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 | |
| 14 | #include "llvm/Transforms/Utils/Local.h" |
Chris Lattner | 723c66d | 2004-02-11 03:36:04 +0000 | [diff] [blame] | 15 | #include "llvm/Constants.h" |
| 16 | #include "llvm/Instructions.h" |
Chris Lattner | 0d56008 | 2004-02-24 05:38:11 +0000 | [diff] [blame] | 17 | #include "llvm/Type.h" |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 18 | #include "llvm/Support/CFG.h" |
| 19 | #include <algorithm> |
| 20 | #include <functional> |
Chris Lattner | d52c261 | 2004-02-24 07:23:58 +0000 | [diff] [blame] | 21 | #include <set> |
Chris Lattner | f7703df | 2004-01-09 06:12:26 +0000 | [diff] [blame] | 22 | using namespace llvm; |
Brian Gaeke | d0fde30 | 2003-11-11 22:41:34 +0000 | [diff] [blame] | 23 | |
Chris Lattner | 0d56008 | 2004-02-24 05:38:11 +0000 | [diff] [blame] | 24 | // PropagatePredecessorsForPHIs - This gets "Succ" ready to have the |
| 25 | // predecessors from "BB". This is a little tricky because "Succ" has PHI |
| 26 | // nodes, which need to have extra slots added to them to hold the merge edges |
| 27 | // from BB's predecessors, and BB itself might have had PHI nodes in it. This |
| 28 | // function returns true (failure) if the Succ BB already has a predecessor that |
| 29 | // 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] | 30 | // |
| 31 | // Assumption: Succ is the single successor for BB. |
| 32 | // |
Misha Brukman | a3bbcb5 | 2002-10-29 23:06:16 +0000 | [diff] [blame] | 33 | static bool PropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) { |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 34 | assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!"); |
Chris Lattner | 3abb95d | 2002-09-24 00:09:26 +0000 | [diff] [blame] | 35 | |
| 36 | if (!isa<PHINode>(Succ->front())) |
| 37 | return false; // We can make the transformation, no problem. |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 38 | |
| 39 | // If there is more than one predecessor, and there are PHI nodes in |
| 40 | // the successor, then we need to add incoming edges for the PHI nodes |
| 41 | // |
| 42 | const std::vector<BasicBlock*> BBPreds(pred_begin(BB), pred_end(BB)); |
| 43 | |
| 44 | // 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] | 45 | // Succ. If so, we cannot do the transformation if there are any PHI nodes |
| 46 | // with incompatible values coming in from the two edges! |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 47 | // |
Chris Lattner | e2ca540 | 2003-03-05 21:01:52 +0000 | [diff] [blame] | 48 | for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ); PI != PE; ++PI) |
| 49 | if (find(BBPreds.begin(), BBPreds.end(), *PI) != BBPreds.end()) { |
| 50 | // Loop over all of the PHI nodes checking to see if there are |
| 51 | // incompatible values coming in. |
Chris Lattner | 46a5f1f | 2003-03-05 21:36:33 +0000 | [diff] [blame] | 52 | for (BasicBlock::iterator I = Succ->begin(); |
Chris Lattner | e408e25 | 2003-04-23 16:37:45 +0000 | [diff] [blame] | 53 | PHINode *PN = dyn_cast<PHINode>(I); ++I) { |
Chris Lattner | e2ca540 | 2003-03-05 21:01:52 +0000 | [diff] [blame] | 54 | // Loop up the entries in the PHI node for BB and for *PI if the values |
| 55 | // coming in are non-equal, we cannot merge these two blocks (instead we |
| 56 | // should insert a conditional move or something, then merge the |
| 57 | // blocks). |
| 58 | int Idx1 = PN->getBasicBlockIndex(BB); |
| 59 | int Idx2 = PN->getBasicBlockIndex(*PI); |
| 60 | assert(Idx1 != -1 && Idx2 != -1 && |
| 61 | "Didn't have entries for my predecessors??"); |
| 62 | if (PN->getIncomingValue(Idx1) != PN->getIncomingValue(Idx2)) |
| 63 | return true; // Values are not equal... |
| 64 | } |
| 65 | } |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 66 | |
| 67 | // Loop over all of the PHI nodes in the successor BB |
| 68 | for (BasicBlock::iterator I = Succ->begin(); |
Chris Lattner | e408e25 | 2003-04-23 16:37:45 +0000 | [diff] [blame] | 69 | PHINode *PN = dyn_cast<PHINode>(I); ++I) { |
Chris Lattner | bb190ac | 2002-10-08 21:36:33 +0000 | [diff] [blame] | 70 | Value *OldVal = PN->removeIncomingValue(BB, false); |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 71 | assert(OldVal && "No entry in PHI for Pred BB!"); |
| 72 | |
Chris Lattner | 46a5f1f | 2003-03-05 21:36:33 +0000 | [diff] [blame] | 73 | // If this incoming value is one of the PHI nodes in BB... |
| 74 | if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) { |
| 75 | PHINode *OldValPN = cast<PHINode>(OldVal); |
| 76 | for (std::vector<BasicBlock*>::const_iterator PredI = BBPreds.begin(), |
| 77 | End = BBPreds.end(); PredI != End; ++PredI) { |
| 78 | PN->addIncoming(OldValPN->getIncomingValueForBlock(*PredI), *PredI); |
| 79 | } |
| 80 | } else { |
| 81 | for (std::vector<BasicBlock*>::const_iterator PredI = BBPreds.begin(), |
| 82 | End = BBPreds.end(); PredI != End; ++PredI) { |
| 83 | // Add an incoming value for each of the new incoming values... |
| 84 | PN->addIncoming(OldVal, *PredI); |
| 85 | } |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 86 | } |
| 87 | } |
| 88 | return false; |
| 89 | } |
| 90 | |
Chris Lattner | 723c66d | 2004-02-11 03:36:04 +0000 | [diff] [blame] | 91 | /// GetIfCondition - Given a basic block (BB) with two predecessors (and |
| 92 | /// presumably PHI nodes in it), check to see if the merge at this block is due |
| 93 | /// to an "if condition". If so, return the boolean condition that determines |
| 94 | /// which entry into BB will be taken. Also, return by references the block |
| 95 | /// that will be entered from if the condition is true, and the block that will |
| 96 | /// be entered if the condition is false. |
| 97 | /// |
| 98 | /// |
| 99 | static Value *GetIfCondition(BasicBlock *BB, |
| 100 | BasicBlock *&IfTrue, BasicBlock *&IfFalse) { |
| 101 | assert(std::distance(pred_begin(BB), pred_end(BB)) == 2 && |
| 102 | "Function can only handle blocks with 2 predecessors!"); |
| 103 | BasicBlock *Pred1 = *pred_begin(BB); |
| 104 | BasicBlock *Pred2 = *++pred_begin(BB); |
| 105 | |
| 106 | // We can only handle branches. Other control flow will be lowered to |
| 107 | // branches if possible anyway. |
| 108 | if (!isa<BranchInst>(Pred1->getTerminator()) || |
| 109 | !isa<BranchInst>(Pred2->getTerminator())) |
| 110 | return 0; |
| 111 | BranchInst *Pred1Br = cast<BranchInst>(Pred1->getTerminator()); |
| 112 | BranchInst *Pred2Br = cast<BranchInst>(Pred2->getTerminator()); |
| 113 | |
| 114 | // Eliminate code duplication by ensuring that Pred1Br is conditional if |
| 115 | // either are. |
| 116 | if (Pred2Br->isConditional()) { |
| 117 | // If both branches are conditional, we don't have an "if statement". In |
| 118 | // reality, we could transform this case, but since the condition will be |
| 119 | // required anyway, we stand no chance of eliminating it, so the xform is |
| 120 | // probably not profitable. |
| 121 | if (Pred1Br->isConditional()) |
| 122 | return 0; |
| 123 | |
| 124 | std::swap(Pred1, Pred2); |
| 125 | std::swap(Pred1Br, Pred2Br); |
| 126 | } |
| 127 | |
| 128 | if (Pred1Br->isConditional()) { |
| 129 | // If we found a conditional branch predecessor, make sure that it branches |
| 130 | // to BB and Pred2Br. If it doesn't, this isn't an "if statement". |
| 131 | if (Pred1Br->getSuccessor(0) == BB && |
| 132 | Pred1Br->getSuccessor(1) == Pred2) { |
| 133 | IfTrue = Pred1; |
| 134 | IfFalse = Pred2; |
| 135 | } else if (Pred1Br->getSuccessor(0) == Pred2 && |
| 136 | Pred1Br->getSuccessor(1) == BB) { |
| 137 | IfTrue = Pred2; |
| 138 | IfFalse = Pred1; |
| 139 | } else { |
| 140 | // We know that one arm of the conditional goes to BB, so the other must |
| 141 | // go somewhere unrelated, and this must not be an "if statement". |
| 142 | return 0; |
| 143 | } |
| 144 | |
| 145 | // The only thing we have to watch out for here is to make sure that Pred2 |
| 146 | // doesn't have incoming edges from other blocks. If it does, the condition |
| 147 | // doesn't dominate BB. |
| 148 | if (++pred_begin(Pred2) != pred_end(Pred2)) |
| 149 | return 0; |
| 150 | |
| 151 | return Pred1Br->getCondition(); |
| 152 | } |
| 153 | |
| 154 | // Ok, if we got here, both predecessors end with an unconditional branch to |
| 155 | // BB. Don't panic! If both blocks only have a single (identical) |
| 156 | // predecessor, and THAT is a conditional branch, then we're all ok! |
| 157 | if (pred_begin(Pred1) == pred_end(Pred1) || |
| 158 | ++pred_begin(Pred1) != pred_end(Pred1) || |
| 159 | pred_begin(Pred2) == pred_end(Pred2) || |
| 160 | ++pred_begin(Pred2) != pred_end(Pred2) || |
| 161 | *pred_begin(Pred1) != *pred_begin(Pred2)) |
| 162 | return 0; |
| 163 | |
| 164 | // Otherwise, if this is a conditional branch, then we can use it! |
| 165 | BasicBlock *CommonPred = *pred_begin(Pred1); |
| 166 | if (BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator())) { |
| 167 | assert(BI->isConditional() && "Two successors but not conditional?"); |
| 168 | if (BI->getSuccessor(0) == Pred1) { |
| 169 | IfTrue = Pred1; |
| 170 | IfFalse = Pred2; |
| 171 | } else { |
| 172 | IfTrue = Pred2; |
| 173 | IfFalse = Pred1; |
| 174 | } |
| 175 | return BI->getCondition(); |
| 176 | } |
| 177 | return 0; |
| 178 | } |
| 179 | |
| 180 | |
| 181 | // If we have a merge point of an "if condition" as accepted above, return true |
| 182 | // if the specified value dominates the block. We don't handle the true |
| 183 | // generality of domination here, just a special case which works well enough |
| 184 | // for us. |
| 185 | static bool DominatesMergePoint(Value *V, BasicBlock *BB) { |
| 186 | if (Instruction *I = dyn_cast<Instruction>(V)) { |
| 187 | BasicBlock *PBB = I->getParent(); |
| 188 | // If this instruction is defined in a block that contains an unconditional |
| 189 | // branch to BB, then it must be in the 'conditional' part of the "if |
| 190 | // statement". |
| 191 | if (isa<BranchInst>(PBB->getTerminator()) && |
| 192 | cast<BranchInst>(PBB->getTerminator())->isUnconditional() && |
| 193 | cast<BranchInst>(PBB->getTerminator())->getSuccessor(0) == BB) |
| 194 | return false; |
| 195 | |
| 196 | // We also don't want to allow wierd loops that might have the "if |
| 197 | // condition" in the bottom of this block. |
| 198 | if (PBB == BB) return false; |
| 199 | } |
| 200 | |
| 201 | // Non-instructions all dominate instructions. |
| 202 | return true; |
| 203 | } |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 204 | |
Chris Lattner | 0d56008 | 2004-02-24 05:38:11 +0000 | [diff] [blame] | 205 | // GatherConstantSetEQs - Given a potentially 'or'd together collection of seteq |
| 206 | // instructions that compare a value against a constant, return the value being |
| 207 | // compared, and stick the constant into the Values vector. |
| 208 | static Value *GatherConstantSetEQs(Value *V, std::vector<Constant*> &Values) { |
| 209 | if (Instruction *Inst = dyn_cast<Instruction>(V)) |
| 210 | if (Inst->getOpcode() == Instruction::SetEQ) { |
| 211 | if (Constant *C = dyn_cast<Constant>(Inst->getOperand(1))) { |
| 212 | Values.push_back(C); |
| 213 | return Inst->getOperand(0); |
| 214 | } else if (Constant *C = dyn_cast<Constant>(Inst->getOperand(0))) { |
| 215 | Values.push_back(C); |
| 216 | return Inst->getOperand(1); |
| 217 | } |
| 218 | } else if (Inst->getOpcode() == Instruction::Or) { |
| 219 | if (Value *LHS = GatherConstantSetEQs(Inst->getOperand(0), Values)) |
| 220 | if (Value *RHS = GatherConstantSetEQs(Inst->getOperand(1), Values)) |
| 221 | if (LHS == RHS) |
| 222 | return LHS; |
| 223 | } |
| 224 | return 0; |
| 225 | } |
| 226 | |
| 227 | // GatherConstantSetNEs - Given a potentially 'and'd together collection of |
| 228 | // setne instructions that compare a value against a constant, return the value |
| 229 | // being compared, and stick the constant into the Values vector. |
| 230 | static Value *GatherConstantSetNEs(Value *V, std::vector<Constant*> &Values) { |
| 231 | if (Instruction *Inst = dyn_cast<Instruction>(V)) |
| 232 | if (Inst->getOpcode() == Instruction::SetNE) { |
| 233 | if (Constant *C = dyn_cast<Constant>(Inst->getOperand(1))) { |
| 234 | Values.push_back(C); |
| 235 | return Inst->getOperand(0); |
| 236 | } else if (Constant *C = dyn_cast<Constant>(Inst->getOperand(0))) { |
| 237 | Values.push_back(C); |
| 238 | return Inst->getOperand(1); |
| 239 | } |
| 240 | } else if (Inst->getOpcode() == Instruction::Cast) { |
| 241 | // Cast of X to bool is really a comparison against zero. |
| 242 | assert(Inst->getType() == Type::BoolTy && "Can only handle bool values!"); |
| 243 | Values.push_back(Constant::getNullValue(Inst->getOperand(0)->getType())); |
| 244 | return Inst->getOperand(0); |
| 245 | } else if (Inst->getOpcode() == Instruction::And) { |
| 246 | if (Value *LHS = GatherConstantSetNEs(Inst->getOperand(0), Values)) |
| 247 | if (Value *RHS = GatherConstantSetNEs(Inst->getOperand(1), Values)) |
| 248 | if (LHS == RHS) |
| 249 | return LHS; |
| 250 | } |
| 251 | return 0; |
| 252 | } |
| 253 | |
| 254 | |
| 255 | |
| 256 | /// GatherValueComparisons - If the specified Cond is an 'and' or 'or' of a |
| 257 | /// bunch of comparisons of one value against constants, return the value and |
| 258 | /// the constants being compared. |
| 259 | static bool GatherValueComparisons(Instruction *Cond, Value *&CompVal, |
| 260 | std::vector<Constant*> &Values) { |
| 261 | if (Cond->getOpcode() == Instruction::Or) { |
| 262 | CompVal = GatherConstantSetEQs(Cond, Values); |
| 263 | |
| 264 | // Return true to indicate that the condition is true if the CompVal is |
| 265 | // equal to one of the constants. |
| 266 | return true; |
| 267 | } else if (Cond->getOpcode() == Instruction::And) { |
| 268 | CompVal = GatherConstantSetNEs(Cond, Values); |
| 269 | |
| 270 | // Return false to indicate that the condition is false if the CompVal is |
| 271 | // equal to one of the constants. |
| 272 | return false; |
| 273 | } |
| 274 | return false; |
| 275 | } |
| 276 | |
| 277 | /// ErasePossiblyDeadInstructionTree - If the specified instruction is dead and |
| 278 | /// has no side effects, nuke it. If it uses any instructions that become dead |
| 279 | /// because the instruction is now gone, nuke them too. |
| 280 | static void ErasePossiblyDeadInstructionTree(Instruction *I) { |
| 281 | if (isInstructionTriviallyDead(I)) { |
| 282 | std::vector<Value*> Operands(I->op_begin(), I->op_end()); |
| 283 | I->getParent()->getInstList().erase(I); |
| 284 | for (unsigned i = 0, e = Operands.size(); i != e; ++i) |
| 285 | if (Instruction *OpI = dyn_cast<Instruction>(Operands[i])) |
| 286 | ErasePossiblyDeadInstructionTree(OpI); |
| 287 | } |
| 288 | } |
| 289 | |
Chris Lattner | d52c261 | 2004-02-24 07:23:58 +0000 | [diff] [blame] | 290 | /// SafeToMergeTerminators - Return true if it is safe to merge these two |
| 291 | /// terminator instructions together. |
| 292 | /// |
| 293 | static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) { |
| 294 | if (SI1 == SI2) return false; // Can't merge with self! |
| 295 | |
| 296 | // It is not safe to merge these two switch instructions if they have a common |
| 297 | // successor, and if that successor has a PHI node, and if that PHI node has |
| 298 | // conflicting incoming values from the two switch blocks. |
| 299 | BasicBlock *SI1BB = SI1->getParent(); |
| 300 | BasicBlock *SI2BB = SI2->getParent(); |
| 301 | std::set<BasicBlock*> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB)); |
| 302 | |
| 303 | for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I) |
| 304 | if (SI1Succs.count(*I)) |
| 305 | for (BasicBlock::iterator BBI = (*I)->begin(); |
| 306 | PHINode *PN = dyn_cast<PHINode>(BBI); ++BBI) |
| 307 | if (PN->getIncomingValueForBlock(SI1BB) != |
| 308 | PN->getIncomingValueForBlock(SI2BB)) |
| 309 | return false; |
| 310 | |
| 311 | return true; |
| 312 | } |
| 313 | |
| 314 | /// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will |
| 315 | /// now be entries in it from the 'NewPred' block. The values that will be |
| 316 | /// flowing into the PHI nodes will be the same as those coming in from |
| 317 | /// ExistPred, and existing predecessor of Succ. |
| 318 | static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred, |
| 319 | BasicBlock *ExistPred) { |
| 320 | assert(std::find(succ_begin(ExistPred), succ_end(ExistPred), Succ) != |
| 321 | succ_end(ExistPred) && "ExistPred is not a predecessor of Succ!"); |
| 322 | if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do |
| 323 | |
| 324 | for (BasicBlock::iterator I = Succ->begin(); |
| 325 | PHINode *PN = dyn_cast<PHINode>(I); ++I) { |
| 326 | Value *V = PN->getIncomingValueForBlock(ExistPred); |
| 327 | PN->addIncoming(V, NewPred); |
| 328 | } |
| 329 | } |
| 330 | |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 331 | // SimplifyCFG - This function is used to do simplification of a CFG. For |
| 332 | // example, it adjusts branches to branches to eliminate the extra hop, it |
| 333 | // eliminates unreachable basic blocks, and does other "peephole" optimization |
Chris Lattner | e2ca540 | 2003-03-05 21:01:52 +0000 | [diff] [blame] | 334 | // of the CFG. It returns true if a modification was made. |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 335 | // |
| 336 | // WARNING: The entry node of a function may not be simplified. |
| 337 | // |
Chris Lattner | f7703df | 2004-01-09 06:12:26 +0000 | [diff] [blame] | 338 | bool llvm::SimplifyCFG(BasicBlock *BB) { |
Chris Lattner | dc3602b | 2003-08-24 18:36:16 +0000 | [diff] [blame] | 339 | bool Changed = false; |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 340 | Function *M = BB->getParent(); |
| 341 | |
| 342 | assert(BB && BB->getParent() && "Block not embedded in function!"); |
| 343 | assert(BB->getTerminator() && "Degenerate basic block encountered!"); |
Chris Lattner | 1896150 | 2002-06-25 16:12:52 +0000 | [diff] [blame] | 344 | assert(&BB->getParent()->front() != BB && "Can't Simplify entry block!"); |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 345 | |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 346 | // Remove basic blocks that have no predecessors... which are unreachable. |
Chris Lattner | d52c261 | 2004-02-24 07:23:58 +0000 | [diff] [blame] | 347 | if (pred_begin(BB) == pred_end(BB) || |
| 348 | *pred_begin(BB) == BB && ++pred_begin(BB) == pred_end(BB)) { |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 349 | //cerr << "Removing BB: \n" << BB; |
| 350 | |
| 351 | // Loop through all of our successors and make sure they know that one |
| 352 | // of their predecessors is going away. |
| 353 | for_each(succ_begin(BB), succ_end(BB), |
| 354 | std::bind2nd(std::mem_fun(&BasicBlock::removePredecessor), BB)); |
| 355 | |
| 356 | while (!BB->empty()) { |
Chris Lattner | 1896150 | 2002-06-25 16:12:52 +0000 | [diff] [blame] | 357 | Instruction &I = BB->back(); |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 358 | // If this instruction is used, replace uses with an arbitrary |
| 359 | // constant value. Because control flow can't get here, we don't care |
| 360 | // what we replace the value with. Note that since this block is |
| 361 | // unreachable, and all values contained within it must dominate their |
| 362 | // uses, that all uses will eventually be removed. |
Chris Lattner | 1896150 | 2002-06-25 16:12:52 +0000 | [diff] [blame] | 363 | if (!I.use_empty()) |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 364 | // Make all users of this instruction reference the constant instead |
Chris Lattner | 1896150 | 2002-06-25 16:12:52 +0000 | [diff] [blame] | 365 | I.replaceAllUsesWith(Constant::getNullValue(I.getType())); |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 366 | |
| 367 | // Remove the instruction from the basic block |
Chris Lattner | 1896150 | 2002-06-25 16:12:52 +0000 | [diff] [blame] | 368 | BB->getInstList().pop_back(); |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 369 | } |
Chris Lattner | 1896150 | 2002-06-25 16:12:52 +0000 | [diff] [blame] | 370 | M->getBasicBlockList().erase(BB); |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 371 | return true; |
| 372 | } |
| 373 | |
Chris Lattner | 694e37f | 2003-08-17 19:41:53 +0000 | [diff] [blame] | 374 | // Check to see if we can constant propagate this terminator instruction |
| 375 | // away... |
Chris Lattner | dc3602b | 2003-08-24 18:36:16 +0000 | [diff] [blame] | 376 | Changed |= ConstantFoldTerminator(BB); |
Chris Lattner | 694e37f | 2003-08-17 19:41:53 +0000 | [diff] [blame] | 377 | |
Chris Lattner | 46a5f1f | 2003-03-05 21:36:33 +0000 | [diff] [blame] | 378 | // Check to see if this block has no non-phi instructions and only a single |
| 379 | // successor. If so, replace references to this basic block with references |
| 380 | // to the successor. |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 381 | succ_iterator SI(succ_begin(BB)); |
| 382 | if (SI != succ_end(BB) && ++SI == succ_end(BB)) { // One succ? |
Chris Lattner | 46a5f1f | 2003-03-05 21:36:33 +0000 | [diff] [blame] | 383 | |
| 384 | BasicBlock::iterator BBI = BB->begin(); // Skip over phi nodes... |
| 385 | while (isa<PHINode>(*BBI)) ++BBI; |
| 386 | |
| 387 | if (BBI->isTerminator()) { // Terminator is the only non-phi instruction! |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 388 | BasicBlock *Succ = *succ_begin(BB); // There is exactly one successor |
| 389 | |
| 390 | if (Succ != BB) { // Arg, don't hurt infinite loops! |
| 391 | // If our successor has PHI nodes, then we need to update them to |
| 392 | // include entries for BB's predecessors, not for BB itself. |
| 393 | // Be careful though, if this transformation fails (returns true) then |
| 394 | // we cannot do this transformation! |
| 395 | // |
Misha Brukman | a3bbcb5 | 2002-10-29 23:06:16 +0000 | [diff] [blame] | 396 | if (!PropagatePredecessorsForPHIs(BB, Succ)) { |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 397 | //cerr << "Killing Trivial BB: \n" << BB; |
Chris Lattner | 1896150 | 2002-06-25 16:12:52 +0000 | [diff] [blame] | 398 | std::string OldName = BB->getName(); |
| 399 | |
Chris Lattner | 3a43837 | 2003-03-07 18:13:41 +0000 | [diff] [blame] | 400 | std::vector<BasicBlock*> |
| 401 | OldSuccPreds(pred_begin(Succ), pred_end(Succ)); |
| 402 | |
Chris Lattner | 46a5f1f | 2003-03-05 21:36:33 +0000 | [diff] [blame] | 403 | // Move all PHI nodes in BB to Succ if they are alive, otherwise |
| 404 | // delete them. |
| 405 | while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) |
| 406 | if (PN->use_empty()) |
| 407 | BB->getInstList().erase(BB->begin()); // Nuke instruction... |
| 408 | else { |
| 409 | // The instruction is alive, so this means that Succ must have |
| 410 | // *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] | 411 | // now. Simply move it into Succ, because we know that BB |
| 412 | // strictly dominated Succ. |
Chris Lattner | 46a5f1f | 2003-03-05 21:36:33 +0000 | [diff] [blame] | 413 | BB->getInstList().remove(BB->begin()); |
| 414 | Succ->getInstList().push_front(PN); |
Chris Lattner | 3a43837 | 2003-03-07 18:13:41 +0000 | [diff] [blame] | 415 | |
| 416 | // We need to add new entries for the PHI node to account for |
| 417 | // predecessors of Succ that the PHI node does not take into |
| 418 | // account. At this point, since we know that BB dominated succ, |
| 419 | // this means that we should any newly added incoming edges should |
| 420 | // use the PHI node as the value for these edges, because they are |
| 421 | // loop back edges. |
| 422 | |
| 423 | for (unsigned i = 0, e = OldSuccPreds.size(); i != e; ++i) |
| 424 | if (OldSuccPreds[i] != BB) |
| 425 | PN->addIncoming(PN, OldSuccPreds[i]); |
Chris Lattner | 46a5f1f | 2003-03-05 21:36:33 +0000 | [diff] [blame] | 426 | } |
| 427 | |
Chris Lattner | 3a43837 | 2003-03-07 18:13:41 +0000 | [diff] [blame] | 428 | // Everything that jumped to BB now goes to Succ... |
| 429 | BB->replaceAllUsesWith(Succ); |
| 430 | |
Chris Lattner | 1896150 | 2002-06-25 16:12:52 +0000 | [diff] [blame] | 431 | // Delete the old basic block... |
| 432 | M->getBasicBlockList().erase(BB); |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 433 | |
Chris Lattner | 1896150 | 2002-06-25 16:12:52 +0000 | [diff] [blame] | 434 | if (!OldName.empty() && !Succ->hasName()) // Transfer name if we can |
| 435 | Succ->setName(OldName); |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 436 | |
| 437 | //cerr << "Function after removal: \n" << M; |
| 438 | return true; |
| 439 | } |
| 440 | } |
| 441 | } |
| 442 | } |
| 443 | |
Chris Lattner | 19831ec | 2004-02-16 06:35:48 +0000 | [diff] [blame] | 444 | // If this is a returning block with only PHI nodes in it, fold the return |
| 445 | // instruction into any unconditional branch predecessors. |
| 446 | if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) { |
| 447 | BasicBlock::iterator BBI = BB->getTerminator(); |
| 448 | if (BBI == BB->begin() || isa<PHINode>(--BBI)) { |
| 449 | // Find predecessors that end with unconditional branches. |
| 450 | std::vector<BasicBlock*> UncondBranchPreds; |
| 451 | for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) { |
| 452 | TerminatorInst *PTI = (*PI)->getTerminator(); |
| 453 | if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) |
| 454 | if (BI->isUnconditional()) |
| 455 | UncondBranchPreds.push_back(*PI); |
| 456 | } |
| 457 | |
| 458 | // If we found some, do the transformation! |
| 459 | if (!UncondBranchPreds.empty()) { |
| 460 | while (!UncondBranchPreds.empty()) { |
| 461 | BasicBlock *Pred = UncondBranchPreds.back(); |
| 462 | UncondBranchPreds.pop_back(); |
| 463 | Instruction *UncondBranch = Pred->getTerminator(); |
| 464 | // Clone the return and add it to the end of the predecessor. |
| 465 | Instruction *NewRet = RI->clone(); |
| 466 | Pred->getInstList().push_back(NewRet); |
| 467 | |
| 468 | // If the return instruction returns a value, and if the value was a |
| 469 | // PHI node in "BB", propagate the right value into the return. |
| 470 | if (NewRet->getNumOperands() == 1) |
| 471 | if (PHINode *PN = dyn_cast<PHINode>(NewRet->getOperand(0))) |
| 472 | if (PN->getParent() == BB) |
| 473 | NewRet->setOperand(0, PN->getIncomingValueForBlock(Pred)); |
| 474 | // Update any PHI nodes in the returning block to realize that we no |
| 475 | // longer branch to them. |
| 476 | BB->removePredecessor(Pred); |
| 477 | Pred->getInstList().erase(UncondBranch); |
| 478 | } |
| 479 | |
| 480 | // If we eliminated all predecessors of the block, delete the block now. |
| 481 | if (pred_begin(BB) == pred_end(BB)) |
| 482 | // We know there are no successors, so just nuke the block. |
| 483 | M->getBasicBlockList().erase(BB); |
| 484 | |
Chris Lattner | 19831ec | 2004-02-16 06:35:48 +0000 | [diff] [blame] | 485 | return true; |
| 486 | } |
| 487 | } |
Chris Lattner | e14ea08 | 2004-02-24 05:54:22 +0000 | [diff] [blame] | 488 | } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->begin())) { |
| 489 | // Check to see if the first instruction in this block is just an unwind. |
| 490 | // If so, replace any invoke instructions which use this as an exception |
| 491 | // destination with call instructions. |
| 492 | // |
| 493 | std::vector<BasicBlock*> Preds(pred_begin(BB), pred_end(BB)); |
| 494 | while (!Preds.empty()) { |
| 495 | BasicBlock *Pred = Preds.back(); |
| 496 | if (InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator())) |
| 497 | if (II->getUnwindDest() == BB) { |
| 498 | // Insert a new branch instruction before the invoke, because this |
| 499 | // is now a fall through... |
| 500 | BranchInst *BI = new BranchInst(II->getNormalDest(), II); |
| 501 | Pred->getInstList().remove(II); // Take out of symbol table |
| 502 | |
| 503 | // Insert the call now... |
| 504 | std::vector<Value*> Args(II->op_begin()+3, II->op_end()); |
| 505 | CallInst *CI = new CallInst(II->getCalledValue(), Args, |
| 506 | II->getName(), BI); |
| 507 | // If the invoke produced a value, the Call now does instead |
| 508 | II->replaceAllUsesWith(CI); |
| 509 | delete II; |
| 510 | Changed = true; |
| 511 | } |
| 512 | |
| 513 | Preds.pop_back(); |
| 514 | } |
Chris Lattner | d52c261 | 2004-02-24 07:23:58 +0000 | [diff] [blame] | 515 | } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->begin())) { |
| 516 | // If the only instruction in this block is a switch instruction, see if we |
| 517 | // can fold the switch instruction into a switch in a predecessor block. |
| 518 | std::vector<BasicBlock*> Preds(pred_begin(BB), pred_end(BB)); |
| 519 | while (!Preds.empty()) { |
| 520 | BasicBlock *Pred = Preds.back(); |
| 521 | Preds.pop_back(); |
| 522 | |
| 523 | // If the two blocks are switching on the same value, we can merge this |
| 524 | // switch into the predecessor's switch. |
| 525 | if (SwitchInst *PSI = dyn_cast<SwitchInst>(Pred->getTerminator())) |
| 526 | if (PSI->getCondition() == SI->getCondition() && |
| 527 | SafeToMergeTerminators(SI, PSI)) { |
| 528 | // Figure out which 'cases' to copy from SI to PSI. |
| 529 | std::vector<std::pair<Constant*, BasicBlock*> > Cases; |
| 530 | BasicBlock *NewDefault = 0; |
| 531 | if (PSI->getDefaultDest() == BB) { |
| 532 | // If this is the default destination from PSI, only the edges in SI |
| 533 | // that don't occur in PSI, or that branch to BB will be activated. |
| 534 | std::set<Constant*> PSIHandled; |
| 535 | for (unsigned i = 1, e = PSI->getNumSuccessors(); i != e; ++i) |
| 536 | if (PSI->getSuccessor(i) != BB) |
| 537 | PSIHandled.insert(PSI->getCaseValue(i)); |
| 538 | else { |
| 539 | // This entry will be replaced. |
| 540 | PSI->removeCase(i); |
| 541 | --i; --e; |
| 542 | } |
| 543 | |
| 544 | NewDefault = SI->getDefaultDest(); |
| 545 | for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) { |
| 546 | Constant *C = SI->getCaseValue(i); |
| 547 | if (!PSIHandled.count(C)) |
| 548 | Cases.push_back(std::make_pair(C, SI->getSuccessor(i))); |
| 549 | } |
| 550 | |
| 551 | } else { |
| 552 | // If this is not the default destination from PSI, only the edges |
| 553 | // in SI that occur in PSI with a destination of BB will be |
| 554 | // activated. |
| 555 | std::set<Constant*> PSIHandled; |
| 556 | for (unsigned i = 1, e = PSI->getNumSuccessors(); i != e; ++i) |
| 557 | if (PSI->getSuccessor(i) == BB) { |
| 558 | // We know that BB doesn't have any PHI nodes in it, so just |
| 559 | // drop the edges. |
| 560 | PSIHandled.insert(PSI->getCaseValue(i)); |
| 561 | PSI->removeCase(i); |
| 562 | --i; --e; |
| 563 | } |
| 564 | |
| 565 | // Okay, now we know which constants were sent to BB from the |
| 566 | // predecessor. Figure out where they will all go now. |
| 567 | for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) { |
| 568 | Constant *C = SI->getCaseValue(i); |
| 569 | if (PSIHandled.count(C)) { |
| 570 | // If this is one we are capable of getting... |
| 571 | Cases.push_back(std::make_pair(C, SI->getSuccessor(i))); |
| 572 | PSIHandled.erase(C); // This constant is taken care of |
| 573 | } |
| 574 | } |
| 575 | |
| 576 | // If there are any constants vectored to BB that SI doesn't handle, |
| 577 | // they must go to the default destination of SI. |
| 578 | for (std::set<Constant*>::iterator I = PSIHandled.begin(), |
| 579 | E = PSIHandled.end(); I != E; ++I) |
| 580 | Cases.push_back(std::make_pair(*I, SI->getDefaultDest())); |
| 581 | } |
| 582 | |
| 583 | // Okay, at this point, we know which cases need to be added to the |
| 584 | // PSI switch and which destinations they go to. If PSI needs its |
| 585 | // default destination changed, NewDefault is set. Start changing |
| 586 | // stuff now. |
| 587 | if (NewDefault) { |
| 588 | AddPredecessorToBlock(NewDefault, Pred, BB); |
| 589 | PSI->setSuccessor(0, NewDefault); |
| 590 | } |
| 591 | |
| 592 | // Okay, add all of the cases now. |
| 593 | for (unsigned i = 0, e = Cases.size(); i != e; ++i) { |
| 594 | AddPredecessorToBlock(Cases[i].second, Pred, BB); |
| 595 | PSI->addCase(Cases[i].first, Cases[i].second); |
| 596 | } |
| 597 | |
| 598 | // Okay, last check. If BB is still a successor of PSI, then we must |
| 599 | // have an infinite loop case. If so, add an infinitely looping block |
| 600 | // to handle the case to preserve the behavior of the code. |
| 601 | BasicBlock *InfLoopBlock = 0; |
| 602 | for (unsigned i = 0, e = PSI->getNumSuccessors(); i != e; ++i) |
| 603 | if (PSI->getSuccessor(i) == BB) { |
| 604 | if (InfLoopBlock == 0) { |
| 605 | // Insert it at the end of the loop, because it's either code, |
| 606 | // or it won't matter if it's hot. :) |
| 607 | InfLoopBlock = new BasicBlock("infloop", BB->getParent()); |
| 608 | new BranchInst(InfLoopBlock, InfLoopBlock); |
| 609 | } |
| 610 | PSI->setSuccessor(i, InfLoopBlock); |
| 611 | } |
| 612 | |
| 613 | Changed = true; |
| 614 | } |
| 615 | } |
| 616 | |
| 617 | // If we removed all predecessors of this block, recursively call |
| 618 | // SimplifyCFG to remove it. |
| 619 | if (pred_begin(BB) == pred_end(BB)) |
| 620 | return SimplifyCFG(BB); |
Chris Lattner | 19831ec | 2004-02-16 06:35:48 +0000 | [diff] [blame] | 621 | } |
| 622 | |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 623 | // Merge basic blocks into their predecessor if there is only one distinct |
| 624 | // pred, and if there is only one distinct successor of the predecessor, and |
| 625 | // if there are no PHI nodes. |
| 626 | // |
Chris Lattner | 2355f94 | 2004-02-11 01:17:07 +0000 | [diff] [blame] | 627 | pred_iterator PI(pred_begin(BB)), PE(pred_end(BB)); |
| 628 | BasicBlock *OnlyPred = *PI++; |
| 629 | for (; PI != PE; ++PI) // Search all predecessors, see if they are all same |
| 630 | if (*PI != OnlyPred) { |
| 631 | OnlyPred = 0; // There are multiple different predecessors... |
| 632 | break; |
| 633 | } |
| 634 | |
| 635 | BasicBlock *OnlySucc = 0; |
| 636 | if (OnlyPred && OnlyPred != BB && // Don't break self loops |
| 637 | OnlyPred->getTerminator()->getOpcode() != Instruction::Invoke) { |
| 638 | // Check to see if there is only one distinct successor... |
| 639 | succ_iterator SI(succ_begin(OnlyPred)), SE(succ_end(OnlyPred)); |
| 640 | OnlySucc = BB; |
| 641 | for (; SI != SE; ++SI) |
| 642 | if (*SI != OnlySucc) { |
| 643 | OnlySucc = 0; // There are multiple distinct successors! |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 644 | break; |
| 645 | } |
Chris Lattner | 2355f94 | 2004-02-11 01:17:07 +0000 | [diff] [blame] | 646 | } |
| 647 | |
| 648 | if (OnlySucc) { |
| 649 | //cerr << "Merging: " << BB << "into: " << OnlyPred; |
| 650 | TerminatorInst *Term = OnlyPred->getTerminator(); |
| 651 | |
| 652 | // Resolve any PHI nodes at the start of the block. They are all |
| 653 | // guaranteed to have exactly one entry if they exist, unless there are |
| 654 | // multiple duplicate (but guaranteed to be equal) entries for the |
| 655 | // incoming edges. This occurs when there are multiple edges from |
| 656 | // OnlyPred to OnlySucc. |
| 657 | // |
| 658 | while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) { |
| 659 | PN->replaceAllUsesWith(PN->getIncomingValue(0)); |
| 660 | BB->getInstList().pop_front(); // Delete the phi node... |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 661 | } |
| 662 | |
Chris Lattner | 2355f94 | 2004-02-11 01:17:07 +0000 | [diff] [blame] | 663 | // Delete the unconditional branch from the predecessor... |
| 664 | OnlyPred->getInstList().pop_back(); |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 665 | |
Chris Lattner | 2355f94 | 2004-02-11 01:17:07 +0000 | [diff] [blame] | 666 | // Move all definitions in the successor to the predecessor... |
| 667 | OnlyPred->getInstList().splice(OnlyPred->end(), BB->getInstList()); |
Chris Lattner | 1896150 | 2002-06-25 16:12:52 +0000 | [diff] [blame] | 668 | |
Chris Lattner | 2355f94 | 2004-02-11 01:17:07 +0000 | [diff] [blame] | 669 | // Make all PHI nodes that referred to BB now refer to Pred as their |
| 670 | // source... |
| 671 | BB->replaceAllUsesWith(OnlyPred); |
Chris Lattner | 1896150 | 2002-06-25 16:12:52 +0000 | [diff] [blame] | 672 | |
Chris Lattner | 2355f94 | 2004-02-11 01:17:07 +0000 | [diff] [blame] | 673 | std::string OldName = BB->getName(); |
Chris Lattner | 1896150 | 2002-06-25 16:12:52 +0000 | [diff] [blame] | 674 | |
Chris Lattner | 2355f94 | 2004-02-11 01:17:07 +0000 | [diff] [blame] | 675 | // Erase basic block from the function... |
| 676 | M->getBasicBlockList().erase(BB); |
Chris Lattner | 1896150 | 2002-06-25 16:12:52 +0000 | [diff] [blame] | 677 | |
Chris Lattner | 2355f94 | 2004-02-11 01:17:07 +0000 | [diff] [blame] | 678 | // Inherit predecessors name if it exists... |
| 679 | if (!OldName.empty() && !OnlyPred->hasName()) |
| 680 | OnlyPred->setName(OldName); |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 681 | |
Chris Lattner | 2355f94 | 2004-02-11 01:17:07 +0000 | [diff] [blame] | 682 | return true; |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 683 | } |
Chris Lattner | 723c66d | 2004-02-11 03:36:04 +0000 | [diff] [blame] | 684 | |
Chris Lattner | 0d56008 | 2004-02-24 05:38:11 +0000 | [diff] [blame] | 685 | for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) |
| 686 | if (BranchInst *BI = dyn_cast<BranchInst>((*PI)->getTerminator())) |
| 687 | // Change br (X == 0 | X == 1), T, F into a switch instruction. |
| 688 | if (BI->isConditional() && isa<Instruction>(BI->getCondition())) { |
| 689 | Instruction *Cond = cast<Instruction>(BI->getCondition()); |
| 690 | // If this is a bunch of seteq's or'd together, or if it's a bunch of |
| 691 | // 'setne's and'ed together, collect them. |
| 692 | Value *CompVal = 0; |
| 693 | std::vector<Constant*> Values; |
| 694 | bool TrueWhenEqual = GatherValueComparisons(Cond, CompVal, Values); |
| 695 | if (CompVal && CompVal->getType()->isInteger()) { |
| 696 | // There might be duplicate constants in the list, which the switch |
| 697 | // instruction can't handle, remove them now. |
| 698 | std::sort(Values.begin(), Values.end()); |
| 699 | Values.erase(std::unique(Values.begin(), Values.end()), Values.end()); |
| 700 | |
| 701 | // Figure out which block is which destination. |
| 702 | BasicBlock *DefaultBB = BI->getSuccessor(1); |
| 703 | BasicBlock *EdgeBB = BI->getSuccessor(0); |
| 704 | if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB); |
| 705 | |
| 706 | // Create the new switch instruction now. |
| 707 | SwitchInst *New = new SwitchInst(CompVal, DefaultBB, BI); |
| 708 | |
| 709 | // Add all of the 'cases' to the switch instruction. |
| 710 | for (unsigned i = 0, e = Values.size(); i != e; ++i) |
| 711 | New->addCase(Values[i], EdgeBB); |
| 712 | |
| 713 | // We added edges from PI to the EdgeBB. As such, if there were any |
| 714 | // PHI nodes in EdgeBB, they need entries to be added corresponding to |
| 715 | // the number of edges added. |
| 716 | for (BasicBlock::iterator BBI = EdgeBB->begin(); |
| 717 | PHINode *PN = dyn_cast<PHINode>(BBI); ++BBI) { |
| 718 | Value *InVal = PN->getIncomingValueForBlock(*PI); |
| 719 | for (unsigned i = 0, e = Values.size()-1; i != e; ++i) |
| 720 | PN->addIncoming(InVal, *PI); |
| 721 | } |
| 722 | |
| 723 | // Erase the old branch instruction. |
| 724 | (*PI)->getInstList().erase(BI); |
| 725 | |
| 726 | // Erase the potentially condition tree that was used to computed the |
| 727 | // branch condition. |
| 728 | ErasePossiblyDeadInstructionTree(Cond); |
| 729 | return true; |
| 730 | } |
| 731 | } |
| 732 | |
Chris Lattner | 723c66d | 2004-02-11 03:36:04 +0000 | [diff] [blame] | 733 | // If there is a trivial two-entry PHI node in this basic block, and we can |
| 734 | // eliminate it, do so now. |
| 735 | if (PHINode *PN = dyn_cast<PHINode>(BB->begin())) |
| 736 | if (PN->getNumIncomingValues() == 2) { |
| 737 | // Ok, this is a two entry PHI node. Check to see if this is a simple "if |
| 738 | // statement", which has a very simple dominance structure. Basically, we |
| 739 | // are trying to find the condition that is being branched on, which |
| 740 | // subsequently causes this merge to happen. We really want control |
| 741 | // dependence information for this check, but simplifycfg can't keep it up |
| 742 | // to date, and this catches most of the cases we care about anyway. |
| 743 | // |
| 744 | BasicBlock *IfTrue, *IfFalse; |
| 745 | if (Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse)) { |
| 746 | //std::cerr << "FOUND IF CONDITION! " << *IfCond << " T: " |
| 747 | // << IfTrue->getName() << " F: " << IfFalse->getName() << "\n"; |
| 748 | |
| 749 | // Figure out where to insert instructions as necessary. |
| 750 | BasicBlock::iterator AfterPHIIt = BB->begin(); |
| 751 | while (isa<PHINode>(AfterPHIIt)) ++AfterPHIIt; |
| 752 | |
| 753 | BasicBlock::iterator I = BB->begin(); |
| 754 | while (PHINode *PN = dyn_cast<PHINode>(I)) { |
| 755 | ++I; |
| 756 | |
| 757 | // If we can eliminate this PHI by directly computing it based on the |
| 758 | // condition, do so now. We can't eliminate PHI nodes where the |
| 759 | // incoming values are defined in the conditional parts of the branch, |
| 760 | // so check for this. |
| 761 | // |
| 762 | if (DominatesMergePoint(PN->getIncomingValue(0), BB) && |
| 763 | DominatesMergePoint(PN->getIncomingValue(1), BB)) { |
| 764 | Value *TrueVal = |
| 765 | PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse); |
| 766 | Value *FalseVal = |
| 767 | PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue); |
| 768 | |
| 769 | // FIXME: when we have a 'select' statement, we can be completely |
| 770 | // generic and clean here and let the instcombine pass clean up |
| 771 | // after us, by folding the select instructions away when possible. |
| 772 | // |
| 773 | if (TrueVal == FalseVal) { |
| 774 | // Degenerate case... |
| 775 | PN->replaceAllUsesWith(TrueVal); |
| 776 | BB->getInstList().erase(PN); |
| 777 | Changed = true; |
| 778 | } else if (isa<ConstantBool>(TrueVal) && |
| 779 | isa<ConstantBool>(FalseVal)) { |
| 780 | if (TrueVal == ConstantBool::True) { |
| 781 | // The PHI node produces the same thing as the condition. |
| 782 | PN->replaceAllUsesWith(IfCond); |
| 783 | } else { |
| 784 | // The PHI node produces the inverse of the condition. Insert a |
| 785 | // "NOT" instruction, which is really a XOR. |
| 786 | Value *InverseCond = |
| 787 | BinaryOperator::createNot(IfCond, IfCond->getName()+".inv", |
| 788 | AfterPHIIt); |
| 789 | PN->replaceAllUsesWith(InverseCond); |
| 790 | } |
| 791 | BB->getInstList().erase(PN); |
| 792 | Changed = true; |
| 793 | } else if (isa<ConstantInt>(TrueVal) && isa<ConstantInt>(FalseVal)){ |
| 794 | // If this is a PHI of two constant integers, we insert a cast of |
| 795 | // the boolean to the integer type in question, giving us 0 or 1. |
| 796 | // Then we multiply this by the difference of the two constants, |
| 797 | // giving us 0 if false, and the difference if true. We add this |
| 798 | // result to the base constant, giving us our final value. We |
| 799 | // rely on the instruction combiner to eliminate many special |
| 800 | // cases, like turning multiplies into shifts when possible. |
| 801 | std::string Name = PN->getName(); PN->setName(""); |
| 802 | Value *TheCast = new CastInst(IfCond, TrueVal->getType(), |
| 803 | Name, AfterPHIIt); |
| 804 | Constant *TheDiff = ConstantExpr::get(Instruction::Sub, |
| 805 | cast<Constant>(TrueVal), |
| 806 | cast<Constant>(FalseVal)); |
| 807 | Value *V = TheCast; |
| 808 | if (TheDiff != ConstantInt::get(TrueVal->getType(), 1)) |
| 809 | V = BinaryOperator::create(Instruction::Mul, TheCast, |
| 810 | TheDiff, TheCast->getName()+".scale", |
| 811 | AfterPHIIt); |
| 812 | if (!cast<Constant>(FalseVal)->isNullValue()) |
| 813 | V = BinaryOperator::create(Instruction::Add, V, FalseVal, |
| 814 | V->getName()+".offs", AfterPHIIt); |
| 815 | PN->replaceAllUsesWith(V); |
| 816 | BB->getInstList().erase(PN); |
| 817 | Changed = true; |
| 818 | } else if (isa<ConstantInt>(FalseVal) && |
| 819 | cast<Constant>(FalseVal)->isNullValue()) { |
| 820 | // If the false condition is an integral zero value, we can |
| 821 | // compute the PHI by multiplying the condition by the other |
| 822 | // value. |
| 823 | std::string Name = PN->getName(); PN->setName(""); |
| 824 | Value *TheCast = new CastInst(IfCond, TrueVal->getType(), |
| 825 | Name+".c", AfterPHIIt); |
| 826 | Value *V = BinaryOperator::create(Instruction::Mul, TrueVal, |
| 827 | TheCast, Name, AfterPHIIt); |
| 828 | PN->replaceAllUsesWith(V); |
| 829 | BB->getInstList().erase(PN); |
| 830 | Changed = true; |
| 831 | } else if (isa<ConstantInt>(TrueVal) && |
| 832 | cast<Constant>(TrueVal)->isNullValue()) { |
| 833 | // If the true condition is an integral zero value, we can compute |
| 834 | // the PHI by multiplying the inverse condition by the other |
| 835 | // value. |
| 836 | std::string Name = PN->getName(); PN->setName(""); |
| 837 | Value *NotCond = BinaryOperator::createNot(IfCond, Name+".inv", |
| 838 | AfterPHIIt); |
| 839 | Value *TheCast = new CastInst(NotCond, TrueVal->getType(), |
| 840 | Name+".inv", AfterPHIIt); |
| 841 | Value *V = BinaryOperator::create(Instruction::Mul, FalseVal, |
| 842 | TheCast, Name, AfterPHIIt); |
| 843 | PN->replaceAllUsesWith(V); |
| 844 | BB->getInstList().erase(PN); |
| 845 | Changed = true; |
| 846 | } |
| 847 | } |
| 848 | } |
| 849 | } |
| 850 | } |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 851 | |
Chris Lattner | 694e37f | 2003-08-17 19:41:53 +0000 | [diff] [blame] | 852 | return Changed; |
Chris Lattner | 01d1ee3 | 2002-05-21 20:50:24 +0000 | [diff] [blame] | 853 | } |