[llvm] r321159 - Give up on array allocas in getPointerDereferenceableBytes

[Bjorn Steinbrink via llvm-commits]

Author: bsteinbr
Date: Wed Dec 20 02:01:30 2017
New Revision: 321159

URL: http://llvm.org/viewvc/llvm-project?rev=321159&view=rev
Log:
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

Modified:
    llvm/trunk/lib/IR/Value.cpp
    llvm/trunk/test/Analysis/ValueTracking/memory-dereferenceable.ll

Modified: llvm/trunk/lib/IR/Value.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/IR/Value.cpp?rev=321159&r1=321158&r2=321159&view=diff
==============================================================================
--- llvm/trunk/lib/IR/Value.cpp (original)
+++ llvm/trunk/lib/IR/Value.cpp Wed Dec 20 02:01:30 2017
@@ -656,10 +656,8 @@ uint64_t Value::getPointerDereferenceabl
       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)) {

Modified: llvm/trunk/test/Analysis/ValueTracking/memory-dereferenceable.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ValueTracking/memory-dereferenceable.ll?rev=321159&r1=321158&r2=321159&view=diff
==============================================================================
--- llvm/trunk/test/Analysis/ValueTracking/memory-dereferenceable.ll (original)
+++ llvm/trunk/test/Analysis/ValueTracking/memory-dereferenceable.ll Wed Dec 20 02:01:30 2017
@@ -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