[llvm] [SimplifyCFG] Only consider provenance capture in store speculation (PR #138548)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Nikita Popov (nikic)

<details>
<summary>Changes</summary>

The capture check here is to protect against concurrent accesses from other threads. This requires the provenance to escape.

---
Full diff: https://github.com/llvm/llvm-project/pull/138548.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/Utils/SimplifyCFG.cpp (+3-1) 
- (modified) llvm/test/Transforms/SimplifyCFG/speculate-store.ll (+2-5) 


``````````diff
diff --git a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
index 33af582a9e0a9..bde2e9d8ab8e3 100644
--- a/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyCFG.cpp
@@ -3057,7 +3057,9 @@ static Value *isSafeToSpeculateStore(Instruction *I, BasicBlock *BrBB,
         Value *Obj = getUnderlyingObject(StorePtr);
         bool ExplicitlyDereferenceableOnly;
         if (isWritableObject(Obj, ExplicitlyDereferenceableOnly) &&
-            !PointerMayBeCaptured(Obj, /*ReturnCaptures=*/false) &&
+            capturesNothing(
+                PointerMayBeCaptured(Obj, /*ReturnCaptures=*/false,
+                                     CaptureComponents::Provenance)) &&
             (!ExplicitlyDereferenceableOnly ||
              isDereferenceablePointer(StorePtr, StoreTy,
                                       LI->getDataLayout()))) {
diff --git a/llvm/test/Transforms/SimplifyCFG/speculate-store.ll b/llvm/test/Transforms/SimplifyCFG/speculate-store.ll
index 22ffe213856b0..161ec380d31cf 100644
--- a/llvm/test/Transforms/SimplifyCFG/speculate-store.ll
+++ b/llvm/test/Transforms/SimplifyCFG/speculate-store.ll
@@ -203,11 +203,8 @@ define i32 @load_before_store_escape_addr_only(i64 %i, i32 %b)  {
 ; CHECK-NEXT:    [[ARRAYIDX:%.*]] = getelementptr inbounds [2 x i32], ptr [[A]], i64 0, i64 [[I:%.*]]
 ; CHECK-NEXT:    [[TMP0:%.*]] = load i32, ptr [[ARRAYIDX]], align 4
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp slt i32 [[TMP0]], [[B:%.*]]
-; CHECK-NEXT:    br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_END:%.*]]
-; CHECK:       if.then:
-; CHECK-NEXT:    store i32 [[B]], ptr [[ARRAYIDX]], align 4
-; CHECK-NEXT:    br label [[IF_END]]
-; CHECK:       if.end:
+; CHECK-NEXT:    [[SPEC_STORE_SELECT:%.*]] = select i1 [[CMP]], i32 [[B]], i32 [[TMP0]]
+; CHECK-NEXT:    store i32 [[SPEC_STORE_SELECT]], ptr [[ARRAYIDX]], align 4
 ; CHECK-NEXT:    [[TMP1:%.*]] = load i32, ptr [[A]], align 4
 ; CHECK-NEXT:    [[ARRAYIDX2:%.*]] = getelementptr inbounds [2 x i32], ptr [[A]], i64 0, i64 1
 ; CHECK-NEXT:    [[TMP2:%.*]] = load i32, ptr [[ARRAYIDX2]], align 4

``````````

</details>


https://github.com/llvm/llvm-project/pull/138548