[InstCombine] Infer inbounds on geps of allocas

llvm-svn: 277950

1 files changed, 19 insertions, 0 deletions

diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 7ffe34a3c26..006deb6b5ff 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -1899,6 +1899,25 @@ Instruction *InstCombiner::visitGetElementPtrInst(GetElementPtrInst &GEP) {
     }
   }
 
+  if (!GEP.isInBounds()) {
+    unsigned PtrWidth =
+        DL.getPointerSizeInBits(PtrOp->getType()->getPointerAddressSpace());
+    APInt BasePtrOffset(PtrWidth, 0);
+    Value *UnderlyingPtrOp =
+            PtrOp->stripAndAccumulateInBoundsConstantOffsets(DL,
+                                                             BasePtrOffset);
+    if (auto *AI = dyn_cast<AllocaInst>(UnderlyingPtrOp)) {
+      if (GEP.accumulateConstantOffset(DL, BasePtrOffset) &&
+          BasePtrOffset.isNonNegative()) {
+        APInt AllocSize(PtrWidth, DL.getTypeAllocSize(AI->getAllocatedType()));
+        if (BasePtrOffset.ule(AllocSize)) {
+          return GetElementPtrInst::CreateInBounds(
+              PtrOp, makeArrayRef(Ops).slice(1), GEP.getName());
+        }
+      }
+    }
+  }
+
   return nullptr;
 }