[clang-tools-extra] [clang-tidy] Fix performance-move-const-arg false negative in ternary… (PR #128402)

[David Rivera via cfe-commits]

https://github.com/RiverDave updated https://github.com/llvm/llvm-project/pull/128402

>From 848be2ccd25fd68b6a2d2037198184b08ff5d6e2 Mon Sep 17 00:00:00 2001
From: Riverdave <davidriverg at gmail.com>
Date: Sat, 22 Feb 2025 03:57:35 -0500
Subject: [PATCH] [clang-tidy] Fix performance-move-const-arg false negative in
 ternary operators

---
 .../performance/MoveConstArgCheck.cpp         | 11 +++++++--
 clang-tools-extra/docs/ReleaseNotes.rst       |  4 ++++
 .../checkers/performance/move-const-arg.cpp   | 23 +++++++++++++++++++
 3 files changed, 36 insertions(+), 2 deletions(-)

diff --git a/clang-tools-extra/clang-tidy/performance/MoveConstArgCheck.cpp b/clang-tools-extra/clang-tidy/performance/MoveConstArgCheck.cpp
index 421ce003975bc..553c1d20cbf1d 100644
--- a/clang-tools-extra/clang-tidy/performance/MoveConstArgCheck.cpp
+++ b/clang-tools-extra/clang-tidy/performance/MoveConstArgCheck.cpp
@@ -44,6 +44,10 @@ void MoveConstArgCheck::registerMatchers(MatchFinder *Finder) {
                unless(isInTemplateInstantiation()))
           .bind("call-move");
 
+  // Match ternary expressions where either branch contains std::move
+  auto TernaryWithMoveMatcher =
+      conditionalOperator(hasDescendant(MoveCallMatcher));
+
   Finder->addMatcher(
       expr(anyOf(
           castExpr(hasSourceExpression(MoveCallMatcher)),
@@ -58,13 +62,16 @@ void MoveConstArgCheck::registerMatchers(MatchFinder *Finder) {
       qualType(rValueReferenceType()).bind("invocation-parm-type");
   // Matches respective ParmVarDecl for a CallExpr or CXXConstructExpr.
   auto ArgumentWithParamMatcher = forEachArgumentWithParam(
-      MoveCallMatcher, parmVarDecl(anyOf(hasType(ConstTypeParmMatcher),
+      anyOf(MoveCallMatcher, TernaryWithMoveMatcher),
+      parmVarDecl(anyOf(hasType(ConstTypeParmMatcher),
                                          hasType(RValueTypeParmMatcher)))
                            .bind("invocation-parm"));
   // Matches respective types of arguments for a CallExpr or CXXConstructExpr
   // and it works on calls through function pointers as well.
   auto ArgumentWithParamTypeMatcher = forEachArgumentWithParamType(
-      MoveCallMatcher, anyOf(ConstTypeParmMatcher, RValueTypeParmMatcher));
+      anyOf(MoveCallMatcher, TernaryWithMoveMatcher),
+      anyOf(ConstTypeParmMatcher, RValueTypeParmMatcher));
+
 
   Finder->addMatcher(
       invocation(anyOf(ArgumentWithParamMatcher, ArgumentWithParamTypeMatcher))
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index 2dcefa2ddec83..b87ea491b3ad1 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -120,6 +120,10 @@ Changes in existing checks
   tolerating fix-it breaking compilation when functions is used as pointers 
   to avoid matching usage of functions within the current compilation unit.
 
+- Improved :doc:`performance-move-const-arg
+  <clang-tidy/checks/performance/move-const-arg>` check by fixing false negatives
+  on ternary operators calling ``std::move``.
+
 Removed checks
 ^^^^^^^^^^^^^^
 
diff --git a/clang-tools-extra/test/clang-tidy/checkers/performance/move-const-arg.cpp b/clang-tools-extra/test/clang-tidy/checkers/performance/move-const-arg.cpp
index 8e325b0ae6ca3..e616cbe78bc3a 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/performance/move-const-arg.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/performance/move-const-arg.cpp
@@ -560,3 +560,26 @@ struct Result {
   // CHECK-MESSAGES: :[[@LINE-1]]:{{[0-9]+}}: warning: passing result of std::move() as a const reference argument; no move will actually happen [performance-move-const-arg]
 };
 } // namespace GH111450
+
+namespace GH126515 {
+
+struct TernaryMoveCall {
+TernaryMoveCall();
+TernaryMoveCall(const TernaryMoveCall&);
+TernaryMoveCall operator=(const TernaryMoveCall&);
+
+void TernaryCheckTriviallyCopyable(const char * c) {}
+
+void testTernaryMove() {
+  TernaryMoveCall t1;
+  TernaryMoveCall other(false ? TernaryMoveCall() : TernaryMoveCall(std::move(t1)) );
+  // CHECK-MESSAGES: :[[@LINE-1]]:69: warning: passing result of std::move() as a const reference argument; no move will actually happen [performance-move-const-arg]
+  // CHECK-MESSAGES: :[[@LINE-11]]:8: note: 'TernaryMoveCall' is not move assignable/constructible
+
+  const char* a = "a";
+  TernaryCheckTriviallyCopyable(true ? std::move(a) : "" );
+  // CHECK-MESSAGES: :[[@LINE-1]]:40: warning: std::move of the variable 'a' of the trivially-copyable type 'const char *' has no effect; remove std::move() [performance-move-const-arg]
+}
+
+};
+} // namespace GH126515