[InstCombine] Infer inbounds on geps of allocas

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@277950 91177308-0d34-0410-b5e6-96231b3b80d8

Author: majnemer

lib/Transforms/InstCombine/InstructionCombining.cpp

@@ -1898,6 +1898,25 @@ 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;
 }
 

test/Transforms/InstCombine/getelementptr.ll

@@ -366,7 +366,7 @@ define i32 @test21() {
         %rval = load i32, i32* %pbobel
         ret i32 %rval
 ; CHECK-LABEL: @test21(
-; CHECK: getelementptr %intstruct, %intstruct* %pbob1, i64 0, i32 0
+; CHECK: getelementptr inbounds %intstruct, %intstruct* %pbob1, i64 0, i32 0
 }
 
 
@@ -540,8 +540,8 @@ define i8* @test32(i8* %v) {
 	%G = load i8*, i8** %F
 	ret i8* %G
 ; CHECK-LABEL: @test32(
-; CHECK: %D = getelementptr [4 x i8*], [4 x i8*]* %A, i64 0, i64 1
-; CHECK: %F = getelementptr [4 x i8*], [4 x i8*]* %A, i64 0, i64 2
+; CHECK: %D = getelementptr inbounds [4 x i8*], [4 x i8*]* %A, i64 0, i64 1
+; CHECK: %F = getelementptr inbounds [4 x i8*], [4 x i8*]* %A, i64 0, i64 2
 }
 
 ; PR3290