Change worklist driven deletion to be an iterative process.

Duncan noticed this!


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@138967 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 12 insertions, 42 deletions

diff --git a/lib/Transforms/InstCombine/InstructionCombining.cpp b/lib/Transforms/InstCombine/InstructionCombining.cpp
index 5e06820803..208375b482 100644
--- a/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -1573,41 +1573,20 @@ bool InstCombiner::DoOneIteration(Function &F, unsigned Iteration) {
     // the instcombine code from having to deal with some bad special cases.
     for (Function::iterator BB = F.begin(), E = F.end(); BB != E; ++BB)
       if (!Visited.count(BB)) {
-        Instruction *Term = BB->getTerminator();
-
-        if (isa<TerminatorInst>(BB->begin()))
-          continue;
-
         // Delete the instructions backwards, as it has a reduced likelihood of
         // having to update as many def-use and use-def chains.
-        std::vector<Instruction*> WorkList;
-        WorkList.reserve(BB->size());
-        BasicBlock::iterator I = Term; --I;
-
-        while (true) {
-          if (!I->getType()->isVoidTy())
-            I->replaceAllUsesWith(UndefValue::get(I->getType()));
-          WorkList.push_back(I);
-          if (I == BB->begin())
+        for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
+          Instruction *Inst = &*I++;
+          if (isa<TerminatorInst>(Inst))
             break;
-          --I;
-        }
-
-        for (std::vector<Instruction*>::iterator
-               II = WorkList.begin(), IE = WorkList.end(); II != IE; ++II) {
-          Instruction *Inst = *II;
-          // Don't remove the landing pad. It should be removed only when its
-          // invokes are removed.
+          if (!Inst->use_empty())
+            Inst->replaceAllUsesWith(UndefValue::get(Inst->getType()));
           if (isa<LandingPadInst>(Inst))
             continue;
-
-          // A debug intrinsic shouldn't force another iteration if we weren't
-          // going to do one without it.
           if (!isa<DbgInfoIntrinsic>(Inst)) {
             ++NumDeadInst;
             MadeIRChange = true;
           }
-
           Inst->eraseFromParent();
         }
       }
diff --git a/lib/Transforms/Scalar/SCCP.cpp b/lib/Transforms/Scalar/SCCP.cpp
index 3d52afa2e1..4ac5b2f910 100644
--- a/lib/Transforms/Scalar/SCCP.cpp
+++ b/lib/Transforms/Scalar/SCCP.cpp
@@ -1688,24 +1688,15 @@ static void DeleteInstructionInBlock(BasicBlock *BB) {
 
   // Delete the instructions backwards, as it has a reduced likelihood of
   // having to update as many def-use and use-def chains.
-  std::vector<Instruction*> WorkList;
-  WorkList.reserve(BB->size());
-  BasicBlock::iterator I = --BasicBlock::iterator(BB->getTerminator());
-
-  while (true) {
-    if (!I->use_empty())
-      I->replaceAllUsesWith(UndefValue::get(I->getType()));
-    WorkList.push_back(I);
-    if (I == BB->begin())
+  for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
+    Instruction *Inst = &*I++;
+    if (isa<TerminatorInst>(Inst))
       break;
-    --I;
-  }
-
-  for (std::vector<Instruction*>::iterator
-         II = WorkList.begin(), IE = WorkList.end(); II != IE; ++II) {
-    if (isa<LandingPadInst>(*II))
+    if (!Inst->use_empty())
+      Inst->replaceAllUsesWith(UndefValue::get(Inst->getType()));
+    if (isa<LandingPadInst>(Inst))
       continue;
-    BB->getInstList().erase(*II);
+    BB->getInstList().erase(Inst);
     ++NumInstRemoved;
   }
 }