[clang] [clang] Detect pointee mutations in placement new expressions (PR #187508)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-clang

Author: Berkay Sahin (berkaysahiin)

<details>
<summary>Changes</summary>

Fixes #<!-- -->187012 which is a false positive on clang-tidy end.

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Full diff: https://github.com/llvm/llvm-project/pull/187508.diff


2 Files Affected:

- (modified) clang/lib/Analysis/ExprMutationAnalyzer.cpp (+2) 
- (modified) clang/unittests/Analysis/ExprMutationAnalyzerTest.cpp (+9) 


``````````diff
diff --git a/clang/lib/Analysis/ExprMutationAnalyzer.cpp b/clang/lib/Analysis/ExprMutationAnalyzer.cpp
index 86d7dcab807d3..5def6ba3cac5a 100644
--- a/clang/lib/Analysis/ExprMutationAnalyzer.cpp
+++ b/clang/lib/Analysis/ExprMutationAnalyzer.cpp
@@ -787,6 +787,8 @@ ExprMutationAnalyzer::Analyzer::findPointeeToNonConst(const Expr *Exp) {
       anyOf(ArgOfNonConstParameter, ArgOfInstantiationDependent);
   const auto PassAsNonConstArg =
       expr(anyOf(cxxUnresolvedConstructExpr(ArgOfInstantiationDependent),
+                 cxxNewExpr(hasAnyPlacementArg(
+                     ignoringParenImpCasts(canResolveToExprPointee(Exp)))),
                  cxxConstructExpr(CallLikeMatcher), callExpr(CallLikeMatcher),
                  parenListExpr(has(canResolveToExprPointee(Exp))),
                  initListExpr(hasAnyInit(canResolveToExprPointee(Exp)))));
diff --git a/clang/unittests/Analysis/ExprMutationAnalyzerTest.cpp b/clang/unittests/Analysis/ExprMutationAnalyzerTest.cpp
index d171d47ac1fef..27c0be6b74fcc 100644
--- a/clang/unittests/Analysis/ExprMutationAnalyzerTest.cpp
+++ b/clang/unittests/Analysis/ExprMutationAnalyzerTest.cpp
@@ -1801,6 +1801,15 @@ TEST(ExprMutationAnalyzerTest, PointeeMutatedByPassAsArgument) {
         match(withEnclosingCompound(declRefTo("x")), AST->getASTContext());
     EXPECT_TRUE(isPointeeMutated(Results, AST.get()));
   }
+  {
+    const std::string Code =
+        "void* operator new(unsigned long, void* p) noexcept;"
+        "void f() { int* x = nullptr; new(x) int{311}; }";
+    auto AST = buildASTFromCodeWithArgs(Code, {});
+    auto Results =
+        match(withEnclosingCompound(declRefTo("x")), AST->getASTContext());
+    EXPECT_TRUE(isPointeeMutated(Results, AST.get()));
+  }
 }
 
 TEST(ExprMutationAnalyzerTest, PointeeMutatedByPassAsArgumentInConstruct) {

``````````

</details>


https://github.com/llvm/llvm-project/pull/187508