From: Bjorn Steinbrink <bsteinbr@gmail.com>
Date: Wed, 20 Dec 2017 10:01:30 +0000 (+0000)
Subject: Give up on array allocas in getPointerDereferenceableBytes
X-Git-Url: https://granicus.if.org/sourcecode?a=commitdiff_plain;h=ea96fe14feb5396d179c4f7681d323b762166e64;p=llvm

Give up on array allocas in getPointerDereferenceableBytes

Summary:
As suggested by Eli Friedman, don't try to handle array allocas here,
because of possible overflows, instead rely on instcombine converting
them to allocations of array types.

Reviewers: efriedma

Subscribers: llvm-commits

Differential Revision: https://reviews.llvm.org/D41398

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@321159 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/IR/Value.cpp b/lib/IR/Value.cpp
index d36b7cd4c64..163c785f5d7 100644
--- a/lib/IR/Value.cpp
+++ b/lib/IR/Value.cpp
@@ -656,10 +656,8 @@ uint64_t Value::getPointerDereferenceableBytes(const DataLayout &DL,
       CanBeNull = true;
     }
   } else if (auto *AI = dyn_cast<AllocaInst>(this)) {
-    const ConstantInt *ArraySize = dyn_cast<ConstantInt>(AI->getArraySize());
-    if (ArraySize && AI->getAllocatedType()->isSized()) {
-      DerefBytes = DL.getTypeStoreSize(AI->getAllocatedType()) *
-        ArraySize->getZExtValue();
+    if (!AI->isArrayAllocation()) {
+      DerefBytes = DL.getTypeStoreSize(AI->getAllocatedType());
       CanBeNull = false;
     }
   } else if (auto *GV = dyn_cast<GlobalVariable>(this)) {
diff --git a/test/Analysis/ValueTracking/memory-dereferenceable.ll b/test/Analysis/ValueTracking/memory-dereferenceable.ll
index 8e474e5a95c..2e9453f670c 100644
--- a/test/Analysis/ValueTracking/memory-dereferenceable.ll
+++ b/test/Analysis/ValueTracking/memory-dereferenceable.ll
@@ -42,18 +42,6 @@ entry:
     %empty_alloca = alloca i8, i64 0
     %empty_load = load i8, i8* %empty_alloca
 
-    ; Load from too small array alloca
-; CHECK-NOT: %small_array_alloca
-    %small_array_alloca = alloca i8, i64 2
-    %saa_cast = bitcast i8* %small_array_alloca to i32*
-    %saa_load = load i32, i32* %saa_cast
-
-    ; Load from array alloca
-; CHECK: %big_array_alloca{{.*}}(unaligned)
-    %big_array_alloca = alloca i8, i64 4
-    %baa_cast = bitcast i8* %big_array_alloca to i32*
-    %baa_load = load i32, i32* %baa_cast
-
     ; Loads from sret arguments
 ; CHECK: %sret_gep{{.*}}(aligned)
     %sret_gep = getelementptr inbounds %struct.A, %struct.A* %result, i64 0, i32 1, i64 2