From 519de4b69205a17df69250e92423d8bd482bbf99 Mon Sep 17 00:00:00 2001
From: Felix Berger <flx@google.com>
Date: Fri, 16 Dec 2016 02:47:56 +0000
Subject: [PATCH] [clang-tidy] Do not move parameter if only DeclRefExpr occurs
 inside of a loop

Summary: This fixes a bug where the performance-unnecessary-value-param check suggests a fix to move the parameter inside of a loop which could be invoked multiple times.

Reviewers: sbenza, aaron.ballman, alexfh

Subscribers: JDevlieghere, cfe-commits

Differential Revision: https://reviews.llvm.org/D27187

llvm-svn: 289912
---
 .../performance/UnnecessaryValueParamCheck.cpp      | 13 +++++++++++++
 .../performance-unnecessary-value-param.cpp         |  9 +++++++++
 2 files changed, 22 insertions(+)

diff --git a/clang-tools-extra/clang-tidy/performance/UnnecessaryValueParamCheck.cpp b/clang-tools-extra/clang-tidy/performance/UnnecessaryValueParamCheck.cpp
index 5d746d6ab771..0b5838432295 100644
--- a/clang-tools-extra/clang-tidy/performance/UnnecessaryValueParamCheck.cpp
+++ b/clang-tools-extra/clang-tidy/performance/UnnecessaryValueParamCheck.cpp
@@ -47,6 +47,17 @@ bool isReferencedOutsideOfCallExpr(const FunctionDecl &Function,
   return !Matches.empty();
 }
 
+bool hasLoopStmtAncestor(const DeclRefExpr &DeclRef, const Stmt &Stmt,
+                         ASTContext &Context) {
+  auto Matches =
+      match(findAll(declRefExpr(
+                equalsNode(&DeclRef),
+                unless(hasAncestor(stmt(anyOf(forStmt(), cxxForRangeStmt(),
+                                              whileStmt(), doStmt())))))),
+            Stmt, Context);
+  return Matches.empty();
+}
+
 } // namespace
 
 UnnecessaryValueParamCheck::UnnecessaryValueParamCheck(
@@ -105,6 +116,8 @@ void UnnecessaryValueParamCheck::check(const MatchFinder::MatchResult &Result) {
   if (!IsConstQualified) {
     auto CanonicalType = Param->getType().getCanonicalType();
     if (AllDeclRefExprs.size() == 1 &&
+        !hasLoopStmtAncestor(**AllDeclRefExprs.begin(), *Function->getBody(),
+                             *Result.Context) &&
         ((utils::type_traits::hasNonTrivialMoveConstructor(CanonicalType) &&
           utils::decl_ref_expr::isCopyConstructorArgument(
               **AllDeclRefExprs.begin(), *Function->getBody(),
diff --git a/clang-tools-extra/test/clang-tidy/performance-unnecessary-value-param.cpp b/clang-tools-extra/test/clang-tidy/performance-unnecessary-value-param.cpp
index 5f7a4dd91d4e..18fcf0ffca2d 100644
--- a/clang-tools-extra/test/clang-tidy/performance-unnecessary-value-param.cpp
+++ b/clang-tools-extra/test/clang-tidy/performance-unnecessary-value-param.cpp
@@ -225,6 +225,15 @@ void PositiveMoveOnCopyAssignment(ExpensiveMovableType E) {
   // CHECK-FIXES: F = std::move(E);
 }
 
+// The argument could be moved but is not since copy statement is inside a loop.
+void PositiveNoMoveInsideLoop(ExpensiveMovableType E) {
+  // CHECK-MESSAGES: [[@LINE-1]]:52: warning: the parameter 'E' is copied
+  // CHECK-FIXES: void PositiveNoMoveInsideLoop(const ExpensiveMovableType& E) {
+  for (;;) {
+    auto F = E;
+  }
+}
+
 void PositiveConstRefNotMoveConstructible(ExpensiveToCopyType T) {
   // CHECK-MESSAGES: [[@LINE-1]]:63: warning: the parameter 'T' is copied
   // CHECK-FIXES: void PositiveConstRefNotMoveConstructible(const ExpensiveToCopyType& T) {