[llvm] [AA] Consider extractvalue and extractelement as escape sources (PR #127640)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-analysis

Author: Nikita Popov (nikic)

<details>
<summary>Changes</summary>

CaptureTracking considers insertions into aggregates and vectors as captures. As such, extractions from aggregates and vectors are escape sources. A non-escaping identified local cannot alias with the result of an extractvalue/extractelement.

Fixes https://github.com/llvm/llvm-project/issues/126670.

---
Full diff: https://github.com/llvm/llvm-project/pull/127640.diff


2 Files Affected:

- (modified) llvm/lib/Analysis/AliasAnalysis.cpp (+6) 
- (modified) llvm/test/Analysis/BasicAA/escape-source-aggregate.ll (+25-2) 


``````````diff
diff --git a/llvm/lib/Analysis/AliasAnalysis.cpp b/llvm/lib/Analysis/AliasAnalysis.cpp
index 58297accc7f1f..aa72fb844ef32 100644
--- a/llvm/lib/Analysis/AliasAnalysis.cpp
+++ b/llvm/lib/Analysis/AliasAnalysis.cpp
@@ -859,6 +859,12 @@ bool llvm::isEscapeSource(const Value *V) {
   if (isa<IntToPtrInst>(V))
     return true;
 
+  // Capture tracking considers insertions into aggregates and vectors as
+  // captures. As such, extractions from aggregates and vectors are escape
+  // sources.
+  if (isa<ExtractValueInst, ExtractElementInst>(V))
+    return true;
+
   // Same for inttoptr constant expressions.
   if (auto *CE = dyn_cast<ConstantExpr>(V))
     if (CE->getOpcode() == Instruction::IntToPtr)
diff --git a/llvm/test/Analysis/BasicAA/escape-source-aggregate.ll b/llvm/test/Analysis/BasicAA/escape-source-aggregate.ll
index cef11b94f3873..872715f31011d 100644
--- a/llvm/test/Analysis/BasicAA/escape-source-aggregate.ll
+++ b/llvm/test/Analysis/BasicAA/escape-source-aggregate.ll
@@ -2,8 +2,9 @@
 
 declare { ptr, i1 } @get_struct()
 declare <2 x ptr> @get_vec()
+declare void @escape(ptr)
 
-; CHECK: MayAlias: i32* %a, i32* %extract
+; CHECK: NoAlias: i32* %a, i32* %extract
 define i32 @test_extractvalue() {
   %a = alloca i32
   %call = call { ptr, i1 } @get_struct()
@@ -13,7 +14,7 @@ define i32 @test_extractvalue() {
   ret i32 %v
 }
 
-; CHECK: MayAlias: i32* %a, i32* %extract
+; CHECK: NoAlias: i32* %a, i32* %extract
 define i32 @test_extractelement() {
   %a = alloca i32
   %call = call <2 x ptr> @get_vec()
@@ -22,3 +23,25 @@ define i32 @test_extractelement() {
   %v = load i32, ptr %a
   ret i32 %v
 }
+
+; CHECK: MayAlias: i32* %a, i32* %extract
+define i32 @test_extractvalue_escape() {
+  %a = alloca i32
+  call void @escape(ptr %a)
+  %call = call { ptr, i1 } @get_struct()
+  %extract = extractvalue { ptr, i1 } %call, 0
+  store i32 0, ptr %extract
+  %v = load i32, ptr %a
+  ret i32 %v
+}
+
+; CHECK: MayAlias: i32* %a, i32* %extract
+define i32 @test_extractelement_escape() {
+  %a = alloca i32
+  call void @escape(ptr %a)
+  %call = call <2 x ptr> @get_vec()
+  %extract = extractelement <2 x ptr> %call, i32 0
+  store i32 0, ptr %extract
+  %v = load i32, ptr %a
+  ret i32 %v
+}

``````````

</details>


https://github.com/llvm/llvm-project/pull/127640