SCEV: Add MarkPendingLoopPredicates to avoid recursive isImpliedCond.

getUDivExpr attempts to simplify by checking for overflow.
isLoopEntryGuardedByCond then evaluates the loop predicate which
may lead to the same getUDivExpr causing endless recursion.

Fixes PR12868: clang 3.2 segmentation fault.

llvm-svn: 157092

1 files changed, 24 insertions, 0 deletions

diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index d1ad8e02d6a..4e3dc60ed50 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -6039,12 +6039,34 @@ ScalarEvolution::isLoopEntryGuardedByCond(const Loop *L,
   return false;
 }
 
+/// RAII wrapper to prevent recursive application of isImpliedCond.
+/// ScalarEvolution's PendingLoopPredicates set must be empty unless we are
+/// currently evaluating isImpliedCond.
+struct MarkPendingLoopPredicate {
+  Value *Cond;
+  DenseSet<Value*> &LoopPreds;
+  bool Pending;
+
+  MarkPendingLoopPredicate(Value *C, DenseSet<Value*> &LP)
+    : Cond(C), LoopPreds(LP) {
+    Pending = !LoopPreds.insert(Cond).second;
+  }
+  ~MarkPendingLoopPredicate() {
+    if (!Pending)
+      LoopPreds.erase(Cond);
+  }
+};
+
 /// isImpliedCond - Test whether the condition described by Pred, LHS,
 /// and RHS is true whenever the given Cond value evaluates to true.
 bool ScalarEvolution::isImpliedCond(ICmpInst::Predicate Pred,
                                     const SCEV *LHS, const SCEV *RHS,
                                     Value *FoundCondValue,
                                     bool Inverse) {
+  MarkPendingLoopPredicate Mark(FoundCondValue, PendingLoopPredicates);
+  if (Mark.Pending)
+    return false;
+
   // Recursively handle And and Or conditions.
   if (BinaryOperator *BO = dyn_cast<BinaryOperator>(FoundCondValue)) {
     if (BO->getOpcode() == Instruction::And) {
@@ -6571,6 +6593,8 @@ void ScalarEvolution::releaseMemory() {
     I->second.clear();
   }
 
+  assert(PendingLoopPredicates.empty() && "isImpliedCond garbage");
+
   BackedgeTakenCounts.clear();
   ConstantEvolutionLoopExitValue.clear();
   ValuesAtScopes.clear();