[clang] [LifetimeSafety] Handle xvalue operand of LValueToRValue cast (PR #192312)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Zhijie Wang (aeft)

<details>
<summary>Changes</summary>

Under C++23, P2266 wraps the operand of `return p;` in an xvalue NoOp cast for 
by-value parameters. The `CK_LValueToRValue` branch in FactsGenerator guarded 
on `!SubExpr-&gt;isLValue()`, breaking origin flow and silencing the suggestion 
for `int* id(int* p) { return p; }`.

Use `isGLValue()`, matching how origins are built and stripped elsewhere in the 
analysis.

Only add a RUN in suggestion test file, since some tests in 
`warn-lifetime-safety.cpp` cause a hard error under C++23. For example: 
`MyObj&amp; f() { MyObj s; return s; }`. `error: non-const lvalue reference to 
type 'MyObj' cannot bind to a temporary of type 'MyObj'`.

Fixes: #<!-- -->176292

---
Full diff: https://github.com/llvm/llvm-project/pull/192312.diff


2 Files Affected:

- (modified) clang/lib/Analysis/LifetimeSafety/FactsGenerator.cpp (+1-2) 
- (modified) clang/test/Sema/warn-lifetime-safety-suggestions.cpp (+1) 


``````````diff
diff --git a/clang/lib/Analysis/LifetimeSafety/FactsGenerator.cpp 
b/clang/lib/Analysis/LifetimeSafety/FactsGenerator.cpp
index 5adf842e5f6d0..0d92c38bce826 100644
--- a/clang/lib/Analysis/LifetimeSafety/FactsGenerator.cpp
+++ b/clang/lib/Analysis/LifetimeSafety/FactsGenerator.cpp
@@ -288,8 +288,7 @@ void FactsGenerator::VisitCastExpr(const CastExpr *CE) {
 
   switch (CE->getCastKind()) {
   case CK_LValueToRValue:
-    // TODO: Decide what to do for x-values here.
-    if (!SubExpr->isLValue())
+    if (!SubExpr->isGLValue())
       return;
 
     assert(Src && "LValue being cast to RValue has no origin list");
diff --git a/clang/test/Sema/warn-lifetime-safety-suggestions.cpp 
b/clang/test/Sema/warn-lifetime-safety-suggestions.cpp
index d2cf1c175eb57..a1ea1182ee5f0 100644
--- a/clang/test/Sema/warn-lifetime-safety-suggestions.cpp
+++ b/clang/test/Sema/warn-lifetime-safety-suggestions.cpp
@@ -1,6 +1,7 @@
 // RUN: rm -rf %t
 // RUN: split-file %s %t
 // RUN: %clang_cc1 -fsyntax-only -flifetime-safety-inference 
-fexperimental-lifetime-safety-tu-analysis -Wlifetime-safety-suggestions 
-Wlifetime-safety -Wno-dangling -I%t -I%S -verify %t/test_source.cpp
+// RUN: %clang_cc1 -fsyntax-only -std=c++23 -flifetime-safety-inference 
-fexperimental-lifetime-safety-tu-analysis -Wlifetime-safety-suggestions 
-Wlifetime-safety -Wno-dangling -I%t -I%S -verify %t/test_source.cpp
 // RUN: %clang_cc1 -flifetime-safety-inference 
-fexperimental-lifetime-safety-tu-analysis -Wlifetime-safety-suggestions 
-Wlifetime-safety -Wno-dangling -I%t -I%S -fixit %t/test_source.cpp
 // RUN: %clang_cc1 -fsyntax-only -flifetime-safety-inference 
-fexperimental-lifetime-safety-tu-analysis -Wlifetime-safety-suggestions 
-Wno-dangling -I%t -I%S -Werror=lifetime-safety-suggestions %t/test_source.cpp
 

``````````

</details>


https://github.com/llvm/llvm-project/pull/192312
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