Fix a problem that nate reduced for me.

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

diff --git a/lib/Transforms/Scalar/DCE.cpp b/lib/Transforms/Scalar/DCE.cpp
index cfeb86858935b6de8b0df28c172632a01b9fb05c..2783f12f05d32f886d6154423d5196232ee59433 100644 (file)
--- a/lib/Transforms/Scalar/DCE.cpp
+++ b/lib/Transforms/Scalar/DCE.cpp
@@ -1,5 +1,12 @@
 //===- DCE.cpp - Code to perform dead code elimination --------------------===//
 //
+//                     The LLVM Compiler Infrastructure
+//
+// This file was developed by the LLVM research group and is distributed under
+// the University of Illinois Open Source License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
 // This file implements dead inst elimination and dead code elimination.
 //
 // Dead Inst Elimination performs a single pass over the function removing
@@ -14,8 +21,9 @@
 #include "llvm/Instruction.h"
 #include "llvm/Pass.h"
 #include "llvm/Support/InstIterator.h"
-#include "Support/Statistic.h"
+#include "llvm/ADT/Statistic.h"
 #include <set>
+using namespace llvm;
 
 namespace {
   Statistic<> DIEEliminated("die", "Number of insts removed");
@@ -38,19 +46,18 @@ namespace {
     }
 
     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
-      AU.preservesCFG();
+      AU.setPreservesCFG();
     }
   };
-  
+
   RegisterOpt<DeadInstElimination> X("die", "Dead Instruction Elimination");
 }
 
-Pass *createDeadInstEliminationPass() {
+FunctionPass *llvm::createDeadInstEliminationPass() {
   return new DeadInstElimination();
 }
 
 
-
 //===----------------------------------------------------------------------===//
 // DeadCodeElimination pass implementation
 //
@@ -60,7 +67,7 @@ namespace {
     virtual bool runOnFunction(Function &F);
 
      virtual void getAnalysisUsage(AnalysisUsage &AU) const {
-      AU.preservesCFG();
+      AU.setPreservesCFG();
     }
  };
 
@@ -69,51 +76,48 @@ namespace {
 
 bool DCE::runOnFunction(Function &F) {
   // Start out with all of the instructions in the worklist...
-  std::vector<Instruction*> WorkList(inst_begin(F), inst_end(F));
-  std::set<Instruction*> DeadInsts;
-  
+  std::vector<Instruction*> WorkList;
+  for (inst_iterator i = inst_begin(F), e = inst_end(F); i != e; ++i)
+    WorkList.push_back(&*i);
+
   // 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;
   while (!WorkList.empty()) {
     Instruction *I = WorkList.back();
     WorkList.pop_back();
-    
-    if (isInstructionTriviallyDead(I)) {       // If the instruction is dead...
+
+    if (isInstructionTriviallyDead(I)) {       // 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::use_iterator UI = I->use_begin(), UE = I->use_end();
-           UI != UE; ++UI)
-        if (Instruction *Used = dyn_cast<Instruction>(*UI))
+      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);
 
-      // Tell the instruction to let go of all of the values it uses...
-      I->dropAllReferences();
+      // Remove the instruction.
+      I->eraseFromParent();
+
+      // Remove the instruction from the worklist if it still exists in it.
+      for (std::vector<Instruction*>::iterator WI = WorkList.begin(),
+             E = WorkList.end(); WI != E; ++WI)
+        if (*WI == I) {
+          WorkList.erase(WI);
+          --E;
+          --WI;
+        }
 
-      // Keep track of this instruction, because we are going to delete it later
-      DeadInsts.insert(I);
+      MadeChange = true;
+      ++DCEEliminated;
     }
   }
-
-  // If we found no dead instructions, we haven't changed the function...
-  if (DeadInsts.empty()) return false;
-
-  // Otherwise, loop over the program, removing and deleting the instructions...
-  for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
-    for (BasicBlock::iterator BI = I->begin(); BI != I->end(); )
-      if (DeadInsts.count(BI)) {             // Is this instruction dead?
-        BI = I->getInstList().erase(BI);     // Yup, remove and delete inst
-        ++DCEEliminated;
-      } else {                               // This instruction is not dead
-        ++BI;                                // Continue on to the next one...
-      }
-
-  return true;
+  return MadeChange;
 }
 
-Pass *createDeadCodeEliminationPass() {
+FunctionPass *llvm::createDeadCodeEliminationPass() {
   return new DCE();
 }
+