r315811 - Re-land r315787, "[Sema] Warn about unused variables if we can constant evaluate the initializer."

[Alexander Kornienko via cfe-commits]

On Sat, Oct 14, 2017 at 5:59 PM, Benjamin Kramer via cfe-commits <
cfe-commits at lists.llvm.org> wrote:

> Author: d0k
> Date: Sat Oct 14 08:59:34 2017
> New Revision: 315811
>
> URL: http://llvm.org/viewvc/llvm-project?rev=315811&view=rev
> Log:
> Re-land r315787, "[Sema] Warn about unused variables if we can constant
> evaluate the initializer."
>
> The warnings in libc++ tests were fixed in the meantime.
>
> Modified:
>     cfe/trunk/lib/Sema/SemaDecl.cpp
>     cfe/trunk/test/SemaCXX/warn-unused-variables.cpp
>
> Modified: cfe/trunk/lib/Sema/SemaDecl.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/
> SemaDecl.cpp?rev=315811&r1=315810&r2=315811&view=diff
> ============================================================
> ==================
> --- cfe/trunk/lib/Sema/SemaDecl.cpp (original)
> +++ cfe/trunk/lib/Sema/SemaDecl.cpp Sat Oct 14 08:59:34 2017
> @@ -1723,7 +1723,8 @@ static bool ShouldDiagnoseUnusedDecl(con
>              dyn_cast<CXXConstructExpr>(Init);
>            if (Construct && !Construct->isElidable()) {
>              CXXConstructorDecl *CD = Construct->getConstructor();
> -            if (!CD->isTrivial() && !RD->hasAttr<WarnUnusedAttr>())
> +            if (!CD->isTrivial() && !RD->hasAttr<WarnUnusedAttr>() &&
> +                !VD->evaluateValue())
>

The evaluateValue call above causes an assertion failure on
instantiation-dependent values:
llvm/tools/clang/lib/AST/Decl.cpp:2196 in clang::APValue
*clang::VarDecl::evaluateValue(SmallVectorImpl<clang::PartialDiagnosticAt>
&) const: !Init->isValueDependent()

I'm not sure why evaluateValue uses an assertion instead of outputting a
note and returning nullptr, but the assertion can be avoided on the caller
site as well.

Working on a reduced test case...


>                return false;
>            }
>          }
>
> Modified: cfe/trunk/test/SemaCXX/warn-unused-variables.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/
> SemaCXX/warn-unused-variables.cpp?rev=315811&r1=315810&r2=315811&view=diff
> ============================================================
> ==================
> --- cfe/trunk/test/SemaCXX/warn-unused-variables.cpp (original)
> +++ cfe/trunk/test/SemaCXX/warn-unused-variables.cpp Sat Oct 14 08:59:34
> 2017
> @@ -1,4 +1,5 @@
>  // 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=c++11 %s
>  template<typename T> void f() {
>    T t;
>    t = 17;
> @@ -194,3 +195,35 @@ void test() {
>  }
>
>  }
> +
> +#if __cplusplus >= 201103L
> +namespace with_constexpr {
> +template <typename T>
> +struct Literal {
> +  T i;
> +  Literal() = default;
> +  constexpr Literal(T i) : i(i) {}
> +};
> +
> +struct NoLiteral {
> +  int i;
> +  NoLiteral() = default;
> +  constexpr NoLiteral(int i) : i(i) {}
> +  ~NoLiteral() {}
> +};
> +
> +static Literal<int> gl1;          // expected-warning {{unused variable
> 'gl1'}}
> +static Literal<int> gl2(1);       // expected-warning {{unused variable
> 'gl2'}}
> +static const Literal<int> gl3(0); // expected-warning {{unused variable
> 'gl3'}}
> +
> +template <typename T>
> +void test(int i) {
> +  Literal<int> l1;     // expected-warning {{unused variable 'l1'}}
> +  Literal<int> l2(42); // expected-warning {{unused variable 'l2'}}
> +  Literal<int> l3(i);  // no-warning
> +  Literal<T> l4(0);    // no-warning
> +  NoLiteral nl1;       // no-warning
> +  NoLiteral nl2(42);   // no-warning
> +}
> +}
> +#endif
>
>
> _______________________________________________
> cfe-commits mailing list
> cfe-commits at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/cfe-commits/attachments/20171019/7ed4f1e9/attachment-0001.html>