diff --git a/clang/docs/ReleaseNotes.rst b/clang/docs/ReleaseNotes.rst index 1286263700963..cfe0ac6a5dca6 100644 --- a/clang/docs/ReleaseNotes.rst +++ b/clang/docs/ReleaseNotes.rst @@ -218,6 +218,10 @@ Bug Fixes in This Version for logical operators in C23. Fixes (`#64356 `_). +- Clang no longer produces a false-positive `-Wunused-variable` warning + for variables created through copy initialization having side-effects in C++17 and later. + Fixes (`#79518 `_). + Bug Fixes to Compiler Builtins ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ diff --git a/clang/lib/Sema/SemaDecl.cpp b/clang/lib/Sema/SemaDecl.cpp index 9fdd8eb236d1e..6289cf75e1741 100644 --- a/clang/lib/Sema/SemaDecl.cpp +++ b/clang/lib/Sema/SemaDecl.cpp @@ -2044,7 +2044,8 @@ static bool ShouldDiagnoseUnusedDecl(const LangOptions &LangOpts, return false; if (Init) { - const auto *Construct = dyn_cast(Init); + const auto *Construct = + dyn_cast(Init->IgnoreImpCasts()); if (Construct && !Construct->isElidable()) { const CXXConstructorDecl *CD = Construct->getConstructor(); if (!CD->isTrivial() && !RD->hasAttr() && diff --git a/clang/test/SemaCXX/warn-unused-variables.cpp b/clang/test/SemaCXX/warn-unused-variables.cpp index b649c7d808935..29e8d08d37d8c 100644 --- a/clang/test/SemaCXX/warn-unused-variables.cpp +++ b/clang/test/SemaCXX/warn-unused-variables.cpp @@ -1,5 +1,7 @@ // RUN: %clang_cc1 -fsyntax-only -Wunused-variable -Wunused-label -Wno-c++1y-extensions -verify %s -// RUN: %clang_cc1 -fsyntax-only -Wunused-variable -Wunused-label -Wno-c++1y-extensions -verify -std=gnu++11 %s +// RUN: %clang_cc1 -fsyntax-only -Wunused-variable -Wunused-label -Wno-c++1y-extensions -verify=expected,cxx98-14 -std=gnu++11 %s +// RUN: %clang_cc1 -fsyntax-only -Wunused-variable -Wunused-label -Wno-c++1y-extensions -verify=expected,cxx98-14 -std=gnu++14 %s +// RUN: %clang_cc1 -fsyntax-only -Wunused-variable -Wunused-label -Wno-c++1y-extensions -verify -std=gnu++17 %s template void f() { T t; t = 17; @@ -183,7 +185,8 @@ void foo(int size) { NonTriviallyDestructible array[2]; // no warning NonTriviallyDestructible nestedArray[2][2]; // no warning - Foo fooScalar = 1; // expected-warning {{unused variable 'fooScalar'}} + // Copy initialzation gives warning before C++17 + Foo fooScalar = 1; // cxx98-14-warning {{unused variable 'fooScalar'}} Foo fooArray[] = {1,2}; // expected-warning {{unused variable 'fooArray'}} Foo fooNested[2][2] = { {1,2}, {3,4} }; // expected-warning {{unused variable 'fooNested'}} } @@ -297,3 +300,29 @@ void RAIIWrapperTest() { } } // namespace gh54489 + +// Ensure that -Wunused-variable does not emit warning +// on copy constructors with side effects (C++17 and later) +#if __cplusplus >= 201703L +namespace gh79518 { + +struct S { + S(int); +}; + +// With an initializer list +struct A { + int x; + A(int x) : x(x) {} +}; + +void foo() { + S s(0); // no warning + S s2 = 0; // no warning + S s3{0}; // no warning + + A a = 1; // no warning +} + +} // namespace gh79518 +#endif