llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-analysis
@llvm/pr-subscribers-llvm-transforms
Author: Nikita Popov (nikic)
<details>
<summary>Changes</summary>
InstSimplify currently folds alloc1 == alloc2 to false, even if one of them is a zero-size allocation. A zero-size allocation may have the same address as another allocation.
This also disables the fold for the case where we're comparing a zero-size alloc with the middle of another allocation. It's possible that this case is legal to fold depending on our precise zero-size allocation semantics, but LangRef currently doesn't specify this either way, so we shouldn't make assumptions here.
---
Full diff: https://github.com/llvm/llvm-project/pull/115728.diff
2 Files Affected:
- (modified) llvm/lib/Analysis/InstructionSimplify.cpp (+2-2)
- (modified) llvm/test/Transforms/InstSimplify/cmp-alloca-offsets.ll (+10-4)
``````````diff
diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index daa468ac095c36..ccb7fd39ba969d 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -2774,8 +2774,8 @@ static Constant *computePointerICmp(CmpInst::Predicate Pred, Value *LHS,
return nullptr;
}(LHS);
Opts.NullIsUnknownSize = F ? NullPointerIsDefined(F) : true;
- if (getObjectSize(LHS, LHSSize, DL, TLI, Opts) &&
- getObjectSize(RHS, RHSSize, DL, TLI, Opts)) {
+ if (getObjectSize(LHS, LHSSize, DL, TLI, Opts) && LHSSize != 0 &&
+ getObjectSize(RHS, RHSSize, DL, TLI, Opts) && RHSSize != 0) {
APInt Dist = LHSOffset - RHSOffset;
if (Dist.isNonNegative() ? Dist.ult(LHSSize) : (-Dist).ult(RHSSize))
return ConstantInt::get(getCompareTy(LHS),
diff --git a/llvm/test/Transforms/InstSimplify/cmp-alloca-offsets.ll b/llvm/test/Transforms/InstSimplify/cmp-alloca-offsets.ll
index d076035b269e46..d2c4b944d21c8f 100644
--- a/llvm/test/Transforms/InstSimplify/cmp-alloca-offsets.ll
+++ b/llvm/test/Transforms/InstSimplify/cmp-alloca-offsets.ll
@@ -234,8 +234,9 @@ define i1 @zst_alloca_start() {
; CHECK-LABEL: @zst_alloca_start(
; CHECK-NEXT: [[A:%.*]] = alloca i64, align 8
; CHECK-NEXT: [[A2:%.*]] = alloca {}, align 8
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq ptr [[A]], [[A2]]
; CHECK-NEXT: call void @escape(ptr [[A]], ptr [[A2]])
-; CHECK-NEXT: ret i1 false
+; CHECK-NEXT: ret i1 [[CMP]]
;
%a = alloca i64
%a2 = alloca {}
@@ -249,8 +250,10 @@ define i1 @zst_alloca_middle() {
; CHECK-LABEL: @zst_alloca_middle(
; CHECK-NEXT: [[A:%.*]] = alloca i64, align 8
; CHECK-NEXT: [[A2:%.*]] = alloca {}, align 8
+; CHECK-NEXT: [[GEP:%.*]] = getelementptr i8, ptr [[A]], i64 4
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq ptr [[GEP]], [[A2]]
; CHECK-NEXT: call void @escape(ptr [[A]], ptr [[A2]])
-; CHECK-NEXT: ret i1 false
+; CHECK-NEXT: ret i1 [[CMP]]
;
%a = alloca i64
%a2 = alloca {}
@@ -282,8 +285,9 @@ define i1 @zst_alloca_end() {
define i1 @zst_global_start() {
; CHECK-LABEL: @zst_global_start(
; CHECK-NEXT: [[A:%.*]] = alloca i64, align 8
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq ptr [[A]], @gz
; CHECK-NEXT: call void @escape(ptr [[A]], ptr @gz)
-; CHECK-NEXT: ret i1 false
+; CHECK-NEXT: ret i1 [[CMP]]
;
%a = alloca i64
%gep = getelementptr i8, ptr %a, i64 0
@@ -295,8 +299,10 @@ define i1 @zst_global_start() {
define i1 @zst_global_middle() {
; CHECK-LABEL: @zst_global_middle(
; CHECK-NEXT: [[A:%.*]] = alloca i64, align 8
+; CHECK-NEXT: [[GEP:%.*]] = getelementptr i8, ptr [[A]], i64 4
+; CHECK-NEXT: [[CMP:%.*]] = icmp eq ptr [[GEP]], @gz
; CHECK-NEXT: call void @escape(ptr [[A]], ptr @gz)
-; CHECK-NEXT: ret i1 false
+; CHECK-NEXT: ret i1 [[CMP]]
;
%a = alloca i64
%gep = getelementptr i8, ptr %a, i64 4
``````````
</details>
https://github.com/llvm/llvm-project/pull/115728