[clang] [analysis] assume expr is not mutated after analysis to avoid recursive (PR #90581)

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llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-clang

@llvm/pr-subscribers-clang-analysis

Author: Congcong Cai (HerrCai0907)

<details>
<summary>Changes</summary>

Fixes: #<!-- -->89376.


---
Full diff: https://github.com/llvm/llvm-project/pull/90581.diff


2 Files Affected:

- (modified) clang/lib/Analysis/ExprMutationAnalyzer.cpp (+4-2) 
- (modified) clang/unittests/Analysis/ExprMutationAnalyzerTest.cpp (+24-2) 


``````````diff
diff --git a/clang/lib/Analysis/ExprMutationAnalyzer.cpp b/clang/lib/Analysis/ExprMutationAnalyzer.cpp
index 941322be8f870b..3b3782fa1db9a0 100644
--- a/clang/lib/Analysis/ExprMutationAnalyzer.cpp
+++ b/clang/lib/Analysis/ExprMutationAnalyzer.cpp
@@ -235,15 +235,17 @@ const Stmt *ExprMutationAnalyzer::Analyzer::findMutationMemoized(
   if (Memoized != MemoizedResults.end())
     return Memoized->second;
 
+  // Assume Exp is not mutated before analyzing Exp.
+  MemoizedResults[Exp] = nullptr;
   if (isUnevaluated(Exp))
-    return MemoizedResults[Exp] = nullptr;
+    return nullptr;
 
   for (const auto &Finder : Finders) {
     if (const Stmt *S = (this->*Finder)(Exp))
       return MemoizedResults[Exp] = S;
   }
 
-  return MemoizedResults[Exp] = nullptr;
+  return nullptr;
 }
 
 const Stmt *
diff --git a/clang/unittests/Analysis/ExprMutationAnalyzerTest.cpp b/clang/unittests/Analysis/ExprMutationAnalyzerTest.cpp
index 9c1dc1a76db63d..79ccb024283c35 100644
--- a/clang/unittests/Analysis/ExprMutationAnalyzerTest.cpp
+++ b/clang/unittests/Analysis/ExprMutationAnalyzerTest.cpp
@@ -10,8 +10,8 @@
 #include "clang/AST/TypeLoc.h"
 #include "clang/ASTMatchers/ASTMatchFinder.h"
 #include "clang/ASTMatchers/ASTMatchers.h"
+#include "clang/Frontend/ASTUnit.h"
 #include "clang/Tooling/Tooling.h"
-#include "llvm/ADT/SmallString.h"
 #include "gmock/gmock.h"
 #include "gtest/gtest.h"
 #include <cctype>
@@ -43,7 +43,7 @@ std::unique_ptr<ASTUnit> buildASTFromCode(const Twine &Code) {
 }
 
 ExprMatcher declRefTo(StringRef Name) {
-  return declRefExpr(to(namedDecl(hasName(Name))));
+  return declRefExpr(to(namedDecl(hasName(Name)).bind("decl")));
 }
 
 StmtMatcher withEnclosingCompound(ExprMatcher Matcher) {
@@ -57,6 +57,13 @@ bool isMutated(const SmallVectorImpl<BoundNodes> &Results, ASTUnit *AST) {
   return ExprMutationAnalyzer(*S, AST->getASTContext()).isMutated(E);
 }
 
+bool isDeclMutated(const SmallVectorImpl<BoundNodes> &Results, ASTUnit *AST) {
+  const auto *const S = selectFirst<Stmt>("stmt", Results);
+  const auto *const D = selectFirst<Decl>("decl", Results);
+  TraversalKindScope RAII(AST->getASTContext(), TK_AsIs);
+  return ExprMutationAnalyzer(*S, AST->getASTContext()).isMutated(D);
+}
+
 SmallVector<std::string, 1>
 mutatedBy(const SmallVectorImpl<BoundNodes> &Results, ASTUnit *AST) {
   const auto *const S = selectFirst<Stmt>("stmt", Results);
@@ -1552,6 +1559,21 @@ TEST(ExprMutationAnalyzerTest, UniquePtr) {
 
 // section: complex problems detected on real code
 
+TEST(ExprMutationAnalyzerTest, SelfRef) {
+  std::unique_ptr<ASTUnit> AST{};
+  SmallVector<BoundNodes, 1> Results{};
+
+  AST = buildASTFromCodeWithArgs("void f() { int &x = x; }",
+                                 {"-Wno-unused-value", "-Wno-uninitialized"});
+  Results = match(withEnclosingCompound(declRefTo("x")), AST->getASTContext());
+  EXPECT_FALSE(isDeclMutated(Results, AST.get()));
+
+  AST = buildASTFromCodeWithArgs("void f() { int &x = x; x = 1; }",
+                                 {"-Wno-unused-value", "-Wno-uninitialized"});
+  Results = match(withEnclosingCompound(declRefTo("x")), AST->getASTContext());
+  EXPECT_TRUE(isDeclMutated(Results, AST.get()));
+}
+
 TEST(ExprMutationAnalyzerTest, UnevaluatedContext) {
   const std::string Example =
       "template <typename T>"

``````````

</details>


https://github.com/llvm/llvm-project/pull/90581