[InstCombine] Don't replace allocas with smaller globals
Summary:
InstCombine replaces large allocas with small globals consts causing buffer overflows
on valid code, see PR33372.
This fix permits this optimization only if the global is dereference for alloca size.
Fixes PR33372
Reviewers: eugenis, majnemer, chandlerc
Subscribers: llvm-commits
Differential Revision: https://reviews.llvm.org/D34311
llvm-svn: 306194
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
index a4d84ae..ee30aa4 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -169,6 +169,18 @@
return nullptr;
}
+/// Returns true if V is dereferenceable for size of alloca.
+static bool isDereferenceableForAllocaSize(const Value *V, const AllocaInst *AI,
+ const DataLayout &DL) {
+ if (AI->isArrayAllocation())
+ return false;
+ uint64_t AllocaSize = DL.getTypeStoreSize(AI->getAllocatedType());
+ if (!AllocaSize)
+ return false;
+ return isDereferenceableAndAlignedPointer(V, AI->getAlignment(),
+ APInt(64, AllocaSize), DL);
+}
+
static Instruction *simplifyAllocaArraySize(InstCombiner &IC, AllocaInst &AI) {
// Check for array size of 1 (scalar allocation).
if (!AI.isArrayAllocation()) {
@@ -390,7 +402,8 @@
if (MemTransferInst *Copy = isOnlyCopiedFromConstantGlobal(&AI, ToDelete)) {
unsigned SourceAlign = getOrEnforceKnownAlignment(
Copy->getSource(), AI.getAlignment(), DL, &AI, &AC, &DT);
- if (AI.getAlignment() <= SourceAlign) {
+ if (AI.getAlignment() <= SourceAlign &&
+ isDereferenceableForAllocaSize(Copy->getSource(), &AI, DL)) {
DEBUG(dbgs() << "Found alloca equal to global: " << AI << '\n');
DEBUG(dbgs() << " memcpy = " << *Copy << '\n');
for (unsigned i = 0, e = ToDelete.size(); i != e; ++i)