Chris Lattner | ea54ab9 | 2002-05-07 22:11:39 +0000 | [diff] [blame] | 1 | //===- ADCE.cpp - Code to perform aggressive dead code elimination --------===// |
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 | 02e90d5 | 2001-06-30 06:39:11 +0000 | [diff] [blame] | 9 | // |
Chris Lattner | ea54ab9 | 2002-05-07 22:11:39 +0000 | [diff] [blame] | 10 | // This file implements "aggressive" dead code elimination. ADCE is DCe where |
Chris Lattner | 02e90d5 | 2001-06-30 06:39:11 +0000 | [diff] [blame] | 11 | // values are assumed to be dead until proven otherwise. This is similar to |
| 12 | // SCCP, except applied to the liveness of values. |
| 13 | // |
| 14 | //===----------------------------------------------------------------------===// |
| 15 | |
Chris Lattner | 022103b | 2002-05-07 20:03:00 +0000 | [diff] [blame] | 16 | #include "llvm/Transforms/Scalar.h" |
Chris Lattner | d9036a1 | 2002-05-22 21:32:16 +0000 | [diff] [blame] | 17 | #include "llvm/Constant.h" |
Chris Lattner | ede6ac6 | 2004-04-10 06:53:09 +0000 | [diff] [blame^] | 18 | #include "llvm/Instructions.h" |
| 19 | #include "llvm/Type.h" |
| 20 | #include "llvm/Analysis/AliasAnalysis.h" |
| 21 | #include "llvm/Analysis/PostDominators.h" |
Chris Lattner | 221d688 | 2002-02-12 21:07:25 +0000 | [diff] [blame] | 22 | #include "llvm/Support/CFG.h" |
Chris Lattner | bd1a90e | 2003-12-19 09:08:34 +0000 | [diff] [blame] | 23 | #include "llvm/Transforms/Utils/BasicBlockUtils.h" |
| 24 | #include "llvm/Transforms/Utils/Local.h" |
| 25 | #include "llvm/Transforms/Utils/UnifyFunctionExitNodes.h" |
Chris Lattner | 6806f56 | 2003-08-01 22:15:03 +0000 | [diff] [blame] | 26 | #include "Support/Debug.h" |
Chris Lattner | cee8f9a | 2001-11-27 00:03:19 +0000 | [diff] [blame] | 27 | #include "Support/DepthFirstIterator.h" |
Chris Lattner | a92f696 | 2002-10-01 22:38:41 +0000 | [diff] [blame] | 28 | #include "Support/Statistic.h" |
Chris Lattner | 6806f56 | 2003-08-01 22:15:03 +0000 | [diff] [blame] | 29 | #include "Support/STLExtras.h" |
Chris Lattner | 72f1e99 | 2001-07-08 18:38:36 +0000 | [diff] [blame] | 30 | #include <algorithm> |
Chris Lattner | bd1a90e | 2003-12-19 09:08:34 +0000 | [diff] [blame] | 31 | using namespace llvm; |
Brian Gaeke | d0fde30 | 2003-11-11 22:41:34 +0000 | [diff] [blame] | 32 | |
Chris Lattner | dfe81ab | 2002-05-06 17:27:57 +0000 | [diff] [blame] | 33 | namespace { |
Chris Lattner | a92f696 | 2002-10-01 22:38:41 +0000 | [diff] [blame] | 34 | Statistic<> NumBlockRemoved("adce", "Number of basic blocks removed"); |
| 35 | Statistic<> NumInstRemoved ("adce", "Number of instructions removed"); |
Chris Lattner | ede6ac6 | 2004-04-10 06:53:09 +0000 | [diff] [blame^] | 36 | Statistic<> NumCallRemoved ("adce", "Number of calls and invokes removed"); |
Chris Lattner | dfe81ab | 2002-05-06 17:27:57 +0000 | [diff] [blame] | 37 | |
Chris Lattner | 02e90d5 | 2001-06-30 06:39:11 +0000 | [diff] [blame] | 38 | //===----------------------------------------------------------------------===// |
| 39 | // ADCE Class |
| 40 | // |
Chris Lattner | ea54ab9 | 2002-05-07 22:11:39 +0000 | [diff] [blame] | 41 | // This class does all of the work of Aggressive Dead Code Elimination. |
Chris Lattner | 02e90d5 | 2001-06-30 06:39:11 +0000 | [diff] [blame] | 42 | // It's public interface consists of a constructor and a doADCE() method. |
| 43 | // |
Chris Lattner | dfe81ab | 2002-05-06 17:27:57 +0000 | [diff] [blame] | 44 | class ADCE : public FunctionPass { |
| 45 | Function *Func; // The function that we are working on |
Chris Lattner | ede6ac6 | 2004-04-10 06:53:09 +0000 | [diff] [blame^] | 46 | AliasAnalysis *AA; // Current AliasAnalysis object |
Chris Lattner | 697954c | 2002-01-20 22:54:45 +0000 | [diff] [blame] | 47 | std::vector<Instruction*> WorkList; // Instructions that just became live |
| 48 | std::set<Instruction*> LiveSet; // The set of live instructions |
Chris Lattner | 02e90d5 | 2001-06-30 06:39:11 +0000 | [diff] [blame] | 49 | |
| 50 | //===--------------------------------------------------------------------===// |
| 51 | // The public interface for this class |
| 52 | // |
| 53 | public: |
Chris Lattner | d9036a1 | 2002-05-22 21:32:16 +0000 | [diff] [blame] | 54 | // Execute the Aggressive Dead Code Elimination Algorithm |
Chris Lattner | dfe81ab | 2002-05-06 17:27:57 +0000 | [diff] [blame] | 55 | // |
Chris Lattner | 7e70829 | 2002-06-25 16:13:24 +0000 | [diff] [blame] | 56 | virtual bool runOnFunction(Function &F) { |
| 57 | Func = &F; |
Chris Lattner | ede6ac6 | 2004-04-10 06:53:09 +0000 | [diff] [blame^] | 58 | AA = &getAnalysis<AliasAnalysis>(); |
Chris Lattner | d9036a1 | 2002-05-22 21:32:16 +0000 | [diff] [blame] | 59 | bool Changed = doADCE(); |
Chris Lattner | dfe81ab | 2002-05-06 17:27:57 +0000 | [diff] [blame] | 60 | assert(WorkList.empty()); |
| 61 | LiveSet.clear(); |
Chris Lattner | d9036a1 | 2002-05-22 21:32:16 +0000 | [diff] [blame] | 62 | return Changed; |
Chris Lattner | dfe81ab | 2002-05-06 17:27:57 +0000 | [diff] [blame] | 63 | } |
| 64 | // getAnalysisUsage - We require post dominance frontiers (aka Control |
| 65 | // Dependence Graph) |
| 66 | virtual void getAnalysisUsage(AnalysisUsage &AU) const { |
Chris Lattner | bd1a90e | 2003-12-19 09:08:34 +0000 | [diff] [blame] | 67 | // We require that all function nodes are unified, because otherwise code |
| 68 | // can be marked live that wouldn't necessarily be otherwise. |
| 69 | AU.addRequired<UnifyFunctionExitNodes>(); |
Chris Lattner | ede6ac6 | 2004-04-10 06:53:09 +0000 | [diff] [blame^] | 70 | AU.addRequired<AliasAnalysis>(); |
Chris Lattner | 5f0eb8d | 2002-08-08 19:01:30 +0000 | [diff] [blame] | 71 | AU.addRequired<PostDominatorTree>(); |
| 72 | AU.addRequired<PostDominanceFrontier>(); |
Chris Lattner | dfe81ab | 2002-05-06 17:27:57 +0000 | [diff] [blame] | 73 | } |
Chris Lattner | 02e90d5 | 2001-06-30 06:39:11 +0000 | [diff] [blame] | 74 | |
Chris Lattner | 02e90d5 | 2001-06-30 06:39:11 +0000 | [diff] [blame] | 75 | |
| 76 | //===--------------------------------------------------------------------===// |
| 77 | // The implementation of this class |
| 78 | // |
| 79 | private: |
Chris Lattner | ea54ab9 | 2002-05-07 22:11:39 +0000 | [diff] [blame] | 80 | // doADCE() - Run the Aggressive Dead Code Elimination algorithm, returning |
Chris Lattner | dfe81ab | 2002-05-06 17:27:57 +0000 | [diff] [blame] | 81 | // true if the function was modified. |
| 82 | // |
Chris Lattner | d9036a1 | 2002-05-22 21:32:16 +0000 | [diff] [blame] | 83 | bool doADCE(); |
| 84 | |
| 85 | void markBlockAlive(BasicBlock *BB); |
Chris Lattner | dfe81ab | 2002-05-06 17:27:57 +0000 | [diff] [blame] | 86 | |
Chris Lattner | 446698b | 2002-07-30 00:22:34 +0000 | [diff] [blame] | 87 | |
| 88 | // dropReferencesOfDeadInstructionsInLiveBlock - Loop over all of the |
| 89 | // instructions in the specified basic block, dropping references on |
| 90 | // instructions that are dead according to LiveSet. |
| 91 | bool dropReferencesOfDeadInstructionsInLiveBlock(BasicBlock *BB); |
| 92 | |
Chris Lattner | 837e42c | 2003-06-24 23:02:45 +0000 | [diff] [blame] | 93 | TerminatorInst *convertToUnconditionalBranch(TerminatorInst *TI); |
| 94 | |
Chris Lattner | 02e90d5 | 2001-06-30 06:39:11 +0000 | [diff] [blame] | 95 | inline void markInstructionLive(Instruction *I) { |
| 96 | if (LiveSet.count(I)) return; |
Chris Lattner | de579f1 | 2003-05-22 22:00:07 +0000 | [diff] [blame] | 97 | DEBUG(std::cerr << "Insn Live: " << I); |
Chris Lattner | 02e90d5 | 2001-06-30 06:39:11 +0000 | [diff] [blame] | 98 | LiveSet.insert(I); |
| 99 | WorkList.push_back(I); |
| 100 | } |
| 101 | |
Chris Lattner | 72f1e99 | 2001-07-08 18:38:36 +0000 | [diff] [blame] | 102 | inline void markTerminatorLive(const BasicBlock *BB) { |
Chris Lattner | 545a76c | 2003-09-10 20:38:14 +0000 | [diff] [blame] | 103 | DEBUG(std::cerr << "Terminator Live: " << BB->getTerminator()); |
| 104 | markInstructionLive(const_cast<TerminatorInst*>(BB->getTerminator())); |
Chris Lattner | 72f1e99 | 2001-07-08 18:38:36 +0000 | [diff] [blame] | 105 | } |
Chris Lattner | 02e90d5 | 2001-06-30 06:39:11 +0000 | [diff] [blame] | 106 | }; |
| 107 | |
Chris Lattner | a6275cc | 2002-07-26 21:12:46 +0000 | [diff] [blame] | 108 | RegisterOpt<ADCE> X("adce", "Aggressive Dead Code Elimination"); |
Chris Lattner | dfe81ab | 2002-05-06 17:27:57 +0000 | [diff] [blame] | 109 | } // End of anonymous namespace |
| 110 | |
Chris Lattner | bd1a90e | 2003-12-19 09:08:34 +0000 | [diff] [blame] | 111 | Pass *llvm::createAggressiveDCEPass() { return new ADCE(); } |
Chris Lattner | d9036a1 | 2002-05-22 21:32:16 +0000 | [diff] [blame] | 112 | |
Chris Lattner | d9036a1 | 2002-05-22 21:32:16 +0000 | [diff] [blame] | 113 | void ADCE::markBlockAlive(BasicBlock *BB) { |
| 114 | // Mark the basic block as being newly ALIVE... and mark all branches that |
Misha Brukman | ef6a6a6 | 2003-08-21 22:14:26 +0000 | [diff] [blame] | 115 | // this block is control dependent on as being alive also... |
Chris Lattner | d9036a1 | 2002-05-22 21:32:16 +0000 | [diff] [blame] | 116 | // |
Chris Lattner | ce6ef11 | 2002-07-26 18:40:14 +0000 | [diff] [blame] | 117 | PostDominanceFrontier &CDG = getAnalysis<PostDominanceFrontier>(); |
Chris Lattner | d9036a1 | 2002-05-22 21:32:16 +0000 | [diff] [blame] | 118 | |
Chris Lattner | ce6ef11 | 2002-07-26 18:40:14 +0000 | [diff] [blame] | 119 | PostDominanceFrontier::const_iterator It = CDG.find(BB); |
Chris Lattner | d9036a1 | 2002-05-22 21:32:16 +0000 | [diff] [blame] | 120 | if (It != CDG.end()) { |
Misha Brukman | ef6a6a6 | 2003-08-21 22:14:26 +0000 | [diff] [blame] | 121 | // Get the blocks that this node is control dependent on... |
Chris Lattner | ce6ef11 | 2002-07-26 18:40:14 +0000 | [diff] [blame] | 122 | const PostDominanceFrontier::DomSetType &CDB = It->second; |
Chris Lattner | d9036a1 | 2002-05-22 21:32:16 +0000 | [diff] [blame] | 123 | for_each(CDB.begin(), CDB.end(), // Mark all their terminators as live |
| 124 | bind_obj(this, &ADCE::markTerminatorLive)); |
| 125 | } |
| 126 | |
Chris Lattner | 99c91e0 | 2003-06-24 21:49:45 +0000 | [diff] [blame] | 127 | // If this basic block is live, and it ends in an unconditional branch, then |
| 128 | // the branch is alive as well... |
| 129 | if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) |
| 130 | if (BI->isUnconditional()) |
| 131 | markTerminatorLive(BB); |
Chris Lattner | dfe81ab | 2002-05-06 17:27:57 +0000 | [diff] [blame] | 132 | } |
Chris Lattner | 02e90d5 | 2001-06-30 06:39:11 +0000 | [diff] [blame] | 133 | |
Chris Lattner | 446698b | 2002-07-30 00:22:34 +0000 | [diff] [blame] | 134 | // dropReferencesOfDeadInstructionsInLiveBlock - Loop over all of the |
| 135 | // instructions in the specified basic block, dropping references on |
| 136 | // instructions that are dead according to LiveSet. |
| 137 | bool ADCE::dropReferencesOfDeadInstructionsInLiveBlock(BasicBlock *BB) { |
| 138 | bool Changed = false; |
| 139 | for (BasicBlock::iterator I = BB->begin(), E = --BB->end(); I != E; ) |
| 140 | if (!LiveSet.count(I)) { // Is this instruction alive? |
| 141 | I->dropAllReferences(); // Nope, drop references... |
Chris Lattner | e408e25 | 2003-04-23 16:37:45 +0000 | [diff] [blame] | 142 | if (PHINode *PN = dyn_cast<PHINode>(I)) { |
Chris Lattner | 446698b | 2002-07-30 00:22:34 +0000 | [diff] [blame] | 143 | // We don't want to leave PHI nodes in the program that have |
| 144 | // #arguments != #predecessors, so we remove them now. |
| 145 | // |
| 146 | PN->replaceAllUsesWith(Constant::getNullValue(PN->getType())); |
| 147 | |
| 148 | // Delete the instruction... |
| 149 | I = BB->getInstList().erase(I); |
| 150 | Changed = true; |
Chris Lattner | e400a09 | 2004-02-01 05:15:07 +0000 | [diff] [blame] | 151 | ++NumInstRemoved; |
Chris Lattner | 446698b | 2002-07-30 00:22:34 +0000 | [diff] [blame] | 152 | } else { |
| 153 | ++I; |
| 154 | } |
| 155 | } else { |
| 156 | ++I; |
| 157 | } |
| 158 | return Changed; |
| 159 | } |
| 160 | |
Chris Lattner | 02e90d5 | 2001-06-30 06:39:11 +0000 | [diff] [blame] | 161 | |
Chris Lattner | 837e42c | 2003-06-24 23:02:45 +0000 | [diff] [blame] | 162 | /// convertToUnconditionalBranch - Transform this conditional terminator |
| 163 | /// instruction into an unconditional branch because we don't care which of the |
| 164 | /// successors it goes to. This eliminate a use of the condition as well. |
| 165 | /// |
| 166 | TerminatorInst *ADCE::convertToUnconditionalBranch(TerminatorInst *TI) { |
| 167 | BranchInst *NB = new BranchInst(TI->getSuccessor(0), TI); |
| 168 | BasicBlock *BB = TI->getParent(); |
| 169 | |
| 170 | // Remove entries from PHI nodes to avoid confusing ourself later... |
| 171 | for (unsigned i = 1, e = TI->getNumSuccessors(); i != e; ++i) |
| 172 | TI->getSuccessor(i)->removePredecessor(BB); |
| 173 | |
| 174 | // Delete the old branch itself... |
| 175 | BB->getInstList().erase(TI); |
| 176 | return NB; |
| 177 | } |
| 178 | |
| 179 | |
Chris Lattner | ea54ab9 | 2002-05-07 22:11:39 +0000 | [diff] [blame] | 180 | // doADCE() - Run the Aggressive Dead Code Elimination algorithm, returning |
Chris Lattner | f57b845 | 2002-04-27 06:56:12 +0000 | [diff] [blame] | 181 | // true if the function was modified. |
Chris Lattner | 02e90d5 | 2001-06-30 06:39:11 +0000 | [diff] [blame] | 182 | // |
Chris Lattner | d9036a1 | 2002-05-22 21:32:16 +0000 | [diff] [blame] | 183 | bool ADCE::doADCE() { |
| 184 | bool MadeChanges = false; |
Chris Lattner | b8259dd | 2001-09-09 22:26:47 +0000 | [diff] [blame] | 185 | |
Chris Lattner | f57b845 | 2002-04-27 06:56:12 +0000 | [diff] [blame] | 186 | // Iterate over all of the instructions in the function, eliminating trivially |
Chris Lattner | b8259dd | 2001-09-09 22:26:47 +0000 | [diff] [blame] | 187 | // dead instructions, and marking instructions live that are known to be |
| 188 | // needed. Perform the walk in depth first order so that we avoid marking any |
| 189 | // instructions live in basic blocks that are unreachable. These blocks will |
| 190 | // be eliminated later, along with the instructions inside. |
| 191 | // |
Chris Lattner | dfe81ab | 2002-05-06 17:27:57 +0000 | [diff] [blame] | 192 | for (df_iterator<Function*> BBI = df_begin(Func), BBE = df_end(Func); |
Chris Lattner | b8259dd | 2001-09-09 22:26:47 +0000 | [diff] [blame] | 193 | BBI != BBE; ++BBI) { |
| 194 | BasicBlock *BB = *BBI; |
| 195 | for (BasicBlock::iterator II = BB->begin(), EI = BB->end(); II != EI; ) { |
Chris Lattner | ede6ac6 | 2004-04-10 06:53:09 +0000 | [diff] [blame^] | 196 | Instruction *I = II++; |
| 197 | if (CallInst *CI = dyn_cast<CallInst>(I)) { |
| 198 | Function *F = CI->getCalledFunction(); |
| 199 | if (F && AA->onlyReadsMemory(F)) { |
| 200 | if (CI->use_empty()) { |
| 201 | BB->getInstList().erase(CI); |
| 202 | ++NumCallRemoved; |
| 203 | } |
| 204 | } else { |
| 205 | markInstructionLive(I); |
| 206 | } |
| 207 | } else if (InvokeInst *II = dyn_cast<InvokeInst>(I)) { |
| 208 | Function *F = II->getCalledFunction(); |
| 209 | if (F && AA->onlyReadsMemory(F)) { |
| 210 | // The function cannot unwind. Convert it to a call with a branch |
| 211 | // after it to the normal destination. |
| 212 | std::vector<Value*> Args(II->op_begin()+1, II->op_end()); |
| 213 | std::string Name = II->getName(); II->setName(""); |
| 214 | Instruction *NewCall = new CallInst(F, Args, Name, II); |
| 215 | II->replaceAllUsesWith(NewCall); |
| 216 | new BranchInst(II->getNormalDest(), II); |
| 217 | BB->getInstList().erase(II); |
| 218 | |
| 219 | if (NewCall->use_empty()) { |
| 220 | BB->getInstList().erase(NewCall); |
| 221 | ++NumCallRemoved; |
| 222 | } |
| 223 | } else { |
| 224 | markInstructionLive(I); |
| 225 | } |
| 226 | } else if (I->mayWriteToMemory() || isa<ReturnInst>(I) || |
| 227 | isa<UnwindInst>(I)) { |
| 228 | markInstructionLive(I); |
| 229 | } else if (isInstructionTriviallyDead(I)) { |
Chris Lattner | ea54ab9 | 2002-05-07 22:11:39 +0000 | [diff] [blame] | 230 | // Remove the instruction from it's basic block... |
Chris Lattner | ede6ac6 | 2004-04-10 06:53:09 +0000 | [diff] [blame^] | 231 | BB->getInstList().erase(I); |
Chris Lattner | d9036a1 | 2002-05-22 21:32:16 +0000 | [diff] [blame] | 232 | ++NumInstRemoved; |
Chris Lattner | b8259dd | 2001-09-09 22:26:47 +0000 | [diff] [blame] | 233 | } |
Chris Lattner | b8259dd | 2001-09-09 22:26:47 +0000 | [diff] [blame] | 234 | } |
| 235 | } |
| 236 | |
Chris Lattner | 34e353e | 2003-06-16 12:10:45 +0000 | [diff] [blame] | 237 | // Check to ensure we have an exit node for this CFG. If we don't, we won't |
| 238 | // have any post-dominance information, thus we cannot perform our |
| 239 | // transformations safely. |
| 240 | // |
| 241 | PostDominatorTree &DT = getAnalysis<PostDominatorTree>(); |
Chris Lattner | 02a3be0 | 2003-09-20 14:39:18 +0000 | [diff] [blame] | 242 | if (DT[&Func->getEntryBlock()] == 0) { |
Chris Lattner | 34e353e | 2003-06-16 12:10:45 +0000 | [diff] [blame] | 243 | WorkList.clear(); |
| 244 | return MadeChanges; |
| 245 | } |
| 246 | |
Chris Lattner | faa45ce | 2003-11-16 21:39:27 +0000 | [diff] [blame] | 247 | // Scan the function marking blocks without post-dominance information as |
| 248 | // live. Blocks without post-dominance information occur when there is an |
| 249 | // infinite loop in the program. Because the infinite loop could contain a |
| 250 | // function which unwinds, exits or has side-effects, we don't want to delete |
| 251 | // the infinite loop or those blocks leading up to it. |
| 252 | for (Function::iterator I = Func->begin(), E = Func->end(); I != E; ++I) |
| 253 | if (DT[I] == 0) |
| 254 | for (pred_iterator PI = pred_begin(I), E = pred_end(I); PI != E; ++PI) |
| 255 | markInstructionLive((*PI)->getTerminator()); |
| 256 | |
| 257 | |
| 258 | |
Chris Lattner | de579f1 | 2003-05-22 22:00:07 +0000 | [diff] [blame] | 259 | DEBUG(std::cerr << "Processing work list\n"); |
Chris Lattner | 02e90d5 | 2001-06-30 06:39:11 +0000 | [diff] [blame] | 260 | |
Chris Lattner | 72f1e99 | 2001-07-08 18:38:36 +0000 | [diff] [blame] | 261 | // AliveBlocks - Set of basic blocks that we know have instructions that are |
| 262 | // alive in them... |
| 263 | // |
Chris Lattner | 697954c | 2002-01-20 22:54:45 +0000 | [diff] [blame] | 264 | std::set<BasicBlock*> AliveBlocks; |
Chris Lattner | 72f1e99 | 2001-07-08 18:38:36 +0000 | [diff] [blame] | 265 | |
Chris Lattner | 02e90d5 | 2001-06-30 06:39:11 +0000 | [diff] [blame] | 266 | // Process the work list of instructions that just became live... if they |
Misha Brukman | 5560c9d | 2003-08-18 14:43:39 +0000 | [diff] [blame] | 267 | // became live, then that means that all of their operands are necessary as |
Chris Lattner | 02e90d5 | 2001-06-30 06:39:11 +0000 | [diff] [blame] | 268 | // well... make them live as well. |
| 269 | // |
| 270 | while (!WorkList.empty()) { |
Chris Lattner | 72f1e99 | 2001-07-08 18:38:36 +0000 | [diff] [blame] | 271 | Instruction *I = WorkList.back(); // Get an instruction that became live... |
Chris Lattner | 02e90d5 | 2001-06-30 06:39:11 +0000 | [diff] [blame] | 272 | WorkList.pop_back(); |
| 273 | |
Chris Lattner | 72f1e99 | 2001-07-08 18:38:36 +0000 | [diff] [blame] | 274 | BasicBlock *BB = I->getParent(); |
Chris Lattner | d9036a1 | 2002-05-22 21:32:16 +0000 | [diff] [blame] | 275 | if (!AliveBlocks.count(BB)) { // Basic block not alive yet... |
| 276 | AliveBlocks.insert(BB); // Block is now ALIVE! |
| 277 | markBlockAlive(BB); // Make it so now! |
Chris Lattner | 72f1e99 | 2001-07-08 18:38:36 +0000 | [diff] [blame] | 278 | } |
| 279 | |
Chris Lattner | d9036a1 | 2002-05-22 21:32:16 +0000 | [diff] [blame] | 280 | // PHI nodes are a special case, because the incoming values are actually |
| 281 | // defined in the predecessor nodes of this block, meaning that the PHI |
| 282 | // makes the predecessors alive. |
| 283 | // |
| 284 | if (PHINode *PN = dyn_cast<PHINode>(I)) |
| 285 | for (pred_iterator PI = pred_begin(BB), PE = pred_end(BB); PI != PE; ++PI) |
| 286 | if (!AliveBlocks.count(*PI)) { |
| 287 | AliveBlocks.insert(BB); // Block is now ALIVE! |
| 288 | markBlockAlive(*PI); |
| 289 | } |
| 290 | |
Chris Lattner | b8259dd | 2001-09-09 22:26:47 +0000 | [diff] [blame] | 291 | // Loop over all of the operands of the live instruction, making sure that |
| 292 | // they are known to be alive as well... |
| 293 | // |
Chris Lattner | ea54ab9 | 2002-05-07 22:11:39 +0000 | [diff] [blame] | 294 | for (unsigned op = 0, End = I->getNumOperands(); op != End; ++op) |
Chris Lattner | 9636a91 | 2001-10-01 16:18:37 +0000 | [diff] [blame] | 295 | if (Instruction *Operand = dyn_cast<Instruction>(I->getOperand(op))) |
Chris Lattner | b8259dd | 2001-09-09 22:26:47 +0000 | [diff] [blame] | 296 | markInstructionLive(Operand); |
Chris Lattner | 02e90d5 | 2001-06-30 06:39:11 +0000 | [diff] [blame] | 297 | } |
| 298 | |
Chris Lattner | de579f1 | 2003-05-22 22:00:07 +0000 | [diff] [blame] | 299 | DEBUG( |
| 300 | std::cerr << "Current Function: X = Live\n"; |
Chris Lattner | 34e353e | 2003-06-16 12:10:45 +0000 | [diff] [blame] | 301 | for (Function::iterator I = Func->begin(), E = Func->end(); I != E; ++I){ |
| 302 | std::cerr << I->getName() << ":\t" |
| 303 | << (AliveBlocks.count(I) ? "LIVE\n" : "DEAD\n"); |
Chris Lattner | 7e70829 | 2002-06-25 16:13:24 +0000 | [diff] [blame] | 304 | for (BasicBlock::iterator BI = I->begin(), BE = I->end(); BI != BE; ++BI){ |
Chris Lattner | de579f1 | 2003-05-22 22:00:07 +0000 | [diff] [blame] | 305 | if (LiveSet.count(BI)) std::cerr << "X "; |
| 306 | std::cerr << *BI; |
Chris Lattner | f016ea4 | 2002-05-22 17:17:27 +0000 | [diff] [blame] | 307 | } |
Chris Lattner | 34e353e | 2003-06-16 12:10:45 +0000 | [diff] [blame] | 308 | }); |
Chris Lattner | b8259dd | 2001-09-09 22:26:47 +0000 | [diff] [blame] | 309 | |
Chris Lattner | d9036a1 | 2002-05-22 21:32:16 +0000 | [diff] [blame] | 310 | // Find the first postdominator of the entry node that is alive. Make it the |
| 311 | // new entry node... |
Chris Lattner | 02e90d5 | 2001-06-30 06:39:11 +0000 | [diff] [blame] | 312 | // |
Chris Lattner | 446698b | 2002-07-30 00:22:34 +0000 | [diff] [blame] | 313 | if (AliveBlocks.size() == Func->size()) { // No dead blocks? |
Chris Lattner | 837e42c | 2003-06-24 23:02:45 +0000 | [diff] [blame] | 314 | for (Function::iterator I = Func->begin(), E = Func->end(); I != E; ++I) { |
Chris Lattner | 446698b | 2002-07-30 00:22:34 +0000 | [diff] [blame] | 315 | // Loop over all of the instructions in the function, telling dead |
| 316 | // instructions to drop their references. This is so that the next sweep |
| 317 | // over the program can safely delete dead instructions without other dead |
Misha Brukman | cf00c4a | 2003-10-10 17:57:28 +0000 | [diff] [blame] | 318 | // instructions still referring to them. |
Chris Lattner | 446698b | 2002-07-30 00:22:34 +0000 | [diff] [blame] | 319 | // |
| 320 | dropReferencesOfDeadInstructionsInLiveBlock(I); |
Chris Lattner | 837e42c | 2003-06-24 23:02:45 +0000 | [diff] [blame] | 321 | |
| 322 | // Check to make sure the terminator instruction is live. If it isn't, |
| 323 | // this means that the condition that it branches on (we know it is not an |
| 324 | // unconditional branch), is not needed to make the decision of where to |
| 325 | // go to, because all outgoing edges go to the same place. We must remove |
| 326 | // the use of the condition (because it's probably dead), so we convert |
| 327 | // the terminator to a conditional branch. |
| 328 | // |
| 329 | TerminatorInst *TI = I->getTerminator(); |
| 330 | if (!LiveSet.count(TI)) |
| 331 | convertToUnconditionalBranch(TI); |
| 332 | } |
Chris Lattner | 446698b | 2002-07-30 00:22:34 +0000 | [diff] [blame] | 333 | |
| 334 | } else { // If there are some blocks dead... |
Chris Lattner | db6e4d6 | 2002-08-14 21:35:02 +0000 | [diff] [blame] | 335 | // If the entry node is dead, insert a new entry node to eliminate the entry |
| 336 | // node as a special case. |
| 337 | // |
| 338 | if (!AliveBlocks.count(&Func->front())) { |
| 339 | BasicBlock *NewEntry = new BasicBlock(); |
Chris Lattner | 108e4ab | 2003-11-21 16:52:05 +0000 | [diff] [blame] | 340 | new BranchInst(&Func->front(), NewEntry); |
Chris Lattner | db6e4d6 | 2002-08-14 21:35:02 +0000 | [diff] [blame] | 341 | Func->getBasicBlockList().push_front(NewEntry); |
| 342 | AliveBlocks.insert(NewEntry); // This block is always alive! |
Chris Lattner | 99c91e0 | 2003-06-24 21:49:45 +0000 | [diff] [blame] | 343 | LiveSet.insert(NewEntry->getTerminator()); // The branch is live |
Chris Lattner | db6e4d6 | 2002-08-14 21:35:02 +0000 | [diff] [blame] | 344 | } |
Chris Lattner | d9036a1 | 2002-05-22 21:32:16 +0000 | [diff] [blame] | 345 | |
| 346 | // Loop over all of the alive blocks in the function. If any successor |
| 347 | // blocks are not alive, we adjust the outgoing branches to branch to the |
| 348 | // first live postdominator of the live block, adjusting any PHI nodes in |
| 349 | // the block to reflect this. |
| 350 | // |
| 351 | for (Function::iterator I = Func->begin(), E = Func->end(); I != E; ++I) |
Chris Lattner | 7e70829 | 2002-06-25 16:13:24 +0000 | [diff] [blame] | 352 | if (AliveBlocks.count(I)) { |
| 353 | BasicBlock *BB = I; |
Chris Lattner | d9036a1 | 2002-05-22 21:32:16 +0000 | [diff] [blame] | 354 | TerminatorInst *TI = BB->getTerminator(); |
| 355 | |
Chris Lattner | 99c91e0 | 2003-06-24 21:49:45 +0000 | [diff] [blame] | 356 | // If the terminator instruction is alive, but the block it is contained |
| 357 | // in IS alive, this means that this terminator is a conditional branch |
| 358 | // on a condition that doesn't matter. Make it an unconditional branch |
| 359 | // to ONE of the successors. This has the side effect of dropping a use |
| 360 | // of the conditional value, which may also be dead. |
Chris Lattner | 837e42c | 2003-06-24 23:02:45 +0000 | [diff] [blame] | 361 | if (!LiveSet.count(TI)) |
| 362 | TI = convertToUnconditionalBranch(TI); |
Chris Lattner | 99c91e0 | 2003-06-24 21:49:45 +0000 | [diff] [blame] | 363 | |
Chris Lattner | 011de07 | 2002-07-29 22:31:39 +0000 | [diff] [blame] | 364 | // Loop over all of the successors, looking for ones that are not alive. |
| 365 | // We cannot save the number of successors in the terminator instruction |
| 366 | // here because we may remove them if we don't have a postdominator... |
| 367 | // |
| 368 | for (unsigned i = 0; i != TI->getNumSuccessors(); ++i) |
Chris Lattner | d9036a1 | 2002-05-22 21:32:16 +0000 | [diff] [blame] | 369 | if (!AliveBlocks.count(TI->getSuccessor(i))) { |
| 370 | // Scan up the postdominator tree, looking for the first |
| 371 | // postdominator that is alive, and the last postdominator that is |
| 372 | // dead... |
| 373 | // |
Chris Lattner | ce6ef11 | 2002-07-26 18:40:14 +0000 | [diff] [blame] | 374 | PostDominatorTree::Node *LastNode = DT[TI->getSuccessor(i)]; |
Chris Lattner | 011de07 | 2002-07-29 22:31:39 +0000 | [diff] [blame] | 375 | |
| 376 | // There is a special case here... if there IS no post-dominator for |
| 377 | // the block we have no owhere to point our branch to. Instead, |
| 378 | // convert it to a return. This can only happen if the code |
| 379 | // branched into an infinite loop. Note that this may not be |
| 380 | // desirable, because we _are_ altering the behavior of the code. |
| 381 | // This is a well known drawback of ADCE, so in the future if we |
| 382 | // choose to revisit the decision, this is where it should be. |
Chris Lattner | d9036a1 | 2002-05-22 21:32:16 +0000 | [diff] [blame] | 383 | // |
Chris Lattner | 011de07 | 2002-07-29 22:31:39 +0000 | [diff] [blame] | 384 | if (LastNode == 0) { // No postdominator! |
| 385 | // Call RemoveSuccessor to transmogrify the terminator instruction |
| 386 | // to not contain the outgoing branch, or to create a new |
Misha Brukman | cf00c4a | 2003-10-10 17:57:28 +0000 | [diff] [blame] | 387 | // terminator if the form fundamentally changes (i.e., |
| 388 | // unconditional branch to return). Note that this will change a |
| 389 | // branch into an infinite loop into a return instruction! |
Chris Lattner | 011de07 | 2002-07-29 22:31:39 +0000 | [diff] [blame] | 390 | // |
| 391 | RemoveSuccessor(TI, i); |
| 392 | |
| 393 | // RemoveSuccessor may replace TI... make sure we have a fresh |
| 394 | // pointer... and e variable. |
| 395 | // |
| 396 | TI = BB->getTerminator(); |
| 397 | |
| 398 | // Rescan this successor... |
| 399 | --i; |
| 400 | } else { |
| 401 | PostDominatorTree::Node *NextNode = LastNode->getIDom(); |
| 402 | |
Chris Lattner | c444a42 | 2003-09-11 16:26:13 +0000 | [diff] [blame] | 403 | while (!AliveBlocks.count(NextNode->getBlock())) { |
Chris Lattner | 011de07 | 2002-07-29 22:31:39 +0000 | [diff] [blame] | 404 | LastNode = NextNode; |
| 405 | NextNode = NextNode->getIDom(); |
| 406 | } |
| 407 | |
| 408 | // Get the basic blocks that we need... |
Chris Lattner | c444a42 | 2003-09-11 16:26:13 +0000 | [diff] [blame] | 409 | BasicBlock *LastDead = LastNode->getBlock(); |
| 410 | BasicBlock *NextAlive = NextNode->getBlock(); |
Chris Lattner | 011de07 | 2002-07-29 22:31:39 +0000 | [diff] [blame] | 411 | |
| 412 | // Make the conditional branch now go to the next alive block... |
| 413 | TI->getSuccessor(i)->removePredecessor(BB); |
| 414 | TI->setSuccessor(i, NextAlive); |
| 415 | |
| 416 | // If there are PHI nodes in NextAlive, we need to add entries to |
| 417 | // the PHI nodes for the new incoming edge. The incoming values |
| 418 | // should be identical to the incoming values for LastDead. |
| 419 | // |
| 420 | for (BasicBlock::iterator II = NextAlive->begin(); |
Chris Lattner | 619f825 | 2003-04-25 22:53:27 +0000 | [diff] [blame] | 421 | PHINode *PN = dyn_cast<PHINode>(II); ++II) |
| 422 | if (LiveSet.count(PN)) { // Only modify live phi nodes |
| 423 | // Get the incoming value for LastDead... |
| 424 | int OldIdx = PN->getBasicBlockIndex(LastDead); |
| 425 | assert(OldIdx != -1 &&"LastDead is not a pred of NextAlive!"); |
| 426 | Value *InVal = PN->getIncomingValue(OldIdx); |
| 427 | |
| 428 | // Add an incoming value for BB now... |
| 429 | PN->addIncoming(InVal, BB); |
| 430 | } |
Chris Lattner | d9036a1 | 2002-05-22 21:32:16 +0000 | [diff] [blame] | 431 | } |
| 432 | } |
Chris Lattner | 5554727 | 2002-05-10 15:37:35 +0000 | [diff] [blame] | 433 | |
Chris Lattner | d9036a1 | 2002-05-22 21:32:16 +0000 | [diff] [blame] | 434 | // Now loop over all of the instructions in the basic block, telling |
| 435 | // dead instructions to drop their references. This is so that the next |
| 436 | // sweep over the program can safely delete dead instructions without |
Misha Brukman | cf00c4a | 2003-10-10 17:57:28 +0000 | [diff] [blame] | 437 | // other dead instructions still referring to them. |
Chris Lattner | d9036a1 | 2002-05-22 21:32:16 +0000 | [diff] [blame] | 438 | // |
Chris Lattner | 446698b | 2002-07-30 00:22:34 +0000 | [diff] [blame] | 439 | dropReferencesOfDeadInstructionsInLiveBlock(BB); |
Chris Lattner | d9036a1 | 2002-05-22 21:32:16 +0000 | [diff] [blame] | 440 | } |
Chris Lattner | b8259dd | 2001-09-09 22:26:47 +0000 | [diff] [blame] | 441 | } |
| 442 | |
Chris Lattner | d7f268d | 2003-01-23 02:12:18 +0000 | [diff] [blame] | 443 | // We make changes if there are any dead blocks in the function... |
| 444 | if (unsigned NumDeadBlocks = Func->size() - AliveBlocks.size()) { |
| 445 | MadeChanges = true; |
| 446 | NumBlockRemoved += NumDeadBlocks; |
| 447 | } |
| 448 | |
| 449 | // Loop over all of the basic blocks in the function, removing control flow |
| 450 | // edges to live blocks (also eliminating any entries in PHI functions in |
| 451 | // referenced blocks). |
Chris Lattner | d9036a1 | 2002-05-22 21:32:16 +0000 | [diff] [blame] | 452 | // |
Chris Lattner | d7f268d | 2003-01-23 02:12:18 +0000 | [diff] [blame] | 453 | for (Function::iterator BB = Func->begin(), E = Func->end(); BB != E; ++BB) |
Chris Lattner | 84369b3 | 2002-05-28 21:38:16 +0000 | [diff] [blame] | 454 | if (!AliveBlocks.count(BB)) { |
Chris Lattner | d9036a1 | 2002-05-22 21:32:16 +0000 | [diff] [blame] | 455 | // Remove all outgoing edges from this basic block and convert the |
| 456 | // terminator into a return instruction. |
Chris Lattner | de579f1 | 2003-05-22 22:00:07 +0000 | [diff] [blame] | 457 | std::vector<BasicBlock*> Succs(succ_begin(BB), succ_end(BB)); |
Chris Lattner | d9036a1 | 2002-05-22 21:32:16 +0000 | [diff] [blame] | 458 | |
| 459 | if (!Succs.empty()) { |
| 460 | // Loop over all of the successors, removing this block from PHI node |
| 461 | // entries that might be in the block... |
| 462 | while (!Succs.empty()) { |
| 463 | Succs.back()->removePredecessor(BB); |
| 464 | Succs.pop_back(); |
| 465 | } |
| 466 | |
| 467 | // Delete the old terminator instruction... |
Chris Lattner | c8ecd22 | 2003-11-22 02:13:08 +0000 | [diff] [blame] | 468 | const Type *TermTy = BB->getTerminator()->getType(); |
| 469 | if (TermTy != Type::VoidTy) |
| 470 | BB->getTerminator()->replaceAllUsesWith( |
| 471 | Constant::getNullValue(TermTy)); |
Chris Lattner | 7e70829 | 2002-06-25 16:13:24 +0000 | [diff] [blame] | 472 | BB->getInstList().pop_back(); |
Chris Lattner | d9036a1 | 2002-05-22 21:32:16 +0000 | [diff] [blame] | 473 | const Type *RetTy = Func->getReturnType(); |
Chris Lattner | f8485c6 | 2003-11-20 18:25:24 +0000 | [diff] [blame] | 474 | new ReturnInst(RetTy != Type::VoidTy ? |
| 475 | Constant::getNullValue(RetTy) : 0, BB); |
Chris Lattner | d9036a1 | 2002-05-22 21:32:16 +0000 | [diff] [blame] | 476 | } |
Chris Lattner | d9036a1 | 2002-05-22 21:32:16 +0000 | [diff] [blame] | 477 | } |
Chris Lattner | d7f268d | 2003-01-23 02:12:18 +0000 | [diff] [blame] | 478 | |
| 479 | |
| 480 | // Loop over all of the basic blocks in the function, dropping references of |
| 481 | // the dead basic blocks. We must do this after the previous step to avoid |
| 482 | // dropping references to PHIs which still have entries... |
| 483 | // |
| 484 | for (Function::iterator BB = Func->begin(), E = Func->end(); BB != E; ++BB) |
| 485 | if (!AliveBlocks.count(BB)) |
| 486 | BB->dropAllReferences(); |
Chris Lattner | 5554727 | 2002-05-10 15:37:35 +0000 | [diff] [blame] | 487 | |
Chris Lattner | 84369b3 | 2002-05-28 21:38:16 +0000 | [diff] [blame] | 488 | // Now loop through all of the blocks and delete the dead ones. We can safely |
| 489 | // do this now because we know that there are no references to dead blocks |
| 490 | // (because they have dropped all of their references... we also remove dead |
| 491 | // instructions from alive blocks. |
Chris Lattner | b8259dd | 2001-09-09 22:26:47 +0000 | [diff] [blame] | 492 | // |
Chris Lattner | d9036a1 | 2002-05-22 21:32:16 +0000 | [diff] [blame] | 493 | for (Function::iterator BI = Func->begin(); BI != Func->end(); ) |
Chris Lattner | 446698b | 2002-07-30 00:22:34 +0000 | [diff] [blame] | 494 | if (!AliveBlocks.count(BI)) { // Delete dead blocks... |
Chris Lattner | 7e70829 | 2002-06-25 16:13:24 +0000 | [diff] [blame] | 495 | BI = Func->getBasicBlockList().erase(BI); |
Chris Lattner | 446698b | 2002-07-30 00:22:34 +0000 | [diff] [blame] | 496 | } else { // Scan alive blocks... |
Chris Lattner | 7e70829 | 2002-06-25 16:13:24 +0000 | [diff] [blame] | 497 | for (BasicBlock::iterator II = BI->begin(); II != --BI->end(); ) |
| 498 | if (!LiveSet.count(II)) { // Is this instruction alive? |
Chris Lattner | 84369b3 | 2002-05-28 21:38:16 +0000 | [diff] [blame] | 499 | // Nope... remove the instruction from it's basic block... |
Chris Lattner | 7e70829 | 2002-06-25 16:13:24 +0000 | [diff] [blame] | 500 | II = BI->getInstList().erase(II); |
Chris Lattner | 84369b3 | 2002-05-28 21:38:16 +0000 | [diff] [blame] | 501 | ++NumInstRemoved; |
| 502 | MadeChanges = true; |
| 503 | } else { |
| 504 | ++II; |
| 505 | } |
| 506 | |
Chris Lattner | d9036a1 | 2002-05-22 21:32:16 +0000 | [diff] [blame] | 507 | ++BI; // Increment iterator... |
Chris Lattner | 84369b3 | 2002-05-28 21:38:16 +0000 | [diff] [blame] | 508 | } |
Chris Lattner | 5554727 | 2002-05-10 15:37:35 +0000 | [diff] [blame] | 509 | |
Chris Lattner | d9036a1 | 2002-05-22 21:32:16 +0000 | [diff] [blame] | 510 | return MadeChanges; |
Chris Lattner | 02e90d5 | 2001-06-30 06:39:11 +0000 | [diff] [blame] | 511 | } |