diff options
| -rw-r--r-- | lib/Analysis/MemoryDependenceAnalysis.cpp | 10 | ||||
| -rw-r--r-- | test/Transforms/GVN/load-constant-mem.ll | 13 |
2 files changed, 22 insertions, 1 deletions
diff --git a/lib/Analysis/MemoryDependenceAnalysis.cpp b/lib/Analysis/MemoryDependenceAnalysis.cpp index 74c9621..3b21029 100644 --- a/lib/Analysis/MemoryDependenceAnalysis.cpp +++ b/lib/Analysis/MemoryDependenceAnalysis.cpp @@ -202,9 +202,17 @@ getPointerDependencyFrom(Value *MemPtr, uint64_t MemSize, bool isLoad, } if (StoreInst *SI = dyn_cast<StoreInst>(Inst)) { + // If alias analysis can tell that this store is guaranteed to not modify + // the query pointer, ignore it. Use getModRefInfo to handle cases where + // the query pointer points to constant memory etc. + if (AA->getModRefInfo(SI, MemPtr, MemSize) == AliasAnalysis::NoModRef) + continue; + + // Ok, this store might clobber the query pointer. Check to see if it is + // a must alias: in this case, we want to return this as a def. Value *Pointer = SI->getPointerOperand(); uint64_t PointerSize = TD->getTypeStoreSize(SI->getOperand(0)->getType()); - + // If we found a pointer, check if it could be the same as our pointer. AliasAnalysis::AliasResult R = AA->alias(Pointer, PointerSize, MemPtr, MemSize); diff --git a/test/Transforms/GVN/load-constant-mem.ll b/test/Transforms/GVN/load-constant-mem.ll new file mode 100644 index 0000000..83b9d38 --- /dev/null +++ b/test/Transforms/GVN/load-constant-mem.ll @@ -0,0 +1,13 @@ +; RUN: llvm-as < %s | opt -gvn -instcombine | llvm-dis | grep {ret i32 0} +; PR4189 +@G = external constant [4 x i32] + +define i32 @test(i8* %p, i32 %i) nounwind { +entry: + %P = getelementptr [4 x i32]* @G, i32 0, i32 %i + %A = load i32* %P + store i8 4, i8* %p + %B = load i32* %P + %C = sub i32 %A, %B + ret i32 %C +} |