[clang-tidy] Fix performance-move-const-arg false negative in ternary… #128402

RiverDave · 2025-02-23T05:41:47Z

This PR aims to fix performance-move-const-arg #126515

Changes

Enhanced the performance-move-arg check in Clang-Tidy to detect cases where std::move is used
in ternary operator expressions which was not being matched therefore being tagged as a false negative

Testing

A new mock class has been where the changes have been tested & all tests pass

I'd appreciate any feedback since this is my first time contributing to LLVM.

github-actions · 2025-02-23T05:42:03Z

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llvmbot · 2025-02-23T05:42:32Z

@llvm/pr-subscribers-clang-tidy

@llvm/pr-subscribers-clang-tools-extra

Author: David Rivera (RiverDave)

Changes

This PR aims to fix performance-move-const-arg #126515

Changes

Enhanced the performance-move-arg check in Clang-Tidy to detect cases where std::move is used
in ternary expressions which was not being detected before

Testing

A new mock class has been where the changes have been tested & all tests pass

Full diff: https://github.com/llvm/llvm-project/pull/128402.diff

3 Files Affected:

(modified) clang-tools-extra/clang-tidy/performance/MoveConstArgCheck.cpp (+11-2)
(modified) clang-tools-extra/docs/ReleaseNotes.rst (+4)
(modified) clang-tools-extra/test/clang-tidy/checkers/performance/move-const-arg.cpp (+23)

diff --git a/clang-tools-extra/clang-tidy/performance/MoveConstArgCheck.cpp b/clang-tools-extra/clang-tidy/performance/MoveConstArgCheck.cpp
index 421ce003975bc..3de41e707cfd7 100644
--- a/clang-tools-extra/clang-tidy/performance/MoveConstArgCheck.cpp
+++ b/clang-tools-extra/clang-tidy/performance/MoveConstArgCheck.cpp
@@ -44,6 +44,12 @@ void MoveConstArgCheck::registerMatchers(MatchFinder *Finder) {
                unless(isInTemplateInstantiation()))
           .bind("call-move");
 
+  // Match ternary expressions where either branch contains std::move
+  auto TernaryWithMoveMatcher =
+      conditionalOperator(
+            hasDescendant(MoveCallMatcher)
+      ).bind("ternary-move");
+
   Finder->addMatcher(
       expr(anyOf(
           castExpr(hasSourceExpression(MoveCallMatcher)),
@@ -58,13 +64,16 @@ 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 41ff1c1016f25..2eb65d61f5e78 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -115,6 +115,10 @@ Changes in existing checks
   <clang-tidy/checks/misc/redundant-expression>` check by providing additional
   examples and fixing some macro related false positives.
 
+- 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

HerrCai0907

lgtm. please run git-clang-format also. i think there are format issue in the new code.

clang-tools-extra/clang-tidy/performance/MoveConstArgCheck.cpp

RiverDave · 2025-02-23T16:34:08Z

lgtm. please run git-clang-format also. i think there are format issue in the new code.

Thx @HerrCai0907, your feedback has been addresed.

github-actions · 2025-02-27T01:21:00Z

✅ With the latest revision this PR passed the C/C++ code formatter.

… operators

RiverDave · 2025-02-27T03:21:15Z

⚠️ C/C++ code formatter, clang-format found issues in your code. ⚠️

You can test this locally with the following command:

git-clang-format --diff 5d501c6137976ff1f14f3b0e2e593fb9740d0146 848be2ccd25fd68b6a2d2037198184b08ff5d6e2 --extensions cpp -- clang-tools-extra/clang-tidy/performance/MoveConstArgCheck.cpp clang-tools-extra/test/clang-tidy/checkers/performance/move-const-arg.cpp

View the diff from clang-format here.

diff --git a/clang-tools-extra/clang-tidy/performance/MoveConstArgCheck.cpp b/clang-tools-extra/clang-tidy/performance/MoveConstArgCheck.cpp
index 553c1d20cb..703ad162f9 100644
--- a/clang-tools-extra/clang-tidy/performance/MoveConstArgCheck.cpp
+++ b/clang-tools-extra/clang-tidy/performance/MoveConstArgCheck.cpp
@@ -63,16 +63,15 @@ void MoveConstArgCheck::registerMatchers(MatchFinder *Finder) {
   // Matches respective ParmVarDecl for a CallExpr or CXXConstructExpr.
   auto ArgumentWithParamMatcher = forEachArgumentWithParam(
       anyOf(MoveCallMatcher, TernaryWithMoveMatcher),
-      parmVarDecl(anyOf(hasType(ConstTypeParmMatcher),
-                                         hasType(RValueTypeParmMatcher)))
-                           .bind("invocation-parm"));
+      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(
       anyOf(MoveCallMatcher, TernaryWithMoveMatcher),
       anyOf(ConstTypeParmMatcher, RValueTypeParmMatcher));
 
-
   Finder->addMatcher(
       invocation(anyOf(ArgumentWithParamMatcher, ArgumentWithParamTypeMatcher))
           .bind("receiving-expr"),

This should be fixed now

github-actions · 2025-02-27T11:35:33Z

@RiverDave Congratulations on having your first Pull Request (PR) merged into the LLVM Project!

Your changes will be combined with recent changes from other authors, then tested by our build bots. If there is a problem with a build, you may receive a report in an email or a comment on this PR.

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llvm#128402) This PR aims to fix `performance-move-const-arg` llvm#126515 ## Changes Enhanced the `performance-move-arg` check in Clang-Tidy to detect cases where `std::move` is used in **ternary operator expressions which was not being matched therefore being tagged as a false negative** ## Testing - A new mock class has been where the changes have been tested & all tests pass I'd appreciate any feedback since this is my first time contributing to LLVM.

llvmbot added clang-tools-extra clang-tidy labels Feb 23, 2025

HerrCai0907 approved these changes Feb 23, 2025

View reviewed changes

clang-tools-extra/clang-tidy/performance/MoveConstArgCheck.cpp Outdated Show resolved Hide resolved

RiverDave force-pushed the performance/performance-move-const-arg_126515 branch from d9dbf1b to 5eef2a5 Compare February 23, 2025 16:23

EugeneZelenko requested review from PiotrZSL and 5chmidti February 24, 2025 16:02

RiverDave force-pushed the performance/performance-move-const-arg_126515 branch 2 times, most recently from 9689edf to 848be2c Compare February 26, 2025 17:50

[clang-tidy] Fix performance-move-const-arg false negative in ternary…

f5e2695

… operators

RiverDave force-pushed the performance/performance-move-const-arg_126515 branch from 848be2c to f5e2695 Compare February 27, 2025 03:21

HerrCai0907 merged commit 556e4db into llvm:main Feb 27, 2025
10 of 12 checks passed

huaatian mentioned this pull request Feb 28, 2025

fix live interval empty issue huaatian/llvm-project#1

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HerrCai0907 linked an issue Mar 4, 2025 that may be closed by this pull request

performance-move-const-arg not detected with ternary #126515

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