Merged to release_90 in r371040.
On Wed, Sep 4, 2019 at 10:17 AM Hans Wennborg via cfe-commits <cfe-commits@lists.llvm.org> wrote: > > Author: hans > Date: Wed Sep 4 01:19:30 2019 > New Revision: 370850 > > URL: http://llvm.org/viewvc/llvm-project?rev=370850&view=rev > Log: > Re-commit r363191 "[MS] Pretend constexpr variable template specializations > are inline" > > While the next Visual Studio update (16.3) will fix this issue, that hasn't > shipped yet. Until then Clang wouldn't work with MSVC's headers which seems > unfortunate. Let's keep this in until VS 16.3 ships. (See also PR42843.) > > > Fixes link errors with clang and the latest Visual C++ 14.21.27702 > > headers, which was reported as PR42027. > > > > I chose to intentionally make these things linkonce_odr, i.e. > > discardable, so that we don't emit definitions of these things in every > > translation unit that includes STL headers. > > > > Note that this is *not* what MSVC does: MSVC has not yet implemented C++ > > DR2387, so they emit fully specialized constexpr variable templates with > > static / internal linkage. > > > > Reviewers: rsmith > > > > Differential Revision: https://reviews.llvm.org/D63175 > > Added: > cfe/trunk/test/CodeGenCXX/ms-constexpr-var-template.cpp > Modified: > cfe/trunk/lib/AST/ASTContext.cpp > > Modified: cfe/trunk/lib/AST/ASTContext.cpp > URL: > http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/AST/ASTContext.cpp?rev=370850&r1=370849&r2=370850&view=diff > ============================================================================== > --- cfe/trunk/lib/AST/ASTContext.cpp (original) > +++ cfe/trunk/lib/AST/ASTContext.cpp Wed Sep 4 01:19:30 2019 > @@ -9905,10 +9905,25 @@ static GVALinkage basicGVALinkageForVari > return StrongLinkage; > > case TSK_ExplicitSpecialization: > - return Context.getTargetInfo().getCXXABI().isMicrosoft() && > - VD->isStaticDataMember() > - ? GVA_StrongODR > - : StrongLinkage; > + if (Context.getTargetInfo().getCXXABI().isMicrosoft()) { > + // If this is a fully specialized constexpr variable template, pretend > it > + // was marked inline. MSVC 14.21.27702 headers define _Is_integral in a > + // header this way, and we don't want to emit non-discardable > definitions > + // of these variables in every TU that includes <type_traits>. This > + // behavior is non-conforming, since another TU could use an extern > + // template declaration for this variable, but for constexpr variables, > + // it's unlikely for a user to want to do that. This behavior can be > + // removed if the headers change to explicitly mark such variable > template > + // specializations inline. > + if (isa<VarTemplateSpecializationDecl>(VD) && VD->isConstexpr()) > + return GVA_DiscardableODR; > + > + // Use ODR linkage for static data members of fully specialized > templates > + // to prevent duplicate definition errors with MSVC. > + if (VD->isStaticDataMember()) > + return GVA_StrongODR; > + } > + return StrongLinkage; > > case TSK_ExplicitInstantiationDefinition: > return GVA_StrongODR; > > Added: cfe/trunk/test/CodeGenCXX/ms-constexpr-var-template.cpp > URL: > http://llvm.org/viewvc/llvm-project/cfe/trunk/test/CodeGenCXX/ms-constexpr-var-template.cpp?rev=370850&view=auto > ============================================================================== > --- cfe/trunk/test/CodeGenCXX/ms-constexpr-var-template.cpp (added) > +++ cfe/trunk/test/CodeGenCXX/ms-constexpr-var-template.cpp Wed Sep 4 > 01:19:30 2019 > @@ -0,0 +1,11 @@ > +// RUN: %clang_cc1 -emit-llvm -triple=x86_64-windows-msvc -fms-compatibility > %s -o - | FileCheck %s > + > +template <typename> constexpr bool _Is_integer = false; > +template <> constexpr bool _Is_integer<int> = true; > +template <> constexpr bool _Is_integer<char> = false; > +extern "C" const bool *escape = &_Is_integer<int>; > + > +// CHECK: @"??$_Is_integer@H@@3_NB" = linkonce_odr dso_local constant i8 1, > comdat, align 1 > +// Should not emit _Is_integer<char>, since it's not referenced. > +// CHECK-NOT: @"??$_Is_integer@D@@3_NB" > +// CHECK: @escape = dso_local global i8* @"??$_Is_integer@H@@3_NB", align 8 > > > _______________________________________________ > cfe-commits mailing list > cfe-commits@lists.llvm.org > https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
