baby steps toward fixing some problems with inbound GEPs that overflow, as discussed...

Make sure we do not emit index computations with NSW flags so that we dont get an undef value if the GEP overflows

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@160589 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/include/llvm/Transforms/Utils/Local.h b/include/llvm/Transforms/Utils/Local.h
index 84c0c5862ed15d41aadaa54acba6614d86cca582..495eab73289e5955791ecfe440a86bc7b0e0f25e 100644 (file)
--- a/include/llvm/Transforms/Utils/Local.h
+++ b/include/llvm/Transforms/Utils/Local.h
@@ -168,15 +168,18 @@ static inline unsigned getKnownAlignment(Value *V, const TargetData *TD = 0) {
 /// EmitGEPOffset - Given a getelementptr instruction/constantexpr, emit the
 /// code necessary to compute the offset from the base pointer (without adding
 /// in the base pointer).  Return the result as a signed integer of intptr size.
+/// When NoAssumptions is true, no assumptions about index computation not
+/// overflowing is made.
 template<typename IRBuilderTy>
-Value *EmitGEPOffset(IRBuilderTy *Builder, const TargetData &TD, User *GEP) {
+Value *EmitGEPOffset(IRBuilderTy *Builder, const TargetData &TD, User *GEP,
+                     bool NoAssumptions = false) {
   gep_type_iterator GTI = gep_type_begin(GEP);
   Type *IntPtrTy = TD.getIntPtrType(GEP->getContext());
   Value *Result = Constant::getNullValue(IntPtrTy);
 
   // If the GEP is inbounds, we know that none of the addressing operations will
   // overflow in an unsigned sense.
-  bool isInBounds = cast<GEPOperator>(GEP)->isInBounds();
+  bool isInBounds = cast<GEPOperator>(GEP)->isInBounds() && !NoAssumptions;
 
   // Build a mask for high order bits.
   unsigned IntPtrWidth = TD.getPointerSizeInBits();

diff --git a/lib/Analysis/MemoryBuiltins.cpp b/lib/Analysis/MemoryBuiltins.cpp
index 39edaaf1c49a00108133874f81d8f208dc6bab8c..8d99ec3e5643600127f701323eda5e94fbaa69de 100644 (file)
--- a/lib/Analysis/MemoryBuiltins.cpp
+++ b/lib/Analysis/MemoryBuiltins.cpp
@@ -645,7 +645,7 @@ ObjectSizeOffsetEvaluator::visitGEPOperator(GEPOperator &GEP) {
   if (!bothKnown(PtrData))
     return unknown();
 
-  Value *Offset = EmitGEPOffset(&Builder, *TD, &GEP);
+  Value *Offset = EmitGEPOffset(&Builder, *TD, &GEP, /*NoAssumptions=*/true);
   Offset = Builder.CreateAdd(PtrData.second, Offset);
   return std::make_pair(PtrData.first, Offset);
 }

diff --git a/test/Instrumentation/BoundsChecking/simple.ll b/test/Instrumentation/BoundsChecking/simple.ll
index 3d532c3cf3b835f8ff0a9e6aecbccccb4675c428..16870c78a87535a54d57d7d618593571e2356e79 100644 (file)
--- a/test/Instrumentation/BoundsChecking/simple.ll
+++ b/test/Instrumentation/BoundsChecking/simple.ll
@@ -116,3 +116,13 @@ define void @f11(i128* byval %x) nounwind {
   %3 = load i8* %2, align 4
   ret void
 }
+
+; CHECK: @f12
+define i64 @f12(i64 %x, i64 %y) nounwind {
+  %1 = tail call i8* @calloc(i64 1, i64 %x)
+; CHECK: mul i64 %y, 8
+  %2 = bitcast i8* %1 to i64*
+  %3 = getelementptr inbounds i64* %2, i64 %y
+  %4 = load i64* %3, align 8
+  ret i64 %4
+}