[MemCpyOpt] Allow stack move optimization if one address captured #165527
+73
−5
Conversation
This file contains hidden or bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Allow the stack move optimization (which merges two allocas) when the address of only one alloca is captured (and the provenance is not captured). Both addresses need to be captured to observe that the allocas were merged.
|
@llvm/pr-subscribers-llvm-transforms Author: Nikita Popov (nikic) ChangesAllow the stack move optimization (which merges two allocas) when the address of only one alloca is captured (and the provenance is not captured). Both addresses need to be captured to observe that the allocas were merged. Fixes #165484. Full diff: https://github.com/llvm/llvm-project/pull/165527.diff 2 Files Affected:
diff --git a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
index e043d072a7638..08be5df9872b7 100644
--- a/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
+++ b/llvm/lib/Transforms/Scalar/MemCpyOptimizer.cpp
@@ -1534,8 +1534,8 @@ bool MemCpyOptPass::performStackMoveOptzn(Instruction *Load, Instruction *Store,
bool SrcNotDom = false;
auto CaptureTrackingWithModRef =
- [&](Instruction *AI,
- function_ref<bool(Instruction *)> ModRefCallback) -> bool {
+ [&](Instruction *AI, function_ref<bool(Instruction *)> ModRefCallback,
+ bool &AddressCaptured) -> bool {
SmallVector<Instruction *, 8> Worklist;
Worklist.push_back(AI);
unsigned MaxUsesToExplore = getDefaultMaxUsesToExploreForCaptureTracking();
@@ -1559,8 +1559,9 @@ bool MemCpyOptPass::performStackMoveOptzn(Instruction *Load, Instruction *Store,
if (!Visited.insert(&U).second)
continue;
UseCaptureInfo CI = DetermineUseCaptureKind(U, AI);
- if (capturesAnything(CI.UseCC))
+ if (capturesAnyProvenance(CI.UseCC))
return false;
+ AddressCaptured |= capturesAddress(CI.UseCC);
if (UI->mayReadOrWriteMemory()) {
if (UI->isLifetimeStartOrEnd()) {
@@ -1627,7 +1628,9 @@ bool MemCpyOptPass::performStackMoveOptzn(Instruction *Load, Instruction *Store,
return true;
};
- if (!CaptureTrackingWithModRef(DestAlloca, DestModRefCallback))
+ bool DestAddressCaptured = false;
+ if (!CaptureTrackingWithModRef(DestAlloca, DestModRefCallback,
+ DestAddressCaptured))
return false;
// Bailout if Dest may have any ModRef before Store.
if (!ReachabilityWorklist.empty() &&
@@ -1653,7 +1656,14 @@ bool MemCpyOptPass::performStackMoveOptzn(Instruction *Load, Instruction *Store,
return true;
};
- if (!CaptureTrackingWithModRef(SrcAlloca, SrcModRefCallback))
+ bool SrcAddressCaptured = false;
+ if (!CaptureTrackingWithModRef(SrcAlloca, SrcModRefCallback,
+ SrcAddressCaptured))
+ return false;
+
+ // If both the source and destination address are captured, the fact that they
+ // are no longer two separate allocations may be observed.
+ if (DestAddressCaptured && SrcAddressCaptured)
return false;
// We can do the transformation. First, move the SrcAlloca to the start of the
diff --git a/llvm/test/Transforms/MemCpyOpt/stack-move.ll b/llvm/test/Transforms/MemCpyOpt/stack-move.ll
index 940e30ec46881..0c2e05fa8fed6 100644
--- a/llvm/test/Transforms/MemCpyOpt/stack-move.ll
+++ b/llvm/test/Transforms/MemCpyOpt/stack-move.ll
@@ -1729,3 +1729,61 @@ define i32 @test_ret_only_capture() {
%v = load i32, ptr %a
ret i32 %v
}
+
+declare ptr @captures_address_only(ptr captures(address))
+
+; Can transform: Only one address captured.
+define void @test_captures_address_captures_none() {
+; CHECK-LABEL: define void @test_captures_address_captures_none() {
+; CHECK-NEXT: [[SRC:%.*]] = alloca [[STRUCT_FOO:%.*]], align 4
+; CHECK-NEXT: store [[STRUCT_FOO]] { i32 10, i32 20, i32 30 }, ptr [[SRC]], align 4
+; CHECK-NEXT: call void @captures_address_only(ptr [[SRC]])
+; CHECK-NEXT: call void @use_nocapture(ptr [[SRC]])
+; CHECK-NEXT: ret void
+;
+ %src = alloca %struct.Foo, align 4
+ %dst = alloca %struct.Foo, align 4
+ store %struct.Foo { i32 10, i32 20, i32 30 }, ptr %src
+ call void @captures_address_only(ptr %src)
+ call void @llvm.memcpy.p0.p0.i64(ptr align 4 %dst, ptr align 4 %src, i64 12, i1 false)
+ call void @use_nocapture(ptr %dst)
+ ret void
+}
+
+; Can transform: Only one address captured.
+define void @test_captures_none_and_captures_address() {
+; CHECK-LABEL: define void @test_captures_none_and_captures_address() {
+; CHECK-NEXT: [[SRC:%.*]] = alloca [[STRUCT_FOO:%.*]], align 4
+; CHECK-NEXT: store [[STRUCT_FOO]] { i32 10, i32 20, i32 30 }, ptr [[SRC]], align 4
+; CHECK-NEXT: call void @use_nocapture(ptr [[SRC]])
+; CHECK-NEXT: call void @captures_address_only(ptr [[SRC]])
+; CHECK-NEXT: ret void
+;
+ %src = alloca %struct.Foo, align 4
+ %dst = alloca %struct.Foo, align 4
+ store %struct.Foo { i32 10, i32 20, i32 30 }, ptr %src
+ call void @use_nocapture(ptr %src)
+ call void @llvm.memcpy.p0.p0.i64(ptr align 4 %dst, ptr align 4 %src, i64 12, i1 false)
+ call void @captures_address_only(ptr %dst)
+ ret void
+}
+
+; Cannot transform: Both addresses captured.
+define void @test_captures_address_and_captures_address() {
+; CHECK-LABEL: define void @test_captures_address_and_captures_address() {
+; CHECK-NEXT: [[SRC:%.*]] = alloca [[STRUCT_FOO:%.*]], align 4
+; CHECK-NEXT: [[DST:%.*]] = alloca [[STRUCT_FOO]], align 4
+; CHECK-NEXT: store [[STRUCT_FOO]] { i32 10, i32 20, i32 30 }, ptr [[SRC]], align 4
+; CHECK-NEXT: call void @captures_address_only(ptr [[SRC]])
+; CHECK-NEXT: call void @llvm.memcpy.p0.p0.i64(ptr align 4 [[DST]], ptr align 4 [[SRC]], i64 12, i1 false)
+; CHECK-NEXT: call void @captures_address_only(ptr [[DST]])
+; CHECK-NEXT: ret void
+;
+ %src = alloca %struct.Foo, align 4
+ %dst = alloca %struct.Foo, align 4
+ store %struct.Foo { i32 10, i32 20, i32 30 }, ptr %src
+ call void @captures_address_only(ptr %src)
+ call void @llvm.memcpy.p0.p0.i64(ptr align 4 %dst, ptr align 4 %src, i64 12, i1 false)
+ call void @captures_address_only(ptr %dst)
+ ret void
+}
|
aokblast
pushed a commit
to aokblast/llvm-project
that referenced
this pull request
Oct 30, 2025
…vm#165527) Allow the stack move optimization (which merges two allocas) when the address of only one alloca is captured (and the provenance is not captured). Both addresses need to be captured to observe that the allocas were merged. Fixes llvm#165484.
Sign up for free
to join this conversation on GitHub.
Already have an account?
Sign in to comment
3 participants
Add this suggestion to a batch that can be applied as a single commit.
This suggestion is invalid because no changes were made to the code.
Suggestions cannot be applied while the pull request is closed.
Suggestions cannot be applied while viewing a subset of changes.
Only one suggestion per line can be applied in a batch.
Add this suggestion to a batch that can be applied as a single commit.
Applying suggestions on deleted lines is not supported.
You must change the existing code in this line in order to create a valid suggestion.
Outdated suggestions cannot be applied.
This suggestion has been applied or marked resolved.
Suggestions cannot be applied from pending reviews.
Suggestions cannot be applied on multi-line comments.
Suggestions cannot be applied while the pull request is queued to merge.
Suggestion cannot be applied right now. Please check back later.
Allow the stack move optimization (which merges two allocas) when the address of only one alloca is captured (and the provenance is not captured). Both addresses need to be captured to observe that the allocas were merged.
Fixes #165484.