Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 1 | //===- SimplifyCFG.cpp - Code to perform CFG simplification ---------------===// |
John Criswell | b576c94 | 2003-10-20 19:43:21 +0000 | [diff] [blame] | 2 | // |
| 3 | // The LLVM Compiler Infrastructure |
| 4 | // |
| 5 | // This file was developed by the LLVM research group and is distributed under |
| 6 | // the University of Illinois Open Source License. See LICENSE.TXT for details. |
| 7 | // |
| 8 | //===----------------------------------------------------------------------===// |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 9 | // |
Chris Lattner | bb190ac | 2002-10-08 21:36:33 +0000 | [diff] [blame] | 10 | // Peephole optimize the CFG. |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 11 | // |
| 12 | //===----------------------------------------------------------------------===// |
| 13 | |
Chris Lattner | 218a822 | 2004-06-20 01:13:18 +0000 | [diff] [blame] | 14 | #define DEBUG_TYPE "simplifycfg" |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 15 | #include "llvm/Transforms/Utils/Local.h" |
Chris Lattner | 723c66d | 2004-02-11 03:36:04 +0000 | [diff] [blame] | 16 | #include "llvm/Constants.h" |
| 17 | #include "llvm/Instructions.h" |
Chris Lattner | 0d56008 | 2004-02-24 05:38:11 +0000 | [diff] [blame] | 18 | #include "llvm/Type.h" |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 19 | #include "llvm/Support/CFG.h" |
Reid Spencer | 551ccae | 2004-09-01 22:55:40 +0000 | [diff] [blame] | 20 | #include "llvm/Support/Debug.h" |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 21 | #include <algorithm> |
| 22 | #include <functional> |
Chris Lattner | d52c261 | 2004-02-24 07:23:58 +0000 | [diff] [blame] | 23 | #include <set> |
Chris Lattner | 698f96f | 2004-10-18 04:07:22 +0000 | [diff] [blame] | 24 | #include <map> |
Chris Lattner | f7703df | 2004-01-09 06:12:26 +0000 | [diff] [blame] | 25 | using namespace llvm; |
Brian Gaeke | d0fde30 | 2003-11-11 22:41:34 +0000 | [diff] [blame] | 26 | |
Chris Lattner | 0d56008 | 2004-02-24 05:38:11 +0000 | [diff] [blame] | 27 | // PropagatePredecessorsForPHIs - This gets "Succ" ready to have the |
| 28 | // predecessors from "BB". This is a little tricky because "Succ" has PHI |
| 29 | // nodes, which need to have extra slots added to them to hold the merge edges |
| 30 | // from BB's predecessors, and BB itself might have had PHI nodes in it. This |
| 31 | // function returns true (failure) if the Succ BB already has a predecessor that |
| 32 | // is a predecessor of BB and incoming PHI arguments would not be discernible. |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 33 | // |
| 34 | // Assumption: Succ is the single successor for BB. |
| 35 | // |
Misha Brukman | a3bbcb5 | 2002-10-29 23:06:16 +0000 | [diff] [blame] | 36 | static bool PropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) { |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 37 | assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!"); |
Chris Lattner | 3abb95d | 2002-09-24 00:09:26 +0000 | [diff] [blame] | 38 | |
| 39 | if (!isa<PHINode>(Succ->front())) |
| 40 | return false; // We can make the transformation, no problem. |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 41 | |
| 42 | // If there is more than one predecessor, and there are PHI nodes in |
| 43 | // the successor, then we need to add incoming edges for the PHI nodes |
| 44 | // |
| 45 | const std::vector<BasicBlock*> BBPreds(pred_begin(BB), pred_end(BB)); |
| 46 | |
| 47 | // Check to see if one of the predecessors of BB is already a predecessor of |
Chris Lattner | e2ca540 | 2003-03-05 21:01:52 +0000 | [diff] [blame] | 48 | // Succ. If so, we cannot do the transformation if there are any PHI nodes |
| 49 | // with incompatible values coming in from the two edges! |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 50 | // |
Chris Lattner | e2ca540 | 2003-03-05 21:01:52 +0000 | [diff] [blame] | 51 | for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ); PI != PE; ++PI) |
Alkis Evlogimenos | 20aa474 | 2004-09-03 18:19:51 +0000 | [diff] [blame] | 52 | if (std::find(BBPreds.begin(), BBPreds.end(), *PI) != BBPreds.end()) { |
Chris Lattner | e2ca540 | 2003-03-05 21:01:52 +0000 | [diff] [blame] | 53 | // Loop over all of the PHI nodes checking to see if there are |
| 54 | // incompatible values coming in. |
Reid Spencer | 2da5c3d | 2004-09-15 17:06:42 +0000 | [diff] [blame] | 55 | for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) { |
| 56 | PHINode *PN = cast<PHINode>(I); |
Chris Lattner | e2ca540 | 2003-03-05 21:01:52 +0000 | [diff] [blame] | 57 | // Loop up the entries in the PHI node for BB and for *PI if the values |
| 58 | // coming in are non-equal, we cannot merge these two blocks (instead we |
| 59 | // should insert a conditional move or something, then merge the |
| 60 | // blocks). |
| 61 | int Idx1 = PN->getBasicBlockIndex(BB); |
| 62 | int Idx2 = PN->getBasicBlockIndex(*PI); |
| 63 | assert(Idx1 != -1 && Idx2 != -1 && |
| 64 | "Didn't have entries for my predecessors??"); |
| 65 | if (PN->getIncomingValue(Idx1) != PN->getIncomingValue(Idx2)) |
| 66 | return true; // Values are not equal... |
| 67 | } |
| 68 | } |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 69 | |
Chris Lattner | 218a822 | 2004-06-20 01:13:18 +0000 | [diff] [blame] | 70 | // Loop over all of the PHI nodes in the successor BB. |
Reid Spencer | 2da5c3d | 2004-09-15 17:06:42 +0000 | [diff] [blame] | 71 | for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) { |
| 72 | PHINode *PN = cast<PHINode>(I); |
Chris Lattner | bb190ac | 2002-10-08 21:36:33 +0000 | [diff] [blame] | 73 | Value *OldVal = PN->removeIncomingValue(BB, false); |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 74 | assert(OldVal && "No entry in PHI for Pred BB!"); |
| 75 | |
Chris Lattner | 218a822 | 2004-06-20 01:13:18 +0000 | [diff] [blame] | 76 | // If this incoming value is one of the PHI nodes in BB, the new entries in |
| 77 | // the PHI node are the entries from the old PHI. |
Chris Lattner | 46a5f1f | 2003-03-05 21:36:33 +0000 | [diff] [blame] | 78 | if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) { |
| 79 | PHINode *OldValPN = cast<PHINode>(OldVal); |
Chris Lattner | 218a822 | 2004-06-20 01:13:18 +0000 | [diff] [blame] | 80 | for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i) |
| 81 | PN->addIncoming(OldValPN->getIncomingValue(i), |
| 82 | OldValPN->getIncomingBlock(i)); |
Chris Lattner | 46a5f1f | 2003-03-05 21:36:33 +0000 | [diff] [blame] | 83 | } else { |
| 84 | for (std::vector<BasicBlock*>::const_iterator PredI = BBPreds.begin(), |
| 85 | End = BBPreds.end(); PredI != End; ++PredI) { |
| 86 | // Add an incoming value for each of the new incoming values... |
| 87 | PN->addIncoming(OldVal, *PredI); |
| 88 | } |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 89 | } |
| 90 | } |
| 91 | return false; |
| 92 | } |
| 93 | |
Chris Lattner | 723c66d | 2004-02-11 03:36:04 +0000 | [diff] [blame] | 94 | /// GetIfCondition - Given a basic block (BB) with two predecessors (and |
| 95 | /// presumably PHI nodes in it), check to see if the merge at this block is due |
| 96 | /// to an "if condition". If so, return the boolean condition that determines |
| 97 | /// which entry into BB will be taken. Also, return by references the block |
| 98 | /// that will be entered from if the condition is true, and the block that will |
| 99 | /// be entered if the condition is false. |
| 100 | /// |
| 101 | /// |
| 102 | static Value *GetIfCondition(BasicBlock *BB, |
| 103 | BasicBlock *&IfTrue, BasicBlock *&IfFalse) { |
| 104 | assert(std::distance(pred_begin(BB), pred_end(BB)) == 2 && |
| 105 | "Function can only handle blocks with 2 predecessors!"); |
| 106 | BasicBlock *Pred1 = *pred_begin(BB); |
| 107 | BasicBlock *Pred2 = *++pred_begin(BB); |
| 108 | |
| 109 | // We can only handle branches. Other control flow will be lowered to |
| 110 | // branches if possible anyway. |
| 111 | if (!isa<BranchInst>(Pred1->getTerminator()) || |
| 112 | !isa<BranchInst>(Pred2->getTerminator())) |
| 113 | return 0; |
| 114 | BranchInst *Pred1Br = cast<BranchInst>(Pred1->getTerminator()); |
| 115 | BranchInst *Pred2Br = cast<BranchInst>(Pred2->getTerminator()); |
| 116 | |
| 117 | // Eliminate code duplication by ensuring that Pred1Br is conditional if |
| 118 | // either are. |
| 119 | if (Pred2Br->isConditional()) { |
| 120 | // If both branches are conditional, we don't have an "if statement". In |
| 121 | // reality, we could transform this case, but since the condition will be |
| 122 | // required anyway, we stand no chance of eliminating it, so the xform is |
| 123 | // probably not profitable. |
| 124 | if (Pred1Br->isConditional()) |
| 125 | return 0; |
| 126 | |
| 127 | std::swap(Pred1, Pred2); |
| 128 | std::swap(Pred1Br, Pred2Br); |
| 129 | } |
| 130 | |
| 131 | if (Pred1Br->isConditional()) { |
| 132 | // If we found a conditional branch predecessor, make sure that it branches |
| 133 | // to BB and Pred2Br. If it doesn't, this isn't an "if statement". |
| 134 | if (Pred1Br->getSuccessor(0) == BB && |
| 135 | Pred1Br->getSuccessor(1) == Pred2) { |
| 136 | IfTrue = Pred1; |
| 137 | IfFalse = Pred2; |
| 138 | } else if (Pred1Br->getSuccessor(0) == Pred2 && |
| 139 | Pred1Br->getSuccessor(1) == BB) { |
| 140 | IfTrue = Pred2; |
| 141 | IfFalse = Pred1; |
| 142 | } else { |
| 143 | // We know that one arm of the conditional goes to BB, so the other must |
| 144 | // go somewhere unrelated, and this must not be an "if statement". |
| 145 | return 0; |
| 146 | } |
| 147 | |
| 148 | // The only thing we have to watch out for here is to make sure that Pred2 |
| 149 | // doesn't have incoming edges from other blocks. If it does, the condition |
| 150 | // doesn't dominate BB. |
| 151 | if (++pred_begin(Pred2) != pred_end(Pred2)) |
| 152 | return 0; |
| 153 | |
| 154 | return Pred1Br->getCondition(); |
| 155 | } |
| 156 | |
| 157 | // Ok, if we got here, both predecessors end with an unconditional branch to |
| 158 | // BB. Don't panic! If both blocks only have a single (identical) |
| 159 | // predecessor, and THAT is a conditional branch, then we're all ok! |
| 160 | if (pred_begin(Pred1) == pred_end(Pred1) || |
| 161 | ++pred_begin(Pred1) != pred_end(Pred1) || |
| 162 | pred_begin(Pred2) == pred_end(Pred2) || |
| 163 | ++pred_begin(Pred2) != pred_end(Pred2) || |
| 164 | *pred_begin(Pred1) != *pred_begin(Pred2)) |
| 165 | return 0; |
| 166 | |
| 167 | // Otherwise, if this is a conditional branch, then we can use it! |
| 168 | BasicBlock *CommonPred = *pred_begin(Pred1); |
| 169 | if (BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator())) { |
| 170 | assert(BI->isConditional() && "Two successors but not conditional?"); |
| 171 | if (BI->getSuccessor(0) == Pred1) { |
| 172 | IfTrue = Pred1; |
| 173 | IfFalse = Pred2; |
| 174 | } else { |
| 175 | IfTrue = Pred2; |
| 176 | IfFalse = Pred1; |
| 177 | } |
| 178 | return BI->getCondition(); |
| 179 | } |
| 180 | return 0; |
| 181 | } |
| 182 | |
| 183 | |
| 184 | // If we have a merge point of an "if condition" as accepted above, return true |
| 185 | // if the specified value dominates the block. We don't handle the true |
| 186 | // generality of domination here, just a special case which works well enough |
| 187 | // for us. |
Chris Lattner | 9c07866 | 2004-10-14 05:13:36 +0000 | [diff] [blame] | 188 | // |
| 189 | // If AggressiveInsts is non-null, and if V does not dominate BB, we check to |
| 190 | // see if V (which must be an instruction) is cheap to compute and is |
| 191 | // non-trapping. If both are true, the instruction is inserted into the set and |
| 192 | // true is returned. |
| 193 | static bool DominatesMergePoint(Value *V, BasicBlock *BB, |
| 194 | std::set<Instruction*> *AggressiveInsts) { |
Chris Lattner | 570751c | 2004-04-09 22:50:22 +0000 | [diff] [blame] | 195 | Instruction *I = dyn_cast<Instruction>(V); |
| 196 | if (!I) return true; // Non-instructions all dominate instructions. |
| 197 | BasicBlock *PBB = I->getParent(); |
Chris Lattner | 723c66d | 2004-02-11 03:36:04 +0000 | [diff] [blame] | 198 | |
Chris Lattner | da895d6 | 2005-02-27 06:18:25 +0000 | [diff] [blame^] | 199 | // We don't want to allow weird loops that might have the "if condition" in |
Chris Lattner | 570751c | 2004-04-09 22:50:22 +0000 | [diff] [blame] | 200 | // the bottom of this block. |
| 201 | if (PBB == BB) return false; |
Chris Lattner | 723c66d | 2004-02-11 03:36:04 +0000 | [diff] [blame] | 202 | |
Chris Lattner | 570751c | 2004-04-09 22:50:22 +0000 | [diff] [blame] | 203 | // If this instruction is defined in a block that contains an unconditional |
| 204 | // branch to BB, then it must be in the 'conditional' part of the "if |
| 205 | // statement". |
| 206 | if (BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator())) |
| 207 | if (BI->isUnconditional() && BI->getSuccessor(0) == BB) { |
Chris Lattner | 9c07866 | 2004-10-14 05:13:36 +0000 | [diff] [blame] | 208 | if (!AggressiveInsts) return false; |
Chris Lattner | 570751c | 2004-04-09 22:50:22 +0000 | [diff] [blame] | 209 | // Okay, it looks like the instruction IS in the "condition". Check to |
| 210 | // see if its a cheap instruction to unconditionally compute, and if it |
| 211 | // only uses stuff defined outside of the condition. If so, hoist it out. |
| 212 | switch (I->getOpcode()) { |
| 213 | default: return false; // Cannot hoist this out safely. |
| 214 | case Instruction::Load: |
| 215 | // We can hoist loads that are non-volatile and obviously cannot trap. |
| 216 | if (cast<LoadInst>(I)->isVolatile()) |
| 217 | return false; |
| 218 | if (!isa<AllocaInst>(I->getOperand(0)) && |
Reid Spencer | 460f16c | 2004-07-18 00:32:14 +0000 | [diff] [blame] | 219 | !isa<Constant>(I->getOperand(0))) |
Chris Lattner | 570751c | 2004-04-09 22:50:22 +0000 | [diff] [blame] | 220 | return false; |
| 221 | |
| 222 | // Finally, we have to check to make sure there are no instructions |
| 223 | // before the load in its basic block, as we are going to hoist the loop |
| 224 | // out to its predecessor. |
| 225 | if (PBB->begin() != BasicBlock::iterator(I)) |
| 226 | return false; |
| 227 | break; |
| 228 | case Instruction::Add: |
| 229 | case Instruction::Sub: |
| 230 | case Instruction::And: |
| 231 | case Instruction::Or: |
| 232 | case Instruction::Xor: |
| 233 | case Instruction::Shl: |
| 234 | case Instruction::Shr: |
| 235 | break; // These are all cheap and non-trapping instructions. |
| 236 | } |
| 237 | |
| 238 | // Okay, we can only really hoist these out if their operands are not |
| 239 | // defined in the conditional region. |
| 240 | for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) |
Chris Lattner | 9c07866 | 2004-10-14 05:13:36 +0000 | [diff] [blame] | 241 | if (!DominatesMergePoint(I->getOperand(i), BB, 0)) |
Chris Lattner | 570751c | 2004-04-09 22:50:22 +0000 | [diff] [blame] | 242 | return false; |
Chris Lattner | 9c07866 | 2004-10-14 05:13:36 +0000 | [diff] [blame] | 243 | // Okay, it's safe to do this! Remember this instruction. |
| 244 | AggressiveInsts->insert(I); |
Chris Lattner | 570751c | 2004-04-09 22:50:22 +0000 | [diff] [blame] | 245 | } |
| 246 | |
Chris Lattner | 723c66d | 2004-02-11 03:36:04 +0000 | [diff] [blame] | 247 | return true; |
| 248 | } |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 249 | |
Chris Lattner | 0d56008 | 2004-02-24 05:38:11 +0000 | [diff] [blame] | 250 | // GatherConstantSetEQs - Given a potentially 'or'd together collection of seteq |
| 251 | // instructions that compare a value against a constant, return the value being |
| 252 | // compared, and stick the constant into the Values vector. |
Chris Lattner | 1654cff | 2004-06-19 07:02:14 +0000 | [diff] [blame] | 253 | static Value *GatherConstantSetEQs(Value *V, std::vector<ConstantInt*> &Values){ |
Chris Lattner | 0d56008 | 2004-02-24 05:38:11 +0000 | [diff] [blame] | 254 | if (Instruction *Inst = dyn_cast<Instruction>(V)) |
| 255 | if (Inst->getOpcode() == Instruction::SetEQ) { |
Chris Lattner | 1654cff | 2004-06-19 07:02:14 +0000 | [diff] [blame] | 256 | if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) { |
Chris Lattner | 0d56008 | 2004-02-24 05:38:11 +0000 | [diff] [blame] | 257 | Values.push_back(C); |
| 258 | return Inst->getOperand(0); |
Chris Lattner | 1654cff | 2004-06-19 07:02:14 +0000 | [diff] [blame] | 259 | } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) { |
Chris Lattner | 0d56008 | 2004-02-24 05:38:11 +0000 | [diff] [blame] | 260 | Values.push_back(C); |
| 261 | return Inst->getOperand(1); |
| 262 | } |
| 263 | } else if (Inst->getOpcode() == Instruction::Or) { |
| 264 | if (Value *LHS = GatherConstantSetEQs(Inst->getOperand(0), Values)) |
| 265 | if (Value *RHS = GatherConstantSetEQs(Inst->getOperand(1), Values)) |
| 266 | if (LHS == RHS) |
| 267 | return LHS; |
| 268 | } |
| 269 | return 0; |
| 270 | } |
| 271 | |
| 272 | // GatherConstantSetNEs - Given a potentially 'and'd together collection of |
| 273 | // setne instructions that compare a value against a constant, return the value |
| 274 | // being compared, and stick the constant into the Values vector. |
Chris Lattner | 1654cff | 2004-06-19 07:02:14 +0000 | [diff] [blame] | 275 | static Value *GatherConstantSetNEs(Value *V, std::vector<ConstantInt*> &Values){ |
Chris Lattner | 0d56008 | 2004-02-24 05:38:11 +0000 | [diff] [blame] | 276 | if (Instruction *Inst = dyn_cast<Instruction>(V)) |
| 277 | if (Inst->getOpcode() == Instruction::SetNE) { |
Chris Lattner | 1654cff | 2004-06-19 07:02:14 +0000 | [diff] [blame] | 278 | if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) { |
Chris Lattner | 0d56008 | 2004-02-24 05:38:11 +0000 | [diff] [blame] | 279 | Values.push_back(C); |
| 280 | return Inst->getOperand(0); |
Chris Lattner | 1654cff | 2004-06-19 07:02:14 +0000 | [diff] [blame] | 281 | } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) { |
Chris Lattner | 0d56008 | 2004-02-24 05:38:11 +0000 | [diff] [blame] | 282 | Values.push_back(C); |
| 283 | return Inst->getOperand(1); |
| 284 | } |
| 285 | } else if (Inst->getOpcode() == Instruction::Cast) { |
| 286 | // Cast of X to bool is really a comparison against zero. |
| 287 | assert(Inst->getType() == Type::BoolTy && "Can only handle bool values!"); |
Chris Lattner | 1654cff | 2004-06-19 07:02:14 +0000 | [diff] [blame] | 288 | Values.push_back(ConstantInt::get(Inst->getOperand(0)->getType(), 0)); |
Chris Lattner | 0d56008 | 2004-02-24 05:38:11 +0000 | [diff] [blame] | 289 | return Inst->getOperand(0); |
| 290 | } else if (Inst->getOpcode() == Instruction::And) { |
| 291 | if (Value *LHS = GatherConstantSetNEs(Inst->getOperand(0), Values)) |
| 292 | if (Value *RHS = GatherConstantSetNEs(Inst->getOperand(1), Values)) |
| 293 | if (LHS == RHS) |
| 294 | return LHS; |
| 295 | } |
| 296 | return 0; |
| 297 | } |
| 298 | |
| 299 | |
| 300 | |
| 301 | /// GatherValueComparisons - If the specified Cond is an 'and' or 'or' of a |
| 302 | /// bunch of comparisons of one value against constants, return the value and |
| 303 | /// the constants being compared. |
| 304 | static bool GatherValueComparisons(Instruction *Cond, Value *&CompVal, |
Chris Lattner | 1654cff | 2004-06-19 07:02:14 +0000 | [diff] [blame] | 305 | std::vector<ConstantInt*> &Values) { |
Chris Lattner | 0d56008 | 2004-02-24 05:38:11 +0000 | [diff] [blame] | 306 | if (Cond->getOpcode() == Instruction::Or) { |
| 307 | CompVal = GatherConstantSetEQs(Cond, Values); |
| 308 | |
| 309 | // Return true to indicate that the condition is true if the CompVal is |
| 310 | // equal to one of the constants. |
| 311 | return true; |
| 312 | } else if (Cond->getOpcode() == Instruction::And) { |
| 313 | CompVal = GatherConstantSetNEs(Cond, Values); |
| 314 | |
| 315 | // Return false to indicate that the condition is false if the CompVal is |
| 316 | // equal to one of the constants. |
| 317 | return false; |
| 318 | } |
| 319 | return false; |
| 320 | } |
| 321 | |
| 322 | /// ErasePossiblyDeadInstructionTree - If the specified instruction is dead and |
| 323 | /// has no side effects, nuke it. If it uses any instructions that become dead |
| 324 | /// because the instruction is now gone, nuke them too. |
| 325 | static void ErasePossiblyDeadInstructionTree(Instruction *I) { |
| 326 | if (isInstructionTriviallyDead(I)) { |
| 327 | std::vector<Value*> Operands(I->op_begin(), I->op_end()); |
| 328 | I->getParent()->getInstList().erase(I); |
| 329 | for (unsigned i = 0, e = Operands.size(); i != e; ++i) |
| 330 | if (Instruction *OpI = dyn_cast<Instruction>(Operands[i])) |
| 331 | ErasePossiblyDeadInstructionTree(OpI); |
| 332 | } |
| 333 | } |
| 334 | |
Chris Lattner | d52c261 | 2004-02-24 07:23:58 +0000 | [diff] [blame] | 335 | /// SafeToMergeTerminators - Return true if it is safe to merge these two |
| 336 | /// terminator instructions together. |
| 337 | /// |
| 338 | static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) { |
| 339 | if (SI1 == SI2) return false; // Can't merge with self! |
| 340 | |
| 341 | // It is not safe to merge these two switch instructions if they have a common |
Chris Lattner | 2636c1b | 2004-06-21 07:19:01 +0000 | [diff] [blame] | 342 | // successor, and if that successor has a PHI node, and if *that* PHI node has |
Chris Lattner | d52c261 | 2004-02-24 07:23:58 +0000 | [diff] [blame] | 343 | // conflicting incoming values from the two switch blocks. |
| 344 | BasicBlock *SI1BB = SI1->getParent(); |
| 345 | BasicBlock *SI2BB = SI2->getParent(); |
| 346 | std::set<BasicBlock*> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB)); |
| 347 | |
| 348 | for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I) |
| 349 | if (SI1Succs.count(*I)) |
| 350 | for (BasicBlock::iterator BBI = (*I)->begin(); |
Reid Spencer | 2da5c3d | 2004-09-15 17:06:42 +0000 | [diff] [blame] | 351 | isa<PHINode>(BBI); ++BBI) { |
| 352 | PHINode *PN = cast<PHINode>(BBI); |
Chris Lattner | d52c261 | 2004-02-24 07:23:58 +0000 | [diff] [blame] | 353 | if (PN->getIncomingValueForBlock(SI1BB) != |
| 354 | PN->getIncomingValueForBlock(SI2BB)) |
| 355 | return false; |
Reid Spencer | 2da5c3d | 2004-09-15 17:06:42 +0000 | [diff] [blame] | 356 | } |
Chris Lattner | d52c261 | 2004-02-24 07:23:58 +0000 | [diff] [blame] | 357 | |
| 358 | return true; |
| 359 | } |
| 360 | |
| 361 | /// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will |
| 362 | /// now be entries in it from the 'NewPred' block. The values that will be |
| 363 | /// flowing into the PHI nodes will be the same as those coming in from |
Chris Lattner | 2636c1b | 2004-06-21 07:19:01 +0000 | [diff] [blame] | 364 | /// ExistPred, an existing predecessor of Succ. |
Chris Lattner | d52c261 | 2004-02-24 07:23:58 +0000 | [diff] [blame] | 365 | static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred, |
| 366 | BasicBlock *ExistPred) { |
| 367 | assert(std::find(succ_begin(ExistPred), succ_end(ExistPred), Succ) != |
| 368 | succ_end(ExistPred) && "ExistPred is not a predecessor of Succ!"); |
| 369 | if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do |
| 370 | |
Reid Spencer | 2da5c3d | 2004-09-15 17:06:42 +0000 | [diff] [blame] | 371 | for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) { |
| 372 | PHINode *PN = cast<PHINode>(I); |
Chris Lattner | d52c261 | 2004-02-24 07:23:58 +0000 | [diff] [blame] | 373 | Value *V = PN->getIncomingValueForBlock(ExistPred); |
| 374 | PN->addIncoming(V, NewPred); |
| 375 | } |
| 376 | } |
| 377 | |
Chris Lattner | 542f149 | 2004-02-28 21:28:10 +0000 | [diff] [blame] | 378 | // isValueEqualityComparison - Return true if the specified terminator checks to |
| 379 | // see if a value is equal to constant integer value. |
| 380 | static Value *isValueEqualityComparison(TerminatorInst *TI) { |
Chris Lattner | 4bebf08 | 2004-03-16 19:45:22 +0000 | [diff] [blame] | 381 | if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { |
| 382 | // Do not permit merging of large switch instructions into their |
| 383 | // predecessors unless there is only one predecessor. |
| 384 | if (SI->getNumSuccessors() * std::distance(pred_begin(SI->getParent()), |
| 385 | pred_end(SI->getParent())) > 128) |
| 386 | return 0; |
| 387 | |
Chris Lattner | 542f149 | 2004-02-28 21:28:10 +0000 | [diff] [blame] | 388 | return SI->getCondition(); |
Chris Lattner | 4bebf08 | 2004-03-16 19:45:22 +0000 | [diff] [blame] | 389 | } |
Chris Lattner | 542f149 | 2004-02-28 21:28:10 +0000 | [diff] [blame] | 390 | if (BranchInst *BI = dyn_cast<BranchInst>(TI)) |
| 391 | if (BI->isConditional() && BI->getCondition()->hasOneUse()) |
| 392 | if (SetCondInst *SCI = dyn_cast<SetCondInst>(BI->getCondition())) |
| 393 | if ((SCI->getOpcode() == Instruction::SetEQ || |
| 394 | SCI->getOpcode() == Instruction::SetNE) && |
| 395 | isa<ConstantInt>(SCI->getOperand(1))) |
| 396 | return SCI->getOperand(0); |
| 397 | return 0; |
| 398 | } |
| 399 | |
| 400 | // Given a value comparison instruction, decode all of the 'cases' that it |
| 401 | // represents and return the 'default' block. |
| 402 | static BasicBlock * |
| 403 | GetValueEqualityComparisonCases(TerminatorInst *TI, |
| 404 | std::vector<std::pair<ConstantInt*, |
| 405 | BasicBlock*> > &Cases) { |
| 406 | if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { |
| 407 | Cases.reserve(SI->getNumCases()); |
| 408 | for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) |
Chris Lattner | be54dcc | 2005-02-26 18:33:28 +0000 | [diff] [blame] | 409 | Cases.push_back(std::make_pair(SI->getCaseValue(i), SI->getSuccessor(i))); |
Chris Lattner | 542f149 | 2004-02-28 21:28:10 +0000 | [diff] [blame] | 410 | return SI->getDefaultDest(); |
| 411 | } |
| 412 | |
| 413 | BranchInst *BI = cast<BranchInst>(TI); |
| 414 | SetCondInst *SCI = cast<SetCondInst>(BI->getCondition()); |
| 415 | Cases.push_back(std::make_pair(cast<ConstantInt>(SCI->getOperand(1)), |
| 416 | BI->getSuccessor(SCI->getOpcode() == |
| 417 | Instruction::SetNE))); |
| 418 | return BI->getSuccessor(SCI->getOpcode() == Instruction::SetEQ); |
| 419 | } |
| 420 | |
| 421 | |
Chris Lattner | 623369a | 2005-02-24 06:17:52 +0000 | [diff] [blame] | 422 | // EliminateBlockCases - Given an vector of bb/value pairs, remove any entries |
| 423 | // in the list that match the specified block. |
| 424 | static void EliminateBlockCases(BasicBlock *BB, |
| 425 | std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) { |
| 426 | for (unsigned i = 0, e = Cases.size(); i != e; ++i) |
| 427 | if (Cases[i].second == BB) { |
| 428 | Cases.erase(Cases.begin()+i); |
| 429 | --i; --e; |
| 430 | } |
| 431 | } |
| 432 | |
| 433 | // ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as |
| 434 | // well. |
| 435 | static bool |
| 436 | ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1, |
| 437 | std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) { |
| 438 | std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2; |
| 439 | |
| 440 | // Make V1 be smaller than V2. |
| 441 | if (V1->size() > V2->size()) |
| 442 | std::swap(V1, V2); |
| 443 | |
| 444 | if (V1->size() == 0) return false; |
| 445 | if (V1->size() == 1) { |
| 446 | // Just scan V2. |
| 447 | ConstantInt *TheVal = (*V1)[0].first; |
| 448 | for (unsigned i = 0, e = V2->size(); i != e; ++i) |
| 449 | if (TheVal == (*V2)[i].first) |
| 450 | return true; |
| 451 | } |
| 452 | |
| 453 | // Otherwise, just sort both lists and compare element by element. |
| 454 | std::sort(V1->begin(), V1->end()); |
| 455 | std::sort(V2->begin(), V2->end()); |
| 456 | unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size(); |
| 457 | while (i1 != e1 && i2 != e2) { |
| 458 | if ((*V1)[i1].first == (*V2)[i2].first) |
| 459 | return true; |
| 460 | if ((*V1)[i1].first < (*V2)[i2].first) |
| 461 | ++i1; |
| 462 | else |
| 463 | ++i2; |
| 464 | } |
| 465 | return false; |
| 466 | } |
| 467 | |
| 468 | // SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a |
| 469 | // terminator instruction and its block is known to only have a single |
| 470 | // predecessor block, check to see if that predecessor is also a value |
| 471 | // comparison with the same value, and if that comparison determines the outcome |
| 472 | // of this comparison. If so, simplify TI. This does a very limited form of |
| 473 | // jump threading. |
| 474 | static bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI, |
| 475 | BasicBlock *Pred) { |
| 476 | Value *PredVal = isValueEqualityComparison(Pred->getTerminator()); |
| 477 | if (!PredVal) return false; // Not a value comparison in predecessor. |
| 478 | |
| 479 | Value *ThisVal = isValueEqualityComparison(TI); |
| 480 | assert(ThisVal && "This isn't a value comparison!!"); |
| 481 | if (ThisVal != PredVal) return false; // Different predicates. |
| 482 | |
| 483 | // Find out information about when control will move from Pred to TI's block. |
| 484 | std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases; |
| 485 | BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(), |
| 486 | PredCases); |
| 487 | EliminateBlockCases(PredDef, PredCases); // Remove default from cases. |
| 488 | |
| 489 | // Find information about how control leaves this block. |
| 490 | std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases; |
| 491 | BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases); |
| 492 | EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases. |
| 493 | |
| 494 | // If TI's block is the default block from Pred's comparison, potentially |
| 495 | // simplify TI based on this knowledge. |
| 496 | if (PredDef == TI->getParent()) { |
| 497 | // If we are here, we know that the value is none of those cases listed in |
| 498 | // PredCases. If there are any cases in ThisCases that are in PredCases, we |
| 499 | // can simplify TI. |
| 500 | if (ValuesOverlap(PredCases, ThisCases)) { |
| 501 | if (BranchInst *BTI = dyn_cast<BranchInst>(TI)) { |
| 502 | // Okay, one of the successors of this condbr is dead. Convert it to a |
| 503 | // uncond br. |
| 504 | assert(ThisCases.size() == 1 && "Branch can only have one case!"); |
| 505 | Value *Cond = BTI->getCondition(); |
| 506 | // Insert the new branch. |
| 507 | Instruction *NI = new BranchInst(ThisDef, TI); |
| 508 | |
| 509 | // Remove PHI node entries for the dead edge. |
| 510 | ThisCases[0].second->removePredecessor(TI->getParent()); |
| 511 | |
| 512 | DEBUG(std::cerr << "Threading pred instr: " << *Pred->getTerminator() |
| 513 | << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n"); |
| 514 | |
| 515 | TI->eraseFromParent(); // Nuke the old one. |
| 516 | // If condition is now dead, nuke it. |
| 517 | if (Instruction *CondI = dyn_cast<Instruction>(Cond)) |
| 518 | ErasePossiblyDeadInstructionTree(CondI); |
| 519 | return true; |
| 520 | |
| 521 | } else { |
| 522 | SwitchInst *SI = cast<SwitchInst>(TI); |
| 523 | // Okay, TI has cases that are statically dead, prune them away. |
| 524 | std::set<Constant*> DeadCases; |
| 525 | for (unsigned i = 0, e = PredCases.size(); i != e; ++i) |
| 526 | DeadCases.insert(PredCases[i].first); |
| 527 | |
| 528 | DEBUG(std::cerr << "Threading pred instr: " << *Pred->getTerminator() |
| 529 | << "Through successor TI: " << *TI); |
| 530 | |
| 531 | for (unsigned i = SI->getNumCases()-1; i != 0; --i) |
| 532 | if (DeadCases.count(SI->getCaseValue(i))) { |
| 533 | SI->getSuccessor(i)->removePredecessor(TI->getParent()); |
| 534 | SI->removeCase(i); |
| 535 | } |
| 536 | |
| 537 | DEBUG(std::cerr << "Leaving: " << *TI << "\n"); |
| 538 | return true; |
| 539 | } |
| 540 | } |
| 541 | |
| 542 | } else { |
| 543 | // Otherwise, TI's block must correspond to some matched value. Find out |
| 544 | // which value (or set of values) this is. |
| 545 | ConstantInt *TIV = 0; |
| 546 | BasicBlock *TIBB = TI->getParent(); |
| 547 | for (unsigned i = 0, e = PredCases.size(); i != e; ++i) |
| 548 | if (PredCases[i].second == TIBB) |
| 549 | if (TIV == 0) |
| 550 | TIV = PredCases[i].first; |
| 551 | else |
| 552 | return false; // Cannot handle multiple values coming to this block. |
| 553 | assert(TIV && "No edge from pred to succ?"); |
| 554 | |
| 555 | // Okay, we found the one constant that our value can be if we get into TI's |
| 556 | // BB. Find out which successor will unconditionally be branched to. |
| 557 | BasicBlock *TheRealDest = 0; |
| 558 | for (unsigned i = 0, e = ThisCases.size(); i != e; ++i) |
| 559 | if (ThisCases[i].first == TIV) { |
| 560 | TheRealDest = ThisCases[i].second; |
| 561 | break; |
| 562 | } |
| 563 | |
| 564 | // If not handled by any explicit cases, it is handled by the default case. |
| 565 | if (TheRealDest == 0) TheRealDest = ThisDef; |
| 566 | |
| 567 | // Remove PHI node entries for dead edges. |
| 568 | BasicBlock *CheckEdge = TheRealDest; |
| 569 | for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI) |
| 570 | if (*SI != CheckEdge) |
| 571 | (*SI)->removePredecessor(TIBB); |
| 572 | else |
| 573 | CheckEdge = 0; |
| 574 | |
| 575 | // Insert the new branch. |
| 576 | Instruction *NI = new BranchInst(TheRealDest, TI); |
| 577 | |
| 578 | DEBUG(std::cerr << "Threading pred instr: " << *Pred->getTerminator() |
| 579 | << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n"); |
| 580 | Instruction *Cond = 0; |
| 581 | if (BranchInst *BI = dyn_cast<BranchInst>(TI)) |
| 582 | Cond = dyn_cast<Instruction>(BI->getCondition()); |
| 583 | TI->eraseFromParent(); // Nuke the old one. |
| 584 | |
| 585 | if (Cond) ErasePossiblyDeadInstructionTree(Cond); |
| 586 | return true; |
| 587 | } |
| 588 | return false; |
| 589 | } |
| 590 | |
Chris Lattner | 542f149 | 2004-02-28 21:28:10 +0000 | [diff] [blame] | 591 | // FoldValueComparisonIntoPredecessors - The specified terminator is a value |
| 592 | // equality comparison instruction (either a switch or a branch on "X == c"). |
| 593 | // See if any of the predecessors of the terminator block are value comparisons |
| 594 | // on the same value. If so, and if safe to do so, fold them together. |
| 595 | static bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI) { |
| 596 | BasicBlock *BB = TI->getParent(); |
| 597 | Value *CV = isValueEqualityComparison(TI); // CondVal |
| 598 | assert(CV && "Not a comparison?"); |
| 599 | bool Changed = false; |
| 600 | |
| 601 | std::vector<BasicBlock*> Preds(pred_begin(BB), pred_end(BB)); |
| 602 | while (!Preds.empty()) { |
| 603 | BasicBlock *Pred = Preds.back(); |
| 604 | Preds.pop_back(); |
| 605 | |
| 606 | // See if the predecessor is a comparison with the same value. |
| 607 | TerminatorInst *PTI = Pred->getTerminator(); |
| 608 | Value *PCV = isValueEqualityComparison(PTI); // PredCondVal |
| 609 | |
| 610 | if (PCV == CV && SafeToMergeTerminators(TI, PTI)) { |
| 611 | // Figure out which 'cases' to copy from SI to PSI. |
| 612 | std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases; |
| 613 | BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases); |
| 614 | |
| 615 | std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases; |
| 616 | BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases); |
| 617 | |
| 618 | // Based on whether the default edge from PTI goes to BB or not, fill in |
| 619 | // PredCases and PredDefault with the new switch cases we would like to |
| 620 | // build. |
| 621 | std::vector<BasicBlock*> NewSuccessors; |
| 622 | |
| 623 | if (PredDefault == BB) { |
| 624 | // If this is the default destination from PTI, only the edges in TI |
| 625 | // that don't occur in PTI, or that branch to BB will be activated. |
| 626 | std::set<ConstantInt*> PTIHandled; |
| 627 | for (unsigned i = 0, e = PredCases.size(); i != e; ++i) |
| 628 | if (PredCases[i].second != BB) |
| 629 | PTIHandled.insert(PredCases[i].first); |
| 630 | else { |
| 631 | // The default destination is BB, we don't need explicit targets. |
| 632 | std::swap(PredCases[i], PredCases.back()); |
| 633 | PredCases.pop_back(); |
| 634 | --i; --e; |
| 635 | } |
| 636 | |
| 637 | // Reconstruct the new switch statement we will be building. |
| 638 | if (PredDefault != BBDefault) { |
| 639 | PredDefault->removePredecessor(Pred); |
| 640 | PredDefault = BBDefault; |
| 641 | NewSuccessors.push_back(BBDefault); |
| 642 | } |
| 643 | for (unsigned i = 0, e = BBCases.size(); i != e; ++i) |
| 644 | if (!PTIHandled.count(BBCases[i].first) && |
| 645 | BBCases[i].second != BBDefault) { |
| 646 | PredCases.push_back(BBCases[i]); |
| 647 | NewSuccessors.push_back(BBCases[i].second); |
| 648 | } |
| 649 | |
| 650 | } else { |
| 651 | // If this is not the default destination from PSI, only the edges |
| 652 | // in SI that occur in PSI with a destination of BB will be |
| 653 | // activated. |
| 654 | std::set<ConstantInt*> PTIHandled; |
| 655 | for (unsigned i = 0, e = PredCases.size(); i != e; ++i) |
| 656 | if (PredCases[i].second == BB) { |
| 657 | PTIHandled.insert(PredCases[i].first); |
| 658 | std::swap(PredCases[i], PredCases.back()); |
| 659 | PredCases.pop_back(); |
| 660 | --i; --e; |
| 661 | } |
| 662 | |
| 663 | // Okay, now we know which constants were sent to BB from the |
| 664 | // predecessor. Figure out where they will all go now. |
| 665 | for (unsigned i = 0, e = BBCases.size(); i != e; ++i) |
| 666 | if (PTIHandled.count(BBCases[i].first)) { |
| 667 | // If this is one we are capable of getting... |
| 668 | PredCases.push_back(BBCases[i]); |
| 669 | NewSuccessors.push_back(BBCases[i].second); |
| 670 | PTIHandled.erase(BBCases[i].first);// This constant is taken care of |
| 671 | } |
| 672 | |
| 673 | // If there are any constants vectored to BB that TI doesn't handle, |
| 674 | // they must go to the default destination of TI. |
| 675 | for (std::set<ConstantInt*>::iterator I = PTIHandled.begin(), |
| 676 | E = PTIHandled.end(); I != E; ++I) { |
| 677 | PredCases.push_back(std::make_pair(*I, BBDefault)); |
| 678 | NewSuccessors.push_back(BBDefault); |
| 679 | } |
| 680 | } |
| 681 | |
| 682 | // Okay, at this point, we know which new successor Pred will get. Make |
| 683 | // sure we update the number of entries in the PHI nodes for these |
| 684 | // successors. |
| 685 | for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i) |
| 686 | AddPredecessorToBlock(NewSuccessors[i], Pred, BB); |
| 687 | |
| 688 | // Now that the successors are updated, create the new Switch instruction. |
Chris Lattner | 3788059 | 2005-01-29 00:38:26 +0000 | [diff] [blame] | 689 | SwitchInst *NewSI = new SwitchInst(CV, PredDefault, PredCases.size(),PTI); |
Chris Lattner | 542f149 | 2004-02-28 21:28:10 +0000 | [diff] [blame] | 690 | for (unsigned i = 0, e = PredCases.size(); i != e; ++i) |
| 691 | NewSI->addCase(PredCases[i].first, PredCases[i].second); |
Chris Lattner | 13b2f76 | 2005-01-01 16:02:12 +0000 | [diff] [blame] | 692 | |
| 693 | Instruction *DeadCond = 0; |
| 694 | if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) |
| 695 | // If PTI is a branch, remember the condition. |
| 696 | DeadCond = dyn_cast<Instruction>(BI->getCondition()); |
Chris Lattner | 542f149 | 2004-02-28 21:28:10 +0000 | [diff] [blame] | 697 | Pred->getInstList().erase(PTI); |
| 698 | |
Chris Lattner | 13b2f76 | 2005-01-01 16:02:12 +0000 | [diff] [blame] | 699 | // If the condition is dead now, remove the instruction tree. |
| 700 | if (DeadCond) ErasePossiblyDeadInstructionTree(DeadCond); |
| 701 | |
Chris Lattner | 542f149 | 2004-02-28 21:28:10 +0000 | [diff] [blame] | 702 | // Okay, last check. If BB is still a successor of PSI, then we must |
| 703 | // have an infinite loop case. If so, add an infinitely looping block |
| 704 | // to handle the case to preserve the behavior of the code. |
| 705 | BasicBlock *InfLoopBlock = 0; |
| 706 | for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i) |
| 707 | if (NewSI->getSuccessor(i) == BB) { |
| 708 | if (InfLoopBlock == 0) { |
| 709 | // Insert it at the end of the loop, because it's either code, |
| 710 | // or it won't matter if it's hot. :) |
| 711 | InfLoopBlock = new BasicBlock("infloop", BB->getParent()); |
| 712 | new BranchInst(InfLoopBlock, InfLoopBlock); |
| 713 | } |
| 714 | NewSI->setSuccessor(i, InfLoopBlock); |
| 715 | } |
| 716 | |
| 717 | Changed = true; |
| 718 | } |
| 719 | } |
| 720 | return Changed; |
| 721 | } |
| 722 | |
Chris Lattner | 37dc938 | 2004-11-30 00:29:14 +0000 | [diff] [blame] | 723 | /// HoistThenElseCodeToIf - Given a conditional branch that codes to BB1 and |
| 724 | /// BB2, hoist any common code in the two blocks up into the branch block. The |
| 725 | /// caller of this function guarantees that BI's block dominates BB1 and BB2. |
| 726 | static bool HoistThenElseCodeToIf(BranchInst *BI) { |
| 727 | // This does very trivial matching, with limited scanning, to find identical |
| 728 | // instructions in the two blocks. In particular, we don't want to get into |
| 729 | // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As |
| 730 | // such, we currently just scan for obviously identical instructions in an |
| 731 | // identical order. |
| 732 | BasicBlock *BB1 = BI->getSuccessor(0); // The true destination. |
| 733 | BasicBlock *BB2 = BI->getSuccessor(1); // The false destination |
| 734 | |
| 735 | Instruction *I1 = BB1->begin(), *I2 = BB2->begin(); |
| 736 | if (I1->getOpcode() != I2->getOpcode() || !I1->isIdenticalTo(I2)) |
| 737 | return false; |
| 738 | |
| 739 | // If we get here, we can hoist at least one instruction. |
| 740 | BasicBlock *BIParent = BI->getParent(); |
Chris Lattner | 37dc938 | 2004-11-30 00:29:14 +0000 | [diff] [blame] | 741 | |
| 742 | do { |
| 743 | // If we are hoisting the terminator instruction, don't move one (making a |
| 744 | // broken BB), instead clone it, and remove BI. |
| 745 | if (isa<TerminatorInst>(I1)) |
| 746 | goto HoistTerminator; |
| 747 | |
| 748 | // For a normal instruction, we just move one to right before the branch, |
| 749 | // then replace all uses of the other with the first. Finally, we remove |
| 750 | // the now redundant second instruction. |
| 751 | BIParent->getInstList().splice(BI, BB1->getInstList(), I1); |
| 752 | if (!I2->use_empty()) |
| 753 | I2->replaceAllUsesWith(I1); |
| 754 | BB2->getInstList().erase(I2); |
| 755 | |
| 756 | I1 = BB1->begin(); |
| 757 | I2 = BB2->begin(); |
Chris Lattner | 37dc938 | 2004-11-30 00:29:14 +0000 | [diff] [blame] | 758 | } while (I1->getOpcode() == I2->getOpcode() && I1->isIdenticalTo(I2)); |
| 759 | |
| 760 | return true; |
| 761 | |
| 762 | HoistTerminator: |
| 763 | // Okay, it is safe to hoist the terminator. |
| 764 | Instruction *NT = I1->clone(); |
| 765 | BIParent->getInstList().insert(BI, NT); |
| 766 | if (NT->getType() != Type::VoidTy) { |
| 767 | I1->replaceAllUsesWith(NT); |
| 768 | I2->replaceAllUsesWith(NT); |
| 769 | NT->setName(I1->getName()); |
| 770 | } |
| 771 | |
| 772 | // Hoisting one of the terminators from our successor is a great thing. |
| 773 | // Unfortunately, the successors of the if/else blocks may have PHI nodes in |
| 774 | // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI |
| 775 | // nodes, so we insert select instruction to compute the final result. |
| 776 | std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects; |
| 777 | for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) { |
| 778 | PHINode *PN; |
| 779 | for (BasicBlock::iterator BBI = SI->begin(); |
Chris Lattner | 0f535c6 | 2004-11-30 07:47:34 +0000 | [diff] [blame] | 780 | (PN = dyn_cast<PHINode>(BBI)); ++BBI) { |
Chris Lattner | 37dc938 | 2004-11-30 00:29:14 +0000 | [diff] [blame] | 781 | Value *BB1V = PN->getIncomingValueForBlock(BB1); |
| 782 | Value *BB2V = PN->getIncomingValueForBlock(BB2); |
| 783 | if (BB1V != BB2V) { |
| 784 | // These values do not agree. Insert a select instruction before NT |
| 785 | // that determines the right value. |
| 786 | SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)]; |
| 787 | if (SI == 0) |
| 788 | SI = new SelectInst(BI->getCondition(), BB1V, BB2V, |
| 789 | BB1V->getName()+"."+BB2V->getName(), NT); |
| 790 | // Make the PHI node use the select for all incoming values for BB1/BB2 |
| 791 | for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) |
| 792 | if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2) |
| 793 | PN->setIncomingValue(i, SI); |
| 794 | } |
| 795 | } |
| 796 | } |
| 797 | |
| 798 | // Update any PHI nodes in our new successors. |
| 799 | for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) |
| 800 | AddPredecessorToBlock(*SI, BIParent, BB1); |
| 801 | |
| 802 | BI->eraseFromParent(); |
| 803 | return true; |
| 804 | } |
| 805 | |
Chris Lattner | 1654cff | 2004-06-19 07:02:14 +0000 | [diff] [blame] | 806 | namespace { |
| 807 | /// ConstantIntOrdering - This class implements a stable ordering of constant |
| 808 | /// integers that does not depend on their address. This is important for |
| 809 | /// applications that sort ConstantInt's to ensure uniqueness. |
| 810 | struct ConstantIntOrdering { |
| 811 | bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const { |
| 812 | return LHS->getRawValue() < RHS->getRawValue(); |
| 813 | } |
| 814 | }; |
| 815 | } |
| 816 | |
Chris Lattner | 542f149 | 2004-02-28 21:28:10 +0000 | [diff] [blame] | 817 | |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 818 | // SimplifyCFG - This function is used to do simplification of a CFG. For |
| 819 | // example, it adjusts branches to branches to eliminate the extra hop, it |
| 820 | // eliminates unreachable basic blocks, and does other "peephole" optimization |
Chris Lattner | e2ca540 | 2003-03-05 21:01:52 +0000 | [diff] [blame] | 821 | // of the CFG. It returns true if a modification was made. |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 822 | // |
| 823 | // WARNING: The entry node of a function may not be simplified. |
| 824 | // |
Chris Lattner | f7703df | 2004-01-09 06:12:26 +0000 | [diff] [blame] | 825 | bool llvm::SimplifyCFG(BasicBlock *BB) { |
Chris Lattner | dc3602b | 2003-08-24 18:36:16 +0000 | [diff] [blame] | 826 | bool Changed = false; |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 827 | Function *M = BB->getParent(); |
| 828 | |
| 829 | assert(BB && BB->getParent() && "Block not embedded in function!"); |
| 830 | assert(BB->getTerminator() && "Degenerate basic block encountered!"); |
Chris Lattner | 1896150 | 2002-06-25 16:12:52 +0000 | [diff] [blame] | 831 | assert(&BB->getParent()->front() != BB && "Can't Simplify entry block!"); |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 832 | |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 833 | // Remove basic blocks that have no predecessors... which are unreachable. |
Chris Lattner | d52c261 | 2004-02-24 07:23:58 +0000 | [diff] [blame] | 834 | if (pred_begin(BB) == pred_end(BB) || |
| 835 | *pred_begin(BB) == BB && ++pred_begin(BB) == pred_end(BB)) { |
Chris Lattner | 30b4344 | 2004-07-15 02:06:12 +0000 | [diff] [blame] | 836 | DEBUG(std::cerr << "Removing BB: \n" << *BB); |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 837 | |
| 838 | // Loop through all of our successors and make sure they know that one |
| 839 | // of their predecessors is going away. |
| 840 | for_each(succ_begin(BB), succ_end(BB), |
| 841 | std::bind2nd(std::mem_fun(&BasicBlock::removePredecessor), BB)); |
| 842 | |
| 843 | while (!BB->empty()) { |
Chris Lattner | 1896150 | 2002-06-25 16:12:52 +0000 | [diff] [blame] | 844 | Instruction &I = BB->back(); |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 845 | // If this instruction is used, replace uses with an arbitrary |
| 846 | // constant value. Because control flow can't get here, we don't care |
| 847 | // what we replace the value with. Note that since this block is |
| 848 | // unreachable, and all values contained within it must dominate their |
| 849 | // uses, that all uses will eventually be removed. |
Chris Lattner | 1896150 | 2002-06-25 16:12:52 +0000 | [diff] [blame] | 850 | if (!I.use_empty()) |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 851 | // Make all users of this instruction reference the constant instead |
Chris Lattner | 1896150 | 2002-06-25 16:12:52 +0000 | [diff] [blame] | 852 | I.replaceAllUsesWith(Constant::getNullValue(I.getType())); |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 853 | |
| 854 | // Remove the instruction from the basic block |
Chris Lattner | 1896150 | 2002-06-25 16:12:52 +0000 | [diff] [blame] | 855 | BB->getInstList().pop_back(); |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 856 | } |
Chris Lattner | 1896150 | 2002-06-25 16:12:52 +0000 | [diff] [blame] | 857 | M->getBasicBlockList().erase(BB); |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 858 | return true; |
| 859 | } |
| 860 | |
Chris Lattner | 694e37f | 2003-08-17 19:41:53 +0000 | [diff] [blame] | 861 | // Check to see if we can constant propagate this terminator instruction |
| 862 | // away... |
Chris Lattner | dc3602b | 2003-08-24 18:36:16 +0000 | [diff] [blame] | 863 | Changed |= ConstantFoldTerminator(BB); |
Chris Lattner | 694e37f | 2003-08-17 19:41:53 +0000 | [diff] [blame] | 864 | |
Chris Lattner | 46a5f1f | 2003-03-05 21:36:33 +0000 | [diff] [blame] | 865 | // Check to see if this block has no non-phi instructions and only a single |
| 866 | // successor. If so, replace references to this basic block with references |
| 867 | // to the successor. |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 868 | succ_iterator SI(succ_begin(BB)); |
| 869 | if (SI != succ_end(BB) && ++SI == succ_end(BB)) { // One succ? |
Chris Lattner | 46a5f1f | 2003-03-05 21:36:33 +0000 | [diff] [blame] | 870 | BasicBlock::iterator BBI = BB->begin(); // Skip over phi nodes... |
| 871 | while (isa<PHINode>(*BBI)) ++BBI; |
| 872 | |
Chris Lattner | bfd3e52 | 2004-11-01 06:53:58 +0000 | [diff] [blame] | 873 | BasicBlock *Succ = *succ_begin(BB); // There is exactly one successor. |
| 874 | if (BBI->isTerminator() && // Terminator is the only non-phi instruction! |
| 875 | Succ != BB) { // Don't hurt infinite loops! |
| 876 | // If our successor has PHI nodes, then we need to update them to include |
| 877 | // entries for BB's predecessors, not for BB itself. Be careful though, |
| 878 | // if this transformation fails (returns true) then we cannot do this |
| 879 | // transformation! |
| 880 | // |
| 881 | if (!PropagatePredecessorsForPHIs(BB, Succ)) { |
| 882 | DEBUG(std::cerr << "Killing Trivial BB: \n" << *BB); |
| 883 | |
| 884 | if (isa<PHINode>(&BB->front())) { |
Chris Lattner | 3a43837 | 2003-03-07 18:13:41 +0000 | [diff] [blame] | 885 | std::vector<BasicBlock*> |
| 886 | OldSuccPreds(pred_begin(Succ), pred_end(Succ)); |
Chris Lattner | bfd3e52 | 2004-11-01 06:53:58 +0000 | [diff] [blame] | 887 | |
Chris Lattner | 46a5f1f | 2003-03-05 21:36:33 +0000 | [diff] [blame] | 888 | // Move all PHI nodes in BB to Succ if they are alive, otherwise |
| 889 | // delete them. |
| 890 | while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) |
| 891 | if (PN->use_empty()) |
Chris Lattner | bfd3e52 | 2004-11-01 06:53:58 +0000 | [diff] [blame] | 892 | BB->getInstList().erase(BB->begin()); // Nuke instruction. |
Chris Lattner | 46a5f1f | 2003-03-05 21:36:33 +0000 | [diff] [blame] | 893 | else { |
| 894 | // The instruction is alive, so this means that Succ must have |
| 895 | // *ONLY* had BB as a predecessor, and the PHI node is still valid |
Chris Lattner | 3a43837 | 2003-03-07 18:13:41 +0000 | [diff] [blame] | 896 | // now. Simply move it into Succ, because we know that BB |
| 897 | // strictly dominated Succ. |
Chris Lattner | 46a5f1f | 2003-03-05 21:36:33 +0000 | [diff] [blame] | 898 | BB->getInstList().remove(BB->begin()); |
| 899 | Succ->getInstList().push_front(PN); |
Chris Lattner | bfd3e52 | 2004-11-01 06:53:58 +0000 | [diff] [blame] | 900 | |
Chris Lattner | 3a43837 | 2003-03-07 18:13:41 +0000 | [diff] [blame] | 901 | // We need to add new entries for the PHI node to account for |
| 902 | // predecessors of Succ that the PHI node does not take into |
| 903 | // account. At this point, since we know that BB dominated succ, |
| 904 | // this means that we should any newly added incoming edges should |
| 905 | // use the PHI node as the value for these edges, because they are |
| 906 | // loop back edges. |
Chris Lattner | 3a43837 | 2003-03-07 18:13:41 +0000 | [diff] [blame] | 907 | for (unsigned i = 0, e = OldSuccPreds.size(); i != e; ++i) |
| 908 | if (OldSuccPreds[i] != BB) |
| 909 | PN->addIncoming(PN, OldSuccPreds[i]); |
Chris Lattner | 46a5f1f | 2003-03-05 21:36:33 +0000 | [diff] [blame] | 910 | } |
Chris Lattner | bfd3e52 | 2004-11-01 06:53:58 +0000 | [diff] [blame] | 911 | } |
| 912 | |
| 913 | // Everything that jumped to BB now goes to Succ. |
| 914 | std::string OldName = BB->getName(); |
| 915 | BB->replaceAllUsesWith(Succ); |
| 916 | BB->eraseFromParent(); // Delete the old basic block. |
Chris Lattner | 46a5f1f | 2003-03-05 21:36:33 +0000 | [diff] [blame] | 917 | |
Chris Lattner | bfd3e52 | 2004-11-01 06:53:58 +0000 | [diff] [blame] | 918 | if (!OldName.empty() && !Succ->hasName()) // Transfer name if we can |
| 919 | Succ->setName(OldName); |
| 920 | return true; |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 921 | } |
| 922 | } |
| 923 | } |
| 924 | |
Chris Lattner | 19831ec | 2004-02-16 06:35:48 +0000 | [diff] [blame] | 925 | // If this is a returning block with only PHI nodes in it, fold the return |
| 926 | // instruction into any unconditional branch predecessors. |
Chris Lattner | 147af6b | 2004-04-02 18:13:43 +0000 | [diff] [blame] | 927 | // |
| 928 | // If any predecessor is a conditional branch that just selects among |
| 929 | // different return values, fold the replace the branch/return with a select |
| 930 | // and return. |
Chris Lattner | 19831ec | 2004-02-16 06:35:48 +0000 | [diff] [blame] | 931 | if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) { |
| 932 | BasicBlock::iterator BBI = BB->getTerminator(); |
| 933 | if (BBI == BB->begin() || isa<PHINode>(--BBI)) { |
Chris Lattner | 147af6b | 2004-04-02 18:13:43 +0000 | [diff] [blame] | 934 | // Find predecessors that end with branches. |
Chris Lattner | 19831ec | 2004-02-16 06:35:48 +0000 | [diff] [blame] | 935 | std::vector<BasicBlock*> UncondBranchPreds; |
Chris Lattner | 147af6b | 2004-04-02 18:13:43 +0000 | [diff] [blame] | 936 | std::vector<BranchInst*> CondBranchPreds; |
Chris Lattner | 19831ec | 2004-02-16 06:35:48 +0000 | [diff] [blame] | 937 | for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { |
| 938 | TerminatorInst *PTI = (*PI)->getTerminator(); |
| 939 | if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) |
| 940 | if (BI->isUnconditional()) |
| 941 | UncondBranchPreds.push_back(*PI); |
Chris Lattner | 147af6b | 2004-04-02 18:13:43 +0000 | [diff] [blame] | 942 | else |
| 943 | CondBranchPreds.push_back(BI); |
Chris Lattner | 19831ec | 2004-02-16 06:35:48 +0000 | [diff] [blame] | 944 | } |
| 945 | |
| 946 | // If we found some, do the transformation! |
| 947 | if (!UncondBranchPreds.empty()) { |
| 948 | while (!UncondBranchPreds.empty()) { |
| 949 | BasicBlock *Pred = UncondBranchPreds.back(); |
| 950 | UncondBranchPreds.pop_back(); |
| 951 | Instruction *UncondBranch = Pred->getTerminator(); |
| 952 | // Clone the return and add it to the end of the predecessor. |
| 953 | Instruction *NewRet = RI->clone(); |
| 954 | Pred->getInstList().push_back(NewRet); |
| 955 | |
| 956 | // If the return instruction returns a value, and if the value was a |
| 957 | // PHI node in "BB", propagate the right value into the return. |
| 958 | if (NewRet->getNumOperands() == 1) |
| 959 | if (PHINode *PN = dyn_cast<PHINode>(NewRet->getOperand(0))) |
| 960 | if (PN->getParent() == BB) |
| 961 | NewRet->setOperand(0, PN->getIncomingValueForBlock(Pred)); |
| 962 | // Update any PHI nodes in the returning block to realize that we no |
| 963 | // longer branch to them. |
| 964 | BB->removePredecessor(Pred); |
| 965 | Pred->getInstList().erase(UncondBranch); |
| 966 | } |
| 967 | |
| 968 | // If we eliminated all predecessors of the block, delete the block now. |
| 969 | if (pred_begin(BB) == pred_end(BB)) |
| 970 | // We know there are no successors, so just nuke the block. |
| 971 | M->getBasicBlockList().erase(BB); |
| 972 | |
Chris Lattner | 19831ec | 2004-02-16 06:35:48 +0000 | [diff] [blame] | 973 | return true; |
| 974 | } |
Chris Lattner | 147af6b | 2004-04-02 18:13:43 +0000 | [diff] [blame] | 975 | |
| 976 | // Check out all of the conditional branches going to this return |
| 977 | // instruction. If any of them just select between returns, change the |
| 978 | // branch itself into a select/return pair. |
| 979 | while (!CondBranchPreds.empty()) { |
| 980 | BranchInst *BI = CondBranchPreds.back(); |
| 981 | CondBranchPreds.pop_back(); |
| 982 | BasicBlock *TrueSucc = BI->getSuccessor(0); |
| 983 | BasicBlock *FalseSucc = BI->getSuccessor(1); |
| 984 | BasicBlock *OtherSucc = TrueSucc == BB ? FalseSucc : TrueSucc; |
| 985 | |
| 986 | // Check to see if the non-BB successor is also a return block. |
| 987 | if (isa<ReturnInst>(OtherSucc->getTerminator())) { |
| 988 | // Check to see if there are only PHI instructions in this block. |
| 989 | BasicBlock::iterator OSI = OtherSucc->getTerminator(); |
| 990 | if (OSI == OtherSucc->begin() || isa<PHINode>(--OSI)) { |
| 991 | // Okay, we found a branch that is going to two return nodes. If |
| 992 | // there is no return value for this function, just change the |
| 993 | // branch into a return. |
| 994 | if (RI->getNumOperands() == 0) { |
| 995 | TrueSucc->removePredecessor(BI->getParent()); |
| 996 | FalseSucc->removePredecessor(BI->getParent()); |
| 997 | new ReturnInst(0, BI); |
| 998 | BI->getParent()->getInstList().erase(BI); |
| 999 | return true; |
| 1000 | } |
| 1001 | |
| 1002 | // Otherwise, figure out what the true and false return values are |
| 1003 | // so we can insert a new select instruction. |
| 1004 | Value *TrueValue = TrueSucc->getTerminator()->getOperand(0); |
| 1005 | Value *FalseValue = FalseSucc->getTerminator()->getOperand(0); |
| 1006 | |
| 1007 | // Unwrap any PHI nodes in the return blocks. |
| 1008 | if (PHINode *TVPN = dyn_cast<PHINode>(TrueValue)) |
| 1009 | if (TVPN->getParent() == TrueSucc) |
| 1010 | TrueValue = TVPN->getIncomingValueForBlock(BI->getParent()); |
| 1011 | if (PHINode *FVPN = dyn_cast<PHINode>(FalseValue)) |
| 1012 | if (FVPN->getParent() == FalseSucc) |
| 1013 | FalseValue = FVPN->getIncomingValueForBlock(BI->getParent()); |
| 1014 | |
Chris Lattner | 7aa773b | 2004-04-02 18:15:10 +0000 | [diff] [blame] | 1015 | TrueSucc->removePredecessor(BI->getParent()); |
| 1016 | FalseSucc->removePredecessor(BI->getParent()); |
| 1017 | |
Chris Lattner | 147af6b | 2004-04-02 18:13:43 +0000 | [diff] [blame] | 1018 | // Insert a new select instruction. |
Chris Lattner | 0ed7f42 | 2004-09-29 05:43:32 +0000 | [diff] [blame] | 1019 | Value *NewRetVal; |
| 1020 | Value *BrCond = BI->getCondition(); |
| 1021 | if (TrueValue != FalseValue) |
| 1022 | NewRetVal = new SelectInst(BrCond, TrueValue, |
| 1023 | FalseValue, "retval", BI); |
| 1024 | else |
| 1025 | NewRetVal = TrueValue; |
| 1026 | |
Chris Lattner | 147af6b | 2004-04-02 18:13:43 +0000 | [diff] [blame] | 1027 | new ReturnInst(NewRetVal, BI); |
| 1028 | BI->getParent()->getInstList().erase(BI); |
Chris Lattner | 0ed7f42 | 2004-09-29 05:43:32 +0000 | [diff] [blame] | 1029 | if (BrCond->use_empty()) |
| 1030 | if (Instruction *BrCondI = dyn_cast<Instruction>(BrCond)) |
| 1031 | BrCondI->getParent()->getInstList().erase(BrCondI); |
Chris Lattner | 147af6b | 2004-04-02 18:13:43 +0000 | [diff] [blame] | 1032 | return true; |
| 1033 | } |
| 1034 | } |
| 1035 | } |
Chris Lattner | 19831ec | 2004-02-16 06:35:48 +0000 | [diff] [blame] | 1036 | } |
Chris Lattner | e14ea08 | 2004-02-24 05:54:22 +0000 | [diff] [blame] | 1037 | } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->begin())) { |
| 1038 | // Check to see if the first instruction in this block is just an unwind. |
| 1039 | // If so, replace any invoke instructions which use this as an exception |
Chris Lattner | af17b1d | 2004-07-20 01:17:38 +0000 | [diff] [blame] | 1040 | // destination with call instructions, and any unconditional branch |
| 1041 | // predecessor with an unwind. |
Chris Lattner | e14ea08 | 2004-02-24 05:54:22 +0000 | [diff] [blame] | 1042 | // |
| 1043 | std::vector<BasicBlock*> Preds(pred_begin(BB), pred_end(BB)); |
| 1044 | while (!Preds.empty()) { |
| 1045 | BasicBlock *Pred = Preds.back(); |
Chris Lattner | af17b1d | 2004-07-20 01:17:38 +0000 | [diff] [blame] | 1046 | if (BranchInst *BI = dyn_cast<BranchInst>(Pred->getTerminator())) { |
| 1047 | if (BI->isUnconditional()) { |
| 1048 | Pred->getInstList().pop_back(); // nuke uncond branch |
| 1049 | new UnwindInst(Pred); // Use unwind. |
| 1050 | Changed = true; |
| 1051 | } |
| 1052 | } else if (InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator())) |
Chris Lattner | e14ea08 | 2004-02-24 05:54:22 +0000 | [diff] [blame] | 1053 | if (II->getUnwindDest() == BB) { |
| 1054 | // Insert a new branch instruction before the invoke, because this |
| 1055 | // is now a fall through... |
| 1056 | BranchInst *BI = new BranchInst(II->getNormalDest(), II); |
| 1057 | Pred->getInstList().remove(II); // Take out of symbol table |
| 1058 | |
| 1059 | // Insert the call now... |
| 1060 | std::vector<Value*> Args(II->op_begin()+3, II->op_end()); |
| 1061 | CallInst *CI = new CallInst(II->getCalledValue(), Args, |
| 1062 | II->getName(), BI); |
| 1063 | // If the invoke produced a value, the Call now does instead |
| 1064 | II->replaceAllUsesWith(CI); |
| 1065 | delete II; |
| 1066 | Changed = true; |
| 1067 | } |
| 1068 | |
| 1069 | Preds.pop_back(); |
| 1070 | } |
Chris Lattner | 8e509dd | 2004-02-24 16:09:21 +0000 | [diff] [blame] | 1071 | |
| 1072 | // If this block is now dead, remove it. |
| 1073 | if (pred_begin(BB) == pred_end(BB)) { |
| 1074 | // We know there are no successors, so just nuke the block. |
| 1075 | M->getBasicBlockList().erase(BB); |
| 1076 | return true; |
| 1077 | } |
| 1078 | |
Chris Lattner | 623369a | 2005-02-24 06:17:52 +0000 | [diff] [blame] | 1079 | } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) { |
| 1080 | if (isValueEqualityComparison(SI)) { |
| 1081 | // If we only have one predecessor, and if it is a branch on this value, |
| 1082 | // see if that predecessor totally determines the outcome of this switch. |
| 1083 | if (BasicBlock *OnlyPred = BB->getSinglePredecessor()) |
| 1084 | if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred)) |
| 1085 | return SimplifyCFG(BB) || 1; |
| 1086 | |
| 1087 | // If the block only contains the switch, see if we can fold the block |
| 1088 | // away into any preds. |
| 1089 | if (SI == &BB->front()) |
| 1090 | if (FoldValueComparisonIntoPredecessors(SI)) |
| 1091 | return SimplifyCFG(BB) || 1; |
| 1092 | } |
Chris Lattner | 542f149 | 2004-02-28 21:28:10 +0000 | [diff] [blame] | 1093 | } else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) { |
Chris Lattner | 92da2c2 | 2004-05-01 22:36:37 +0000 | [diff] [blame] | 1094 | if (BI->isConditional()) { |
Chris Lattner | e67fa05 | 2004-05-01 23:35:43 +0000 | [diff] [blame] | 1095 | if (Value *CompVal = isValueEqualityComparison(BI)) { |
Chris Lattner | 623369a | 2005-02-24 06:17:52 +0000 | [diff] [blame] | 1096 | // If we only have one predecessor, and if it is a branch on this value, |
| 1097 | // see if that predecessor totally determines the outcome of this |
| 1098 | // switch. |
| 1099 | if (BasicBlock *OnlyPred = BB->getSinglePredecessor()) |
| 1100 | if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred)) |
| 1101 | return SimplifyCFG(BB) || 1; |
| 1102 | |
Chris Lattner | e67fa05 | 2004-05-01 23:35:43 +0000 | [diff] [blame] | 1103 | // This block must be empty, except for the setcond inst, if it exists. |
| 1104 | BasicBlock::iterator I = BB->begin(); |
| 1105 | if (&*I == BI || |
| 1106 | (&*I == cast<Instruction>(BI->getCondition()) && |
| 1107 | &*++I == BI)) |
| 1108 | if (FoldValueComparisonIntoPredecessors(BI)) |
| 1109 | return SimplifyCFG(BB) | true; |
| 1110 | } |
| 1111 | |
| 1112 | // If this basic block is ONLY a setcc and a branch, and if a predecessor |
| 1113 | // branches to us and one of our successors, fold the setcc into the |
| 1114 | // predecessor and use logical operations to pick the right destination. |
Chris Lattner | 12fe2b1 | 2004-05-02 05:02:03 +0000 | [diff] [blame] | 1115 | BasicBlock *TrueDest = BI->getSuccessor(0); |
| 1116 | BasicBlock *FalseDest = BI->getSuccessor(1); |
Chris Lattner | bdcc0b8 | 2004-05-02 05:19:36 +0000 | [diff] [blame] | 1117 | if (BinaryOperator *Cond = dyn_cast<BinaryOperator>(BI->getCondition())) |
Chris Lattner | e67fa05 | 2004-05-01 23:35:43 +0000 | [diff] [blame] | 1118 | if (Cond->getParent() == BB && &BB->front() == Cond && |
Chris Lattner | 12fe2b1 | 2004-05-02 05:02:03 +0000 | [diff] [blame] | 1119 | Cond->getNext() == BI && Cond->hasOneUse() && |
| 1120 | TrueDest != BB && FalseDest != BB) |
Chris Lattner | e67fa05 | 2004-05-01 23:35:43 +0000 | [diff] [blame] | 1121 | for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI!=E; ++PI) |
| 1122 | if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator())) |
Chris Lattner | a1f79fb | 2004-05-02 01:00:44 +0000 | [diff] [blame] | 1123 | if (PBI->isConditional() && SafeToMergeTerminators(BI, PBI)) { |
Chris Lattner | 2636c1b | 2004-06-21 07:19:01 +0000 | [diff] [blame] | 1124 | BasicBlock *PredBlock = *PI; |
Chris Lattner | e67fa05 | 2004-05-01 23:35:43 +0000 | [diff] [blame] | 1125 | if (PBI->getSuccessor(0) == FalseDest || |
| 1126 | PBI->getSuccessor(1) == TrueDest) { |
| 1127 | // Invert the predecessors condition test (xor it with true), |
| 1128 | // which allows us to write this code once. |
| 1129 | Value *NewCond = |
| 1130 | BinaryOperator::createNot(PBI->getCondition(), |
| 1131 | PBI->getCondition()->getName()+".not", PBI); |
| 1132 | PBI->setCondition(NewCond); |
| 1133 | BasicBlock *OldTrue = PBI->getSuccessor(0); |
| 1134 | BasicBlock *OldFalse = PBI->getSuccessor(1); |
| 1135 | PBI->setSuccessor(0, OldFalse); |
| 1136 | PBI->setSuccessor(1, OldTrue); |
| 1137 | } |
| 1138 | |
| 1139 | if (PBI->getSuccessor(0) == TrueDest || |
| 1140 | PBI->getSuccessor(1) == FalseDest) { |
Chris Lattner | 2636c1b | 2004-06-21 07:19:01 +0000 | [diff] [blame] | 1141 | // Clone Cond into the predecessor basic block, and or/and the |
Chris Lattner | e67fa05 | 2004-05-01 23:35:43 +0000 | [diff] [blame] | 1142 | // two conditions together. |
| 1143 | Instruction *New = Cond->clone(); |
| 1144 | New->setName(Cond->getName()); |
| 1145 | Cond->setName(Cond->getName()+".old"); |
Chris Lattner | 2636c1b | 2004-06-21 07:19:01 +0000 | [diff] [blame] | 1146 | PredBlock->getInstList().insert(PBI, New); |
Chris Lattner | e67fa05 | 2004-05-01 23:35:43 +0000 | [diff] [blame] | 1147 | Instruction::BinaryOps Opcode = |
| 1148 | PBI->getSuccessor(0) == TrueDest ? |
| 1149 | Instruction::Or : Instruction::And; |
| 1150 | Value *NewCond = |
| 1151 | BinaryOperator::create(Opcode, PBI->getCondition(), |
| 1152 | New, "bothcond", PBI); |
| 1153 | PBI->setCondition(NewCond); |
| 1154 | if (PBI->getSuccessor(0) == BB) { |
Chris Lattner | 2636c1b | 2004-06-21 07:19:01 +0000 | [diff] [blame] | 1155 | AddPredecessorToBlock(TrueDest, PredBlock, BB); |
Chris Lattner | e67fa05 | 2004-05-01 23:35:43 +0000 | [diff] [blame] | 1156 | PBI->setSuccessor(0, TrueDest); |
| 1157 | } |
| 1158 | if (PBI->getSuccessor(1) == BB) { |
Chris Lattner | 2636c1b | 2004-06-21 07:19:01 +0000 | [diff] [blame] | 1159 | AddPredecessorToBlock(FalseDest, PredBlock, BB); |
Chris Lattner | e67fa05 | 2004-05-01 23:35:43 +0000 | [diff] [blame] | 1160 | PBI->setSuccessor(1, FalseDest); |
| 1161 | } |
| 1162 | return SimplifyCFG(BB) | 1; |
| 1163 | } |
| 1164 | } |
Chris Lattner | e67fa05 | 2004-05-01 23:35:43 +0000 | [diff] [blame] | 1165 | |
Chris Lattner | 92da2c2 | 2004-05-01 22:36:37 +0000 | [diff] [blame] | 1166 | // If this block ends with a branch instruction, and if there is one |
| 1167 | // predecessor, see if the previous block ended with a branch on the same |
| 1168 | // condition, which makes this conditional branch redundant. |
| 1169 | pred_iterator PI(pred_begin(BB)), PE(pred_end(BB)); |
| 1170 | BasicBlock *OnlyPred = *PI++; |
| 1171 | for (; PI != PE; ++PI)// Search all predecessors, see if they are all same |
| 1172 | if (*PI != OnlyPred) { |
| 1173 | OnlyPred = 0; // There are multiple different predecessors... |
| 1174 | break; |
| 1175 | } |
| 1176 | |
| 1177 | if (OnlyPred) |
| 1178 | if (BranchInst *PBI = dyn_cast<BranchInst>(OnlyPred->getTerminator())) |
| 1179 | if (PBI->isConditional() && |
| 1180 | PBI->getCondition() == BI->getCondition() && |
Chris Lattner | 951fdb9 | 2004-05-01 22:41:51 +0000 | [diff] [blame] | 1181 | (PBI->getSuccessor(0) != BB || PBI->getSuccessor(1) != BB)) { |
Chris Lattner | 92da2c2 | 2004-05-01 22:36:37 +0000 | [diff] [blame] | 1182 | // Okay, the outcome of this conditional branch is statically |
| 1183 | // knowable. Delete the outgoing CFG edge that is impossible to |
| 1184 | // execute. |
| 1185 | bool CondIsTrue = PBI->getSuccessor(0) == BB; |
| 1186 | BI->getSuccessor(CondIsTrue)->removePredecessor(BB); |
| 1187 | new BranchInst(BI->getSuccessor(!CondIsTrue), BB); |
| 1188 | BB->getInstList().erase(BI); |
| 1189 | return SimplifyCFG(BB) | true; |
| 1190 | } |
Chris Lattner | d52c261 | 2004-02-24 07:23:58 +0000 | [diff] [blame] | 1191 | } |
Chris Lattner | 698f96f | 2004-10-18 04:07:22 +0000 | [diff] [blame] | 1192 | } else if (isa<UnreachableInst>(BB->getTerminator())) { |
| 1193 | // If there are any instructions immediately before the unreachable that can |
| 1194 | // be removed, do so. |
| 1195 | Instruction *Unreachable = BB->getTerminator(); |
| 1196 | while (Unreachable != BB->begin()) { |
| 1197 | BasicBlock::iterator BBI = Unreachable; |
| 1198 | --BBI; |
| 1199 | if (isa<CallInst>(BBI)) break; |
| 1200 | // Delete this instruction |
| 1201 | BB->getInstList().erase(BBI); |
| 1202 | Changed = true; |
| 1203 | } |
| 1204 | |
| 1205 | // If the unreachable instruction is the first in the block, take a gander |
| 1206 | // at all of the predecessors of this instruction, and simplify them. |
| 1207 | if (&BB->front() == Unreachable) { |
| 1208 | std::vector<BasicBlock*> Preds(pred_begin(BB), pred_end(BB)); |
| 1209 | for (unsigned i = 0, e = Preds.size(); i != e; ++i) { |
| 1210 | TerminatorInst *TI = Preds[i]->getTerminator(); |
| 1211 | |
| 1212 | if (BranchInst *BI = dyn_cast<BranchInst>(TI)) { |
| 1213 | if (BI->isUnconditional()) { |
| 1214 | if (BI->getSuccessor(0) == BB) { |
| 1215 | new UnreachableInst(TI); |
| 1216 | TI->eraseFromParent(); |
| 1217 | Changed = true; |
| 1218 | } |
| 1219 | } else { |
| 1220 | if (BI->getSuccessor(0) == BB) { |
| 1221 | new BranchInst(BI->getSuccessor(1), BI); |
| 1222 | BI->eraseFromParent(); |
| 1223 | } else if (BI->getSuccessor(1) == BB) { |
| 1224 | new BranchInst(BI->getSuccessor(0), BI); |
| 1225 | BI->eraseFromParent(); |
| 1226 | Changed = true; |
| 1227 | } |
| 1228 | } |
| 1229 | } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) { |
| 1230 | for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) |
| 1231 | if (SI->getSuccessor(i) == BB) { |
| 1232 | SI->removeCase(i); |
| 1233 | --i; --e; |
| 1234 | Changed = true; |
| 1235 | } |
| 1236 | // If the default value is unreachable, figure out the most popular |
| 1237 | // destination and make it the default. |
| 1238 | if (SI->getSuccessor(0) == BB) { |
| 1239 | std::map<BasicBlock*, unsigned> Popularity; |
| 1240 | for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) |
| 1241 | Popularity[SI->getSuccessor(i)]++; |
| 1242 | |
| 1243 | // Find the most popular block. |
| 1244 | unsigned MaxPop = 0; |
| 1245 | BasicBlock *MaxBlock = 0; |
| 1246 | for (std::map<BasicBlock*, unsigned>::iterator |
| 1247 | I = Popularity.begin(), E = Popularity.end(); I != E; ++I) { |
| 1248 | if (I->second > MaxPop) { |
| 1249 | MaxPop = I->second; |
| 1250 | MaxBlock = I->first; |
| 1251 | } |
| 1252 | } |
| 1253 | if (MaxBlock) { |
| 1254 | // Make this the new default, allowing us to delete any explicit |
| 1255 | // edges to it. |
| 1256 | SI->setSuccessor(0, MaxBlock); |
| 1257 | Changed = true; |
| 1258 | |
| 1259 | for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i) |
| 1260 | if (SI->getSuccessor(i) == MaxBlock) { |
| 1261 | SI->removeCase(i); |
| 1262 | --i; --e; |
| 1263 | } |
| 1264 | } |
| 1265 | } |
| 1266 | } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) { |
| 1267 | if (II->getUnwindDest() == BB) { |
| 1268 | // Convert the invoke to a call instruction. This would be a good |
| 1269 | // place to note that the call does not throw though. |
| 1270 | BranchInst *BI = new BranchInst(II->getNormalDest(), II); |
| 1271 | II->removeFromParent(); // Take out of symbol table |
| 1272 | |
| 1273 | // Insert the call now... |
| 1274 | std::vector<Value*> Args(II->op_begin()+3, II->op_end()); |
| 1275 | CallInst *CI = new CallInst(II->getCalledValue(), Args, |
| 1276 | II->getName(), BI); |
| 1277 | // If the invoke produced a value, the Call does now instead. |
| 1278 | II->replaceAllUsesWith(CI); |
| 1279 | delete II; |
| 1280 | Changed = true; |
| 1281 | } |
| 1282 | } |
| 1283 | } |
| 1284 | |
| 1285 | // If this block is now dead, remove it. |
| 1286 | if (pred_begin(BB) == pred_end(BB)) { |
| 1287 | // We know there are no successors, so just nuke the block. |
| 1288 | M->getBasicBlockList().erase(BB); |
| 1289 | return true; |
| 1290 | } |
| 1291 | } |
Chris Lattner | 19831ec | 2004-02-16 06:35:48 +0000 | [diff] [blame] | 1292 | } |
| 1293 | |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 1294 | // Merge basic blocks into their predecessor if there is only one distinct |
| 1295 | // pred, and if there is only one distinct successor of the predecessor, and |
| 1296 | // if there are no PHI nodes. |
| 1297 | // |
Chris Lattner | 2355f94 | 2004-02-11 01:17:07 +0000 | [diff] [blame] | 1298 | pred_iterator PI(pred_begin(BB)), PE(pred_end(BB)); |
| 1299 | BasicBlock *OnlyPred = *PI++; |
| 1300 | for (; PI != PE; ++PI) // Search all predecessors, see if they are all same |
| 1301 | if (*PI != OnlyPred) { |
| 1302 | OnlyPred = 0; // There are multiple different predecessors... |
| 1303 | break; |
| 1304 | } |
Chris Lattner | 92da2c2 | 2004-05-01 22:36:37 +0000 | [diff] [blame] | 1305 | |
Chris Lattner | 2355f94 | 2004-02-11 01:17:07 +0000 | [diff] [blame] | 1306 | BasicBlock *OnlySucc = 0; |
| 1307 | if (OnlyPred && OnlyPred != BB && // Don't break self loops |
| 1308 | OnlyPred->getTerminator()->getOpcode() != Instruction::Invoke) { |
| 1309 | // Check to see if there is only one distinct successor... |
| 1310 | succ_iterator SI(succ_begin(OnlyPred)), SE(succ_end(OnlyPred)); |
| 1311 | OnlySucc = BB; |
| 1312 | for (; SI != SE; ++SI) |
| 1313 | if (*SI != OnlySucc) { |
| 1314 | OnlySucc = 0; // There are multiple distinct successors! |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 1315 | break; |
| 1316 | } |
Chris Lattner | 2355f94 | 2004-02-11 01:17:07 +0000 | [diff] [blame] | 1317 | } |
| 1318 | |
| 1319 | if (OnlySucc) { |
Chris Lattner | 30b4344 | 2004-07-15 02:06:12 +0000 | [diff] [blame] | 1320 | DEBUG(std::cerr << "Merging: " << *BB << "into: " << *OnlyPred); |
Chris Lattner | 2355f94 | 2004-02-11 01:17:07 +0000 | [diff] [blame] | 1321 | TerminatorInst *Term = OnlyPred->getTerminator(); |
| 1322 | |
| 1323 | // Resolve any PHI nodes at the start of the block. They are all |
| 1324 | // guaranteed to have exactly one entry if they exist, unless there are |
| 1325 | // multiple duplicate (but guaranteed to be equal) entries for the |
| 1326 | // incoming edges. This occurs when there are multiple edges from |
| 1327 | // OnlyPred to OnlySucc. |
| 1328 | // |
| 1329 | while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) { |
| 1330 | PN->replaceAllUsesWith(PN->getIncomingValue(0)); |
| 1331 | BB->getInstList().pop_front(); // Delete the phi node... |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 1332 | } |
| 1333 | |
Chris Lattner | 2355f94 | 2004-02-11 01:17:07 +0000 | [diff] [blame] | 1334 | // Delete the unconditional branch from the predecessor... |
| 1335 | OnlyPred->getInstList().pop_back(); |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 1336 | |
Chris Lattner | 2355f94 | 2004-02-11 01:17:07 +0000 | [diff] [blame] | 1337 | // Move all definitions in the successor to the predecessor... |
| 1338 | OnlyPred->getInstList().splice(OnlyPred->end(), BB->getInstList()); |
Chris Lattner | 1896150 | 2002-06-25 16:12:52 +0000 | [diff] [blame] | 1339 | |
Chris Lattner | 2355f94 | 2004-02-11 01:17:07 +0000 | [diff] [blame] | 1340 | // Make all PHI nodes that referred to BB now refer to Pred as their |
| 1341 | // source... |
| 1342 | BB->replaceAllUsesWith(OnlyPred); |
Chris Lattner | 1896150 | 2002-06-25 16:12:52 +0000 | [diff] [blame] | 1343 | |
Chris Lattner | 2355f94 | 2004-02-11 01:17:07 +0000 | [diff] [blame] | 1344 | std::string OldName = BB->getName(); |
Chris Lattner | 1896150 | 2002-06-25 16:12:52 +0000 | [diff] [blame] | 1345 | |
Chris Lattner | 2355f94 | 2004-02-11 01:17:07 +0000 | [diff] [blame] | 1346 | // Erase basic block from the function... |
| 1347 | M->getBasicBlockList().erase(BB); |
Chris Lattner | 1896150 | 2002-06-25 16:12:52 +0000 | [diff] [blame] | 1348 | |
Chris Lattner | 2355f94 | 2004-02-11 01:17:07 +0000 | [diff] [blame] | 1349 | // Inherit predecessors name if it exists... |
| 1350 | if (!OldName.empty() && !OnlyPred->hasName()) |
| 1351 | OnlyPred->setName(OldName); |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 1352 | |
Chris Lattner | 2355f94 | 2004-02-11 01:17:07 +0000 | [diff] [blame] | 1353 | return true; |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 1354 | } |
Chris Lattner | 723c66d | 2004-02-11 03:36:04 +0000 | [diff] [blame] | 1355 | |
Chris Lattner | 37dc938 | 2004-11-30 00:29:14 +0000 | [diff] [blame] | 1356 | // Otherwise, if this block only has a single predecessor, and if that block |
| 1357 | // is a conditional branch, see if we can hoist any code from this block up |
| 1358 | // into our predecessor. |
| 1359 | if (OnlyPred) |
Chris Lattner | 7613437 | 2004-12-10 17:42:31 +0000 | [diff] [blame] | 1360 | if (BranchInst *BI = dyn_cast<BranchInst>(OnlyPred->getTerminator())) |
| 1361 | if (BI->isConditional()) { |
| 1362 | // Get the other block. |
| 1363 | BasicBlock *OtherBB = BI->getSuccessor(BI->getSuccessor(0) == BB); |
| 1364 | PI = pred_begin(OtherBB); |
| 1365 | ++PI; |
| 1366 | if (PI == pred_end(OtherBB)) { |
| 1367 | // We have a conditional branch to two blocks that are only reachable |
| 1368 | // from the condbr. We know that the condbr dominates the two blocks, |
| 1369 | // so see if there is any identical code in the "then" and "else" |
| 1370 | // blocks. If so, we can hoist it up to the branching block. |
| 1371 | Changed |= HoistThenElseCodeToIf(BI); |
| 1372 | } |
Chris Lattner | 37dc938 | 2004-11-30 00:29:14 +0000 | [diff] [blame] | 1373 | } |
Chris Lattner | 37dc938 | 2004-11-30 00:29:14 +0000 | [diff] [blame] | 1374 | |
Chris Lattner | 0d56008 | 2004-02-24 05:38:11 +0000 | [diff] [blame] | 1375 | for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) |
| 1376 | if (BranchInst *BI = dyn_cast<BranchInst>((*PI)->getTerminator())) |
| 1377 | // Change br (X == 0 | X == 1), T, F into a switch instruction. |
| 1378 | if (BI->isConditional() && isa<Instruction>(BI->getCondition())) { |
| 1379 | Instruction *Cond = cast<Instruction>(BI->getCondition()); |
| 1380 | // If this is a bunch of seteq's or'd together, or if it's a bunch of |
| 1381 | // 'setne's and'ed together, collect them. |
| 1382 | Value *CompVal = 0; |
Chris Lattner | 1654cff | 2004-06-19 07:02:14 +0000 | [diff] [blame] | 1383 | std::vector<ConstantInt*> Values; |
Chris Lattner | 0d56008 | 2004-02-24 05:38:11 +0000 | [diff] [blame] | 1384 | bool TrueWhenEqual = GatherValueComparisons(Cond, CompVal, Values); |
| 1385 | if (CompVal && CompVal->getType()->isInteger()) { |
| 1386 | // There might be duplicate constants in the list, which the switch |
| 1387 | // instruction can't handle, remove them now. |
Chris Lattner | 1654cff | 2004-06-19 07:02:14 +0000 | [diff] [blame] | 1388 | std::sort(Values.begin(), Values.end(), ConstantIntOrdering()); |
Chris Lattner | 0d56008 | 2004-02-24 05:38:11 +0000 | [diff] [blame] | 1389 | Values.erase(std::unique(Values.begin(), Values.end()), Values.end()); |
| 1390 | |
| 1391 | // Figure out which block is which destination. |
| 1392 | BasicBlock *DefaultBB = BI->getSuccessor(1); |
| 1393 | BasicBlock *EdgeBB = BI->getSuccessor(0); |
| 1394 | if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB); |
| 1395 | |
| 1396 | // Create the new switch instruction now. |
Chris Lattner | 3788059 | 2005-01-29 00:38:26 +0000 | [diff] [blame] | 1397 | SwitchInst *New = new SwitchInst(CompVal, DefaultBB,Values.size(),BI); |
Chris Lattner | 0d56008 | 2004-02-24 05:38:11 +0000 | [diff] [blame] | 1398 | |
| 1399 | // Add all of the 'cases' to the switch instruction. |
| 1400 | for (unsigned i = 0, e = Values.size(); i != e; ++i) |
| 1401 | New->addCase(Values[i], EdgeBB); |
| 1402 | |
| 1403 | // We added edges from PI to the EdgeBB. As such, if there were any |
| 1404 | // PHI nodes in EdgeBB, they need entries to be added corresponding to |
| 1405 | // the number of edges added. |
| 1406 | for (BasicBlock::iterator BBI = EdgeBB->begin(); |
Reid Spencer | 2da5c3d | 2004-09-15 17:06:42 +0000 | [diff] [blame] | 1407 | isa<PHINode>(BBI); ++BBI) { |
| 1408 | PHINode *PN = cast<PHINode>(BBI); |
Chris Lattner | 0d56008 | 2004-02-24 05:38:11 +0000 | [diff] [blame] | 1409 | Value *InVal = PN->getIncomingValueForBlock(*PI); |
| 1410 | for (unsigned i = 0, e = Values.size()-1; i != e; ++i) |
| 1411 | PN->addIncoming(InVal, *PI); |
| 1412 | } |
| 1413 | |
| 1414 | // Erase the old branch instruction. |
| 1415 | (*PI)->getInstList().erase(BI); |
| 1416 | |
| 1417 | // Erase the potentially condition tree that was used to computed the |
| 1418 | // branch condition. |
| 1419 | ErasePossiblyDeadInstructionTree(Cond); |
| 1420 | return true; |
| 1421 | } |
| 1422 | } |
| 1423 | |
Chris Lattner | 723c66d | 2004-02-11 03:36:04 +0000 | [diff] [blame] | 1424 | // If there is a trivial two-entry PHI node in this basic block, and we can |
| 1425 | // eliminate it, do so now. |
| 1426 | if (PHINode *PN = dyn_cast<PHINode>(BB->begin())) |
| 1427 | if (PN->getNumIncomingValues() == 2) { |
| 1428 | // Ok, this is a two entry PHI node. Check to see if this is a simple "if |
| 1429 | // statement", which has a very simple dominance structure. Basically, we |
| 1430 | // are trying to find the condition that is being branched on, which |
| 1431 | // subsequently causes this merge to happen. We really want control |
| 1432 | // dependence information for this check, but simplifycfg can't keep it up |
| 1433 | // to date, and this catches most of the cases we care about anyway. |
| 1434 | // |
| 1435 | BasicBlock *IfTrue, *IfFalse; |
| 1436 | if (Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse)) { |
Chris Lattner | 218a822 | 2004-06-20 01:13:18 +0000 | [diff] [blame] | 1437 | DEBUG(std::cerr << "FOUND IF CONDITION! " << *IfCond << " T: " |
| 1438 | << IfTrue->getName() << " F: " << IfFalse->getName() << "\n"); |
Chris Lattner | 723c66d | 2004-02-11 03:36:04 +0000 | [diff] [blame] | 1439 | |
Chris Lattner | 9c07866 | 2004-10-14 05:13:36 +0000 | [diff] [blame] | 1440 | // Loop over the PHI's seeing if we can promote them all to select |
| 1441 | // instructions. While we are at it, keep track of the instructions |
| 1442 | // that need to be moved to the dominating block. |
| 1443 | std::set<Instruction*> AggressiveInsts; |
| 1444 | bool CanPromote = true; |
| 1445 | |
Chris Lattner | 723c66d | 2004-02-11 03:36:04 +0000 | [diff] [blame] | 1446 | BasicBlock::iterator AfterPHIIt = BB->begin(); |
Chris Lattner | 9c07866 | 2004-10-14 05:13:36 +0000 | [diff] [blame] | 1447 | while (isa<PHINode>(AfterPHIIt)) { |
| 1448 | PHINode *PN = cast<PHINode>(AfterPHIIt++); |
| 1449 | if (PN->getIncomingValue(0) == PN->getIncomingValue(1)) |
| 1450 | PN->replaceAllUsesWith(PN->getIncomingValue(0)); |
| 1451 | else if (!DominatesMergePoint(PN->getIncomingValue(0), BB, |
| 1452 | &AggressiveInsts) || |
| 1453 | !DominatesMergePoint(PN->getIncomingValue(1), BB, |
| 1454 | &AggressiveInsts)) { |
| 1455 | CanPromote = false; |
| 1456 | break; |
| 1457 | } |
| 1458 | } |
Chris Lattner | 723c66d | 2004-02-11 03:36:04 +0000 | [diff] [blame] | 1459 | |
Chris Lattner | 9c07866 | 2004-10-14 05:13:36 +0000 | [diff] [blame] | 1460 | // Did we eliminate all PHI's? |
| 1461 | CanPromote |= AfterPHIIt == BB->begin(); |
Chris Lattner | 723c66d | 2004-02-11 03:36:04 +0000 | [diff] [blame] | 1462 | |
Chris Lattner | 9c07866 | 2004-10-14 05:13:36 +0000 | [diff] [blame] | 1463 | // If we all PHI nodes are promotable, check to make sure that all |
| 1464 | // instructions in the predecessor blocks can be promoted as well. If |
| 1465 | // not, we won't be able to get rid of the control flow, so it's not |
| 1466 | // worth promoting to select instructions. |
Reid Spencer | 4e073a8 | 2004-10-22 16:10:39 +0000 | [diff] [blame] | 1467 | BasicBlock *DomBlock = 0, *IfBlock1 = 0, *IfBlock2 = 0; |
Chris Lattner | 9c07866 | 2004-10-14 05:13:36 +0000 | [diff] [blame] | 1468 | if (CanPromote) { |
| 1469 | PN = cast<PHINode>(BB->begin()); |
| 1470 | BasicBlock *Pred = PN->getIncomingBlock(0); |
| 1471 | if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) { |
| 1472 | IfBlock1 = Pred; |
| 1473 | DomBlock = *pred_begin(Pred); |
| 1474 | for (BasicBlock::iterator I = Pred->begin(); |
| 1475 | !isa<TerminatorInst>(I); ++I) |
| 1476 | if (!AggressiveInsts.count(I)) { |
| 1477 | // This is not an aggressive instruction that we can promote. |
| 1478 | // Because of this, we won't be able to get rid of the control |
| 1479 | // flow, so the xform is not worth it. |
| 1480 | CanPromote = false; |
| 1481 | break; |
| 1482 | } |
| 1483 | } |
| 1484 | |
| 1485 | Pred = PN->getIncomingBlock(1); |
| 1486 | if (CanPromote && |
| 1487 | cast<BranchInst>(Pred->getTerminator())->isUnconditional()) { |
| 1488 | IfBlock2 = Pred; |
| 1489 | DomBlock = *pred_begin(Pred); |
| 1490 | for (BasicBlock::iterator I = Pred->begin(); |
| 1491 | !isa<TerminatorInst>(I); ++I) |
| 1492 | if (!AggressiveInsts.count(I)) { |
| 1493 | // This is not an aggressive instruction that we can promote. |
| 1494 | // Because of this, we won't be able to get rid of the control |
| 1495 | // flow, so the xform is not worth it. |
| 1496 | CanPromote = false; |
| 1497 | break; |
| 1498 | } |
| 1499 | } |
| 1500 | } |
| 1501 | |
| 1502 | // If we can still promote the PHI nodes after this gauntlet of tests, |
| 1503 | // do all of the PHI's now. |
| 1504 | if (CanPromote) { |
| 1505 | // Move all 'aggressive' instructions, which are defined in the |
| 1506 | // conditional parts of the if's up to the dominating block. |
| 1507 | if (IfBlock1) { |
| 1508 | DomBlock->getInstList().splice(DomBlock->getTerminator(), |
| 1509 | IfBlock1->getInstList(), |
| 1510 | IfBlock1->begin(), |
| 1511 | IfBlock1->getTerminator()); |
| 1512 | } |
| 1513 | if (IfBlock2) { |
| 1514 | DomBlock->getInstList().splice(DomBlock->getTerminator(), |
| 1515 | IfBlock2->getInstList(), |
| 1516 | IfBlock2->begin(), |
| 1517 | IfBlock2->getTerminator()); |
| 1518 | } |
| 1519 | |
| 1520 | while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) { |
| 1521 | // Change the PHI node into a select instruction. |
Chris Lattner | 723c66d | 2004-02-11 03:36:04 +0000 | [diff] [blame] | 1522 | Value *TrueVal = |
| 1523 | PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse); |
| 1524 | Value *FalseVal = |
| 1525 | PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue); |
| 1526 | |
Chris Lattner | 552112f | 2004-03-30 19:44:05 +0000 | [diff] [blame] | 1527 | std::string Name = PN->getName(); PN->setName(""); |
| 1528 | PN->replaceAllUsesWith(new SelectInst(IfCond, TrueVal, FalseVal, |
Chris Lattner | 9c07866 | 2004-10-14 05:13:36 +0000 | [diff] [blame] | 1529 | Name, AfterPHIIt)); |
Chris Lattner | 552112f | 2004-03-30 19:44:05 +0000 | [diff] [blame] | 1530 | BB->getInstList().erase(PN); |
Chris Lattner | 723c66d | 2004-02-11 03:36:04 +0000 | [diff] [blame] | 1531 | } |
Chris Lattner | 9c07866 | 2004-10-14 05:13:36 +0000 | [diff] [blame] | 1532 | Changed = true; |
Chris Lattner | 723c66d | 2004-02-11 03:36:04 +0000 | [diff] [blame] | 1533 | } |
| 1534 | } |
| 1535 | } |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 1536 | |
Chris Lattner | 694e37f | 2003-08-17 19:41:53 +0000 | [diff] [blame] | 1537 | return Changed; |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 1538 | } |