[clang-tools-extra] [clang-tidy]improve performance-unnecessary-value-param performance (PR #128383)

[Congcong Cai via cfe-commits]

https://github.com/HerrCai0907 updated https://github.com/llvm/llvm-project/pull/128383

>From 721393e8f1a464931884be95fef48518f8c351f1 Mon Sep 17 00:00:00 2001
From: Congcong Cai <congcongcai0907 at 163.com>
Date: Sun, 23 Feb 2025 08:36:53 +0800
Subject: [PATCH 1/2] [clang-tidy]improve performance-unnecessary-value-param
 performance

Tolerate fix-it breaking compilation when functions is used as pointers.
`isReferencedOutsideOfCallExpr` will visit the whole translate unit for each matched function decls. It will waste lots of cpu time in some big cpp files.
But the benefits of this validation are limited. Lots of function usage are out of current translation unit.

After removing this validation step, the check profiling changes from 5.7 to 1.1 in SemaExprCXX.cpp, which is similar to version 18.
---
 .../performance/UnnecessaryValueParamCheck.cpp     | 14 +-------------
 clang-tools-extra/docs/ReleaseNotes.rst            |  5 +++++
 .../performance/unnecessary-value-param.cpp        |  6 +-----
 3 files changed, 7 insertions(+), 18 deletions(-)

diff --git a/clang-tools-extra/clang-tidy/performance/UnnecessaryValueParamCheck.cpp b/clang-tools-extra/clang-tidy/performance/UnnecessaryValueParamCheck.cpp
index d356f866a8804..a877f9a7ee912 100644
--- a/clang-tools-extra/clang-tidy/performance/UnnecessaryValueParamCheck.cpp
+++ b/clang-tools-extra/clang-tidy/performance/UnnecessaryValueParamCheck.cpp
@@ -7,7 +7,6 @@
 //===----------------------------------------------------------------------===//
 
 #include "UnnecessaryValueParamCheck.h"
-
 #include "../utils/DeclRefExprUtils.h"
 #include "../utils/FixItHintUtils.h"
 #include "../utils/Matchers.h"
@@ -30,14 +29,6 @@ std::string paramNameOrIndex(StringRef Name, size_t Index) {
       .str();
 }
 
-bool isReferencedOutsideOfCallExpr(const FunctionDecl &Function,
-                                   ASTContext &Context) {
-  auto Matches = match(declRefExpr(to(functionDecl(equalsNode(&Function))),
-                                   unless(hasAncestor(callExpr()))),
-                       Context);
-  return !Matches.empty();
-}
-
 bool hasLoopStmtAncestor(const DeclRefExpr &DeclRef, const Decl &Decl,
                          ASTContext &Context) {
   auto Matches = match(
@@ -155,12 +146,9 @@ void UnnecessaryValueParamCheck::handleConstRefFix(const FunctionDecl &Function,
   // Do not propose fixes when:
   // 1. the ParmVarDecl is in a macro, since we cannot place them correctly
   // 2. the function is virtual as it might break overrides
-  // 3. the function is referenced outside of a call expression within the
-  //    compilation unit as the signature change could introduce build errors.
-  // 4. the function is an explicit template/ specialization.
+  // 3. the function is an explicit template/ specialization.
   const auto *Method = llvm::dyn_cast<CXXMethodDecl>(&Function);
   if (Param.getBeginLoc().isMacroID() || (Method && Method->isVirtual()) ||
-      isReferencedOutsideOfCallExpr(Function, Context) ||
       Function.getTemplateSpecializationKind() == TSK_ExplicitSpecialization)
     return;
   for (const auto *FunctionDecl = &Function; FunctionDecl != nullptr;
diff --git a/clang-tools-extra/docs/ReleaseNotes.rst b/clang-tools-extra/docs/ReleaseNotes.rst
index 6b8fe22242417..22ed7fe07fff9 100644
--- a/clang-tools-extra/docs/ReleaseNotes.rst
+++ b/clang-tools-extra/docs/ReleaseNotes.rst
@@ -110,6 +110,11 @@ 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/unnecessary-value-param
+  <clang-tidy/checks/performance/unnecessary-value-param>` check performance by
+  tolerating fix-it breaking compilation when functions is used as pointers 
+  to avoid matching usage of functions within the current compilation unit.
+
 Removed checks
 ^^^^^^^^^^^^^^
 
diff --git a/clang-tools-extra/test/clang-tidy/checkers/performance/unnecessary-value-param.cpp b/clang-tools-extra/test/clang-tidy/checkers/performance/unnecessary-value-param.cpp
index 7c7ae43698929..60ba7d01420b8 100644
--- a/clang-tools-extra/test/clang-tidy/checkers/performance/unnecessary-value-param.cpp
+++ b/clang-tools-extra/test/clang-tidy/checkers/performance/unnecessary-value-param.cpp
@@ -332,11 +332,7 @@ void PositiveNonConstDeclaration(const ExpensiveToCopyType A) {
 
 void PositiveOnlyMessageAsReferencedInCompilationUnit(ExpensiveToCopyType A) {
   // CHECK-MESSAGES: [[@LINE-1]]:75: warning: the parameter 'A' is copied
-  // CHECK-FIXES: void PositiveOnlyMessageAsReferencedInCompilationUnit(ExpensiveToCopyType A) {
-}
-
-void ReferenceFunctionOutsideOfCallExpr() {
-  void (*ptr)(ExpensiveToCopyType) = &PositiveOnlyMessageAsReferencedInCompilationUnit;
+  // CHECK-FIXES: void PositiveOnlyMessageAsReferencedInCompilationUnit(const ExpensiveToCopyType& A) {
 }
 
 void PositiveMessageAndFixAsFunctionIsCalled(ExpensiveToCopyType A) {

>From ec04d451240c663f03c1e314d3096d5ca72e86fe Mon Sep 17 00:00:00 2001
From: Congcong Cai <congcongcai0907 at 163.com>
Date: Mon, 24 Feb 2025 13:08:17 +0800
Subject: [PATCH 2/2] note break build in doc

---
 .../clang-tidy/checks/performance/unnecessary-value-param.rst | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/clang-tools-extra/docs/clang-tidy/checks/performance/unnecessary-value-param.rst b/clang-tools-extra/docs/clang-tidy/checks/performance/unnecessary-value-param.rst
index d13c53eea994e..dc86530b95f13 100644
--- a/clang-tools-extra/docs/clang-tidy/checks/performance/unnecessary-value-param.rst
+++ b/clang-tools-extra/docs/clang-tidy/checks/performance/unnecessary-value-param.rst
@@ -54,6 +54,10 @@ Will become:
     Field = std::move(Value);
   }
 
+Because the fix-it needs to change the signature of the function, it may break
+builds if the function is used in multiple translation units or some codes
+depends on funcion signatures.
+
 Options
 -------