Use Duncan's patch to delete the instructions in reverse order (minus the landingpad...

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

diff --git a/lib/Transforms/Scalar/SCCP.cpp b/lib/Transforms/Scalar/SCCP.cpp
index 0091a3df7d723ac1061d7ad20d2917ffb0405017..02e6b72d3afd13c5240d0df4338ba48bd0ab73d2 100644 (file)
--- a/lib/Transforms/Scalar/SCCP.cpp
+++ b/lib/Transforms/Scalar/SCCP.cpp
@@ -1686,15 +1686,19 @@ static void DeleteInstructionInBlock(BasicBlock *BB) {
   if (isa<TerminatorInst>(BB->begin()))
     return;
 
-  // Delete the instructions.
-  for (BasicBlock::iterator I = BB->begin(), E = BB->end(); I != E; ) {
-    Instruction *Inst = &*I++;
-    if (isa<TerminatorInst>(Inst))
-      break;
+  // Delete the instructions backwards, as it has a reduced likelihood of having
+  // to update as many def-use and use-def chains.
+  Instruction *EndInst = BB->getTerminator(); // Last not to be deleted.
+  while (EndInst != BB->begin()) {
+    // Delete the next to last instruction.
+    BasicBlock::iterator I = EndInst;
+    Instruction *Inst = --I;
     if (!Inst->use_empty())
       Inst->replaceAllUsesWith(UndefValue::get(Inst->getType()));
-    if (isa<LandingPadInst>(Inst))
+    if (isa<LandingPadInst>(Inst)) {
+      EndInst = Inst;
       continue;
+    }
     BB->getInstList().erase(Inst);
     ++NumInstRemoved;
   }