r311857 - Emit static constexpr member as available_externally definition

[Hans Wennborg via cfe-commits]

I reverted this in r311898 as it caused Chromium builds to fail with
an assertion; see PR34348.

On Sun, Aug 27, 2017 at 1:24 PM, Mehdi Amini via cfe-commits
<cfe-commits at lists.llvm.org> wrote:
> Author: mehdi_amini
> Date: Sun Aug 27 13:24:09 2017
> New Revision: 311857
>
> URL: http://llvm.org/viewvc/llvm-project?rev=311857&view=rev
> Log:
> Emit static constexpr member as available_externally definition
>
> By exposing the constant initializer, the optimizer can fold many
> of these constructs.
>
> Differential Revision: https://reviews.llvm.org/D34992
>
> Added:
>     cfe/trunk/test/CodeGenCXX/cxx11-extern-constexpr.cpp
> Modified:
>     cfe/trunk/lib/CodeGen/CodeGenModule.cpp
>
> Modified: cfe/trunk/lib/CodeGen/CodeGenModule.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/CodeGen/CodeGenModule.cpp?rev=311857&r1=311856&r2=311857&view=diff
> ==============================================================================
> --- cfe/trunk/lib/CodeGen/CodeGenModule.cpp (original)
> +++ cfe/trunk/lib/CodeGen/CodeGenModule.cpp Sun Aug 27 13:24:09 2017
> @@ -2437,6 +2437,28 @@ CodeGenModule::GetOrCreateLLVMGlobal(Str
>          D->getType().isConstant(Context) &&
>          isExternallyVisible(D->getLinkageAndVisibility().getLinkage()))
>        GV->setSection(".cp.rodata");
> +
> +    // Check if we a have a const declaration with an initializer, we may be
> +    // able to emit it as available_externally to expose it's value to the
> +    // optimizer.
> +    if (Context.getLangOpts().CPlusPlus && GV->hasExternalLinkage() &&
> +        D->getType().isConstQualified() && !GV->hasInitializer() &&
> +        !D->hasDefinition() && D->hasInit() && !D->hasAttr<DLLImportAttr>()) {
> +      const auto *Record =
> +          Context.getBaseElementType(D->getType())->getAsCXXRecordDecl();
> +      bool HasMutableFields = Record && Record->hasMutableFields();
> +      if (!HasMutableFields) {
> +        const VarDecl *InitDecl;
> +        const Expr *InitExpr = D->getAnyInitializer(InitDecl);
> +        if (InitExpr) {
> +          GV->setConstant(true);
> +          GV->setLinkage(llvm::GlobalValue::AvailableExternallyLinkage);
> +          ConstantEmitter emitter(*this);
> +          GV->setInitializer(emitter.tryEmitForInitializer(*InitDecl));
> +          emitter.finalize(GV);
> +        }
> +      }
> +    }
>    }
>
>    auto ExpectedAS =
>
> Added: cfe/trunk/test/CodeGenCXX/cxx11-extern-constexpr.cpp
> URL: http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGenCXX/cxx11-extern-constexpr.cpp?rev=311857&view=auto
> ==============================================================================
> --- cfe/trunk/test/CodeGenCXX/cxx11-extern-constexpr.cpp (added)
> +++ cfe/trunk/test/CodeGenCXX/cxx11-extern-constexpr.cpp Sun Aug 27 13:24:09 2017
> @@ -0,0 +1,55 @@
> +// RUN: %clang_cc1 -std=c++11 %s -emit-llvm -o - -triple x86_64-linux-gnu | FileCheck %s --check-prefix=CHECK --check-prefix=CXX11
> +// RUN: %clang_cc1 -std=c++1z %s -emit-llvm -o - -triple x86_64-linux-gnu | FileCheck %s --check-prefix=CHECK --check-prefix=CXX17
> +
> +struct A {
> +  static const int Foo = 123;
> +};
> +// CHECK: @_ZN1A3FooE = constant i32 123, align 4
> +const int *p = &A::Foo; // emit available_externally
> +const int A::Foo;       // convert to full definition
> +
> +struct Bar {
> +  int b;
> +};
> +
> +struct MutableBar {
> +  mutable int b;
> +};
> +
> +struct Foo {
> +  // CXX11: @_ZN3Foo21ConstexprStaticMemberE = available_externally constant i32 42,
> +  // CXX17: @_ZN3Foo21ConstexprStaticMemberE = linkonce_odr constant i32 42,
> +  static constexpr int ConstexprStaticMember = 42;
> +  // CHECK: @_ZN3Foo17ConstStaticMemberE = available_externally constant i32 43,
> +  static const int ConstStaticMember = 43;
> +
> +  // CXX11: @_ZN3Foo23ConstStaticStructMemberE = available_externally constant %struct.Bar { i32 44 },
> +  // CXX17: @_ZN3Foo23ConstStaticStructMemberE = linkonce_odr constant %struct.Bar { i32 44 },
> +  static constexpr Bar ConstStaticStructMember = {44};
> +
> +  // CXX11: @_ZN3Foo34ConstexprStaticMutableStructMemberE = external global %struct.MutableBar,
> +  // CXX17: @_ZN3Foo34ConstexprStaticMutableStructMemberE = linkonce_odr global %struct.MutableBar { i32 45 },
> +  static constexpr MutableBar ConstexprStaticMutableStructMember = {45};
> +};
> +// CHECK: @_ZL15ConstStaticexpr = internal constant i32 46,
> +static constexpr int ConstStaticexpr = 46;
> +// CHECK: @_ZL9ConstExpr = internal constant i32 46, align 4
> +static const int ConstExpr = 46;
> +
> +// CHECK: @_ZL21ConstexprStaticStruct = internal constant %struct.Bar { i32 47 },
> +static constexpr Bar ConstexprStaticStruct = {47};
> +
> +// CHECK: @_ZL28ConstexprStaticMutableStruct = internal global %struct.MutableBar { i32 48 },
> +static constexpr MutableBar ConstexprStaticMutableStruct = {48};
> +
> +void use(const int &);
> +void foo() {
> +  use(Foo::ConstexprStaticMember);
> +  use(Foo::ConstStaticMember);
> +  use(Foo::ConstStaticStructMember.b);
> +  use(Foo::ConstexprStaticMutableStructMember.b);
> +  use(ConstStaticexpr);
> +  use(ConstExpr);
> +  use(ConstexprStaticStruct.b);
> +  use(ConstexprStaticMutableStruct.b);
> +}
>
>
> _______________________________________________
> cfe-commits mailing list
> cfe-commits at lists.llvm.org
> http://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits