From d48ab845563c06f12278cfb66148bd350e9814dc Mon Sep 17 00:00:00 2001
From: Nick Lewycky <nicholas@mxc.ca>
Date: Sat, 12 Nov 2011 03:09:12 +0000
Subject: Don't try to loop on iterators that are potentially invalidated
 inside the loop. Fixes PR11361!

llvm-svn: 144454
---
 llvm/lib/Analysis/ScalarEvolution.cpp | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

(limited to 'llvm/lib')

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index b940d93d6ee..ac00259c5bb 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -4853,10 +4853,18 @@ ScalarEvolution::getConstantEvolutionLoopExitValue(PHINode *PN,
     // Also evaluate the other PHI nodes.  However, we don't get to stop if we
     // cease to be able to evaluate one of them or if they stop evolving,
     // because that doesn't necessarily prevent us from computing PN.
+    SmallVector<std::pair<PHINode *, Constant *>, 8> PHIsToCompute;
     for (DenseMap<Instruction *, Constant *>::const_iterator
            I = CurrentIterVals.begin(), E = CurrentIterVals.end(); I != E; ++I){
       PHINode *PHI = dyn_cast<PHINode>(I->first);
       if (!PHI || PHI == PN || PHI->getParent() != Header) continue;
+      PHIsToCompute.push_back(std::make_pair(PHI, I->second));
+    }
+    // We use two distinct loops because EvaluateExpression may invalidate any
+    // iterators into CurrentIterVals.
+    for (SmallVectorImpl<std::pair<PHINode *, Constant*> >::const_iterator
+             I = PHIsToCompute.begin(), E = PHIsToCompute.end(); I != E; ++I) {
+      PHINode *PHI = I->first;
       Constant *&NextPHI = NextIterVals[PHI];
       if (!NextPHI) {   // Not already computed.
         Value *BEValue = PHI->getIncomingValue(SecondIsBackedge);
@@ -4928,10 +4936,20 @@ const SCEV *ScalarEvolution::ComputeExitCountExhaustively(const Loop *L,
 
     // Update all the PHI nodes for the next iteration.
     DenseMap<Instruction *, Constant *> NextIterVals;
+
+    // Create a list of which PHIs we need to compute. We want to do this before
+    // calling EvaluateExpression on them because that may invalidate iterators
+    // into CurrentIterVals.
+    SmallVector<PHINode *, 8> PHIsToCompute;
     for (DenseMap<Instruction *, Constant *>::const_iterator
            I = CurrentIterVals.begin(), E = CurrentIterVals.end(); I != E; ++I){
       PHINode *PHI = dyn_cast<PHINode>(I->first);
       if (!PHI || PHI->getParent() != Header) continue;
+      PHIsToCompute.push_back(PHI);
+    }
+    for (SmallVectorImpl<PHINode *>::const_iterator I = PHIsToCompute.begin(),
+             E = PHIsToCompute.end(); I != E; ++I) {
+      PHINode *PHI = *I;
       Constant *&NextPHI = NextIterVals[PHI];
       if (NextPHI) continue;    // Already computed!
 
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