[RS4GC] Use an value handle to help isolate errors quickly

[oota-llvm.git] / lib / Transforms / Scalar / DCE.cpp

diff --git a/lib/Transforms/Scalar/DCE.cpp b/lib/Transforms/Scalar/DCE.cpp
index d32f7c33f17db850423ac0e062722d377f796ddc..b67c3c7742fd7d37bbf53b9c6e603c7880f0cd91 100644 (file)
--- a/lib/Transforms/Scalar/DCE.cpp
+++ b/lib/Transforms/Scalar/DCE.cpp
@@ -16,16 +16,18 @@
 //
 //===----------------------------------------------------------------------===//
 
-#define DEBUG_TYPE "dce"
 #include "llvm/Transforms/Scalar.h"
+#include "llvm/ADT/SetVector.h"
 #include "llvm/ADT/Statistic.h"
 #include "llvm/IR/InstIterator.h"
 #include "llvm/IR/Instruction.h"
 #include "llvm/Pass.h"
-#include "llvm/Target/TargetLibraryInfo.h"
+#include "llvm/Analysis/TargetLibraryInfo.h"
 #include "llvm/Transforms/Utils/Local.h"
 using namespace llvm;
 
+#define DEBUG_TYPE "dce"
+
 STATISTIC(DIEEliminated, "Number of insts removed by DIE pass");
 STATISTIC(DCEEliminated, "Number of insts removed");
 
@@ -38,13 +40,14 @@ namespace {
     DeadInstElimination() : BasicBlockPass(ID) {
       initializeDeadInstEliminationPass(*PassRegistry::getPassRegistry());
     }
-    virtual bool runOnBasicBlock(BasicBlock &BB) {
+    bool runOnBasicBlock(BasicBlock &BB) override {
       if (skipOptnoneFunction(BB))
         return false;
-      TargetLibraryInfo *TLI = getAnalysisIfAvailable<TargetLibraryInfo>();
+      auto *TLIP = getAnalysisIfAvailable<TargetLibraryInfoWrapperPass>();
+      TargetLibraryInfo *TLI = TLIP ? &TLIP->getTLI() : nullptr;
       bool Changed = false;
       for (BasicBlock::iterator DI = BB.begin(); DI != BB.end(); ) {
-        Instruction *Inst = DI++;
+        Instruction *Inst = &*DI++;
         if (isInstructionTriviallyDead(Inst, TLI)) {
           Inst->eraseFromParent();
           Changed = true;
@@ -54,7 +57,7 @@ namespace {
       return Changed;
     }
 
-    virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+    void getAnalysisUsage(AnalysisUsage &AU) const override {
       AU.setPreservesCFG();
     }
   };
@@ -79,9 +82,9 @@ namespace {
       initializeDCEPass(*PassRegistry::getPassRegistry());
     }
 
-    virtual bool runOnFunction(Function &F);
+    bool runOnFunction(Function &F) override;
 
-     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
+    void getAnalysisUsage(AnalysisUsage &AU) const override {
       AU.setPreservesCFG();
     }
  };
@@ -90,45 +93,59 @@ namespace {
 char DCE::ID = 0;
 INITIALIZE_PASS(DCE, "dce", "Dead Code Elimination", false, false)
 
+static bool DCEInstruction(Instruction *I,
+                           SmallSetVector<Instruction *, 16> &WorkList,
+                           const TargetLibraryInfo *TLI) {
+  if (isInstructionTriviallyDead(I, TLI)) {
+    // Null out all of the instruction's operands to see if any operand becomes
+    // dead as we go.
+    for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i) {
+      Value *OpV = I->getOperand(i);
+      I->setOperand(i, nullptr);
+
+      if (!OpV->use_empty() || I == OpV)
+        continue;
+
+      // If the operand is an instruction that became dead as we nulled out the
+      // operand, and if it is 'trivially' dead, delete it in a future loop
+      // iteration.
+      if (Instruction *OpI = dyn_cast<Instruction>(OpV))
+        if (isInstructionTriviallyDead(OpI, TLI))
+          WorkList.insert(OpI);
+    }
+
+    I->eraseFromParent();
+    ++DCEEliminated;
+    return true;
+  }
+  return false;
+}
+
 bool DCE::runOnFunction(Function &F) {
   if (skipOptnoneFunction(F))
     return false;
 
-  TargetLibraryInfo *TLI = getAnalysisIfAvailable<TargetLibraryInfo>();
-
-  // Start out with all of the instructions in the worklist...
-  std::vector<Instruction*> WorkList;
-  for (inst_iterator i = inst_begin(F), e = inst_end(F); i != e; ++i)
-    WorkList.push_back(&*i);
+  auto *TLIP = getAnalysisIfAvailable<TargetLibraryInfoWrapperPass>();
+  TargetLibraryInfo *TLI = TLIP ? &TLIP->getTLI() : nullptr;
 
-  // Loop over the worklist finding instructions that are dead.  If they are
-  // dead make them drop all of their uses, making other instructions
-  // potentially dead, and work until the worklist is empty.
-  //
   bool MadeChange = false;
+  SmallSetVector<Instruction *, 16> WorkList;
+  // Iterate over the original function, only adding insts to the worklist
+  // if they actually need to be revisited. This avoids having to pre-init
+  // the worklist with the entire function's worth of instructions.
+  for (inst_iterator FI = inst_begin(F), FE = inst_end(F); FI != FE;) {
+    Instruction *I = &*FI;
+    ++FI;
+
+    // We're visiting this instruction now, so make sure it's not in the
+    // worklist from an earlier visit.
+    if (!WorkList.count(I))
+      MadeChange |= DCEInstruction(I, WorkList, TLI);
+  }
+
   while (!WorkList.empty()) {
-    Instruction *I = WorkList.back();
-    WorkList.pop_back();
-
-    if (isInstructionTriviallyDead(I, TLI)) { // If the instruction is dead.
-      // Loop over all of the values that the instruction uses, if there are
-      // instructions being used, add them to the worklist, because they might
-      // go dead after this one is removed.
-      //
-      for (User::op_iterator OI = I->op_begin(), E = I->op_end(); OI != E; ++OI)
-        if (Instruction *Used = dyn_cast<Instruction>(*OI))
-          WorkList.push_back(Used);
-
-      // Remove the instruction.
-      I->eraseFromParent();
-
-      // Remove the instruction from the worklist if it still exists in it.
-      WorkList.erase(std::remove(WorkList.begin(), WorkList.end(), I),
-                     WorkList.end());
-
-      MadeChange = true;
-      ++DCEEliminated;
-    }
+    Instruction *I = WorkList.pop_back_val();
+    MadeChange |= DCEInstruction(I, WorkList, TLI);
   }
   return MadeChange;
 }