[PATCH] D41398: Give up on array allocas in getPointerDereferenceableBytes

[Björn Steinbrink via Phabricator via llvm-commits]

dotdash created this revision.
dotdash added a reviewer: efriedma.

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.


https://reviews.llvm.org/D41398

Files:
  lib/IR/Value.cpp
  test/Analysis/ValueTracking/memory-dereferenceable.ll


Index: test/Analysis/ValueTracking/memory-dereferenceable.ll
===================================================================
--- test/Analysis/ValueTracking/memory-dereferenceable.ll
+++ test/Analysis/ValueTracking/memory-dereferenceable.ll
@@ -42,18 +42,6 @@
     %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
Index: lib/IR/Value.cpp
===================================================================
--- lib/IR/Value.cpp
+++ lib/IR/Value.cpp
@@ -656,10 +656,8 @@
       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->getAllocatedType()->isSized() && !AI->isArrayAllocation()) {
+      DerefBytes = DL.getTypeStoreSize(AI->getAllocatedType());
       CanBeNull = false;
     }
   } else if (auto *GV = dyn_cast<GlobalVariable>(this)) {


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