchCases(SwitchInst *SI) {
2488 Value *Cond = SI->getCondition();
2489 unsigned Bits = cast<IntegerType>(Cond->getType())->getBitWidth();
2490 APInt KnownZero(Bits, 0), KnownOne(Bits, 0);
2491 ComputeMaskedBits(Cond, APInt::getAllOnesValue(Bits), KnownZero, KnownOne);
2492
2493 // Gather dead cases.
2494 SmallVector<ConstantInt*, 8> DeadCases;
2495 for (unsigned I = 1, E = SI->getNumCases(); I != E; ++I) {
2496 if ((SI->getCaseValue(I)->getValue() & KnownZero) != 0 ||
2497 (SI->getCaseValue(I)->getValue() & KnownOne) != KnownOne) {
2498 DeadCases.push_back(SI->getCaseValue(I));
2499 DEBUG(dbgs() << "SimplifyCFG: switch case '"
2500 << SI->getCaseValue(I)->getValue() << "' is dead.\n");
2501 }
2502 }
2503
2504 // Remove dead cases from the switch.
2505 for (unsigned I = 0, E = DeadCases.size(); I != E; ++I) {
2506 unsigned Case = SI->findCaseValue(DeadCases[I]);
2507 // Prune unused values from PHI nodes.
2508 SI->getSuccessor(Case)->removePredecessor(SI->getParent());
2509 SI->removeCase(Case);
2510 }
2511
2512 return !DeadCases.empty();
2513}
2514
Hans Wennborg448da512011-06-18 10:28:47 +00002515/// FindPHIForConditionForwarding - If BB would be eligible for simplification
2516/// by TryToSimplifyUncondBranchFromEmptyBlock (i.e. it is empty and terminated
2517/// by an unconditional branch), look at the phi node for BB in the successor
2518/// block and see if the incoming value is equal to CaseValue. If so, return
2519/// the phi node, and set PhiIndex to BB's index in the phi node.
2520static PHINode *FindPHIForConditionForwarding(ConstantInt *CaseValue,
2521 BasicBlock *BB,
2522 int *PhiIndex) {
2523 if (BB->getFirstNonPHIOrDbg() != BB->getTerminator())
2524 return NULL; // BB must be empty to be a candidate for simplification.
2525 if (!BB->getSinglePredecessor())
2526 return NULL; // BB must be dominated by the switch.
2527
2528 BranchInst *Branch = dyn_cast<BranchInst>(BB->getTerminator());
2529 if (!Branch || !Branch->isUnconditional())
2530 return NULL; // Terminator must be unconditional branch.
2531
2532 BasicBlock *Succ = Branch->getSuccessor(0);
2533
2534 BasicBlock::iterator I = Succ->begin();
2535 while (PHINode *PHI = dyn_cast<PHINode>(I++)) {
2536 int Idx = PHI->getBasicBlockIndex(BB);
2537 assert(Idx >= 0 && "PHI has no entry for predecessor?");
2538
2539 Value *InValue = PHI->getIncomingValue(Idx);
2540 if (InValue != CaseValue) continue;
2541
2542 *PhiIndex = Idx;
2543 return PHI;
2544 }
2545
2546 return NULL;
2547}
2548
2549/// ForwardSwitchConditionToPHI - Try to forward the condition of a switch
2550/// instruction to a phi node dominated by the switch, if that would mean that
2551/// some of the destination blocks of the switch can be folded away.
2552/// Returns true if a change is made.
2553static bool ForwardSwitchConditionToPHI(SwitchInst *SI) {
2554 typedef DenseMap<PHINode*, SmallVector<int,4> > ForwardingNodesMap;
2555 ForwardingNodesMap ForwardingNodes;
2556
2557 for (unsigned I = 1; I < SI->getNumCases(); ++I) { // 0 is the default case.
2558 ConstantInt *CaseValue = SI->getCaseValue(I);
2559 BasicBlock *CaseDest = SI->getSuccessor(I);
2560
2561 int PhiIndex;
2562 PHINode *PHI = FindPHIForConditionForwarding(CaseValue, CaseDest,
2563 &PhiIndex);
2564 if (!PHI) continue;
2565
2566 ForwardingNodes[PHI].push_back(PhiIndex);
2567 }
2568
2569 bool Changed = false;
2570
2571 for (ForwardingNodesMap::iterator I = ForwardingNodes.begin(),
2572 E = ForwardingNodes.end(); I != E; ++I) {
2573 PHINode *Phi = I->first;
2574 SmallVector<int,4> &Indexes = I->second;
2575
2576 if (Indexes.size() < 2) continue;
2577
2578 for (size_t I = 0, E = Indexes.size(); I != E; ++I)
2579 Phi->setIncomingValue(Indexes[I], SI->getCondition());
2580 Changed = true;
2581 }
2582
2583 return Changed;
2584}
2585
Devang Patel007349d2011-05-18 20:35:38 +00002586bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI, IRBuilder<> &Builder) {
Chris Lattner3d512132010-12-13 06:25:44 +00002587 // If this switch is too complex to want to look at, ignore it.
2588 if (!isValueEqualityComparison(SI))
2589 return false;
2590
2591 BasicBlock *BB = SI->getParent();
2592
2593 // If we only have one predecessor, and if it is a branch on this value,
2594 // see if that predecessor totally determines the outcome of this switch.
2595 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
Devang Patel007349d2011-05-18 20:35:38 +00002596 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred, Builder))
Chris Lattner021c9d32010-12-13 06:36:51 +00002597 return SimplifyCFG(BB) | true;
Frits van Bommelf7b2a9d2011-02-28 09:44:07 +00002598
2599 Value *Cond = SI->getCondition();
2600 if (SelectInst *Select = dyn_cast<SelectInst>(Cond))
2601 if (SimplifySwitchOnSelect(SI, Select))
2602 return SimplifyCFG(BB) | true;
2603
Chris Lattner3d512132010-12-13 06:25:44 +00002604 // If the block only contains the switch, see if we can fold the block
2605 // away into any preds.
2606 BasicBlock::iterator BBI = BB->begin();
2607 // Ignore dbg intrinsics.
2608 while (isa<DbgInfoIntrinsic>(BBI))
2609 ++BBI;
2610 if (SI == &*BBI)
Devang Patelb55d9242011-05-18 20:53:17 +00002611 if (FoldValueComparisonIntoPredecessors(SI, Builder))
Chris Lattner021c9d32010-12-13 06:36:51 +00002612 return SimplifyCFG(BB) | true;
Benjamin Kramer56442df2011-02-02 15:56:22 +00002613
2614 // Try to transform the switch into an icmp and a branch.
Devang Patel007349d2011-05-18 20:35:38 +00002615 if (TurnSwitchRangeIntoICmp(SI, Builder))
Benjamin Kramer56442df2011-02-02 15:56:22 +00002616 return SimplifyCFG(BB) | true;
Benjamin Kramer10fcfb52011-05-14 15:57:25 +00002617
2618 // Remove unreachable cases.
2619 if (EliminateDeadSwitchCases(SI))
2620 return SimplifyCFG(BB) | true;
2621
Hans Wennborg448da512011-06-18 10:28:47 +00002622 if (ForwardSwitchConditionToPHI(SI))
2623 return SimplifyCFG(BB) | true;
2624
Chris Lattner3d512132010-12-13 06:25:44 +00002625 return false;
2626}
2627
2628bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) {
2629 BasicBlock *BB = IBI->getParent();
2630 bool Changed = false;
2631
2632 // Eliminate redundant destinations.
2633 SmallPtrSet<Value *, 8> Succs;
2634 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
2635 BasicBlock *Dest = IBI->getDestination(i);
2636 if (!Dest->hasAddressTaken() || !Succs.insert(Dest)) {
2637 Dest->removePredecessor(BB);
2638 IBI->removeDestination(i);
2639 --i; --e;
2640 Changed = true;
2641 }
2642 }
2643
2644 if (IBI->getNumDestinations() == 0) {
2645 // If the indirectbr has no successors, change it to unreachable.
2646 new UnreachableInst(IBI->getContext(), IBI);
2647 EraseTerminatorInstAndDCECond(IBI);
2648 return true;
2649 }
2650
2651 if (IBI->getNumDestinations() == 1) {
2652 // If the indirectbr has one successor, change it to a direct branch.
2653 BranchInst::Create(IBI->getDestination(0), IBI);
2654 EraseTerminatorInstAndDCECond(IBI);
2655 return true;
2656 }
2657
2658 if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
2659 if (SimplifyIndirectBrOnSelect(IBI, SI))
2660 return SimplifyCFG(BB) | true;
2661 }
2662 return Changed;
2663}
2664
Devang Patela23812c2011-05-18 18:28:48 +00002665bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI, IRBuilder<> &Builder){
Chris Lattner3d512132010-12-13 06:25:44 +00002666 BasicBlock *BB = BI->getParent();
2667
2668 // If the Terminator is the only non-phi instruction, simplify the block.
Rafael Espindola77a2c372011-06-30 20:14:24 +00002669 BasicBlock::iterator I = BB->getFirstNonPHIOrDbgOrLifetime();
Chris Lattner3d512132010-12-13 06:25:44 +00002670 if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
2671 TryToSimplifyUncondBranchFromEmptyBlock(BB))
2672 return true;
2673
2674 // If the only instruction in the block is a seteq/setne comparison
2675 // against a constant, try to simplify the block.
2676 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
2677 if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) {
2678 for (++I; isa<DbgInfoIntrinsic>(I); ++I)
2679 ;
Nick Lewycky9d523102011-12-26 20:37:40 +00002680 if (I->isTerminator() &&
2681 TryToSimplifyUncondBranchWithICmpInIt(ICI, TD, Builder))
Chris Lattner3d512132010-12-13 06:25:44 +00002682 return true;
2683 }
2684
2685 return false;
2686}
2687
2688
Devang Patel007349d2011-05-18 20:35:38 +00002689bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI, IRBuilder<> &Builder) {
Chris Lattner3d512132010-12-13 06:25:44 +00002690 BasicBlock *BB = BI->getParent();
2691
2692 // Conditional branch
2693 if (isValueEqualityComparison(BI)) {
2694 // If we only have one predecessor, and if it is a branch on this value,
2695 // see if that predecessor totally determines the outcome of this
2696 // switch.
2697 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
Devang Patel007349d2011-05-18 20:35:38 +00002698 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred, Builder))
Chris Lattner3d512132010-12-13 06:25:44 +00002699 return SimplifyCFG(BB) | true;
2700
2701 // This block must be empty, except for the setcond inst, if it exists.
2702 // Ignore dbg intrinsics.
2703 BasicBlock::iterator I = BB->begin();
2704 // Ignore dbg intrinsics.
2705 while (isa<DbgInfoIntrinsic>(I))
2706 ++I;
2707 if (&*I == BI) {
Devang Patelb55d9242011-05-18 20:53:17 +00002708 if (FoldValueComparisonIntoPredecessors(BI, Builder))
Chris Lattner3d512132010-12-13 06:25:44 +00002709 return SimplifyCFG(BB) | true;
2710 } else if (&*I == cast<Instruction>(BI->getCondition())){
2711 ++I;
2712 // Ignore dbg intrinsics.
2713 while (isa<DbgInfoIntrinsic>(I))
2714 ++I;
Devang Patelb55d9242011-05-18 20:53:17 +00002715 if (&*I == BI && FoldValueComparisonIntoPredecessors(BI, Builder))
Chris Lattner3d512132010-12-13 06:25:44 +00002716 return SimplifyCFG(BB) | true;
2717 }
2718 }
2719
2720 // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction.
Devang Patel02dd5412011-05-18 23:18:47 +00002721 if (SimplifyBranchOnICmpChain(BI, TD, Builder))
Chris Lattner3d512132010-12-13 06:25:44 +00002722 return true;
2723
2724 // We have a conditional branch to two blocks that are only reachable
2725 // from BI. We know that the condbr dominates the two blocks, so see if
2726 // there is any identical code in the "then" and "else" blocks. If so, we
2727 // can hoist it up to the branching block.
2728 if (BI->getSuccessor(0)->getSinglePredecessor() != 0) {
2729 if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
Rafael Espindola216dde92011-05-19 02:26:30 +00002730 if (HoistThenElseCodeToIf(BI))
Chris Lattner3d512132010-12-13 06:25:44 +00002731 return SimplifyCFG(BB) | true;
2732 } else {
2733 // If Successor #1 has multiple preds, we may be able to conditionally
2734 // execute Successor #0 if it branches to successor #1.
2735 TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator();
2736 if (Succ0TI->getNumSuccessors() == 1 &&
2737 Succ0TI->getSuccessor(0) == BI->getSuccessor(1))
Rafael Espindola216dde92011-05-19 02:26:30 +00002738 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0)))
Chris Lattner3d512132010-12-13 06:25:44 +00002739 return SimplifyCFG(BB) | true;
2740 }
2741 } else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
2742 // If Successor #0 has multiple preds, we may be able to conditionally
2743 // execute Successor #1 if it branches to successor #0.
2744 TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator();
2745 if (Succ1TI->getNumSuccessors() == 1 &&
2746 Succ1TI->getSuccessor(0) == BI->getSuccessor(0))
Rafael Espindola216dde92011-05-19 02:26:30 +00002747 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1)))
Chris Lattner3d512132010-12-13 06:25:44 +00002748 return SimplifyCFG(BB) | true;
2749 }
2750
2751 // If this is a branch on a phi node in the current block, thread control
2752 // through this block if any PHI node entries are constants.
2753 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
2754 if (PN->getParent() == BI->getParent())
Chris Lattner302ba6f2010-12-14 06:17:25 +00002755 if (FoldCondBranchOnPHI(BI, TD))
Chris Lattner3d512132010-12-13 06:25:44 +00002756 return SimplifyCFG(BB) | true;
2757
Nick Lewycky9d523102011-12-26 20:37:40 +00002758 // If this basic block is ONLY a compare and a branch, and if a predecessor
2759 // branches to us and one of our successors, fold the comparison into the
Chris Lattner3d512132010-12-13 06:25:44 +00002760 // predecessor and use logical operations to pick the right destination.
2761 if (FoldBranchToCommonDest(BI))
Owen Anderson2d9220e2010-12-13 23:49:28 +00002762 return SimplifyCFG(BB) | true;
Chris Lattner3d512132010-12-13 06:25:44 +00002763
2764 // Scan predecessor blocks for conditional branches.
2765 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2766 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2767 if (PBI != BI && PBI->isConditional())
2768 if (SimplifyCondBranchToCondBranch(PBI, BI))
2769 return SimplifyCFG(BB) | true;
2770
2771 return false;
2772}
2773
Benjamin Kramer98d6d232011-08-26 01:22:29 +00002774/// Check if passing a value to an instruction will cause undefined behavior.
2775static bool passingValueIsAlwaysUndefined(Value *V, Instruction *I) {
2776 Constant *C = dyn_cast<Constant>(V);
2777 if (!C)
2778 return false;
2779
Benjamin Kramer9bb54882011-08-26 02:25:55 +00002780 if (!I->hasOneUse()) // Only look at single-use instructions, for compile time
Benjamin Kramer98d6d232011-08-26 01:22:29 +00002781 return false;
2782
2783 if (C->isNullValue()) {
2784 Instruction *Use = I->use_back();
2785
2786 // Now make sure that there are no instructions in between that can alter
2787 // control flow (eg. calls)
2788 for (BasicBlock::iterator i = ++BasicBlock::iterator(I); &*i != Use; ++i)
Benjamin Kramer9bb54882011-08-26 02:25:55 +00002789 if (i == I->getParent()->end() || i->mayHaveSideEffects())
Benjamin Kramer98d6d232011-08-26 01:22:29 +00002790 return false;
2791
2792 // Look through GEPs. A load from a GEP derived from NULL is still undefined
2793 if (GetElementPtrInst *GEP = dyn_cast<GetElementPtrInst>(Use))
2794 if (GEP->getPointerOperand() == I)
2795 return passingValueIsAlwaysUndefined(V, GEP);
2796
2797 // Look through bitcasts.
2798 if (BitCastInst *BC = dyn_cast<BitCastInst>(Use))
2799 return passingValueIsAlwaysUndefined(V, BC);
2800
Benjamin Kramer9bb54882011-08-26 02:25:55 +00002801 // Load from null is undefined.
2802 if (LoadInst *LI = dyn_cast<LoadInst>(Use))
2803 return LI->getPointerAddressSpace() == 0;
Benjamin Kramer98d6d232011-08-26 01:22:29 +00002804
Benjamin Kramer9bb54882011-08-26 02:25:55 +00002805 // Store to null is undefined.
2806 if (StoreInst *SI = dyn_cast<StoreInst>(Use))
2807 return SI->getPointerAddressSpace() == 0 && SI->getPointerOperand() == I;
Benjamin Kramer98d6d232011-08-26 01:22:29 +00002808 }
2809 return false;
2810}
2811
2812/// If BB has an incoming value that will always trigger undefined behavior
Nick Lewycky9d523102011-12-26 20:37:40 +00002813/// (eg. null pointer dereference), remove the branch leading here.
Benjamin Kramer98d6d232011-08-26 01:22:29 +00002814static bool removeUndefIntroducingPredecessor(BasicBlock *BB) {
2815 for (BasicBlock::iterator i = BB->begin();
2816 PHINode *PHI = dyn_cast<PHINode>(i); ++i)
2817 for (unsigned i = 0, e = PHI->getNumIncomingValues(); i != e; ++i)
2818 if (passingValueIsAlwaysUndefined(PHI->getIncomingValue(i), PHI)) {
2819 TerminatorInst *T = PHI->getIncomingBlock(i)->getTerminator();
2820 IRBuilder<> Builder(T);
2821 if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
2822 BB->removePredecessor(PHI->getIncomingBlock(i));
2823 // Turn uncoditional branches into unreachables and remove the dead
2824 // destination from conditional branches.
2825 if (BI->isUnconditional())
2826 Builder.CreateUnreachable();
2827 else
2828 Builder.CreateBr(BI->getSuccessor(0) == BB ? BI->getSuccessor(1) :
2829 BI->getSuccessor(0));
2830 BI->eraseFromParent();
2831 return true;
2832 }
2833 // TODO: SwitchInst.
2834 }
2835
2836 return false;
2837}
2838
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +00002839bool SimplifyCFGOpt::run(BasicBlock *BB) {
Chris Lattnerdc3602b2003-08-24 18:36:16 +00002840 bool Changed = false;
Chris Lattner01d1ee32002-05-21 20:50:24 +00002841
Chris Lattner302ba6f2010-12-14 06:17:25 +00002842 assert(BB && BB->getParent() && "Block not embedded in function!");
Chris Lattner01d1ee32002-05-21 20:50:24 +00002843 assert(BB->getTerminator() && "Degenerate basic block encountered!");
Chris Lattner01d1ee32002-05-21 20:50:24 +00002844
Dan Gohmane2c6d132010-08-14 00:29:42 +00002845 // Remove basic blocks that have no predecessors (except the entry block)...
2846 // or that just have themself as a predecessor. These are unreachable.
Chris Lattner302ba6f2010-12-14 06:17:25 +00002847 if ((pred_begin(BB) == pred_end(BB) &&
2848 BB != &BB->getParent()->getEntryBlock()) ||
Dan Gohmane2c6d132010-08-14 00:29:42 +00002849 BB->getSinglePredecessor() == BB) {
David Greene89d6fd32010-01-05 01:26:52 +00002850 DEBUG(dbgs() << "Removing BB: \n" << *BB);
Chris Lattner71af9b02008-12-03 06:40:52 +00002851 DeleteDeadBlock(BB);
Chris Lattner01d1ee32002-05-21 20:50:24 +00002852 return true;
2853 }
2854
Chris Lattner694e37f2003-08-17 19:41:53 +00002855 // Check to see if we can constant propagate this terminator instruction
2856 // away...
Frits van Bommel5649ba72011-05-22 16:24:18 +00002857 Changed |= ConstantFoldTerminator(BB, true);
Chris Lattner694e37f2003-08-17 19:41:53 +00002858
Dan Gohman2c635662009-10-30 22:39:04 +00002859 // Check for and eliminate duplicate PHI nodes in this block.
2860 Changed |= EliminateDuplicatePHINodes(BB);
2861
Benjamin Kramer98d6d232011-08-26 01:22:29 +00002862 // Check for and remove branches that will always cause undefined behavior.
2863 Changed |= removeUndefIntroducingPredecessor(BB);
2864
Chris Lattnerddb97a22010-12-13 05:10:48 +00002865 // Merge basic blocks into their predecessor if there is only one distinct
2866 // pred, and if there is only one distinct successor of the predecessor, and
2867 // if there are no PHI nodes.
2868 //
2869 if (MergeBlockIntoPredecessor(BB))
2870 return true;
2871
Devang Patel3e410c62011-05-18 18:01:27 +00002872 IRBuilder<> Builder(BB);
2873
Dan Gohman882d87d2008-03-11 21:53:06 +00002874 // If there is a trivial two-entry PHI node in this basic block, and we can
2875 // eliminate it, do so now.
2876 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
2877 if (PN->getNumIncomingValues() == 2)
Devang Pateld3a17882011-05-19 20:52:46 +00002878 Changed |= FoldTwoEntryPHINode(PN, TD);
Dan Gohman882d87d2008-03-11 21:53:06 +00002879
Devang Patel007349d2011-05-18 20:35:38 +00002880 Builder.SetInsertPoint(BB->getTerminator());
Chris Lattner3d512132010-12-13 06:25:44 +00002881 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
Chris Lattner021c9d32010-12-13 06:36:51 +00002882 if (BI->isUnconditional()) {
Devang Patela23812c2011-05-18 18:28:48 +00002883 if (SimplifyUncondBranch(BI, Builder)) return true;
Chris Lattner021c9d32010-12-13 06:36:51 +00002884 } else {
Devang Patel007349d2011-05-18 20:35:38 +00002885 if (SimplifyCondBranch(BI, Builder)) return true;
Chris Lattner021c9d32010-12-13 06:36:51 +00002886 }
Duncan Sandsad99ef82011-09-05 12:57:57 +00002887 } else if (ResumeInst *RI = dyn_cast<ResumeInst>(BB->getTerminator())) {
2888 if (SimplifyResume(RI, Builder)) return true;
Chris Lattner021c9d32010-12-13 06:36:51 +00002889 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
Devang Patel176ec402011-05-18 21:33:11 +00002890 if (SimplifyReturn(RI, Builder)) return true;
Chris Lattner021c9d32010-12-13 06:36:51 +00002891 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
Devang Patel007349d2011-05-18 20:35:38 +00002892 if (SimplifySwitch(SI, Builder)) return true;
Chris Lattner021c9d32010-12-13 06:36:51 +00002893 } else if (UnreachableInst *UI =
2894 dyn_cast<UnreachableInst>(BB->getTerminator())) {
2895 if (SimplifyUnreachable(UI)) return true;
2896 } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) {
Devang Pateld46ba262011-05-18 20:01:18 +00002897 if (SimplifyUnwind(UI, Builder)) return true;
Chris Lattner021c9d32010-12-13 06:36:51 +00002898 } else if (IndirectBrInst *IBI =
2899 dyn_cast<IndirectBrInst>(BB->getTerminator())) {
2900 if (SimplifyIndirectBr(IBI)) return true;
Chris Lattner19831ec2004-02-16 06:35:48 +00002901 }
2902
Chris Lattner694e37f2003-08-17 19:41:53 +00002903 return Changed;
Chris Lattner01d1ee32002-05-21 20:50:24 +00002904}
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +00002905
2906/// SimplifyCFG - This function is used to do simplification of a CFG. For
2907/// example, it adjusts branches to branches to eliminate the extra hop, it
2908/// eliminates unreachable basic blocks, and does other "peephole" optimization
2909/// of the CFG. It returns true if a modification was made.
2910///
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +00002911bool llvm::SimplifyCFG(BasicBlock *BB, const TargetData *TD) {
2912 return SimplifyCFGOpt(TD).run(BB);
2913}