[clang] [Clang] enhance loop analysis to handle variable changes inside lambdas (PR #135573)

[Oleksandr T. via cfe-commits]

https://github.com/a-tarasyuk created https://github.com/llvm/llvm-project/pull/135573

Fixes #132038 

--- 

This PR extends `-Wloop-analysis` to handle variable modifications inside lambda expressions.


>From 05125bafc45755624973feba0f4e6c2050fad36f Mon Sep 17 00:00:00 2001
From: Oleksandr Tarasiuk <oleksandr.tarasiuk at outlook.com>
Date: Mon, 14 Apr 2025 01:37:05 +0300
Subject: [PATCH] [Clang] enhance loop analysis to handle variable changes
 inside lambdas

---
 clang/docs/ReleaseNotes.rst               |  2 ++
 clang/lib/Sema/SemaStmt.cpp               | 14 ++++++++++++--
 clang/test/SemaCXX/warn-loop-analysis.cpp | 15 +++++++++++++++
 3 files changed, 29 insertions(+), 2 deletions(-)

diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst
index 5217e04b5e83f..77d15d798097b 100644
--- a/clang/docs/ReleaseNotes.rst
+++ b/clang/docs/ReleaseNotes.rst
@@ -319,6 +319,8 @@ Improvements to Clang's diagnostics
 - ``-Wc++98-compat`` no longer diagnoses use of ``__auto_type`` or
   ``decltype(auto)`` as though it was the extension for ``auto``. (#GH47900)
 
+- The ``-Wloop-analysis`` warning now handles variable modifications inside lambda expressions (#GH132038).
+
 Improvements to Clang's time-trace
 ----------------------------------
 
diff --git a/clang/lib/Sema/SemaStmt.cpp b/clang/lib/Sema/SemaStmt.cpp
index e1b9ccc693bd5..a1718d5a549e4 100644
--- a/clang/lib/Sema/SemaStmt.cpp
+++ b/clang/lib/Sema/SemaStmt.cpp
@@ -1995,9 +1995,19 @@ namespace {
     }
 
     void VisitDeclRefExpr(DeclRefExpr *E) {
-      if (VarDecl *VD = dyn_cast<VarDecl>(E->getDecl()))
+      if (VarDecl *VD = dyn_cast<VarDecl>(E->getDecl())) {
         if (Decls.count(VD))
           FoundDecl = true;
+      } else {
+        if (CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(E->getDecl()))
+          if (isLambdaCallOperator(MD))
+            Visit(MD->getBody());
+      }
+    }
+
+    void VisitCXXOperatorCallExpr(CXXOperatorCallExpr *E) {
+      if (Expr *Callee = E->getCallee())
+        Visit(Callee);
     }
 
     void VisitPseudoObjectExpr(PseudoObjectExpr *POE) {
@@ -2014,7 +2024,7 @@ namespace {
 
     bool FoundDeclInUse() { return FoundDecl; }
 
-  };  // end class DeclMatcher
+  }; // end class DeclMatcher
 
   void CheckForLoopConditionalStatement(Sema &S, Expr *Second,
                                         Expr *Third, Stmt *Body) {
diff --git a/clang/test/SemaCXX/warn-loop-analysis.cpp b/clang/test/SemaCXX/warn-loop-analysis.cpp
index 324dd386292ac..cfed3c23a2e9e 100644
--- a/clang/test/SemaCXX/warn-loop-analysis.cpp
+++ b/clang/test/SemaCXX/warn-loop-analysis.cpp
@@ -299,3 +299,18 @@ void test10() {
   for (auto[i, j, k] = arr; i < a; ++i) { }
   for (auto[i, j, k] = arr; i < a; ++arr[0]) { }
 };
+
+extern void foo(int);
+void test11() {
+  int a = 0;
+  auto incr_a = [&a]() { ++a; };
+
+  for (int b = 10; a <= b; incr_a())
+    foo(a);
+
+  for (int b = 10; a <= b;)
+    incr_a();
+
+  for (int b = 10; a <= b; [&a]() { ++a; }()) { }
+  for (int b = 10; a <= b; [&a]() { }()) { } // expected-warning {{variables 'a' and 'b' used in loop condition not modified in loop body}}
+}