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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"
17#include "llvm/Instructions.h"
Devang Patel383d7ed2009-02-03 22:12:02 +000018#include "llvm/IntrinsicInst.h"
Chris Lattner0d560082004-02-24 05:38:11 +000019#include "llvm/Type.h"
Reid Spencerc1030572007-01-19 21:13:56 +000020#include "llvm/DerivedTypes.h"
Dale Johannesenf8bc3002009-05-13 18:25:07 +000021#include "llvm/GlobalVariable.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"
Chris Lattner302ba6f2010-12-14 06:17:25 +000036#include "llvm/Support/raw_ostream.h"
Chris Lattner01d1ee32002-05-21 20:50:24 +000037#include <algorithm>
Chris Lattnerd52c2612004-02-24 07:23:58 +000038#include <set>
Chris Lattner698f96f2004-10-18 04:07:22 +000039#include <map>
Chris Lattnerf7703df2004-01-09 06:12:26 +000040using namespace llvm;
Brian Gaeked0fde302003-11-11 22:41:34 +000041
Peter Collingbourne57808b32011-04-29 18:47:38 +000042static cl::opt<unsigned>
43PHINodeFoldingThreshold("phi-node-folding-threshold", cl::Hidden, cl::init(1),
44 cl::desc("Control the amount of phi node folding to perform (default = 1)"));
45
Evan Chengc3f507f2011-01-29 04:46:23 +000046static cl::opt<bool>
47DupRet("simplifycfg-dup-ret", cl::Hidden, cl::init(false),
48 cl::desc("Duplicate return instructions into unconditional branches"));
49
Evan Cheng502a4f52008-06-12 21:15:59 +000050STATISTIC(NumSpeculations, "Number of speculative executed instructions");
51
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +000052namespace {
53class SimplifyCFGOpt {
54 const TargetData *const TD;
55
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +000056 Value *isValueEqualityComparison(TerminatorInst *TI);
57 BasicBlock *GetValueEqualityComparisonCases(TerminatorInst *TI,
58 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases);
59 bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
60 BasicBlock *Pred);
61 bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI);
62
Chris Lattner3d512132010-12-13 06:25:44 +000063 bool SimplifyReturn(ReturnInst *RI);
64 bool SimplifyUnwind(UnwindInst *UI);
65 bool SimplifyUnreachable(UnreachableInst *UI);
66 bool SimplifySwitch(SwitchInst *SI);
67 bool SimplifyIndirectBr(IndirectBrInst *IBI);
68 bool SimplifyUncondBranch(BranchInst *BI);
69 bool SimplifyCondBranch(BranchInst *BI);
70
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +000071public:
72 explicit SimplifyCFGOpt(const TargetData *td) : TD(td) {}
73 bool run(BasicBlock *BB);
74};
75}
76
Chris Lattner2bdcb562005-08-03 00:19:45 +000077/// SafeToMergeTerminators - Return true if it is safe to merge these two
78/// terminator instructions together.
79///
80static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
81 if (SI1 == SI2) return false; // Can't merge with self!
82
83 // It is not safe to merge these two switch instructions if they have a common
84 // successor, and if that successor has a PHI node, and if *that* PHI node has
85 // conflicting incoming values from the two switch blocks.
86 BasicBlock *SI1BB = SI1->getParent();
87 BasicBlock *SI2BB = SI2->getParent();
Chris Lattnerc9951232007-04-02 01:44:59 +000088 SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
Chris Lattner2bdcb562005-08-03 00:19:45 +000089
90 for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
91 if (SI1Succs.count(*I))
92 for (BasicBlock::iterator BBI = (*I)->begin();
93 isa<PHINode>(BBI); ++BBI) {
94 PHINode *PN = cast<PHINode>(BBI);
95 if (PN->getIncomingValueForBlock(SI1BB) !=
96 PN->getIncomingValueForBlock(SI2BB))
97 return false;
98 }
99
100 return true;
101}
102
103/// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
104/// now be entries in it from the 'NewPred' block. The values that will be
105/// flowing into the PHI nodes will be the same as those coming in from
106/// ExistPred, an existing predecessor of Succ.
107static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
108 BasicBlock *ExistPred) {
Chris Lattner2bdcb562005-08-03 00:19:45 +0000109 if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
110
Chris Lattner093a4382008-07-13 22:23:11 +0000111 PHINode *PN;
112 for (BasicBlock::iterator I = Succ->begin();
113 (PN = dyn_cast<PHINode>(I)); ++I)
114 PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
Chris Lattner2bdcb562005-08-03 00:19:45 +0000115}
116
Chris Lattner7e663482005-08-03 00:11:16 +0000117
Chris Lattner73c50a62010-12-14 07:00:00 +0000118/// GetIfCondition - Given a basic block (BB) with two predecessors (and at
119/// least one PHI node in it), check to see if the merge at this block is due
Chris Lattner723c66d2004-02-11 03:36:04 +0000120/// to an "if condition". If so, return the boolean condition that determines
121/// which entry into BB will be taken. Also, return by references the block
122/// that will be entered from if the condition is true, and the block that will
123/// be entered if the condition is false.
Misha Brukmanfd939082005-04-21 23:48:37 +0000124///
Chris Lattner995ba1b2010-12-14 07:15:21 +0000125/// This does no checking to see if the true/false blocks have large or unsavory
126/// instructions in them.
Chris Lattner73c50a62010-12-14 07:00:00 +0000127static Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
128 BasicBlock *&IfFalse) {
129 PHINode *SomePHI = cast<PHINode>(BB->begin());
130 assert(SomePHI->getNumIncomingValues() == 2 &&
Chris Lattner723c66d2004-02-11 03:36:04 +0000131 "Function can only handle blocks with 2 predecessors!");
Chris Lattner73c50a62010-12-14 07:00:00 +0000132 BasicBlock *Pred1 = SomePHI->getIncomingBlock(0);
133 BasicBlock *Pred2 = SomePHI->getIncomingBlock(1);
Chris Lattner723c66d2004-02-11 03:36:04 +0000134
135 // We can only handle branches. Other control flow will be lowered to
136 // branches if possible anyway.
Chris Lattner995ba1b2010-12-14 07:15:21 +0000137 BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator());
138 BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator());
139 if (Pred1Br == 0 || Pred2Br == 0)
Chris Lattner723c66d2004-02-11 03:36:04 +0000140 return 0;
Chris Lattner723c66d2004-02-11 03:36:04 +0000141
142 // Eliminate code duplication by ensuring that Pred1Br is conditional if
143 // either are.
144 if (Pred2Br->isConditional()) {
145 // If both branches are conditional, we don't have an "if statement". In
146 // reality, we could transform this case, but since the condition will be
147 // required anyway, we stand no chance of eliminating it, so the xform is
148 // probably not profitable.
149 if (Pred1Br->isConditional())
150 return 0;
151
152 std::swap(Pred1, Pred2);
153 std::swap(Pred1Br, Pred2Br);
154 }
155
156 if (Pred1Br->isConditional()) {
Chris Lattner995ba1b2010-12-14 07:15:21 +0000157 // The only thing we have to watch out for here is to make sure that Pred2
158 // doesn't have incoming edges from other blocks. If it does, the condition
159 // doesn't dominate BB.
160 if (Pred2->getSinglePredecessor() == 0)
161 return 0;
162
Chris Lattner723c66d2004-02-11 03:36:04 +0000163 // If we found a conditional branch predecessor, make sure that it branches
164 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
165 if (Pred1Br->getSuccessor(0) == BB &&
166 Pred1Br->getSuccessor(1) == Pred2) {
167 IfTrue = Pred1;
168 IfFalse = Pred2;
169 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
170 Pred1Br->getSuccessor(1) == BB) {
171 IfTrue = Pred2;
172 IfFalse = Pred1;
173 } else {
174 // We know that one arm of the conditional goes to BB, so the other must
175 // go somewhere unrelated, and this must not be an "if statement".
176 return 0;
177 }
178
Chris Lattner723c66d2004-02-11 03:36:04 +0000179 return Pred1Br->getCondition();
180 }
181
182 // Ok, if we got here, both predecessors end with an unconditional branch to
183 // BB. Don't panic! If both blocks only have a single (identical)
184 // predecessor, and THAT is a conditional branch, then we're all ok!
Chris Lattner995ba1b2010-12-14 07:15:21 +0000185 BasicBlock *CommonPred = Pred1->getSinglePredecessor();
186 if (CommonPred == 0 || CommonPred != Pred2->getSinglePredecessor())
Chris Lattner723c66d2004-02-11 03:36:04 +0000187 return 0;
188
189 // Otherwise, if this is a conditional branch, then we can use it!
Chris Lattner995ba1b2010-12-14 07:15:21 +0000190 BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator());
191 if (BI == 0) return 0;
192
193 assert(BI->isConditional() && "Two successors but not conditional?");
194 if (BI->getSuccessor(0) == Pred1) {
195 IfTrue = Pred1;
196 IfFalse = Pred2;
197 } else {
198 IfTrue = Pred2;
199 IfFalse = Pred1;
Chris Lattner723c66d2004-02-11 03:36:04 +0000200 }
Chris Lattner995ba1b2010-12-14 07:15:21 +0000201 return BI->getCondition();
Chris Lattner723c66d2004-02-11 03:36:04 +0000202}
203
Bill Wendling5049fa62009-01-19 23:43:56 +0000204/// DominatesMergePoint - If we have a merge point of an "if condition" as
205/// accepted above, return true if the specified value dominates the block. We
206/// don't handle the true generality of domination here, just a special case
207/// which works well enough for us.
208///
209/// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
Peter Collingbournef15907f2011-04-29 18:47:31 +0000210/// see if V (which must be an instruction) and its recursive operands
211/// that do not dominate BB have a combined cost lower than CostRemaining and
212/// are non-trapping. If both are true, the instruction is inserted into the
213/// set and true is returned.
214///
215/// The cost for most non-trapping instructions is defined as 1 except for
216/// Select whose cost is 2.
217///
218/// After this function returns, CostRemaining is decreased by the cost of
219/// V plus its non-dominating operands. If that cost is greater than
220/// CostRemaining, false is returned and CostRemaining is undefined.
Chris Lattner9c078662004-10-14 05:13:36 +0000221static bool DominatesMergePoint(Value *V, BasicBlock *BB,
Peter Collingbournef15907f2011-04-29 18:47:31 +0000222 SmallPtrSet<Instruction*, 4> *AggressiveInsts,
223 unsigned &CostRemaining) {
Chris Lattner570751c2004-04-09 22:50:22 +0000224 Instruction *I = dyn_cast<Instruction>(V);
Chris Lattnerb74b1812006-10-20 00:42:07 +0000225 if (!I) {
226 // Non-instructions all dominate instructions, but not all constantexprs
227 // can be executed unconditionally.
228 if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
229 if (C->canTrap())
230 return false;
231 return true;
232 }
Chris Lattner570751c2004-04-09 22:50:22 +0000233 BasicBlock *PBB = I->getParent();
Chris Lattner723c66d2004-02-11 03:36:04 +0000234
Chris Lattnerda895d62005-02-27 06:18:25 +0000235 // We don't want to allow weird loops that might have the "if condition" in
Chris Lattner570751c2004-04-09 22:50:22 +0000236 // the bottom of this block.
237 if (PBB == BB) return false;
Chris Lattner723c66d2004-02-11 03:36:04 +0000238
Chris Lattner570751c2004-04-09 22:50:22 +0000239 // If this instruction is defined in a block that contains an unconditional
240 // branch to BB, then it must be in the 'conditional' part of the "if
Chris Lattner44da7ca2010-12-14 07:41:39 +0000241 // statement". If not, it definitely dominates the region.
242 BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator());
243 if (BI == 0 || BI->isConditional() || BI->getSuccessor(0) != BB)
244 return true;
Eli Friedman0b79a772009-07-17 04:28:42 +0000245
Chris Lattner44da7ca2010-12-14 07:41:39 +0000246 // If we aren't allowing aggressive promotion anymore, then don't consider
247 // instructions in the 'if region'.
248 if (AggressiveInsts == 0) return false;
249
Peter Collingbournef15907f2011-04-29 18:47:31 +0000250 // If we have seen this instruction before, don't count it again.
251 if (AggressiveInsts->count(I)) return true;
252
Chris Lattner44da7ca2010-12-14 07:41:39 +0000253 // Okay, it looks like the instruction IS in the "condition". Check to
254 // see if it's a cheap instruction to unconditionally compute, and if it
255 // only uses stuff defined outside of the condition. If so, hoist it out.
256 if (!I->isSafeToSpeculativelyExecute())
257 return false;
Misha Brukmanfd939082005-04-21 23:48:37 +0000258
Peter Collingbournef15907f2011-04-29 18:47:31 +0000259 unsigned Cost = 0;
260
Chris Lattner44da7ca2010-12-14 07:41:39 +0000261 switch (I->getOpcode()) {
262 default: return false; // Cannot hoist this out safely.
263 case Instruction::Load:
264 // We have to check to make sure there are no instructions before the
265 // load in its basic block, as we are going to hoist the load out to its
266 // predecessor.
267 if (PBB->getFirstNonPHIOrDbg() != I)
268 return false;
Peter Collingbournef15907f2011-04-29 18:47:31 +0000269 Cost = 1;
Chris Lattner44da7ca2010-12-14 07:41:39 +0000270 break;
Benjamin Kramer278be782011-02-25 10:33:33 +0000271 case Instruction::GetElementPtr:
272 // GEPs are cheap if all indices are constant.
273 if (!cast<GetElementPtrInst>(I)->hasAllConstantIndices())
Benjamin Kramer9b61c552011-02-24 22:46:11 +0000274 return false;
Peter Collingbournef15907f2011-04-29 18:47:31 +0000275 Cost = 1;
Benjamin Kramer9b61c552011-02-24 22:46:11 +0000276 break;
Chris Lattner44da7ca2010-12-14 07:41:39 +0000277 case Instruction::Add:
278 case Instruction::Sub:
279 case Instruction::And:
280 case Instruction::Or:
281 case Instruction::Xor:
282 case Instruction::Shl:
283 case Instruction::LShr:
284 case Instruction::AShr:
285 case Instruction::ICmp:
Peter Collingbourne8a701922011-04-29 18:47:25 +0000286 case Instruction::Trunc:
287 case Instruction::ZExt:
288 case Instruction::SExt:
Peter Collingbournef15907f2011-04-29 18:47:31 +0000289 Cost = 1;
Chris Lattner44da7ca2010-12-14 07:41:39 +0000290 break; // These are all cheap and non-trapping instructions.
Peter Collingbournef15907f2011-04-29 18:47:31 +0000291
292 case Instruction::Select:
293 Cost = 2;
294 break;
Chris Lattner44da7ca2010-12-14 07:41:39 +0000295 }
Chris Lattner570751c2004-04-09 22:50:22 +0000296
Peter Collingbournef15907f2011-04-29 18:47:31 +0000297 if (Cost > CostRemaining)
298 return false;
299
300 CostRemaining -= Cost;
301
302 // Okay, we can only really hoist these out if their operands do
303 // not take us over the cost threshold.
Chris Lattner44da7ca2010-12-14 07:41:39 +0000304 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
Peter Collingbournef15907f2011-04-29 18:47:31 +0000305 if (!DominatesMergePoint(*i, BB, AggressiveInsts, CostRemaining))
Chris Lattner44da7ca2010-12-14 07:41:39 +0000306 return false;
307 // Okay, it's safe to do this! Remember this instruction.
308 AggressiveInsts->insert(I);
Chris Lattner723c66d2004-02-11 03:36:04 +0000309 return true;
310}
Chris Lattner01d1ee32002-05-21 20:50:24 +0000311
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +0000312/// GetConstantInt - Extract ConstantInt from value, looking through IntToPtr
313/// and PointerNullValue. Return NULL if value is not a constant int.
Chris Lattner28acc132010-12-13 03:30:12 +0000314static ConstantInt *GetConstantInt(Value *V, const TargetData *TD) {
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +0000315 // Normal constant int.
316 ConstantInt *CI = dyn_cast<ConstantInt>(V);
Duncan Sands1df98592010-02-16 11:11:14 +0000317 if (CI || !TD || !isa<Constant>(V) || !V->getType()->isPointerTy())
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +0000318 return CI;
319
320 // This is some kind of pointer constant. Turn it into a pointer-sized
321 // ConstantInt if possible.
322 const IntegerType *PtrTy = TD->getIntPtrType(V->getContext());
323
324 // Null pointer means 0, see SelectionDAGBuilder::getValue(const Value*).
325 if (isa<ConstantPointerNull>(V))
326 return ConstantInt::get(PtrTy, 0);
327
328 // IntToPtr const int.
329 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(V))
330 if (CE->getOpcode() == Instruction::IntToPtr)
331 if (ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(0))) {
332 // The constant is very likely to have the right type already.
333 if (CI->getType() == PtrTy)
334 return CI;
335 else
336 return cast<ConstantInt>
337 (ConstantExpr::getIntegerCast(CI, PtrTy, /*isSigned=*/false));
338 }
339 return 0;
340}
341
Chris Lattner0aa749b2010-12-13 04:26:26 +0000342/// GatherConstantCompares - Given a potentially 'or'd or 'and'd together
343/// collection of icmp eq/ne instructions that compare a value against a
344/// constant, return the value being compared, and stick the constant into the
345/// Values vector.
Chris Lattner28acc132010-12-13 03:30:12 +0000346static Value *
Chris Lattner0aa749b2010-12-13 04:26:26 +0000347GatherConstantCompares(Value *V, std::vector<ConstantInt*> &Vals, Value *&Extra,
Benjamin Kramer33828bc2011-02-07 22:37:28 +0000348 const TargetData *TD, bool isEQ, unsigned &UsedICmps) {
Chris Lattner0aa749b2010-12-13 04:26:26 +0000349 Instruction *I = dyn_cast<Instruction>(V);
350 if (I == 0) return 0;
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000351
Chris Lattner7312a222010-12-13 04:50:38 +0000352 // If this is an icmp against a constant, handle this as one of the cases.
Chris Lattner0aa749b2010-12-13 04:26:26 +0000353 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) {
Chris Lattnere27db742010-12-17 06:20:15 +0000354 if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) {
355 if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ:ICmpInst::ICMP_NE)) {
Benjamin Kramer33828bc2011-02-07 22:37:28 +0000356 UsedICmps++;
Chris Lattner0aa749b2010-12-13 04:26:26 +0000357 Vals.push_back(C);
358 return I->getOperand(0);
359 }
Chris Lattnere27db742010-12-17 06:20:15 +0000360
361 // If we have "x ult 3" comparison, for example, then we can add 0,1,2 to
362 // the set.
363 ConstantRange Span =
Chris Lattnera37029c2010-12-18 20:22:49 +0000364 ConstantRange::makeICmpRegion(ICI->getPredicate(), C->getValue());
Chris Lattnere27db742010-12-17 06:20:15 +0000365
366 // If this is an and/!= check then we want to optimize "x ugt 2" into
367 // x != 0 && x != 1.
368 if (!isEQ)
369 Span = Span.inverse();
370
371 // If there are a ton of values, we don't want to make a ginormous switch.
Benjamin Kramer14c09872010-12-17 10:48:14 +0000372 if (Span.getSetSize().ugt(8) || Span.isEmptySet() ||
Chris Lattnere27db742010-12-17 06:20:15 +0000373 // We don't handle wrapped sets yet.
374 Span.isWrappedSet())
375 return 0;
376
377 for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp)
378 Vals.push_back(ConstantInt::get(V->getContext(), Tmp));
Benjamin Kramer33828bc2011-02-07 22:37:28 +0000379 UsedICmps++;
Chris Lattnere27db742010-12-17 06:20:15 +0000380 return I->getOperand(0);
381 }
Chris Lattner662269d2010-12-13 04:18:32 +0000382 return 0;
383 }
384
Chris Lattner7312a222010-12-13 04:50:38 +0000385 // Otherwise, we can only handle an | or &, depending on isEQ.
Chris Lattner0aa749b2010-12-13 04:26:26 +0000386 if (I->getOpcode() != (isEQ ? Instruction::Or : Instruction::And))
Chris Lattner662269d2010-12-13 04:18:32 +0000387 return 0;
Chris Lattner662269d2010-12-13 04:18:32 +0000388
Chris Lattner7312a222010-12-13 04:50:38 +0000389 unsigned NumValsBeforeLHS = Vals.size();
Benjamin Kramer33828bc2011-02-07 22:37:28 +0000390 unsigned UsedICmpsBeforeLHS = UsedICmps;
Chris Lattner0aa749b2010-12-13 04:26:26 +0000391 if (Value *LHS = GatherConstantCompares(I->getOperand(0), Vals, Extra, TD,
Benjamin Kramer33828bc2011-02-07 22:37:28 +0000392 isEQ, UsedICmps)) {
Chris Lattner7312a222010-12-13 04:50:38 +0000393 unsigned NumVals = Vals.size();
Benjamin Kramer33828bc2011-02-07 22:37:28 +0000394 unsigned UsedICmpsBeforeRHS = UsedICmps;
Chris Lattner0aa749b2010-12-13 04:26:26 +0000395 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
Benjamin Kramer33828bc2011-02-07 22:37:28 +0000396 isEQ, UsedICmps)) {
Chris Lattner0aa749b2010-12-13 04:26:26 +0000397 if (LHS == RHS)
398 return LHS;
Chris Lattner92407e52010-12-13 07:41:29 +0000399 Vals.resize(NumVals);
Benjamin Kramer33828bc2011-02-07 22:37:28 +0000400 UsedICmps = UsedICmpsBeforeRHS;
Chris Lattner0aa749b2010-12-13 04:26:26 +0000401 }
Chris Lattner7312a222010-12-13 04:50:38 +0000402
403 // The RHS of the or/and can't be folded in and we haven't used "Extra" yet,
404 // set it and return success.
405 if (Extra == 0 || Extra == I->getOperand(1)) {
406 Extra = I->getOperand(1);
407 return LHS;
408 }
409
410 Vals.resize(NumValsBeforeLHS);
Benjamin Kramer33828bc2011-02-07 22:37:28 +0000411 UsedICmps = UsedICmpsBeforeLHS;
Chris Lattner7312a222010-12-13 04:50:38 +0000412 return 0;
Anton Korobeynikov07e6e562008-02-20 11:26:25 +0000413 }
Chris Lattner7312a222010-12-13 04:50:38 +0000414
415 // If the LHS can't be folded in, but Extra is available and RHS can, try to
416 // use LHS as Extra.
417 if (Extra == 0 || Extra == I->getOperand(0)) {
Chris Lattner92407e52010-12-13 07:41:29 +0000418 Value *OldExtra = Extra;
Chris Lattner7312a222010-12-13 04:50:38 +0000419 Extra = I->getOperand(0);
420 if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
Benjamin Kramer33828bc2011-02-07 22:37:28 +0000421 isEQ, UsedICmps))
Chris Lattner7312a222010-12-13 04:50:38 +0000422 return RHS;
Chris Lattner92407e52010-12-13 07:41:29 +0000423 assert(Vals.size() == NumValsBeforeLHS);
424 Extra = OldExtra;
Chris Lattner7312a222010-12-13 04:50:38 +0000425 }
426
Chris Lattner0d560082004-02-24 05:38:11 +0000427 return 0;
428}
Chris Lattner0aa749b2010-12-13 04:26:26 +0000429
Eli Friedman080efb82008-12-16 20:54:32 +0000430static void EraseTerminatorInstAndDCECond(TerminatorInst *TI) {
431 Instruction* Cond = 0;
432 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
433 Cond = dyn_cast<Instruction>(SI->getCondition());
434 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
435 if (BI->isConditional())
436 Cond = dyn_cast<Instruction>(BI->getCondition());
Frits van Bommel7ac40c32010-12-05 18:29:03 +0000437 } else if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(TI)) {
438 Cond = dyn_cast<Instruction>(IBI->getAddress());
Eli Friedman080efb82008-12-16 20:54:32 +0000439 }
440
441 TI->eraseFromParent();
442 if (Cond) RecursivelyDeleteTriviallyDeadInstructions(Cond);
443}
444
Chris Lattner9fd49552008-11-27 23:25:44 +0000445/// isValueEqualityComparison - Return true if the specified terminator checks
446/// to see if a value is equal to constant integer value.
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +0000447Value *SimplifyCFGOpt::isValueEqualityComparison(TerminatorInst *TI) {
448 Value *CV = 0;
Chris Lattner4bebf082004-03-16 19:45:22 +0000449 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
450 // Do not permit merging of large switch instructions into their
451 // predecessors unless there is only one predecessor.
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +0000452 if (SI->getNumSuccessors()*std::distance(pred_begin(SI->getParent()),
453 pred_end(SI->getParent())) <= 128)
454 CV = SI->getCondition();
455 } else if (BranchInst *BI = dyn_cast<BranchInst>(TI))
Chris Lattner542f1492004-02-28 21:28:10 +0000456 if (BI->isConditional() && BI->getCondition()->hasOneUse())
Reid Spencere4d87aa2006-12-23 06:05:41 +0000457 if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
458 if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
459 ICI->getPredicate() == ICmpInst::ICMP_NE) &&
Chris Lattner28acc132010-12-13 03:30:12 +0000460 GetConstantInt(ICI->getOperand(1), TD))
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +0000461 CV = ICI->getOperand(0);
462
463 // Unwrap any lossless ptrtoint cast.
464 if (TD && CV && CV->getType() == TD->getIntPtrType(CV->getContext()))
465 if (PtrToIntInst *PTII = dyn_cast<PtrToIntInst>(CV))
466 CV = PTII->getOperand(0);
467 return CV;
Chris Lattner542f1492004-02-28 21:28:10 +0000468}
469
Bill Wendling5049fa62009-01-19 23:43:56 +0000470/// GetValueEqualityComparisonCases - Given a value comparison instruction,
471/// decode all of the 'cases' that it represents and return the 'default' block.
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +0000472BasicBlock *SimplifyCFGOpt::
Misha Brukmanfd939082005-04-21 23:48:37 +0000473GetValueEqualityComparisonCases(TerminatorInst *TI,
Chris Lattner542f1492004-02-28 21:28:10 +0000474 std::vector<std::pair<ConstantInt*,
475 BasicBlock*> > &Cases) {
476 if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
477 Cases.reserve(SI->getNumCases());
478 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
Chris Lattnerbe54dcc2005-02-26 18:33:28 +0000479 Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i)));
Chris Lattner542f1492004-02-28 21:28:10 +0000480 return SI->getDefaultDest();
481 }
482
483 BranchInst *BI = cast<BranchInst>(TI);
Reid Spencere4d87aa2006-12-23 06:05:41 +0000484 ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
Chris Lattner28acc132010-12-13 03:30:12 +0000485 Cases.push_back(std::make_pair(GetConstantInt(ICI->getOperand(1), TD),
Reid Spencere4d87aa2006-12-23 06:05:41 +0000486 BI->getSuccessor(ICI->getPredicate() ==
487 ICmpInst::ICMP_NE)));
488 return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
Chris Lattner542f1492004-02-28 21:28:10 +0000489}
490
491
Bill Wendling5049fa62009-01-19 23:43:56 +0000492/// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
493/// in the list that match the specified block.
Misha Brukmanfd939082005-04-21 23:48:37 +0000494static void EliminateBlockCases(BasicBlock *BB,
Chris Lattner623369a2005-02-24 06:17:52 +0000495 std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
496 for (unsigned i = 0, e = Cases.size(); i != e; ++i)
497 if (Cases[i].second == BB) {
498 Cases.erase(Cases.begin()+i);
499 --i; --e;
500 }
501}
502
Bill Wendling5049fa62009-01-19 23:43:56 +0000503/// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
504/// well.
Chris Lattner623369a2005-02-24 06:17:52 +0000505static bool
506ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
507 std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
508 std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2;
509
510 // Make V1 be smaller than V2.
511 if (V1->size() > V2->size())
512 std::swap(V1, V2);
513
514 if (V1->size() == 0) return false;
515 if (V1->size() == 1) {
516 // Just scan V2.
517 ConstantInt *TheVal = (*V1)[0].first;
518 for (unsigned i = 0, e = V2->size(); i != e; ++i)
519 if (TheVal == (*V2)[i].first)
520 return true;
521 }
522
523 // Otherwise, just sort both lists and compare element by element.
Chris Lattnerfca20f52010-12-13 03:24:30 +0000524 array_pod_sort(V1->begin(), V1->end());
525 array_pod_sort(V2->begin(), V2->end());
Chris Lattner623369a2005-02-24 06:17:52 +0000526 unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
527 while (i1 != e1 && i2 != e2) {
528 if ((*V1)[i1].first == (*V2)[i2].first)
529 return true;
530 if ((*V1)[i1].first < (*V2)[i2].first)
531 ++i1;
532 else
533 ++i2;
534 }
535 return false;
536}
537
Bill Wendling5049fa62009-01-19 23:43:56 +0000538/// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
539/// terminator instruction and its block is known to only have a single
540/// predecessor block, check to see if that predecessor is also a value
541/// comparison with the same value, and if that comparison determines the
542/// outcome of this comparison. If so, simplify TI. This does a very limited
543/// form of jump threading.
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +0000544bool SimplifyCFGOpt::
545SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
546 BasicBlock *Pred) {
Chris Lattner623369a2005-02-24 06:17:52 +0000547 Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
548 if (!PredVal) return false; // Not a value comparison in predecessor.
549
550 Value *ThisVal = isValueEqualityComparison(TI);
551 assert(ThisVal && "This isn't a value comparison!!");
552 if (ThisVal != PredVal) return false; // Different predicates.
553
554 // Find out information about when control will move from Pred to TI's block.
555 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
556 BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
557 PredCases);
558 EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
Misha Brukmanfd939082005-04-21 23:48:37 +0000559
Chris Lattner623369a2005-02-24 06:17:52 +0000560 // Find information about how control leaves this block.
561 std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases;
562 BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
563 EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
564
565 // If TI's block is the default block from Pred's comparison, potentially
566 // simplify TI based on this knowledge.
567 if (PredDef == TI->getParent()) {
568 // If we are here, we know that the value is none of those cases listed in
569 // PredCases. If there are any cases in ThisCases that are in PredCases, we
570 // can simplify TI.
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000571 if (!ValuesOverlap(PredCases, ThisCases))
572 return false;
573
574 if (isa<BranchInst>(TI)) {
575 // Okay, one of the successors of this condbr is dead. Convert it to a
576 // uncond br.
577 assert(ThisCases.size() == 1 && "Branch can only have one case!");
578 // Insert the new branch.
579 Instruction *NI = BranchInst::Create(ThisDef, TI);
580 (void) NI;
Chris Lattner623369a2005-02-24 06:17:52 +0000581
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000582 // Remove PHI node entries for the dead edge.
583 ThisCases[0].second->removePredecessor(TI->getParent());
Chris Lattner623369a2005-02-24 06:17:52 +0000584
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000585 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
586 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
Chris Lattner623369a2005-02-24 06:17:52 +0000587
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000588 EraseTerminatorInstAndDCECond(TI);
589 return true;
Chris Lattner623369a2005-02-24 06:17:52 +0000590 }
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000591
592 SwitchInst *SI = cast<SwitchInst>(TI);
593 // Okay, TI has cases that are statically dead, prune them away.
594 SmallPtrSet<Constant*, 16> DeadCases;
Chris Lattner623369a2005-02-24 06:17:52 +0000595 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000596 DeadCases.insert(PredCases[i].first);
Chris Lattner623369a2005-02-24 06:17:52 +0000597
David Greene89d6fd32010-01-05 01:26:52 +0000598 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000599 << "Through successor TI: " << *TI);
Chris Lattner623369a2005-02-24 06:17:52 +0000600
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000601 for (unsigned i = SI->getNumCases()-1; i != 0; --i)
602 if (DeadCases.count(SI->getCaseValue(i))) {
603 SI->getSuccessor(i)->removePredecessor(TI->getParent());
604 SI->removeCase(i);
605 }
606
607 DEBUG(dbgs() << "Leaving: " << *TI << "\n");
Chris Lattner623369a2005-02-24 06:17:52 +0000608 return true;
609 }
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000610
611 // Otherwise, TI's block must correspond to some matched value. Find out
612 // which value (or set of values) this is.
613 ConstantInt *TIV = 0;
614 BasicBlock *TIBB = TI->getParent();
615 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
616 if (PredCases[i].second == TIBB) {
617 if (TIV != 0)
618 return false; // Cannot handle multiple values coming to this block.
619 TIV = PredCases[i].first;
620 }
621 assert(TIV && "No edge from pred to succ?");
622
623 // Okay, we found the one constant that our value can be if we get into TI's
624 // BB. Find out which successor will unconditionally be branched to.
625 BasicBlock *TheRealDest = 0;
626 for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
627 if (ThisCases[i].first == TIV) {
628 TheRealDest = ThisCases[i].second;
629 break;
630 }
631
632 // If not handled by any explicit cases, it is handled by the default case.
633 if (TheRealDest == 0) TheRealDest = ThisDef;
634
635 // Remove PHI node entries for dead edges.
636 BasicBlock *CheckEdge = TheRealDest;
637 for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
638 if (*SI != CheckEdge)
639 (*SI)->removePredecessor(TIBB);
640 else
641 CheckEdge = 0;
642
643 // Insert the new branch.
644 Instruction *NI = BranchInst::Create(TheRealDest, TI);
645 (void) NI;
646
647 DEBUG(dbgs() << "Threading pred instr: " << *Pred->getTerminator()
648 << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
649
650 EraseTerminatorInstAndDCECond(TI);
651 return true;
Chris Lattner623369a2005-02-24 06:17:52 +0000652}
653
Dale Johannesenc81f5442009-03-12 21:01:11 +0000654namespace {
655 /// ConstantIntOrdering - This class implements a stable ordering of constant
656 /// integers that does not depend on their address. This is important for
657 /// applications that sort ConstantInt's to ensure uniqueness.
658 struct ConstantIntOrdering {
659 bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
660 return LHS->getValue().ult(RHS->getValue());
661 }
662 };
663}
Dale Johannesena9537cf2009-03-12 01:00:26 +0000664
Chris Lattner6d4d21e2010-12-13 02:00:58 +0000665static int ConstantIntSortPredicate(const void *P1, const void *P2) {
666 const ConstantInt *LHS = *(const ConstantInt**)P1;
667 const ConstantInt *RHS = *(const ConstantInt**)P2;
Chris Lattnerba3c8152010-12-15 04:52:41 +0000668 if (LHS->getValue().ult(RHS->getValue()))
669 return 1;
670 if (LHS->getValue() == RHS->getValue())
671 return 0;
672 return -1;
Chris Lattner6d4d21e2010-12-13 02:00:58 +0000673}
674
Bill Wendling5049fa62009-01-19 23:43:56 +0000675/// FoldValueComparisonIntoPredecessors - The specified terminator is a value
676/// equality comparison instruction (either a switch or a branch on "X == c").
677/// See if any of the predecessors of the terminator block are value comparisons
678/// on the same value. If so, and if safe to do so, fold them together.
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +0000679bool SimplifyCFGOpt::FoldValueComparisonIntoPredecessors(TerminatorInst *TI) {
Chris Lattner542f1492004-02-28 21:28:10 +0000680 BasicBlock *BB = TI->getParent();
681 Value *CV = isValueEqualityComparison(TI); // CondVal
682 assert(CV && "Not a comparison?");
683 bool Changed = false;
684
Chris Lattner82442432008-02-18 07:42:56 +0000685 SmallVector<BasicBlock*, 16> Preds(pred_begin(BB), pred_end(BB));
Chris Lattner542f1492004-02-28 21:28:10 +0000686 while (!Preds.empty()) {
Dan Gohmane9d87f42009-05-06 17:22:41 +0000687 BasicBlock *Pred = Preds.pop_back_val();
Misha Brukmanfd939082005-04-21 23:48:37 +0000688
Chris Lattner542f1492004-02-28 21:28:10 +0000689 // See if the predecessor is a comparison with the same value.
690 TerminatorInst *PTI = Pred->getTerminator();
691 Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
692
693 if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
694 // Figure out which 'cases' to copy from SI to PSI.
695 std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
696 BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
697
698 std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
699 BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
700
701 // Based on whether the default edge from PTI goes to BB or not, fill in
702 // PredCases and PredDefault with the new switch cases we would like to
703 // build.
Chris Lattner82442432008-02-18 07:42:56 +0000704 SmallVector<BasicBlock*, 8> NewSuccessors;
Chris Lattner542f1492004-02-28 21:28:10 +0000705
706 if (PredDefault == BB) {
707 // If this is the default destination from PTI, only the edges in TI
708 // that don't occur in PTI, or that branch to BB will be activated.
Dale Johannesenc81f5442009-03-12 21:01:11 +0000709 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
Chris Lattner542f1492004-02-28 21:28:10 +0000710 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
711 if (PredCases[i].second != BB)
712 PTIHandled.insert(PredCases[i].first);
713 else {
714 // The default destination is BB, we don't need explicit targets.
715 std::swap(PredCases[i], PredCases.back());
716 PredCases.pop_back();
717 --i; --e;
718 }
719
720 // Reconstruct the new switch statement we will be building.
721 if (PredDefault != BBDefault) {
722 PredDefault->removePredecessor(Pred);
723 PredDefault = BBDefault;
724 NewSuccessors.push_back(BBDefault);
725 }
726 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
727 if (!PTIHandled.count(BBCases[i].first) &&
728 BBCases[i].second != BBDefault) {
729 PredCases.push_back(BBCases[i]);
730 NewSuccessors.push_back(BBCases[i].second);
731 }
732
733 } else {
734 // If this is not the default destination from PSI, only the edges
735 // in SI that occur in PSI with a destination of BB will be
736 // activated.
Dale Johannesenc81f5442009-03-12 21:01:11 +0000737 std::set<ConstantInt*, ConstantIntOrdering> PTIHandled;
Chris Lattner542f1492004-02-28 21:28:10 +0000738 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
739 if (PredCases[i].second == BB) {
740 PTIHandled.insert(PredCases[i].first);
741 std::swap(PredCases[i], PredCases.back());
742 PredCases.pop_back();
743 --i; --e;
744 }
745
746 // Okay, now we know which constants were sent to BB from the
747 // predecessor. Figure out where they will all go now.
748 for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
749 if (PTIHandled.count(BBCases[i].first)) {
750 // If this is one we are capable of getting...
751 PredCases.push_back(BBCases[i]);
752 NewSuccessors.push_back(BBCases[i].second);
753 PTIHandled.erase(BBCases[i].first);// This constant is taken care of
754 }
755
756 // If there are any constants vectored to BB that TI doesn't handle,
757 // they must go to the default destination of TI.
Dale Johannesenc81f5442009-03-12 21:01:11 +0000758 for (std::set<ConstantInt*, ConstantIntOrdering>::iterator I =
759 PTIHandled.begin(),
Chris Lattner542f1492004-02-28 21:28:10 +0000760 E = PTIHandled.end(); I != E; ++I) {
761 PredCases.push_back(std::make_pair(*I, BBDefault));
762 NewSuccessors.push_back(BBDefault);
763 }
764 }
765
766 // Okay, at this point, we know which new successor Pred will get. Make
767 // sure we update the number of entries in the PHI nodes for these
768 // successors.
769 for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
770 AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
771
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +0000772 // Convert pointer to int before we switch.
Duncan Sands1df98592010-02-16 11:11:14 +0000773 if (CV->getType()->isPointerTy()) {
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +0000774 assert(TD && "Cannot switch on pointer without TargetData");
775 CV = new PtrToIntInst(CV, TD->getIntPtrType(CV->getContext()),
776 "magicptr", PTI);
Devang Pateld80e8ed2011-05-17 23:29:05 +0000777 cast<PtrToIntInst>(CV)->setDebugLoc(PTI->getDebugLoc());
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +0000778 }
779
Chris Lattner542f1492004-02-28 21:28:10 +0000780 // Now that the successors are updated, create the new Switch instruction.
Gabor Greifb1dbcd82008-05-15 10:04:30 +0000781 SwitchInst *NewSI = SwitchInst::Create(CV, PredDefault,
782 PredCases.size(), PTI);
Devang Pateld80e8ed2011-05-17 23:29:05 +0000783 NewSI->setDebugLoc(PTI->getDebugLoc());
Chris Lattner542f1492004-02-28 21:28:10 +0000784 for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
785 NewSI->addCase(PredCases[i].first, PredCases[i].second);
Chris Lattner13b2f762005-01-01 16:02:12 +0000786
Eli Friedman080efb82008-12-16 20:54:32 +0000787 EraseTerminatorInstAndDCECond(PTI);
Chris Lattner13b2f762005-01-01 16:02:12 +0000788
Chris Lattner542f1492004-02-28 21:28:10 +0000789 // Okay, last check. If BB is still a successor of PSI, then we must
790 // have an infinite loop case. If so, add an infinitely looping block
791 // to handle the case to preserve the behavior of the code.
792 BasicBlock *InfLoopBlock = 0;
793 for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
794 if (NewSI->getSuccessor(i) == BB) {
795 if (InfLoopBlock == 0) {
Chris Lattner093a4382008-07-13 22:23:11 +0000796 // Insert it at the end of the function, because it's either code,
Chris Lattner542f1492004-02-28 21:28:10 +0000797 // or it won't matter if it's hot. :)
Owen Anderson1d0be152009-08-13 21:58:54 +0000798 InfLoopBlock = BasicBlock::Create(BB->getContext(),
799 "infloop", BB->getParent());
Gabor Greif051a9502008-04-06 20:25:17 +0000800 BranchInst::Create(InfLoopBlock, InfLoopBlock);
Chris Lattner542f1492004-02-28 21:28:10 +0000801 }
802 NewSI->setSuccessor(i, InfLoopBlock);
803 }
Misha Brukmanfd939082005-04-21 23:48:37 +0000804
Chris Lattner542f1492004-02-28 21:28:10 +0000805 Changed = true;
806 }
807 }
808 return Changed;
809}
810
Dale Johannesenc1f10402009-06-15 20:59:27 +0000811// isSafeToHoistInvoke - If we would need to insert a select that uses the
812// value of this invoke (comments in HoistThenElseCodeToIf explain why we
813// would need to do this), we can't hoist the invoke, as there is nowhere
814// to put the select in this case.
815static bool isSafeToHoistInvoke(BasicBlock *BB1, BasicBlock *BB2,
816 Instruction *I1, Instruction *I2) {
817 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
818 PHINode *PN;
819 for (BasicBlock::iterator BBI = SI->begin();
820 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
821 Value *BB1V = PN->getIncomingValueForBlock(BB1);
822 Value *BB2V = PN->getIncomingValueForBlock(BB2);
823 if (BB1V != BB2V && (BB1V==I1 || BB2V==I2)) {
824 return false;
825 }
826 }
827 }
828 return true;
829}
830
Chris Lattner6306d072005-08-03 17:59:45 +0000831/// HoistThenElseCodeToIf - Given a conditional branch that goes to BB1 and
Chris Lattner37dc9382004-11-30 00:29:14 +0000832/// BB2, hoist any common code in the two blocks up into the branch block. The
833/// caller of this function guarantees that BI's block dominates BB1 and BB2.
834static bool HoistThenElseCodeToIf(BranchInst *BI) {
835 // This does very trivial matching, with limited scanning, to find identical
836 // instructions in the two blocks. In particular, we don't want to get into
837 // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
838 // such, we currently just scan for obviously identical instructions in an
839 // identical order.
840 BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
841 BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
842
Devang Patel65085cf2009-02-04 00:03:08 +0000843 BasicBlock::iterator BB1_Itr = BB1->begin();
844 BasicBlock::iterator BB2_Itr = BB2->begin();
845
846 Instruction *I1 = BB1_Itr++, *I2 = BB2_Itr++;
Devang Patel949666e2011-04-07 17:27:36 +0000847 // Skip debug info if it is not identical.
848 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
849 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
850 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
851 while (isa<DbgInfoIntrinsic>(I1))
852 I1 = BB1_Itr++;
853 while (isa<DbgInfoIntrinsic>(I2))
854 I2 = BB2_Itr++;
855 }
Devang Patelae6c95b2011-04-07 00:30:15 +0000856 if (isa<PHINode>(I1) || !I1->isIdenticalToWhenDefined(I2) ||
Dale Johannesenc1f10402009-06-15 20:59:27 +0000857 (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2)))
Chris Lattner37dc9382004-11-30 00:29:14 +0000858 return false;
859
860 // If we get here, we can hoist at least one instruction.
861 BasicBlock *BIParent = BI->getParent();
Chris Lattner37dc9382004-11-30 00:29:14 +0000862
863 do {
864 // If we are hoisting the terminator instruction, don't move one (making a
865 // broken BB), instead clone it, and remove BI.
866 if (isa<TerminatorInst>(I1))
867 goto HoistTerminator;
Misha Brukmanfd939082005-04-21 23:48:37 +0000868
Chris Lattner37dc9382004-11-30 00:29:14 +0000869 // For a normal instruction, we just move one to right before the branch,
870 // then replace all uses of the other with the first. Finally, we remove
871 // the now redundant second instruction.
872 BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
873 if (!I2->use_empty())
874 I2->replaceAllUsesWith(I1);
Dan Gohman58cfa3b2009-08-25 22:11:20 +0000875 I1->intersectOptionalDataWith(I2);
Chris Lattner302ba6f2010-12-14 06:17:25 +0000876 I2->eraseFromParent();
Misha Brukmanfd939082005-04-21 23:48:37 +0000877
Devang Patel65085cf2009-02-04 00:03:08 +0000878 I1 = BB1_Itr++;
Devang Patel65085cf2009-02-04 00:03:08 +0000879 I2 = BB2_Itr++;
Devang Patel949666e2011-04-07 17:27:36 +0000880 // Skip debug info if it is not identical.
881 DbgInfoIntrinsic *DBI1 = dyn_cast<DbgInfoIntrinsic>(I1);
882 DbgInfoIntrinsic *DBI2 = dyn_cast<DbgInfoIntrinsic>(I2);
883 if (!DBI1 || !DBI2 || !DBI1->isIdenticalToWhenDefined(DBI2)) {
884 while (isa<DbgInfoIntrinsic>(I1))
885 I1 = BB1_Itr++;
886 while (isa<DbgInfoIntrinsic>(I2))
887 I2 = BB2_Itr++;
888 }
Devang Patelae6c95b2011-04-07 00:30:15 +0000889 } while (I1->isIdenticalToWhenDefined(I2));
Chris Lattner37dc9382004-11-30 00:29:14 +0000890
891 return true;
892
893HoistTerminator:
Dale Johannesenc1f10402009-06-15 20:59:27 +0000894 // It may not be possible to hoist an invoke.
895 if (isa<InvokeInst>(I1) && !isSafeToHoistInvoke(BB1, BB2, I1, I2))
896 return true;
897
Chris Lattner37dc9382004-11-30 00:29:14 +0000898 // Okay, it is safe to hoist the terminator.
Nick Lewycky67760642009-09-27 07:38:41 +0000899 Instruction *NT = I1->clone();
Chris Lattner37dc9382004-11-30 00:29:14 +0000900 BIParent->getInstList().insert(BI, NT);
Benjamin Kramerf0127052010-01-05 13:12:22 +0000901 if (!NT->getType()->isVoidTy()) {
Chris Lattner37dc9382004-11-30 00:29:14 +0000902 I1->replaceAllUsesWith(NT);
903 I2->replaceAllUsesWith(NT);
Chris Lattner86cc4232007-02-11 01:37:51 +0000904 NT->takeName(I1);
Chris Lattner37dc9382004-11-30 00:29:14 +0000905 }
906
907 // Hoisting one of the terminators from our successor is a great thing.
908 // Unfortunately, the successors of the if/else blocks may have PHI nodes in
909 // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
910 // nodes, so we insert select instruction to compute the final result.
911 std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
912 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
913 PHINode *PN;
914 for (BasicBlock::iterator BBI = SI->begin();
Chris Lattner0f535c62004-11-30 07:47:34 +0000915 (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
Chris Lattner37dc9382004-11-30 00:29:14 +0000916 Value *BB1V = PN->getIncomingValueForBlock(BB1);
917 Value *BB2V = PN->getIncomingValueForBlock(BB2);
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000918 if (BB1V == BB2V) continue;
919
920 // These values do not agree. Insert a select instruction before NT
921 // that determines the right value.
922 SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
Devang Pateld80e8ed2011-05-17 23:29:05 +0000923 if (SI == 0) {
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000924 SI = SelectInst::Create(BI->getCondition(), BB1V, BB2V,
925 BB1V->getName()+"."+BB2V->getName(), NT);
Devang Pateld80e8ed2011-05-17 23:29:05 +0000926 SI->setDebugLoc(BI->getDebugLoc());
927 }
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000928 // Make the PHI node use the select for all incoming values for BB1/BB2
929 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
930 if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
931 PN->setIncomingValue(i, SI);
Chris Lattner37dc9382004-11-30 00:29:14 +0000932 }
933 }
934
935 // Update any PHI nodes in our new successors.
936 for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
937 AddPredecessorToBlock(*SI, BIParent, BB1);
Misha Brukmanfd939082005-04-21 23:48:37 +0000938
Eli Friedman080efb82008-12-16 20:54:32 +0000939 EraseTerminatorInstAndDCECond(BI);
Chris Lattner37dc9382004-11-30 00:29:14 +0000940 return true;
941}
942
Evan Cheng4d09efd2008-06-07 08:52:29 +0000943/// SpeculativelyExecuteBB - Given a conditional branch that goes to BB1
944/// and an BB2 and the only successor of BB1 is BB2, hoist simple code
945/// (for now, restricted to a single instruction that's side effect free) from
946/// the BB1 into the branch block to speculatively execute it.
947static bool SpeculativelyExecuteBB(BranchInst *BI, BasicBlock *BB1) {
948 // Only speculatively execution a single instruction (not counting the
949 // terminator) for now.
Devang Patel06b1e672009-03-06 06:00:17 +0000950 Instruction *HInst = NULL;
951 Instruction *Term = BB1->getTerminator();
952 for (BasicBlock::iterator BBI = BB1->begin(), BBE = BB1->end();
953 BBI != BBE; ++BBI) {
954 Instruction *I = BBI;
955 // Skip debug info.
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000956 if (isa<DbgInfoIntrinsic>(I)) continue;
957 if (I == Term) break;
Devang Patel06b1e672009-03-06 06:00:17 +0000958
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000959 if (HInst)
Devang Patel06b1e672009-03-06 06:00:17 +0000960 return false;
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000961 HInst = I;
Devang Patel06b1e672009-03-06 06:00:17 +0000962 }
963 if (!HInst)
964 return false;
Evan Cheng4d09efd2008-06-07 08:52:29 +0000965
Evan Cheng797d9512008-06-11 19:18:20 +0000966 // Be conservative for now. FP select instruction can often be expensive.
967 Value *BrCond = BI->getCondition();
Chris Lattner9a2b72a2010-12-13 01:47:07 +0000968 if (isa<FCmpInst>(BrCond))
Evan Cheng797d9512008-06-11 19:18:20 +0000969 return false;
970
Evan Cheng4d09efd2008-06-07 08:52:29 +0000971 // If BB1 is actually on the false edge of the conditional branch, remember
972 // to swap the select operands later.
973 bool Invert = false;
974 if (BB1 != BI->getSuccessor(0)) {
975 assert(BB1 == BI->getSuccessor(1) && "No edge from 'if' block?");
976 Invert = true;
977 }
978
979 // Turn
980 // BB:
981 // %t1 = icmp
982 // br i1 %t1, label %BB1, label %BB2
983 // BB1:
984 // %t3 = add %t2, c
985 // br label BB2
986 // BB2:
987 // =>
988 // BB:
989 // %t1 = icmp
990 // %t4 = add %t2, c
991 // %t3 = select i1 %t1, %t2, %t3
Devang Patel06b1e672009-03-06 06:00:17 +0000992 switch (HInst->getOpcode()) {
Evan Cheng4d09efd2008-06-07 08:52:29 +0000993 default: return false; // Not safe / profitable to hoist.
994 case Instruction::Add:
995 case Instruction::Sub:
Dan Gohmanae3a0be2009-06-04 22:49:04 +0000996 // Not worth doing for vector ops.
Duncan Sands1df98592010-02-16 11:11:14 +0000997 if (HInst->getType()->isVectorTy())
Chris Lattner9dd3b612009-01-18 23:22:07 +0000998 return false;
999 break;
Evan Cheng4d09efd2008-06-07 08:52:29 +00001000 case Instruction::And:
1001 case Instruction::Or:
1002 case Instruction::Xor:
1003 case Instruction::Shl:
1004 case Instruction::LShr:
1005 case Instruction::AShr:
Chris Lattner9dd3b612009-01-18 23:22:07 +00001006 // Don't mess with vector operations.
Duncan Sands1df98592010-02-16 11:11:14 +00001007 if (HInst->getType()->isVectorTy())
Evan Chenge5334ea2008-06-25 07:50:12 +00001008 return false;
Evan Cheng4d09efd2008-06-07 08:52:29 +00001009 break; // These are all cheap and non-trapping instructions.
1010 }
Chris Lattner6fe73bb2009-01-19 00:36:37 +00001011
1012 // If the instruction is obviously dead, don't try to predicate it.
Devang Patel06b1e672009-03-06 06:00:17 +00001013 if (HInst->use_empty()) {
1014 HInst->eraseFromParent();
Chris Lattner6fe73bb2009-01-19 00:36:37 +00001015 return true;
1016 }
Evan Cheng4d09efd2008-06-07 08:52:29 +00001017
1018 // Can we speculatively execute the instruction? And what is the value
1019 // if the condition is false? Consider the phi uses, if the incoming value
1020 // from the "if" block are all the same V, then V is the value of the
1021 // select if the condition is false.
1022 BasicBlock *BIParent = BI->getParent();
1023 SmallVector<PHINode*, 4> PHIUses;
1024 Value *FalseV = NULL;
Chris Lattner6fe73bb2009-01-19 00:36:37 +00001025
1026 BasicBlock *BB2 = BB1->getTerminator()->getSuccessor(0);
Devang Patel06b1e672009-03-06 06:00:17 +00001027 for (Value::use_iterator UI = HInst->use_begin(), E = HInst->use_end();
Evan Cheng4d09efd2008-06-07 08:52:29 +00001028 UI != E; ++UI) {
Chris Lattner6fe73bb2009-01-19 00:36:37 +00001029 // Ignore any user that is not a PHI node in BB2. These can only occur in
1030 // unreachable blocks, because they would not be dominated by the instr.
Gabor Greif20361b92010-07-22 11:43:44 +00001031 PHINode *PN = dyn_cast<PHINode>(*UI);
Chris Lattner6fe73bb2009-01-19 00:36:37 +00001032 if (!PN || PN->getParent() != BB2)
1033 return false;
Evan Cheng4d09efd2008-06-07 08:52:29 +00001034 PHIUses.push_back(PN);
Chris Lattner6fe73bb2009-01-19 00:36:37 +00001035
Evan Cheng4d09efd2008-06-07 08:52:29 +00001036 Value *PHIV = PN->getIncomingValueForBlock(BIParent);
1037 if (!FalseV)
1038 FalseV = PHIV;
1039 else if (FalseV != PHIV)
Chris Lattner6fe73bb2009-01-19 00:36:37 +00001040 return false; // Inconsistent value when condition is false.
Evan Cheng4d09efd2008-06-07 08:52:29 +00001041 }
Chris Lattner6fe73bb2009-01-19 00:36:37 +00001042
1043 assert(FalseV && "Must have at least one user, and it must be a PHI");
Evan Cheng4d09efd2008-06-07 08:52:29 +00001044
Evan Cheng502a4f52008-06-12 21:15:59 +00001045 // Do not hoist the instruction if any of its operands are defined but not
1046 // used in this BB. The transformation will prevent the operand from
1047 // being sunk into the use block.
Devang Patel06b1e672009-03-06 06:00:17 +00001048 for (User::op_iterator i = HInst->op_begin(), e = HInst->op_end();
1049 i != e; ++i) {
Evan Cheng502a4f52008-06-12 21:15:59 +00001050 Instruction *OpI = dyn_cast<Instruction>(*i);
1051 if (OpI && OpI->getParent() == BIParent &&
1052 !OpI->isUsedInBasicBlock(BIParent))
1053 return false;
1054 }
1055
Devang Patel3d0a9a32008-09-18 22:50:42 +00001056 // If we get here, we can hoist the instruction. Try to place it
Dale Johannesen990afed2009-03-13 01:05:24 +00001057 // before the icmp instruction preceding the conditional branch.
Devang Patel3d0a9a32008-09-18 22:50:42 +00001058 BasicBlock::iterator InsertPos = BI;
Dale Johannesen990afed2009-03-13 01:05:24 +00001059 if (InsertPos != BIParent->begin())
1060 --InsertPos;
1061 // Skip debug info between condition and branch.
1062 while (InsertPos != BIParent->begin() && isa<DbgInfoIntrinsic>(InsertPos))
Devang Patel3d0a9a32008-09-18 22:50:42 +00001063 --InsertPos;
Devang Patel20da1f02008-10-03 18:57:37 +00001064 if (InsertPos == BrCond && !isa<PHINode>(BrCond)) {
Devang Patel3d0a9a32008-09-18 22:50:42 +00001065 SmallPtrSet<Instruction *, 4> BB1Insns;
1066 for(BasicBlock::iterator BB1I = BB1->begin(), BB1E = BB1->end();
1067 BB1I != BB1E; ++BB1I)
1068 BB1Insns.insert(BB1I);
1069 for(Value::use_iterator UI = BrCond->use_begin(), UE = BrCond->use_end();
1070 UI != UE; ++UI) {
1071 Instruction *Use = cast<Instruction>(*UI);
Chris Lattner9a2b72a2010-12-13 01:47:07 +00001072 if (!BB1Insns.count(Use)) continue;
1073
1074 // If BrCond uses the instruction that place it just before
1075 // branch instruction.
1076 InsertPos = BI;
1077 break;
Devang Patel3d0a9a32008-09-18 22:50:42 +00001078 }
1079 } else
1080 InsertPos = BI;
Devang Patel06b1e672009-03-06 06:00:17 +00001081 BIParent->getInstList().splice(InsertPos, BB1->getInstList(), HInst);
Evan Cheng4d09efd2008-06-07 08:52:29 +00001082
1083 // Create a select whose true value is the speculatively executed value and
1084 // false value is the previously determined FalseV.
1085 SelectInst *SI;
1086 if (Invert)
Devang Patel06b1e672009-03-06 06:00:17 +00001087 SI = SelectInst::Create(BrCond, FalseV, HInst,
1088 FalseV->getName() + "." + HInst->getName(), BI);
Evan Cheng4d09efd2008-06-07 08:52:29 +00001089 else
Devang Patel06b1e672009-03-06 06:00:17 +00001090 SI = SelectInst::Create(BrCond, HInst, FalseV,
1091 HInst->getName() + "." + FalseV->getName(), BI);
Devang Pateld80e8ed2011-05-17 23:29:05 +00001092 SI->setDebugLoc(BI->getDebugLoc());
Evan Cheng4d09efd2008-06-07 08:52:29 +00001093
1094 // Make the PHI node use the select for all incoming values for "then" and
1095 // "if" blocks.
1096 for (unsigned i = 0, e = PHIUses.size(); i != e; ++i) {
1097 PHINode *PN = PHIUses[i];
1098 for (unsigned j = 0, ee = PN->getNumIncomingValues(); j != ee; ++j)
Chris Lattner9a2b72a2010-12-13 01:47:07 +00001099 if (PN->getIncomingBlock(j) == BB1 || PN->getIncomingBlock(j) == BIParent)
Evan Cheng4d09efd2008-06-07 08:52:29 +00001100 PN->setIncomingValue(j, SI);
1101 }
1102
Evan Cheng502a4f52008-06-12 21:15:59 +00001103 ++NumSpeculations;
Evan Cheng4d09efd2008-06-07 08:52:29 +00001104 return true;
1105}
1106
Chris Lattner2e42e362005-09-20 00:43:16 +00001107/// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
1108/// across this block.
1109static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
1110 BranchInst *BI = cast<BranchInst>(BB->getTerminator());
Chris Lattnere9487f02005-09-20 01:48:40 +00001111 unsigned Size = 0;
1112
Devang Patel9200c892009-03-10 18:00:05 +00001113 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
Dale Johannesen8483e542009-03-12 23:18:09 +00001114 if (isa<DbgInfoIntrinsic>(BBI))
1115 continue;
Chris Lattnere9487f02005-09-20 01:48:40 +00001116 if (Size > 10) return false; // Don't clone large BB's.
Dale Johannesen8483e542009-03-12 23:18:09 +00001117 ++Size;
Chris Lattner2e42e362005-09-20 00:43:16 +00001118
Dale Johannesen8483e542009-03-12 23:18:09 +00001119 // We can only support instructions that do not define values that are
Chris Lattnere9487f02005-09-20 01:48:40 +00001120 // live outside of the current basic block.
1121 for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
1122 UI != E; ++UI) {
1123 Instruction *U = cast<Instruction>(*UI);
1124 if (U->getParent() != BB || isa<PHINode>(U)) return false;
1125 }
Chris Lattner2e42e362005-09-20 00:43:16 +00001126
1127 // Looks ok, continue checking.
1128 }
Chris Lattnere9487f02005-09-20 01:48:40 +00001129
Chris Lattner2e42e362005-09-20 00:43:16 +00001130 return true;
1131}
1132
Chris Lattnereaba3a12005-09-19 23:49:37 +00001133/// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
1134/// that is defined in the same block as the branch and if any PHI entries are
1135/// constants, thread edges corresponding to that entry to be branches to their
1136/// ultimate destination.
Chris Lattner302ba6f2010-12-14 06:17:25 +00001137static bool FoldCondBranchOnPHI(BranchInst *BI, const TargetData *TD) {
Chris Lattnereaba3a12005-09-19 23:49:37 +00001138 BasicBlock *BB = BI->getParent();
1139 PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
Chris Lattner9c88d982005-09-19 23:57:04 +00001140 // NOTE: we currently cannot transform this case if the PHI node is used
1141 // outside of the block.
Chris Lattner2e42e362005-09-20 00:43:16 +00001142 if (!PN || PN->getParent() != BB || !PN->hasOneUse())
1143 return false;
Chris Lattnereaba3a12005-09-19 23:49:37 +00001144
1145 // Degenerate case of a single entry PHI.
1146 if (PN->getNumIncomingValues() == 1) {
Chris Lattner29874e02008-12-03 19:44:02 +00001147 FoldSingleEntryPHINodes(PN->getParent());
Chris Lattnereaba3a12005-09-19 23:49:37 +00001148 return true;
1149 }
1150
1151 // Now we know that this block has multiple preds and two succs.
Chris Lattner2e42e362005-09-20 00:43:16 +00001152 if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
Chris Lattnereaba3a12005-09-19 23:49:37 +00001153
1154 // Okay, this is a simple enough basic block. See if any phi values are
1155 // constants.
Zhou Sheng6b6b6ef2007-01-11 12:24:14 +00001156 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
Chris Lattner9a2b72a2010-12-13 01:47:07 +00001157 ConstantInt *CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i));
1158 if (CB == 0 || !CB->getType()->isIntegerTy(1)) continue;
1159
1160 // Okay, we now know that all edges from PredBB should be revectored to
1161 // branch to RealDest.
1162 BasicBlock *PredBB = PN->getIncomingBlock(i);
1163 BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
1164
1165 if (RealDest == BB) continue; // Skip self loops.
1166
1167 // The dest block might have PHI nodes, other predecessors and other
1168 // difficult cases. Instead of being smart about this, just insert a new
1169 // block that jumps to the destination block, effectively splitting
1170 // the edge we are about to create.
1171 BasicBlock *EdgeBB = BasicBlock::Create(BB->getContext(),
1172 RealDest->getName()+".critedge",
1173 RealDest->getParent(), RealDest);
1174 BranchInst::Create(RealDest, EdgeBB);
Chris Lattner6de0a282010-12-14 07:09:42 +00001175
1176 // Update PHI nodes.
1177 AddPredecessorToBlock(RealDest, EdgeBB, BB);
Chris Lattner9a2b72a2010-12-13 01:47:07 +00001178
1179 // BB may have instructions that are being threaded over. Clone these
1180 // instructions into EdgeBB. We know that there will be no uses of the
1181 // cloned instructions outside of EdgeBB.
1182 BasicBlock::iterator InsertPt = EdgeBB->begin();
1183 DenseMap<Value*, Value*> TranslateMap; // Track translated values.
1184 for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
1185 if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
1186 TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
1187 continue;
1188 }
1189 // Clone the instruction.
1190 Instruction *N = BBI->clone();
1191 if (BBI->hasName()) N->setName(BBI->getName()+".c");
1192
1193 // Update operands due to translation.
1194 for (User::op_iterator i = N->op_begin(), e = N->op_end();
1195 i != e; ++i) {
1196 DenseMap<Value*, Value*>::iterator PI = TranslateMap.find(*i);
1197 if (PI != TranslateMap.end())
1198 *i = PI->second;
1199 }
1200
1201 // Check for trivial simplification.
Chris Lattner302ba6f2010-12-14 06:17:25 +00001202 if (Value *V = SimplifyInstruction(N, TD)) {
1203 TranslateMap[BBI] = V;
1204 delete N; // Instruction folded away, don't need actual inst
Chris Lattner9a2b72a2010-12-13 01:47:07 +00001205 } else {
1206 // Insert the new instruction into its new home.
1207 EdgeBB->getInstList().insert(InsertPt, N);
1208 if (!BBI->use_empty())
1209 TranslateMap[BBI] = N;
1210 }
1211 }
1212
1213 // Loop over all of the edges from PredBB to BB, changing them to branch
1214 // to EdgeBB instead.
1215 TerminatorInst *PredBBTI = PredBB->getTerminator();
1216 for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
1217 if (PredBBTI->getSuccessor(i) == BB) {
1218 BB->removePredecessor(PredBB);
1219 PredBBTI->setSuccessor(i, EdgeBB);
1220 }
1221
1222 // Recurse, simplifying any other constants.
Chris Lattner302ba6f2010-12-14 06:17:25 +00001223 return FoldCondBranchOnPHI(BI, TD) | true;
Zhou Sheng6b6b6ef2007-01-11 12:24:14 +00001224 }
Chris Lattnereaba3a12005-09-19 23:49:37 +00001225
1226 return false;
1227}
1228
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001229/// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
1230/// PHI node, see if we can eliminate it.
Devang Patelf60364d2011-05-18 18:16:44 +00001231static bool FoldTwoEntryPHINode(PHINode *PN, const TargetData *TD,
1232 IRBuilder<> &Builder) {
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001233 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
1234 // statement", which has a very simple dominance structure. Basically, we
1235 // are trying to find the condition that is being branched on, which
1236 // subsequently causes this merge to happen. We really want control
1237 // dependence information for this check, but simplifycfg can't keep it up
1238 // to date, and this catches most of the cases we care about anyway.
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001239 BasicBlock *BB = PN->getParent();
1240 BasicBlock *IfTrue, *IfFalse;
1241 Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
Chris Lattner60d410d2010-12-14 08:01:53 +00001242 if (!IfCond ||
1243 // Don't bother if the branch will be constant folded trivially.
1244 isa<ConstantInt>(IfCond))
1245 return false;
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001246
Chris Lattner822a8792006-11-18 19:19:36 +00001247 // Okay, we found that we can merge this two-entry phi node into a select.
1248 // Doing so would require us to fold *all* two entry phi nodes in this block.
1249 // At some point this becomes non-profitable (particularly if the target
1250 // doesn't support cmov's). Only do this transformation if there are two or
1251 // fewer PHI nodes in this block.
1252 unsigned NumPhis = 0;
1253 for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
1254 if (NumPhis > 2)
1255 return false;
1256
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001257 // Loop over the PHI's seeing if we can promote them all to select
1258 // instructions. While we are at it, keep track of the instructions
1259 // that need to be moved to the dominating block.
Chris Lattner44da7ca2010-12-14 07:41:39 +00001260 SmallPtrSet<Instruction*, 4> AggressiveInsts;
Peter Collingbourne57808b32011-04-29 18:47:38 +00001261 unsigned MaxCostVal0 = PHINodeFoldingThreshold,
1262 MaxCostVal1 = PHINodeFoldingThreshold;
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001263
Chris Lattner3aff13b2010-12-14 08:46:09 +00001264 for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) {
1265 PHINode *PN = cast<PHINode>(II++);
Chris Lattner07ff3532010-12-14 07:20:29 +00001266 if (Value *V = SimplifyInstruction(PN, TD)) {
1267 PN->replaceAllUsesWith(V);
Chris Lattner3aff13b2010-12-14 08:46:09 +00001268 PN->eraseFromParent();
Chris Lattner07ff3532010-12-14 07:20:29 +00001269 continue;
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001270 }
Chris Lattner07ff3532010-12-14 07:20:29 +00001271
Peter Collingbournef15907f2011-04-29 18:47:31 +00001272 if (!DominatesMergePoint(PN->getIncomingValue(0), BB, &AggressiveInsts,
1273 MaxCostVal0) ||
1274 !DominatesMergePoint(PN->getIncomingValue(1), BB, &AggressiveInsts,
1275 MaxCostVal1))
Chris Lattner07ff3532010-12-14 07:20:29 +00001276 return false;
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001277 }
1278
Chris Lattner44da7ca2010-12-14 07:41:39 +00001279 // If we folded the the first phi, PN dangles at this point. Refresh it. If
1280 // we ran out of PHIs then we simplified them all.
1281 PN = dyn_cast<PHINode>(BB->begin());
1282 if (PN == 0) return true;
1283
Chris Lattner3aff13b2010-12-14 08:46:09 +00001284 // Don't fold i1 branches on PHIs which contain binary operators. These can
1285 // often be turned into switches and other things.
1286 if (PN->getType()->isIntegerTy(1) &&
1287 (isa<BinaryOperator>(PN->getIncomingValue(0)) ||
1288 isa<BinaryOperator>(PN->getIncomingValue(1)) ||
1289 isa<BinaryOperator>(IfCond)))
1290 return false;
1291
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001292 // If we all PHI nodes are promotable, check to make sure that all
1293 // instructions in the predecessor blocks can be promoted as well. If
1294 // not, we won't be able to get rid of the control flow, so it's not
1295 // worth promoting to select instructions.
Chris Lattner44da7ca2010-12-14 07:41:39 +00001296 BasicBlock *DomBlock = 0;
1297 BasicBlock *IfBlock1 = PN->getIncomingBlock(0);
1298 BasicBlock *IfBlock2 = PN->getIncomingBlock(1);
1299 if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) {
1300 IfBlock1 = 0;
1301 } else {
1302 DomBlock = *pred_begin(IfBlock1);
1303 for (BasicBlock::iterator I = IfBlock1->begin();!isa<TerminatorInst>(I);++I)
Devang Patel383d7ed2009-02-03 22:12:02 +00001304 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001305 // This is not an aggressive instruction that we can promote.
1306 // Because of this, we won't be able to get rid of the control
1307 // flow, so the xform is not worth it.
1308 return false;
1309 }
1310 }
1311
Chris Lattner44da7ca2010-12-14 07:41:39 +00001312 if (cast<BranchInst>(IfBlock2->getTerminator())->isConditional()) {
1313 IfBlock2 = 0;
1314 } else {
1315 DomBlock = *pred_begin(IfBlock2);
1316 for (BasicBlock::iterator I = IfBlock2->begin();!isa<TerminatorInst>(I);++I)
Devang Patel383d7ed2009-02-03 22:12:02 +00001317 if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(I)) {
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001318 // This is not an aggressive instruction that we can promote.
1319 // Because of this, we won't be able to get rid of the control
1320 // flow, so the xform is not worth it.
1321 return false;
1322 }
1323 }
Chris Lattnere0b18e52010-12-14 07:23:10 +00001324
1325 DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: "
Chris Lattner44da7ca2010-12-14 07:41:39 +00001326 << IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001327
1328 // If we can still promote the PHI nodes after this gauntlet of tests,
1329 // do all of the PHI's now.
Chris Lattner3aff13b2010-12-14 08:46:09 +00001330 Instruction *InsertPt = DomBlock->getTerminator();
Devang Patelf60364d2011-05-18 18:16:44 +00001331 Builder.SetInsertPoint(InsertPt);
Chris Lattner3aff13b2010-12-14 08:46:09 +00001332
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001333 // Move all 'aggressive' instructions, which are defined in the
1334 // conditional parts of the if's up to the dominating block.
Chris Lattner9a2b72a2010-12-13 01:47:07 +00001335 if (IfBlock1)
Chris Lattner3aff13b2010-12-14 08:46:09 +00001336 DomBlock->getInstList().splice(InsertPt,
Chris Lattner9a2b72a2010-12-13 01:47:07 +00001337 IfBlock1->getInstList(), IfBlock1->begin(),
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001338 IfBlock1->getTerminator());
Chris Lattner9a2b72a2010-12-13 01:47:07 +00001339 if (IfBlock2)
Chris Lattner3aff13b2010-12-14 08:46:09 +00001340 DomBlock->getInstList().splice(InsertPt,
Chris Lattner9a2b72a2010-12-13 01:47:07 +00001341 IfBlock2->getInstList(), IfBlock2->begin(),
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001342 IfBlock2->getTerminator());
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001343
1344 while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
1345 // Change the PHI node into a select instruction.
Chris Lattner9a2b72a2010-12-13 01:47:07 +00001346 Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
1347 Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001348
Devang Patelf60364d2011-05-18 18:16:44 +00001349 SelectInst *NV =
1350 cast<SelectInst>(Builder.CreateSelect(IfCond, TrueVal, FalseVal, ""));
Chris Lattner86cc4232007-02-11 01:37:51 +00001351 PN->replaceAllUsesWith(NV);
1352 NV->takeName(PN);
Chris Lattner302ba6f2010-12-14 06:17:25 +00001353 PN->eraseFromParent();
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001354 }
Chris Lattner60d410d2010-12-14 08:01:53 +00001355
1356 // At this point, IfBlock1 and IfBlock2 are both empty, so our if statement
1357 // has been flattened. Change DomBlock to jump directly to our new block to
1358 // avoid other simplifycfg's kicking in on the diamond.
1359 TerminatorInst *OldTI = DomBlock->getTerminator();
Devang Patelf60364d2011-05-18 18:16:44 +00001360 Builder.SetInsertPoint(OldTI);
1361 Builder.CreateBr(BB);
Chris Lattner60d410d2010-12-14 08:01:53 +00001362 OldTI->eraseFromParent();
Chris Lattnerf58c1a52005-09-23 06:39:30 +00001363 return true;
1364}
Chris Lattnereaba3a12005-09-19 23:49:37 +00001365
Chris Lattnerc9e495c2008-04-24 00:01:19 +00001366/// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
1367/// to two returning blocks, try to merge them together into one return,
1368/// introducing a select if the return values disagree.
1369static bool SimplifyCondBranchToTwoReturns(BranchInst *BI) {
1370 assert(BI->isConditional() && "Must be a conditional branch");
1371 BasicBlock *TrueSucc = BI->getSuccessor(0);
1372 BasicBlock *FalseSucc = BI->getSuccessor(1);
1373 ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
1374 ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
1375
1376 // Check to ensure both blocks are empty (just a return) or optionally empty
1377 // with PHI nodes. If there are other instructions, merging would cause extra
1378 // computation on one path or the other.
Chris Lattner9a2b72a2010-12-13 01:47:07 +00001379 if (!TrueSucc->getFirstNonPHIOrDbg()->isTerminator())
Devang Patel2cc86a12009-02-05 00:30:42 +00001380 return false;
Chris Lattner9a2b72a2010-12-13 01:47:07 +00001381 if (!FalseSucc->getFirstNonPHIOrDbg()->isTerminator())
Devang Patel2cc86a12009-02-05 00:30:42 +00001382 return false;
Chris Lattnerc9e495c2008-04-24 00:01:19 +00001383
1384 // Okay, we found a branch that is going to two return nodes. If
1385 // there is no return value for this function, just change the
1386 // branch into a return.
1387 if (FalseRet->getNumOperands() == 0) {
1388 TrueSucc->removePredecessor(BI->getParent());
1389 FalseSucc->removePredecessor(BI->getParent());
Owen Anderson1d0be152009-08-13 21:58:54 +00001390 ReturnInst::Create(BI->getContext(), 0, BI);
Eli Friedman080efb82008-12-16 20:54:32 +00001391 EraseTerminatorInstAndDCECond(BI);
Chris Lattnerc9e495c2008-04-24 00:01:19 +00001392 return true;
1393 }
1394
Dan Gohmanfc74abf2008-07-23 00:34:11 +00001395 // Otherwise, figure out what the true and false return values are
1396 // so we can insert a new select instruction.
1397 Value *TrueValue = TrueRet->getReturnValue();
1398 Value *FalseValue = FalseRet->getReturnValue();
Chris Lattnerc9e495c2008-04-24 00:01:19 +00001399
Dan Gohmanfc74abf2008-07-23 00:34:11 +00001400 // Unwrap any PHI nodes in the return blocks.
1401 if (PHINode *TVPN = dyn_cast_or_null<PHINode>(TrueValue))
1402 if (TVPN->getParent() == TrueSucc)
1403 TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
1404 if (PHINode *FVPN = dyn_cast_or_null<PHINode>(FalseValue))
1405 if (FVPN->getParent() == FalseSucc)
1406 FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
1407
1408 // In order for this transformation to be safe, we must be able to
1409 // unconditionally execute both operands to the return. This is
1410 // normally the case, but we could have a potentially-trapping
1411 // constant expression that prevents this transformation from being
1412 // safe.
1413 if (ConstantExpr *TCV = dyn_cast_or_null<ConstantExpr>(TrueValue))
1414 if (TCV->canTrap())
1415 return false;
1416 if (ConstantExpr *FCV = dyn_cast_or_null<ConstantExpr>(FalseValue))
1417 if (FCV->canTrap())
1418 return false;
1419
Chris Lattnerc9e495c2008-04-24 00:01:19 +00001420 // Okay, we collected all the mapped values and checked them for sanity, and
1421 // defined to really do this transformation. First, update the CFG.
1422 TrueSucc->removePredecessor(BI->getParent());
1423 FalseSucc->removePredecessor(BI->getParent());
1424
1425 // Insert select instructions where needed.
1426 Value *BrCond = BI->getCondition();
Dan Gohmanfc74abf2008-07-23 00:34:11 +00001427 if (TrueValue) {
Chris Lattnerc9e495c2008-04-24 00:01:19 +00001428 // Insert a select if the results differ.
Dan Gohmanfc74abf2008-07-23 00:34:11 +00001429 if (TrueValue == FalseValue || isa<UndefValue>(FalseValue)) {
1430 } else if (isa<UndefValue>(TrueValue)) {
1431 TrueValue = FalseValue;
1432 } else {
1433 TrueValue = SelectInst::Create(BrCond, TrueValue,
1434 FalseValue, "retval", BI);
Chris Lattnerc9e495c2008-04-24 00:01:19 +00001435 }
Chris Lattnerc9e495c2008-04-24 00:01:19 +00001436 }
1437
Dan Gohmanfc74abf2008-07-23 00:34:11 +00001438 Value *RI = !TrueValue ?
Owen Anderson1d0be152009-08-13 21:58:54 +00001439 ReturnInst::Create(BI->getContext(), BI) :
1440 ReturnInst::Create(BI->getContext(), TrueValue, BI);
Daniel Dunbare317bcc2009-08-23 10:29:55 +00001441 (void) RI;
Chris Lattnerc9e495c2008-04-24 00:01:19 +00001442
David Greene89d6fd32010-01-05 01:26:52 +00001443 DEBUG(dbgs() << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
Chris Lattnerbdff5482009-08-23 04:37:46 +00001444 << "\n " << *BI << "NewRet = " << *RI
1445 << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc);
Chris Lattnerc9e495c2008-04-24 00:01:19 +00001446
Eli Friedman080efb82008-12-16 20:54:32 +00001447 EraseTerminatorInstAndDCECond(BI);
1448
Chris Lattnerc9e495c2008-04-24 00:01:19 +00001449 return true;
1450}
1451
Chris Lattnerc8fbc342011-04-11 23:24:57 +00001452/// FoldBranchToCommonDest - If this basic block is simple enough, and if a
1453/// predecessor branches to us and one of our successors, fold the block into
1454/// the predecessor and use logical operations to pick the right destination.
Dan Gohman4b35f832009-06-27 21:30:38 +00001455bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
Chris Lattner093a4382008-07-13 22:23:11 +00001456 BasicBlock *BB = BI->getParent();
Chris Lattner1347e872008-07-13 21:12:01 +00001457 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
Owen Andersone84178a2010-07-14 19:52:16 +00001458 if (Cond == 0 || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
1459 Cond->getParent() != BB || !Cond->hasOneUse())
1460 return false;
Devang Pateld4181942011-04-06 22:37:20 +00001461
Chris Lattner1347e872008-07-13 21:12:01 +00001462 // Only allow this if the condition is a simple instruction that can be
1463 // executed unconditionally. It must be in the same block as the branch, and
1464 // must be at the front of the block.
Devang Pateld0a203d2009-02-04 21:39:48 +00001465 BasicBlock::iterator FrontIt = BB->front();
Chris Lattner3c6e7462011-04-14 02:44:53 +00001466
Devang Pateld0a203d2009-02-04 21:39:48 +00001467 // Ignore dbg intrinsics.
Chris Lattner3c6e7462011-04-14 02:44:53 +00001468 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
Owen Andersone84178a2010-07-14 19:52:16 +00001469
1470 // Allow a single instruction to be hoisted in addition to the compare
1471 // that feeds the branch. We later ensure that any values that _it_ uses
1472 // were also live in the predecessor, so that we don't unnecessarily create
1473 // register pressure or inhibit out-of-order execution.
1474 Instruction *BonusInst = 0;
1475 if (&*FrontIt != Cond &&
Owen Anderson2722dfa2010-07-15 16:38:22 +00001476 FrontIt->hasOneUse() && *FrontIt->use_begin() == Cond &&
1477 FrontIt->isSafeToSpeculativelyExecute()) {
Owen Andersone84178a2010-07-14 19:52:16 +00001478 BonusInst = &*FrontIt;
1479 ++FrontIt;
Chris Lattner3c6e7462011-04-14 02:44:53 +00001480
1481 // Ignore dbg intrinsics.
1482 while (isa<DbgInfoIntrinsic>(FrontIt)) ++FrontIt;
Devang Patel60d490c2011-04-07 23:11:25 +00001483 }
1484
Owen Andersone84178a2010-07-14 19:52:16 +00001485 // Only a single bonus inst is allowed.
1486 if (&*FrontIt != Cond)
1487 return false;
1488
Chris Lattner1347e872008-07-13 21:12:01 +00001489 // Make sure the instruction after the condition is the cond branch.
1490 BasicBlock::iterator CondIt = Cond; ++CondIt;
Chris Lattner3c6e7462011-04-14 02:44:53 +00001491
Devang Pateld0a203d2009-02-04 21:39:48 +00001492 // Ingore dbg intrinsics.
Chris Lattner3c6e7462011-04-14 02:44:53 +00001493 while (isa<DbgInfoIntrinsic>(CondIt)) ++CondIt;
1494
1495 if (&*CondIt != BI)
Chris Lattner1347e872008-07-13 21:12:01 +00001496 return false;
Chris Lattner6ff645b2009-01-19 23:03:13 +00001497
1498 // Cond is known to be a compare or binary operator. Check to make sure that
1499 // neither operand is a potentially-trapping constant expression.
1500 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(0)))
1501 if (CE->canTrap())
1502 return false;
1503 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Cond->getOperand(1)))
1504 if (CE->canTrap())
1505 return false;
1506
Chris Lattner1347e872008-07-13 21:12:01 +00001507 // Finally, don't infinitely unroll conditional loops.
1508 BasicBlock *TrueDest = BI->getSuccessor(0);
1509 BasicBlock *FalseDest = BI->getSuccessor(1);
1510 if (TrueDest == BB || FalseDest == BB)
1511 return false;
Devang Pateld4181942011-04-06 22:37:20 +00001512
Chris Lattner1347e872008-07-13 21:12:01 +00001513 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
1514 BasicBlock *PredBlock = *PI;
1515 BranchInst *PBI = dyn_cast<BranchInst>(PredBlock->getTerminator());
Chris Lattner6ff645b2009-01-19 23:03:13 +00001516
Chris Lattner093a4382008-07-13 22:23:11 +00001517 // Check that we have two conditional branches. If there is a PHI node in
1518 // the common successor, verify that the same value flows in from both
1519 // blocks.
Chris Lattner3c6e7462011-04-14 02:44:53 +00001520 if (PBI == 0 || PBI->isUnconditional() || !SafeToMergeTerminators(BI, PBI))
Chris Lattner1347e872008-07-13 21:12:01 +00001521 continue;
1522
Chris Lattner3c6e7462011-04-14 02:44:53 +00001523 // Determine if the two branches share a common destination.
1524 Instruction::BinaryOps Opc;
1525 bool InvertPredCond = false;
1526
1527 if (PBI->getSuccessor(0) == TrueDest)
1528 Opc = Instruction::Or;
1529 else if (PBI->getSuccessor(1) == FalseDest)
1530 Opc = Instruction::And;
1531 else if (PBI->getSuccessor(0) == FalseDest)
1532 Opc = Instruction::And, InvertPredCond = true;
1533 else if (PBI->getSuccessor(1) == TrueDest)
1534 Opc = Instruction::Or, InvertPredCond = true;
1535 else
1536 continue;
1537
Owen Andersone84178a2010-07-14 19:52:16 +00001538 // Ensure that any values used in the bonus instruction are also used
1539 // by the terminator of the predecessor. This means that those values
1540 // must already have been resolved, so we won't be inhibiting the
1541 // out-of-order core by speculating them earlier.
1542 if (BonusInst) {
1543 // Collect the values used by the bonus inst
1544 SmallPtrSet<Value*, 4> UsedValues;
1545 for (Instruction::op_iterator OI = BonusInst->op_begin(),
1546 OE = BonusInst->op_end(); OI != OE; ++OI) {
1547 Value* V = *OI;
1548 if (!isa<Constant>(V))
1549 UsedValues.insert(V);
1550 }
1551
1552 SmallVector<std::pair<Value*, unsigned>, 4> Worklist;
1553 Worklist.push_back(std::make_pair(PBI->getOperand(0), 0));
1554
1555 // Walk up to four levels back up the use-def chain of the predecessor's
1556 // terminator to see if all those values were used. The choice of four
1557 // levels is arbitrary, to provide a compile-time-cost bound.
1558 while (!Worklist.empty()) {
1559 std::pair<Value*, unsigned> Pair = Worklist.back();
1560 Worklist.pop_back();
1561
1562 if (Pair.second >= 4) continue;
1563 UsedValues.erase(Pair.first);
1564 if (UsedValues.empty()) break;
1565
Chris Lattnerdaa02ab2010-12-13 07:00:06 +00001566 if (Instruction *I = dyn_cast<Instruction>(Pair.first)) {
Owen Andersone84178a2010-07-14 19:52:16 +00001567 for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end();
1568 OI != OE; ++OI)
1569 Worklist.push_back(std::make_pair(OI->get(), Pair.second+1));
1570 }
1571 }
1572
1573 if (!UsedValues.empty()) return false;
1574 }
Chris Lattner36989092008-07-13 21:20:19 +00001575
David Greene89d6fd32010-01-05 01:26:52 +00001576 DEBUG(dbgs() << "FOLDING BRANCH TO COMMON DEST:\n" << *PBI << *BB);
Chris Lattner6ff645b2009-01-19 23:03:13 +00001577
Chris Lattner36989092008-07-13 21:20:19 +00001578 // If we need to invert the condition in the pred block to match, do so now.
1579 if (InvertPredCond) {
Chris Lattnerdaa02ab2010-12-13 07:00:06 +00001580 Value *NewCond = PBI->getCondition();
1581
1582 if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) {
1583 CmpInst *CI = cast<CmpInst>(NewCond);
1584 CI->setPredicate(CI->getInversePredicate());
1585 } else {
1586 NewCond = BinaryOperator::CreateNot(NewCond,
Chris Lattner36989092008-07-13 21:20:19 +00001587 PBI->getCondition()->getName()+".not", PBI);
Chris Lattnerdaa02ab2010-12-13 07:00:06 +00001588 }
1589
Chris Lattner1347e872008-07-13 21:12:01 +00001590 PBI->setCondition(NewCond);
1591 BasicBlock *OldTrue = PBI->getSuccessor(0);
1592 BasicBlock *OldFalse = PBI->getSuccessor(1);
1593 PBI->setSuccessor(0, OldFalse);
1594 PBI->setSuccessor(1, OldTrue);
1595 }
Chris Lattner70087f32008-07-13 21:15:11 +00001596
Owen Andersone84178a2010-07-14 19:52:16 +00001597 // If we have a bonus inst, clone it into the predecessor block.
1598 Instruction *NewBonus = 0;
1599 if (BonusInst) {
1600 NewBonus = BonusInst->clone();
1601 PredBlock->getInstList().insert(PBI, NewBonus);
1602 NewBonus->takeName(BonusInst);
1603 BonusInst->setName(BonusInst->getName()+".old");
1604 }
1605
Chris Lattner36989092008-07-13 21:20:19 +00001606 // Clone Cond into the predecessor basic block, and or/and the
1607 // two conditions together.
Nick Lewycky67760642009-09-27 07:38:41 +00001608 Instruction *New = Cond->clone();
Owen Andersone84178a2010-07-14 19:52:16 +00001609 if (BonusInst) New->replaceUsesOfWith(BonusInst, NewBonus);
Chris Lattner36989092008-07-13 21:20:19 +00001610 PredBlock->getInstList().insert(PBI, New);
1611 New->takeName(Cond);
1612 Cond->setName(New->getName()+".old");
Chris Lattner70087f32008-07-13 21:15:11 +00001613
Devang Pateld80e8ed2011-05-17 23:29:05 +00001614 Instruction *NewCond = BinaryOperator::Create(Opc, PBI->getCondition(),
1615 New, "or.cond", PBI);
1616 NewCond->setDebugLoc(PBI->getDebugLoc());
Chris Lattner36989092008-07-13 21:20:19 +00001617 PBI->setCondition(NewCond);
1618 if (PBI->getSuccessor(0) == BB) {
1619 AddPredecessorToBlock(TrueDest, PredBlock, BB);
1620 PBI->setSuccessor(0, TrueDest);
Chris Lattner1347e872008-07-13 21:12:01 +00001621 }
Chris Lattner36989092008-07-13 21:20:19 +00001622 if (PBI->getSuccessor(1) == BB) {
1623 AddPredecessorToBlock(FalseDest, PredBlock, BB);
1624 PBI->setSuccessor(1, FalseDest);
1625 }
Devang Pateld4181942011-04-06 22:37:20 +00001626
Chris Lattner3c6e7462011-04-14 02:44:53 +00001627 // Copy any debug value intrinsics into the end of PredBlock.
1628 for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ++I)
1629 if (isa<DbgInfoIntrinsic>(*I))
1630 I->clone()->insertBefore(PBI);
1631
Chris Lattner117f8cf2010-12-14 05:57:30 +00001632 return true;
Chris Lattner1347e872008-07-13 21:12:01 +00001633 }
1634 return false;
1635}
1636
Chris Lattner867661a2008-07-13 21:53:26 +00001637/// SimplifyCondBranchToCondBranch - If we have a conditional branch as a
1638/// predecessor of another block, this function tries to simplify it. We know
1639/// that PBI and BI are both conditional branches, and BI is in one of the
1640/// successor blocks of PBI - PBI branches to BI.
1641static bool SimplifyCondBranchToCondBranch(BranchInst *PBI, BranchInst *BI) {
1642 assert(PBI->isConditional() && BI->isConditional());
1643 BasicBlock *BB = BI->getParent();
Dan Gohman4ae51262009-08-12 16:23:25 +00001644
Chris Lattner867661a2008-07-13 21:53:26 +00001645 // If this block ends with a branch instruction, and if there is a
1646 // predecessor that ends on a branch of the same condition, make
1647 // this conditional branch redundant.
1648 if (PBI->getCondition() == BI->getCondition() &&
1649 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1650 // Okay, the outcome of this conditional branch is statically
1651 // knowable. If this block had a single pred, handle specially.
1652 if (BB->getSinglePredecessor()) {
1653 // Turn this into a branch on constant.
1654 bool CondIsTrue = PBI->getSuccessor(0) == BB;
Owen Anderson1d0be152009-08-13 21:58:54 +00001655 BI->setCondition(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
1656 CondIsTrue));
Chris Lattner867661a2008-07-13 21:53:26 +00001657 return true; // Nuke the branch on constant.
1658 }
1659
1660 // Otherwise, if there are multiple predecessors, insert a PHI that merges
1661 // in the constant and simplify the block result. Subsequent passes of
1662 // simplifycfg will thread the block.
1663 if (BlockIsSimpleEnoughToThreadThrough(BB)) {
Jay Foadd8b4fb42011-03-30 11:19:20 +00001664 pred_iterator PB = pred_begin(BB), PE = pred_end(BB);
Owen Anderson1d0be152009-08-13 21:58:54 +00001665 PHINode *NewPN = PHINode::Create(Type::getInt1Ty(BB->getContext()),
Jay Foad3ecfc862011-03-30 11:28:46 +00001666 std::distance(PB, PE),
Chris Lattner867661a2008-07-13 21:53:26 +00001667 BI->getCondition()->getName() + ".pr",
1668 BB->begin());
Chris Lattnereb388af2008-07-13 21:55:46 +00001669 // Okay, we're going to insert the PHI node. Since PBI is not the only
1670 // predecessor, compute the PHI'd conditional value for all of the preds.
1671 // Any predecessor where the condition is not computable we keep symbolic.
Jay Foadd8b4fb42011-03-30 11:19:20 +00001672 for (pred_iterator PI = PB; PI != PE; ++PI) {
Gabor Greif62539832010-07-12 10:59:23 +00001673 BasicBlock *P = *PI;
1674 if ((PBI = dyn_cast<BranchInst>(P->getTerminator())) &&
Chris Lattner867661a2008-07-13 21:53:26 +00001675 PBI != BI && PBI->isConditional() &&
1676 PBI->getCondition() == BI->getCondition() &&
1677 PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
1678 bool CondIsTrue = PBI->getSuccessor(0) == BB;
Owen Anderson1d0be152009-08-13 21:58:54 +00001679 NewPN->addIncoming(ConstantInt::get(Type::getInt1Ty(BB->getContext()),
Gabor Greif62539832010-07-12 10:59:23 +00001680 CondIsTrue), P);
Chris Lattner867661a2008-07-13 21:53:26 +00001681 } else {
Gabor Greif62539832010-07-12 10:59:23 +00001682 NewPN->addIncoming(BI->getCondition(), P);
Chris Lattner867661a2008-07-13 21:53:26 +00001683 }
Gabor Greif62539832010-07-12 10:59:23 +00001684 }
Chris Lattner867661a2008-07-13 21:53:26 +00001685
1686 BI->setCondition(NewPN);
Chris Lattner867661a2008-07-13 21:53:26 +00001687 return true;
1688 }
1689 }
1690
1691 // If this is a conditional branch in an empty block, and if any
1692 // predecessors is a conditional branch to one of our destinations,
1693 // fold the conditions into logical ops and one cond br.
Zhou Shenga8d57fe2009-02-26 06:56:37 +00001694 BasicBlock::iterator BBI = BB->begin();
1695 // Ignore dbg intrinsics.
1696 while (isa<DbgInfoIntrinsic>(BBI))
1697 ++BBI;
1698 if (&*BBI != BI)
Chris Lattnerb8245122008-07-13 22:04:41 +00001699 return false;
Chris Lattner63bf29b2009-01-20 01:15:41 +00001700
1701
1702 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(BI->getCondition()))
1703 if (CE->canTrap())
1704 return false;
Chris Lattnerb8245122008-07-13 22:04:41 +00001705
1706 int PBIOp, BIOp;
1707 if (PBI->getSuccessor(0) == BI->getSuccessor(0))
1708 PBIOp = BIOp = 0;
1709 else if (PBI->getSuccessor(0) == BI->getSuccessor(1))
1710 PBIOp = 0, BIOp = 1;
1711 else if (PBI->getSuccessor(1) == BI->getSuccessor(0))
1712 PBIOp = 1, BIOp = 0;
1713 else if (PBI->getSuccessor(1) == BI->getSuccessor(1))
1714 PBIOp = BIOp = 1;
1715 else
1716 return false;
Chris Lattner867661a2008-07-13 21:53:26 +00001717
Chris Lattnerb8245122008-07-13 22:04:41 +00001718 // Check to make sure that the other destination of this branch
1719 // isn't BB itself. If so, this is an infinite loop that will
1720 // keep getting unwound.
1721 if (PBI->getSuccessor(PBIOp) == BB)
1722 return false;
Chris Lattner867661a2008-07-13 21:53:26 +00001723
Chris Lattnerb8245122008-07-13 22:04:41 +00001724 // Do not perform this transformation if it would require
1725 // insertion of a large number of select instructions. For targets
1726 // without predication/cmovs, this is a big pessimization.
1727 BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
Chris Lattner867661a2008-07-13 21:53:26 +00001728
Chris Lattnerb8245122008-07-13 22:04:41 +00001729 unsigned NumPhis = 0;
1730 for (BasicBlock::iterator II = CommonDest->begin();
1731 isa<PHINode>(II); ++II, ++NumPhis)
1732 if (NumPhis > 2) // Disable this xform.
1733 return false;
Chris Lattner867661a2008-07-13 21:53:26 +00001734
Chris Lattnerb8245122008-07-13 22:04:41 +00001735 // Finally, if everything is ok, fold the branches to logical ops.
1736 BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
1737
David Greene89d6fd32010-01-05 01:26:52 +00001738 DEBUG(dbgs() << "FOLDING BRs:" << *PBI->getParent()
Chris Lattnerbdff5482009-08-23 04:37:46 +00001739 << "AND: " << *BI->getParent());
Chris Lattnerb8245122008-07-13 22:04:41 +00001740
Chris Lattner093a4382008-07-13 22:23:11 +00001741
1742 // If OtherDest *is* BB, then BB is a basic block with a single conditional
1743 // branch in it, where one edge (OtherDest) goes back to itself but the other
1744 // exits. We don't *know* that the program avoids the infinite loop
1745 // (even though that seems likely). If we do this xform naively, we'll end up
1746 // recursively unpeeling the loop. Since we know that (after the xform is
1747 // done) that the block *is* infinite if reached, we just make it an obviously
1748 // infinite loop with no cond branch.
1749 if (OtherDest == BB) {
1750 // Insert it at the end of the function, because it's either code,
1751 // or it won't matter if it's hot. :)
Owen Anderson1d0be152009-08-13 21:58:54 +00001752 BasicBlock *InfLoopBlock = BasicBlock::Create(BB->getContext(),
1753 "infloop", BB->getParent());
Chris Lattner093a4382008-07-13 22:23:11 +00001754 BranchInst::Create(InfLoopBlock, InfLoopBlock);
1755 OtherDest = InfLoopBlock;
1756 }
1757
David Greene89d6fd32010-01-05 01:26:52 +00001758 DEBUG(dbgs() << *PBI->getParent()->getParent());
Chris Lattnerb8245122008-07-13 22:04:41 +00001759
1760 // BI may have other predecessors. Because of this, we leave
1761 // it alone, but modify PBI.
1762
1763 // Make sure we get to CommonDest on True&True directions.
1764 Value *PBICond = PBI->getCondition();
1765 if (PBIOp)
Dan Gohman4ae51262009-08-12 16:23:25 +00001766 PBICond = BinaryOperator::CreateNot(PBICond,
Chris Lattnerb8245122008-07-13 22:04:41 +00001767 PBICond->getName()+".not",
1768 PBI);
1769 Value *BICond = BI->getCondition();
1770 if (BIOp)
Dan Gohman4ae51262009-08-12 16:23:25 +00001771 BICond = BinaryOperator::CreateNot(BICond,
Chris Lattnerb8245122008-07-13 22:04:41 +00001772 BICond->getName()+".not",
1773 PBI);
1774 // Merge the conditions.
1775 Value *Cond = BinaryOperator::CreateOr(PBICond, BICond, "brmerge", PBI);
1776
1777 // Modify PBI to branch on the new condition to the new dests.
1778 PBI->setCondition(Cond);
1779 PBI->setSuccessor(0, CommonDest);
1780 PBI->setSuccessor(1, OtherDest);
1781
1782 // OtherDest may have phi nodes. If so, add an entry from PBI's
1783 // block that are identical to the entries for BI's block.
Chris Lattner6de0a282010-12-14 07:09:42 +00001784 AddPredecessorToBlock(OtherDest, PBI->getParent(), BB);
Chris Lattnerb8245122008-07-13 22:04:41 +00001785
1786 // We know that the CommonDest already had an edge from PBI to
1787 // it. If it has PHIs though, the PHIs may have different
1788 // entries for BB and PBI's BB. If so, insert a select to make
1789 // them agree.
Chris Lattner6de0a282010-12-14 07:09:42 +00001790 PHINode *PN;
Chris Lattnerb8245122008-07-13 22:04:41 +00001791 for (BasicBlock::iterator II = CommonDest->begin();
1792 (PN = dyn_cast<PHINode>(II)); ++II) {
1793 Value *BIV = PN->getIncomingValueForBlock(BB);
1794 unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
1795 Value *PBIV = PN->getIncomingValue(PBBIdx);
1796 if (BIV != PBIV) {
1797 // Insert a select in PBI to pick the right value.
1798 Value *NV = SelectInst::Create(PBICond, PBIV, BIV,
1799 PBIV->getName()+".mux", PBI);
1800 PN->setIncomingValue(PBBIdx, NV);
Chris Lattner867661a2008-07-13 21:53:26 +00001801 }
1802 }
Chris Lattnerb8245122008-07-13 22:04:41 +00001803
David Greene89d6fd32010-01-05 01:26:52 +00001804 DEBUG(dbgs() << "INTO: " << *PBI->getParent());
1805 DEBUG(dbgs() << *PBI->getParent()->getParent());
Chris Lattnerb8245122008-07-13 22:04:41 +00001806
1807 // This basic block is probably dead. We know it has at least
1808 // one fewer predecessor.
1809 return true;
Chris Lattner867661a2008-07-13 21:53:26 +00001810}
1811
Frits van Bommel65fdded2011-01-11 12:52:11 +00001812// SimplifyTerminatorOnSelect - Simplifies a terminator by replacing it with a
1813// branch to TrueBB if Cond is true or to FalseBB if Cond is false.
1814// Takes care of updating the successors and removing the old terminator.
1815// Also makes sure not to introduce new successors by assuming that edges to
1816// non-successor TrueBBs and FalseBBs aren't reachable.
1817static bool SimplifyTerminatorOnSelect(TerminatorInst *OldTerm, Value *Cond,
1818 BasicBlock *TrueBB, BasicBlock *FalseBB){
1819 // Remove any superfluous successor edges from the CFG.
1820 // First, figure out which successors to preserve.
1821 // If TrueBB and FalseBB are equal, only try to preserve one copy of that
1822 // successor.
1823 BasicBlock *KeepEdge1 = TrueBB;
1824 BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : 0;
1825
1826 // Then remove the rest.
1827 for (unsigned I = 0, E = OldTerm->getNumSuccessors(); I != E; ++I) {
1828 BasicBlock *Succ = OldTerm->getSuccessor(I);
1829 // Make sure only to keep exactly one copy of each edge.
1830 if (Succ == KeepEdge1)
1831 KeepEdge1 = 0;
1832 else if (Succ == KeepEdge2)
1833 KeepEdge2 = 0;
1834 else
1835 Succ->removePredecessor(OldTerm->getParent());
1836 }
1837
1838 // Insert an appropriate new terminator.
1839 if ((KeepEdge1 == 0) && (KeepEdge2 == 0)) {
1840 if (TrueBB == FalseBB)
1841 // We were only looking for one successor, and it was present.
1842 // Create an unconditional branch to it.
1843 BranchInst::Create(TrueBB, OldTerm);
1844 else
1845 // We found both of the successors we were looking for.
1846 // Create a conditional branch sharing the condition of the select.
1847 BranchInst::Create(TrueBB, FalseBB, Cond, OldTerm);
1848 } else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) {
1849 // Neither of the selected blocks were successors, so this
1850 // terminator must be unreachable.
1851 new UnreachableInst(OldTerm->getContext(), OldTerm);
1852 } else {
1853 // One of the selected values was a successor, but the other wasn't.
1854 // Insert an unconditional branch to the one that was found;
1855 // the edge to the one that wasn't must be unreachable.
1856 if (KeepEdge1 == 0)
1857 // Only TrueBB was found.
1858 BranchInst::Create(TrueBB, OldTerm);
1859 else
1860 // Only FalseBB was found.
1861 BranchInst::Create(FalseBB, OldTerm);
1862 }
1863
1864 EraseTerminatorInstAndDCECond(OldTerm);
1865 return true;
1866}
1867
Frits van Bommelf7b2a9d2011-02-28 09:44:07 +00001868// SimplifySwitchOnSelect - Replaces
1869// (switch (select cond, X, Y)) on constant X, Y
1870// with a branch - conditional if X and Y lead to distinct BBs,
1871// unconditional otherwise.
1872static bool SimplifySwitchOnSelect(SwitchInst *SI, SelectInst *Select) {
1873 // Check for constant integer values in the select.
1874 ConstantInt *TrueVal = dyn_cast<ConstantInt>(Select->getTrueValue());
1875 ConstantInt *FalseVal = dyn_cast<ConstantInt>(Select->getFalseValue());
1876 if (!TrueVal || !FalseVal)
1877 return false;
1878
1879 // Find the relevant condition and destinations.
1880 Value *Condition = Select->getCondition();
1881 BasicBlock *TrueBB = SI->getSuccessor(SI->findCaseValue(TrueVal));
1882 BasicBlock *FalseBB = SI->getSuccessor(SI->findCaseValue(FalseVal));
1883
1884 // Perform the actual simplification.
1885 return SimplifyTerminatorOnSelect(SI, Condition, TrueBB, FalseBB);
1886}
1887
Frits van Bommel7ac40c32010-12-05 18:29:03 +00001888// SimplifyIndirectBrOnSelect - Replaces
1889// (indirectbr (select cond, blockaddress(@fn, BlockA),
1890// blockaddress(@fn, BlockB)))
1891// with
1892// (br cond, BlockA, BlockB).
1893static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) {
1894 // Check that both operands of the select are block addresses.
1895 BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
1896 BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
1897 if (!TBA || !FBA)
1898 return false;
1899
1900 // Extract the actual blocks.
1901 BasicBlock *TrueBB = TBA->getBasicBlock();
1902 BasicBlock *FalseBB = FBA->getBasicBlock();
1903
Frits van Bommel65fdded2011-01-11 12:52:11 +00001904 // Perform the actual simplification.
1905 return SimplifyTerminatorOnSelect(IBI, SI->getCondition(), TrueBB, FalseBB);
Frits van Bommel7ac40c32010-12-05 18:29:03 +00001906}
1907
Chris Lattner61c77442010-12-13 03:18:54 +00001908/// TryToSimplifyUncondBranchWithICmpInIt - This is called when we find an icmp
1909/// instruction (a seteq/setne with a constant) as the only instruction in a
1910/// block that ends with an uncond branch. We are looking for a very specific
1911/// pattern that occurs when "A == 1 || A == 2 || A == 3" gets simplified. In
1912/// this case, we merge the first two "or's of icmp" into a switch, but then the
1913/// default value goes to an uncond block with a seteq in it, we get something
1914/// like:
1915///
1916/// switch i8 %A, label %DEFAULT [ i8 1, label %end i8 2, label %end ]
1917/// DEFAULT:
1918/// %tmp = icmp eq i8 %A, 92
1919/// br label %end
1920/// end:
1921/// ... = phi i1 [ true, %entry ], [ %tmp, %DEFAULT ], [ true, %entry ]
1922///
1923/// We prefer to split the edge to 'end' so that there is a true/false entry to
1924/// the PHI, merging the third icmp into the switch.
Chris Lattner302ba6f2010-12-14 06:17:25 +00001925static bool TryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI,
1926 const TargetData *TD) {
Chris Lattner61c77442010-12-13 03:18:54 +00001927 BasicBlock *BB = ICI->getParent();
1928 // If the block has any PHIs in it or the icmp has multiple uses, it is too
1929 // complex.
1930 if (isa<PHINode>(BB->begin()) || !ICI->hasOneUse()) return false;
1931
1932 Value *V = ICI->getOperand(0);
1933 ConstantInt *Cst = cast<ConstantInt>(ICI->getOperand(1));
1934
1935 // The pattern we're looking for is where our only predecessor is a switch on
1936 // 'V' and this block is the default case for the switch. In this case we can
1937 // fold the compared value into the switch to simplify things.
1938 BasicBlock *Pred = BB->getSinglePredecessor();
1939 if (Pred == 0 || !isa<SwitchInst>(Pred->getTerminator())) return false;
1940
1941 SwitchInst *SI = cast<SwitchInst>(Pred->getTerminator());
1942 if (SI->getCondition() != V)
1943 return false;
1944
1945 // If BB is reachable on a non-default case, then we simply know the value of
1946 // V in this block. Substitute it and constant fold the icmp instruction
1947 // away.
1948 if (SI->getDefaultDest() != BB) {
1949 ConstantInt *VVal = SI->findCaseDest(BB);
1950 assert(VVal && "Should have a unique destination value");
1951 ICI->setOperand(0, VVal);
1952
Chris Lattner302ba6f2010-12-14 06:17:25 +00001953 if (Value *V = SimplifyInstruction(ICI, TD)) {
1954 ICI->replaceAllUsesWith(V);
Chris Lattner61c77442010-12-13 03:18:54 +00001955 ICI->eraseFromParent();
1956 }
1957 // BB is now empty, so it is likely to simplify away.
1958 return SimplifyCFG(BB) | true;
1959 }
1960
Chris Lattnerabf70672010-12-13 03:43:57 +00001961 // Ok, the block is reachable from the default dest. If the constant we're
1962 // comparing exists in one of the other edges, then we can constant fold ICI
1963 // and zap it.
1964 if (SI->findCaseValue(Cst) != 0) {
1965 Value *V;
1966 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
1967 V = ConstantInt::getFalse(BB->getContext());
1968 else
1969 V = ConstantInt::getTrue(BB->getContext());
1970
1971 ICI->replaceAllUsesWith(V);
1972 ICI->eraseFromParent();
1973 // BB is now empty, so it is likely to simplify away.
1974 return SimplifyCFG(BB) | true;
1975 }
1976
Chris Lattner61c77442010-12-13 03:18:54 +00001977 // The use of the icmp has to be in the 'end' block, by the only PHI node in
1978 // the block.
1979 BasicBlock *SuccBlock = BB->getTerminator()->getSuccessor(0);
1980 PHINode *PHIUse = dyn_cast<PHINode>(ICI->use_back());
1981 if (PHIUse == 0 || PHIUse != &SuccBlock->front() ||
1982 isa<PHINode>(++BasicBlock::iterator(PHIUse)))
1983 return false;
1984
1985 // If the icmp is a SETEQ, then the default dest gets false, the new edge gets
1986 // true in the PHI.
1987 Constant *DefaultCst = ConstantInt::getTrue(BB->getContext());
1988 Constant *NewCst = ConstantInt::getFalse(BB->getContext());
1989
1990 if (ICI->getPredicate() == ICmpInst::ICMP_EQ)
1991 std::swap(DefaultCst, NewCst);
1992
1993 // Replace ICI (which is used by the PHI for the default value) with true or
1994 // false depending on if it is EQ or NE.
1995 ICI->replaceAllUsesWith(DefaultCst);
1996 ICI->eraseFromParent();
1997
1998 // Okay, the switch goes to this block on a default value. Add an edge from
1999 // the switch to the merge point on the compared value.
2000 BasicBlock *NewBB = BasicBlock::Create(BB->getContext(), "switch.edge",
2001 BB->getParent(), BB);
2002 SI->addCase(Cst, NewBB);
2003
2004 // NewBB branches to the phi block, add the uncond branch and the phi entry.
2005 BranchInst::Create(SuccBlock, NewBB);
2006 PHIUse->addIncoming(NewCst, NewBB);
2007 return true;
2008}
2009
Chris Lattner97fdb892010-12-13 05:03:41 +00002010/// SimplifyBranchOnICmpChain - The specified branch is a conditional branch.
2011/// Check to see if it is branching on an or/and chain of icmp instructions, and
2012/// fold it into a switch instruction if so.
2013static bool SimplifyBranchOnICmpChain(BranchInst *BI, const TargetData *TD) {
2014 Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
2015 if (Cond == 0) return false;
2016
2017
2018 // Change br (X == 0 | X == 1), T, F into a switch instruction.
2019 // If this is a bunch of seteq's or'd together, or if it's a bunch of
2020 // 'setne's and'ed together, collect them.
2021 Value *CompVal = 0;
2022 std::vector<ConstantInt*> Values;
2023 bool TrueWhenEqual = true;
2024 Value *ExtraCase = 0;
Benjamin Kramer33828bc2011-02-07 22:37:28 +00002025 unsigned UsedICmps = 0;
Chris Lattner97fdb892010-12-13 05:03:41 +00002026
2027 if (Cond->getOpcode() == Instruction::Or) {
Benjamin Kramer33828bc2011-02-07 22:37:28 +00002028 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, true,
2029 UsedICmps);
Chris Lattner97fdb892010-12-13 05:03:41 +00002030 } else if (Cond->getOpcode() == Instruction::And) {
Benjamin Kramer33828bc2011-02-07 22:37:28 +00002031 CompVal = GatherConstantCompares(Cond, Values, ExtraCase, TD, false,
2032 UsedICmps);
Chris Lattner97fdb892010-12-13 05:03:41 +00002033 TrueWhenEqual = false;
2034 }
2035
2036 // If we didn't have a multiply compared value, fail.
2037 if (CompVal == 0) return false;
2038
Benjamin Kramer33828bc2011-02-07 22:37:28 +00002039 // Avoid turning single icmps into a switch.
2040 if (UsedICmps <= 1)
2041 return false;
2042
Chris Lattner97fdb892010-12-13 05:03:41 +00002043 // There might be duplicate constants in the list, which the switch
2044 // instruction can't handle, remove them now.
2045 array_pod_sort(Values.begin(), Values.end(), ConstantIntSortPredicate);
2046 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
2047
2048 // If Extra was used, we require at least two switch values to do the
2049 // transformation. A switch with one value is just an cond branch.
2050 if (ExtraCase && Values.size() < 2) return false;
2051
2052 // Figure out which block is which destination.
2053 BasicBlock *DefaultBB = BI->getSuccessor(1);
2054 BasicBlock *EdgeBB = BI->getSuccessor(0);
2055 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
2056
2057 BasicBlock *BB = BI->getParent();
2058
Chris Lattner302ba6f2010-12-14 06:17:25 +00002059 DEBUG(dbgs() << "Converting 'icmp' chain with " << Values.size()
Chris Lattner117f8cf2010-12-14 05:57:30 +00002060 << " cases into SWITCH. BB is:\n" << *BB);
2061
Chris Lattner97fdb892010-12-13 05:03:41 +00002062 // If there are any extra values that couldn't be folded into the switch
2063 // then we evaluate them with an explicit branch first. Split the block
2064 // right before the condbr to handle it.
2065 if (ExtraCase) {
2066 BasicBlock *NewBB = BB->splitBasicBlock(BI, "switch.early.test");
2067 // Remove the uncond branch added to the old block.
2068 TerminatorInst *OldTI = BB->getTerminator();
2069
Chris Lattner117f8cf2010-12-14 05:57:30 +00002070 if (TrueWhenEqual)
2071 BranchInst::Create(EdgeBB, NewBB, ExtraCase, OldTI);
2072 else
2073 BranchInst::Create(NewBB, EdgeBB, ExtraCase, OldTI);
2074
Chris Lattner97fdb892010-12-13 05:03:41 +00002075 OldTI->eraseFromParent();
Chris Lattner97bd89e2010-12-13 05:34:18 +00002076
2077 // If there are PHI nodes in EdgeBB, then we need to add a new entry to them
2078 // for the edge we just added.
Chris Lattner6de0a282010-12-14 07:09:42 +00002079 AddPredecessorToBlock(EdgeBB, BB, NewBB);
Chris Lattner302ba6f2010-12-14 06:17:25 +00002080
2081 DEBUG(dbgs() << " ** 'icmp' chain unhandled condition: " << *ExtraCase
2082 << "\nEXTRABB = " << *BB);
Chris Lattner97fdb892010-12-13 05:03:41 +00002083 BB = NewBB;
2084 }
2085
2086 // Convert pointer to int before we switch.
2087 if (CompVal->getType()->isPointerTy()) {
2088 assert(TD && "Cannot switch on pointer without TargetData");
2089 CompVal = new PtrToIntInst(CompVal,
2090 TD->getIntPtrType(CompVal->getContext()),
2091 "magicptr", BI);
Devang Pateld80e8ed2011-05-17 23:29:05 +00002092 cast<PtrToIntInst>(CompVal)->setDebugLoc(BI->getDebugLoc());
Chris Lattner97fdb892010-12-13 05:03:41 +00002093 }
2094
2095 // Create the new switch instruction now.
Chris Lattner3d512132010-12-13 06:25:44 +00002096 SwitchInst *New = SwitchInst::Create(CompVal, DefaultBB, Values.size(), BI);
Devang Pateld80e8ed2011-05-17 23:29:05 +00002097 New->setDebugLoc(BI->getDebugLoc());
2098
Chris Lattner97fdb892010-12-13 05:03:41 +00002099 // Add all of the 'cases' to the switch instruction.
2100 for (unsigned i = 0, e = Values.size(); i != e; ++i)
2101 New->addCase(Values[i], EdgeBB);
2102
2103 // We added edges from PI to the EdgeBB. As such, if there were any
2104 // PHI nodes in EdgeBB, they need entries to be added corresponding to
2105 // the number of edges added.
2106 for (BasicBlock::iterator BBI = EdgeBB->begin();
2107 isa<PHINode>(BBI); ++BBI) {
2108 PHINode *PN = cast<PHINode>(BBI);
2109 Value *InVal = PN->getIncomingValueForBlock(BB);
2110 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
2111 PN->addIncoming(InVal, BB);
2112 }
2113
2114 // Erase the old branch instruction.
2115 EraseTerminatorInstAndDCECond(BI);
Chris Lattner117f8cf2010-12-14 05:57:30 +00002116
Chris Lattner302ba6f2010-12-14 06:17:25 +00002117 DEBUG(dbgs() << " ** 'icmp' chain result is:\n" << *BB << '\n');
Chris Lattner97fdb892010-12-13 05:03:41 +00002118 return true;
2119}
2120
Chris Lattner3d512132010-12-13 06:25:44 +00002121bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI) {
2122 BasicBlock *BB = RI->getParent();
2123 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
2124
2125 // Find predecessors that end with branches.
2126 SmallVector<BasicBlock*, 8> UncondBranchPreds;
2127 SmallVector<BranchInst*, 8> CondBranchPreds;
2128 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
2129 BasicBlock *P = *PI;
2130 TerminatorInst *PTI = P->getTerminator();
2131 if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
2132 if (BI->isUnconditional())
2133 UncondBranchPreds.push_back(P);
2134 else
2135 CondBranchPreds.push_back(BI);
2136 }
2137 }
2138
2139 // If we found some, do the transformation!
Evan Chengc3f507f2011-01-29 04:46:23 +00002140 if (!UncondBranchPreds.empty() && DupRet) {
Chris Lattner3d512132010-12-13 06:25:44 +00002141 while (!UncondBranchPreds.empty()) {
2142 BasicBlock *Pred = UncondBranchPreds.pop_back_val();
2143 DEBUG(dbgs() << "FOLDING: " << *BB
2144 << "INTO UNCOND BRANCH PRED: " << *Pred);
Evan Chengc3f507f2011-01-29 04:46:23 +00002145 (void)FoldReturnIntoUncondBranch(RI, BB, Pred);
Chris Lattner3d512132010-12-13 06:25:44 +00002146 }
2147
2148 // If we eliminated all predecessors of the block, delete the block now.
2149 if (pred_begin(BB) == pred_end(BB))
2150 // We know there are no successors, so just nuke the block.
2151 BB->eraseFromParent();
2152
2153 return true;
2154 }
2155
2156 // Check out all of the conditional branches going to this return
2157 // instruction. If any of them just select between returns, change the
2158 // branch itself into a select/return pair.
2159 while (!CondBranchPreds.empty()) {
2160 BranchInst *BI = CondBranchPreds.pop_back_val();
2161
2162 // Check to see if the non-BB successor is also a return block.
2163 if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
2164 isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
2165 SimplifyCondBranchToTwoReturns(BI))
2166 return true;
2167 }
2168 return false;
2169}
2170
2171bool SimplifyCFGOpt::SimplifyUnwind(UnwindInst *UI) {
2172 // Check to see if the first instruction in this block is just an unwind.
2173 // If so, replace any invoke instructions which use this as an exception
2174 // destination with call instructions.
2175 BasicBlock *BB = UI->getParent();
2176 if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
2177
2178 bool Changed = false;
2179 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2180 while (!Preds.empty()) {
2181 BasicBlock *Pred = Preds.back();
2182 InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator());
2183 if (II && II->getUnwindDest() == BB) {
2184 // Insert a new branch instruction before the invoke, because this
2185 // is now a fall through.
2186 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
2187 Pred->getInstList().remove(II); // Take out of symbol table
2188
2189 // Insert the call now.
2190 SmallVector<Value*,8> Args(II->op_begin(), II->op_end()-3);
2191 CallInst *CI = CallInst::Create(II->getCalledValue(),
2192 Args.begin(), Args.end(),
2193 II->getName(), BI);
2194 CI->setCallingConv(II->getCallingConv());
2195 CI->setAttributes(II->getAttributes());
2196 // If the invoke produced a value, the Call now does instead.
2197 II->replaceAllUsesWith(CI);
2198 delete II;
2199 Changed = true;
2200 }
2201
2202 Preds.pop_back();
2203 }
2204
2205 // If this block is now dead (and isn't the entry block), remove it.
2206 if (pred_begin(BB) == pred_end(BB) &&
2207 BB != &BB->getParent()->getEntryBlock()) {
2208 // We know there are no successors, so just nuke the block.
2209 BB->eraseFromParent();
2210 return true;
2211 }
2212
2213 return Changed;
2214}
2215
2216bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
2217 BasicBlock *BB = UI->getParent();
2218
2219 bool Changed = false;
2220
2221 // If there are any instructions immediately before the unreachable that can
2222 // be removed, do so.
2223 while (UI != BB->begin()) {
2224 BasicBlock::iterator BBI = UI;
2225 --BBI;
2226 // Do not delete instructions that can have side effects, like calls
2227 // (which may never return) and volatile loads and stores.
2228 if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
2229
2230 if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
2231 if (SI->isVolatile())
2232 break;
2233
2234 if (LoadInst *LI = dyn_cast<LoadInst>(BBI))
2235 if (LI->isVolatile())
2236 break;
2237
Eli Friedman2adc5b62011-03-09 00:48:33 +00002238 // Delete this instruction (any uses are guaranteed to be dead)
2239 if (!BBI->use_empty())
2240 BBI->replaceAllUsesWith(UndefValue::get(BBI->getType()));
Chris Lattner302ba6f2010-12-14 06:17:25 +00002241 BBI->eraseFromParent();
Chris Lattner3d512132010-12-13 06:25:44 +00002242 Changed = true;
2243 }
2244
2245 // If the unreachable instruction is the first in the block, take a gander
2246 // at all of the predecessors of this instruction, and simplify them.
2247 if (&BB->front() != UI) return Changed;
2248
2249 SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
2250 for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
2251 TerminatorInst *TI = Preds[i]->getTerminator();
2252
2253 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
2254 if (BI->isUnconditional()) {
2255 if (BI->getSuccessor(0) == BB) {
2256 new UnreachableInst(TI->getContext(), TI);
2257 TI->eraseFromParent();
2258 Changed = true;
2259 }
2260 } else {
2261 if (BI->getSuccessor(0) == BB) {
2262 BranchInst::Create(BI->getSuccessor(1), BI);
2263 EraseTerminatorInstAndDCECond(BI);
2264 } else if (BI->getSuccessor(1) == BB) {
2265 BranchInst::Create(BI->getSuccessor(0), BI);
2266 EraseTerminatorInstAndDCECond(BI);
2267 Changed = true;
2268 }
2269 }
2270 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
2271 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2272 if (SI->getSuccessor(i) == BB) {
2273 BB->removePredecessor(SI->getParent());
2274 SI->removeCase(i);
2275 --i; --e;
2276 Changed = true;
2277 }
2278 // If the default value is unreachable, figure out the most popular
2279 // destination and make it the default.
2280 if (SI->getSuccessor(0) == BB) {
Eli Friedmanb1a6eab2011-03-15 02:23:35 +00002281 std::map<BasicBlock*, std::pair<unsigned, unsigned> > Popularity;
2282 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) {
2283 std::pair<unsigned, unsigned>& entry =
2284 Popularity[SI->getSuccessor(i)];
2285 if (entry.first == 0) {
2286 entry.first = 1;
2287 entry.second = i;
2288 } else {
2289 entry.first++;
2290 }
2291 }
2292
Chris Lattner3d512132010-12-13 06:25:44 +00002293 // Find the most popular block.
2294 unsigned MaxPop = 0;
Eli Friedmanb1a6eab2011-03-15 02:23:35 +00002295 unsigned MaxIndex = 0;
Chris Lattner3d512132010-12-13 06:25:44 +00002296 BasicBlock *MaxBlock = 0;
Eli Friedmanb1a6eab2011-03-15 02:23:35 +00002297 for (std::map<BasicBlock*, std::pair<unsigned, unsigned> >::iterator
Chris Lattner3d512132010-12-13 06:25:44 +00002298 I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
Eli Friedmanb1a6eab2011-03-15 02:23:35 +00002299 if (I->second.first > MaxPop ||
2300 (I->second.first == MaxPop && MaxIndex > I->second.second)) {
2301 MaxPop = I->second.first;
2302 MaxIndex = I->second.second;
Chris Lattner3d512132010-12-13 06:25:44 +00002303 MaxBlock = I->first;
2304 }
2305 }
2306 if (MaxBlock) {
2307 // Make this the new default, allowing us to delete any explicit
2308 // edges to it.
2309 SI->setSuccessor(0, MaxBlock);
2310 Changed = true;
2311
2312 // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
2313 // it.
2314 if (isa<PHINode>(MaxBlock->begin()))
2315 for (unsigned i = 0; i != MaxPop-1; ++i)
2316 MaxBlock->removePredecessor(SI->getParent());
2317
2318 for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
2319 if (SI->getSuccessor(i) == MaxBlock) {
2320 SI->removeCase(i);
2321 --i; --e;
2322 }
2323 }
2324 }
2325 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
2326 if (II->getUnwindDest() == BB) {
2327 // Convert the invoke to a call instruction. This would be a good
2328 // place to note that the call does not throw though.
2329 BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
2330 II->removeFromParent(); // Take out of symbol table
2331
2332 // Insert the call now...
2333 SmallVector<Value*, 8> Args(II->op_begin(), II->op_end()-3);
2334 CallInst *CI = CallInst::Create(II->getCalledValue(),
2335 Args.begin(), Args.end(),
2336 II->getName(), BI);
2337 CI->setCallingConv(II->getCallingConv());
2338 CI->setAttributes(II->getAttributes());
2339 // If the invoke produced a value, the call does now instead.
2340 II->replaceAllUsesWith(CI);
2341 delete II;
2342 Changed = true;
2343 }
2344 }
2345 }
2346
2347 // If this block is now dead, remove it.
2348 if (pred_begin(BB) == pred_end(BB) &&
2349 BB != &BB->getParent()->getEntryBlock()) {
2350 // We know there are no successors, so just nuke the block.
2351 BB->eraseFromParent();
2352 return true;
2353 }
2354
2355 return Changed;
2356}
2357
Benjamin Kramer56442df2011-02-02 15:56:22 +00002358/// TurnSwitchRangeIntoICmp - Turns a switch with that contains only a
2359/// integer range comparison into a sub, an icmp and a branch.
2360static bool TurnSwitchRangeIntoICmp(SwitchInst *SI) {
2361 assert(SI->getNumCases() > 2 && "Degenerate switch?");
Benjamin Kramer56442df2011-02-02 15:56:22 +00002362
Benjamin Kramer042b27f2011-02-03 22:51:41 +00002363 // Make sure all cases point to the same destination and gather the values.
2364 SmallVector<ConstantInt *, 16> Cases;
2365 Cases.push_back(SI->getCaseValue(1));
2366 for (unsigned I = 2, E = SI->getNumCases(); I != E; ++I) {
2367 if (SI->getSuccessor(I-1) != SI->getSuccessor(I))
2368 return false;
2369 Cases.push_back(SI->getCaseValue(I));
2370 }
2371 assert(Cases.size() == SI->getNumCases()-1 && "Not all cases gathered");
2372
2373 // Sort the case values, then check if they form a range we can transform.
2374 array_pod_sort(Cases.begin(), Cases.end(), ConstantIntSortPredicate);
2375 for (unsigned I = 1, E = Cases.size(); I != E; ++I) {
2376 if (Cases[I-1]->getValue() != Cases[I]->getValue()+1)
2377 return false;
2378 }
2379
2380 Constant *Offset = ConstantExpr::getNeg(Cases.back());
Benjamin Kramer56442df2011-02-02 15:56:22 +00002381 Constant *NumCases = ConstantInt::get(Offset->getType(), SI->getNumCases()-1);
2382
Benjamin Kramer33828bc2011-02-07 22:37:28 +00002383 Value *Sub = SI->getCondition();
2384 if (!Offset->isNullValue())
2385 Sub = BinaryOperator::CreateAdd(Sub, Offset, Sub->getName()+".off", SI);
Benjamin Kramer56442df2011-02-02 15:56:22 +00002386 Value *Cmp = new ICmpInst(SI, ICmpInst::ICMP_ULT, Sub, NumCases, "switch");
2387 BranchInst::Create(SI->getSuccessor(1), SI->getDefaultDest(), Cmp, SI);
2388
2389 // Prune obsolete incoming values off the successor's PHI nodes.
2390 for (BasicBlock::iterator BBI = SI->getSuccessor(1)->begin();
2391 isa<PHINode>(BBI); ++BBI) {
2392 for (unsigned I = 0, E = SI->getNumCases()-2; I != E; ++I)
2393 cast<PHINode>(BBI)->removeIncomingValue(SI->getParent());
2394 }
2395 SI->eraseFromParent();
2396
2397 return true;
2398}
Chris Lattner3d512132010-12-13 06:25:44 +00002399
Benjamin Kramer10fcfb52011-05-14 15:57:25 +00002400/// EliminateDeadSwitchCases - Compute masked bits for the condition of a switch
2401/// and use it to remove dead cases.
2402static bool EliminateDeadSwitchCases(SwitchInst *SI) {
2403 Value *Cond = SI->getCondition();
2404 unsigned Bits = cast<IntegerType>(Cond->getType())->getBitWidth();
2405 APInt KnownZero(Bits, 0), KnownOne(Bits, 0);
2406 ComputeMaskedBits(Cond, APInt::getAllOnesValue(Bits), KnownZero, KnownOne);
2407
2408 // Gather dead cases.
2409 SmallVector<ConstantInt*, 8> DeadCases;
2410 for (unsigned I = 1, E = SI->getNumCases(); I != E; ++I) {
2411 if ((SI->getCaseValue(I)->getValue() & KnownZero) != 0 ||
2412 (SI->getCaseValue(I)->getValue() & KnownOne) != KnownOne) {
2413 DeadCases.push_back(SI->getCaseValue(I));
2414 DEBUG(dbgs() << "SimplifyCFG: switch case '"
2415 << SI->getCaseValue(I)->getValue() << "' is dead.\n");
2416 }
2417 }
2418
2419 // Remove dead cases from the switch.
2420 for (unsigned I = 0, E = DeadCases.size(); I != E; ++I) {
2421 unsigned Case = SI->findCaseValue(DeadCases[I]);
2422 // Prune unused values from PHI nodes.
2423 SI->getSuccessor(Case)->removePredecessor(SI->getParent());
2424 SI->removeCase(Case);
2425 }
2426
2427 return !DeadCases.empty();
2428}
2429
Chris Lattner3d512132010-12-13 06:25:44 +00002430bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI) {
2431 // If this switch is too complex to want to look at, ignore it.
2432 if (!isValueEqualityComparison(SI))
2433 return false;
2434
2435 BasicBlock *BB = SI->getParent();
2436
2437 // If we only have one predecessor, and if it is a branch on this value,
2438 // see if that predecessor totally determines the outcome of this switch.
2439 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2440 if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred))
Chris Lattner021c9d32010-12-13 06:36:51 +00002441 return SimplifyCFG(BB) | true;
Frits van Bommelf7b2a9d2011-02-28 09:44:07 +00002442
2443 Value *Cond = SI->getCondition();
2444 if (SelectInst *Select = dyn_cast<SelectInst>(Cond))
2445 if (SimplifySwitchOnSelect(SI, Select))
2446 return SimplifyCFG(BB) | true;
2447
Chris Lattner3d512132010-12-13 06:25:44 +00002448 // If the block only contains the switch, see if we can fold the block
2449 // away into any preds.
2450 BasicBlock::iterator BBI = BB->begin();
2451 // Ignore dbg intrinsics.
2452 while (isa<DbgInfoIntrinsic>(BBI))
2453 ++BBI;
2454 if (SI == &*BBI)
2455 if (FoldValueComparisonIntoPredecessors(SI))
Chris Lattner021c9d32010-12-13 06:36:51 +00002456 return SimplifyCFG(BB) | true;
Benjamin Kramer56442df2011-02-02 15:56:22 +00002457
2458 // Try to transform the switch into an icmp and a branch.
2459 if (TurnSwitchRangeIntoICmp(SI))
2460 return SimplifyCFG(BB) | true;
Benjamin Kramer10fcfb52011-05-14 15:57:25 +00002461
2462 // Remove unreachable cases.
2463 if (EliminateDeadSwitchCases(SI))
2464 return SimplifyCFG(BB) | true;
2465
Chris Lattner3d512132010-12-13 06:25:44 +00002466 return false;
2467}
2468
2469bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) {
2470 BasicBlock *BB = IBI->getParent();
2471 bool Changed = false;
2472
2473 // Eliminate redundant destinations.
2474 SmallPtrSet<Value *, 8> Succs;
2475 for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
2476 BasicBlock *Dest = IBI->getDestination(i);
2477 if (!Dest->hasAddressTaken() || !Succs.insert(Dest)) {
2478 Dest->removePredecessor(BB);
2479 IBI->removeDestination(i);
2480 --i; --e;
2481 Changed = true;
2482 }
2483 }
2484
2485 if (IBI->getNumDestinations() == 0) {
2486 // If the indirectbr has no successors, change it to unreachable.
2487 new UnreachableInst(IBI->getContext(), IBI);
2488 EraseTerminatorInstAndDCECond(IBI);
2489 return true;
2490 }
2491
2492 if (IBI->getNumDestinations() == 1) {
2493 // If the indirectbr has one successor, change it to a direct branch.
2494 BranchInst::Create(IBI->getDestination(0), IBI);
2495 EraseTerminatorInstAndDCECond(IBI);
2496 return true;
2497 }
2498
2499 if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
2500 if (SimplifyIndirectBrOnSelect(IBI, SI))
2501 return SimplifyCFG(BB) | true;
2502 }
2503 return Changed;
2504}
2505
2506bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI) {
2507 BasicBlock *BB = BI->getParent();
2508
2509 // If the Terminator is the only non-phi instruction, simplify the block.
2510 BasicBlock::iterator I = BB->getFirstNonPHIOrDbg();
2511 if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
2512 TryToSimplifyUncondBranchFromEmptyBlock(BB))
2513 return true;
2514
2515 // If the only instruction in the block is a seteq/setne comparison
2516 // against a constant, try to simplify the block.
2517 if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
2518 if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) {
2519 for (++I; isa<DbgInfoIntrinsic>(I); ++I)
2520 ;
Chris Lattner302ba6f2010-12-14 06:17:25 +00002521 if (I->isTerminator() && TryToSimplifyUncondBranchWithICmpInIt(ICI, TD))
Chris Lattner3d512132010-12-13 06:25:44 +00002522 return true;
2523 }
2524
2525 return false;
2526}
2527
2528
2529bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI) {
2530 BasicBlock *BB = BI->getParent();
2531
2532 // Conditional branch
2533 if (isValueEqualityComparison(BI)) {
2534 // If we only have one predecessor, and if it is a branch on this value,
2535 // see if that predecessor totally determines the outcome of this
2536 // switch.
2537 if (BasicBlock *OnlyPred = BB->getSinglePredecessor())
2538 if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred))
2539 return SimplifyCFG(BB) | true;
2540
2541 // This block must be empty, except for the setcond inst, if it exists.
2542 // Ignore dbg intrinsics.
2543 BasicBlock::iterator I = BB->begin();
2544 // Ignore dbg intrinsics.
2545 while (isa<DbgInfoIntrinsic>(I))
2546 ++I;
2547 if (&*I == BI) {
2548 if (FoldValueComparisonIntoPredecessors(BI))
2549 return SimplifyCFG(BB) | true;
2550 } else if (&*I == cast<Instruction>(BI->getCondition())){
2551 ++I;
2552 // Ignore dbg intrinsics.
2553 while (isa<DbgInfoIntrinsic>(I))
2554 ++I;
2555 if (&*I == BI && FoldValueComparisonIntoPredecessors(BI))
2556 return SimplifyCFG(BB) | true;
2557 }
2558 }
2559
2560 // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction.
2561 if (SimplifyBranchOnICmpChain(BI, TD))
2562 return true;
2563
2564 // We have a conditional branch to two blocks that are only reachable
2565 // from BI. We know that the condbr dominates the two blocks, so see if
2566 // there is any identical code in the "then" and "else" blocks. If so, we
2567 // can hoist it up to the branching block.
2568 if (BI->getSuccessor(0)->getSinglePredecessor() != 0) {
2569 if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
2570 if (HoistThenElseCodeToIf(BI))
2571 return SimplifyCFG(BB) | true;
2572 } else {
2573 // If Successor #1 has multiple preds, we may be able to conditionally
2574 // execute Successor #0 if it branches to successor #1.
2575 TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator();
2576 if (Succ0TI->getNumSuccessors() == 1 &&
2577 Succ0TI->getSuccessor(0) == BI->getSuccessor(1))
2578 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0)))
2579 return SimplifyCFG(BB) | true;
2580 }
2581 } else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
2582 // If Successor #0 has multiple preds, we may be able to conditionally
2583 // execute Successor #1 if it branches to successor #0.
2584 TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator();
2585 if (Succ1TI->getNumSuccessors() == 1 &&
2586 Succ1TI->getSuccessor(0) == BI->getSuccessor(0))
2587 if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1)))
2588 return SimplifyCFG(BB) | true;
2589 }
2590
2591 // If this is a branch on a phi node in the current block, thread control
2592 // through this block if any PHI node entries are constants.
2593 if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
2594 if (PN->getParent() == BI->getParent())
Chris Lattner302ba6f2010-12-14 06:17:25 +00002595 if (FoldCondBranchOnPHI(BI, TD))
Chris Lattner3d512132010-12-13 06:25:44 +00002596 return SimplifyCFG(BB) | true;
2597
2598 // If this basic block is ONLY a setcc and a branch, and if a predecessor
2599 // branches to us and one of our successors, fold the setcc into the
2600 // predecessor and use logical operations to pick the right destination.
2601 if (FoldBranchToCommonDest(BI))
Owen Anderson2d9220e2010-12-13 23:49:28 +00002602 return SimplifyCFG(BB) | true;
Chris Lattner3d512132010-12-13 06:25:44 +00002603
2604 // Scan predecessor blocks for conditional branches.
2605 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
2606 if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
2607 if (PBI != BI && PBI->isConditional())
2608 if (SimplifyCondBranchToCondBranch(PBI, BI))
2609 return SimplifyCFG(BB) | true;
2610
2611 return false;
2612}
2613
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +00002614bool SimplifyCFGOpt::run(BasicBlock *BB) {
Chris Lattnerdc3602b2003-08-24 18:36:16 +00002615 bool Changed = false;
Chris Lattner01d1ee32002-05-21 20:50:24 +00002616
Chris Lattner302ba6f2010-12-14 06:17:25 +00002617 assert(BB && BB->getParent() && "Block not embedded in function!");
Chris Lattner01d1ee32002-05-21 20:50:24 +00002618 assert(BB->getTerminator() && "Degenerate basic block encountered!");
Chris Lattner01d1ee32002-05-21 20:50:24 +00002619
Dan Gohmane2c6d132010-08-14 00:29:42 +00002620 // Remove basic blocks that have no predecessors (except the entry block)...
2621 // or that just have themself as a predecessor. These are unreachable.
Chris Lattner302ba6f2010-12-14 06:17:25 +00002622 if ((pred_begin(BB) == pred_end(BB) &&
2623 BB != &BB->getParent()->getEntryBlock()) ||
Dan Gohmane2c6d132010-08-14 00:29:42 +00002624 BB->getSinglePredecessor() == BB) {
David Greene89d6fd32010-01-05 01:26:52 +00002625 DEBUG(dbgs() << "Removing BB: \n" << *BB);
Chris Lattner71af9b02008-12-03 06:40:52 +00002626 DeleteDeadBlock(BB);
Chris Lattner01d1ee32002-05-21 20:50:24 +00002627 return true;
2628 }
2629
Chris Lattner694e37f2003-08-17 19:41:53 +00002630 // Check to see if we can constant propagate this terminator instruction
2631 // away...
Chris Lattnerdc3602b2003-08-24 18:36:16 +00002632 Changed |= ConstantFoldTerminator(BB);
Chris Lattner694e37f2003-08-17 19:41:53 +00002633
Dan Gohman2c635662009-10-30 22:39:04 +00002634 // Check for and eliminate duplicate PHI nodes in this block.
2635 Changed |= EliminateDuplicatePHINodes(BB);
2636
Chris Lattnerddb97a22010-12-13 05:10:48 +00002637 // Merge basic blocks into their predecessor if there is only one distinct
2638 // pred, and if there is only one distinct successor of the predecessor, and
2639 // if there are no PHI nodes.
2640 //
2641 if (MergeBlockIntoPredecessor(BB))
2642 return true;
2643
Devang Patel3e410c62011-05-18 18:01:27 +00002644 IRBuilder<> Builder(BB);
2645
Dan Gohman882d87d2008-03-11 21:53:06 +00002646 // If there is a trivial two-entry PHI node in this basic block, and we can
2647 // eliminate it, do so now.
2648 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
2649 if (PN->getNumIncomingValues() == 2)
Devang Patelf60364d2011-05-18 18:16:44 +00002650 Changed |= FoldTwoEntryPHINode(PN, TD, Builder);
Dan Gohman882d87d2008-03-11 21:53:06 +00002651
Chris Lattner3d512132010-12-13 06:25:44 +00002652 if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
Chris Lattner021c9d32010-12-13 06:36:51 +00002653 if (BI->isUnconditional()) {
2654 if (SimplifyUncondBranch(BI)) return true;
2655 } else {
Chris Lattner117f8cf2010-12-14 05:57:30 +00002656 if (SimplifyCondBranch(BI)) return true;
Chris Lattner021c9d32010-12-13 06:36:51 +00002657 }
2658 } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
2659 if (SimplifyReturn(RI)) return true;
2660 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
2661 if (SimplifySwitch(SI)) return true;
2662 } else if (UnreachableInst *UI =
2663 dyn_cast<UnreachableInst>(BB->getTerminator())) {
2664 if (SimplifyUnreachable(UI)) return true;
2665 } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) {
2666 if (SimplifyUnwind(UI)) return true;
2667 } else if (IndirectBrInst *IBI =
2668 dyn_cast<IndirectBrInst>(BB->getTerminator())) {
2669 if (SimplifyIndirectBr(IBI)) return true;
Chris Lattner19831ec2004-02-16 06:35:48 +00002670 }
2671
Chris Lattner694e37f2003-08-17 19:41:53 +00002672 return Changed;
Chris Lattner01d1ee32002-05-21 20:50:24 +00002673}
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +00002674
2675/// SimplifyCFG - This function is used to do simplification of a CFG. For
2676/// example, it adjusts branches to branches to eliminate the extra hop, it
2677/// eliminates unreachable basic blocks, and does other "peephole" optimization
2678/// of the CFG. It returns true if a modification was made.
2679///
Jakob Stoklund Olesen58e9ee82010-02-05 22:03:18 +00002680bool llvm::SimplifyCFG(BasicBlock *BB, const TargetData *TD) {
2681 return SimplifyCFGOpt(TD).run(BB);
2682}