r255371 - Error on redeclaring with a conflicting asm label and on redeclaring with an asm label after the first ODR-use. Detects problems like the one in PR22830 where gcc and clang both compiled the file but with different behaviour.

[Nick Lewycky via cfe-commits]

On 12/17/2015 10:47 AM, Kostya Serebryany wrote:
> I am now observing this error message when building glibc with clang
> (from trunk):
> ../include/string.h:101:28: error: cannot apply asm label to function
> after its first use
> libc_hidden_builtin_proto (memcpy)
> (many more instances)
>
>
> Do you think this is a bug in glibc code, or the error message could be
> more relaxed?

Could you email me a .i copy of a failing build? That will help me 
decide whether it's a bug in the error or in glibc.

>
>
>
>
>
> On Fri, Dec 11, 2015 at 1:28 PM, Nick Lewycky via cfe-commits
> <cfe-commits at lists.llvm.org <mailto:cfe-commits at lists.llvm.org>> wrote:
>
>     Author: nicholas
>     Date: Fri Dec 11 15:28:55 2015
>     New Revision: 255371
>
>     URL: http://llvm.org/viewvc/llvm-project?rev=255371&view=rev
>     Log:
>     Error on redeclaring with a conflicting asm label and on redeclaring
>     with an asm label after the first ODR-use. Detects problems like the
>     one in PR22830 where gcc and clang both compiled the file but with
>     different behaviour.
>
>     Added:
>          cfe/trunk/test/Sema/asm-label.c
>     Modified:
>          cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
>          cfe/trunk/lib/Sema/SemaDecl.cpp
>
>     Modified: cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td
>     URL:
>     http://llvm.org/viewvc/llvm-project/cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td?rev=255371&r1=255370&r2=255371&view=diff
>     ==============================================================================
>     --- cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td (original)
>     +++ cfe/trunk/include/clang/Basic/DiagnosticSemaKinds.td Fri Dec 11
>     15:28:55 2015
>     @@ -4259,6 +4259,9 @@ def err_tag_definition_of_typedef : Erro
>       def err_conflicting_types : Error<"conflicting types for %0">;
>       def err_different_pass_object_size_params : Error<
>         "conflicting pass_object_size attributes on parameters">;
>     +def err_late_asm_label_name : Error<
>     +  "cannot apply asm label to %select{variable|function}0 after its
>     first use">;
>     +def err_different_asm_label : Error<"conflicting asm label">;
>       def err_nested_redefinition : Error<"nested redefinition of %0">;
>       def err_use_with_wrong_tag : Error<
>         "use of %0 with tag type that does not match previous declaration">;
>
>     Modified: cfe/trunk/lib/Sema/SemaDecl.cpp
>     URL:
>     http://llvm.org/viewvc/llvm-project/cfe/trunk/lib/Sema/SemaDecl.cpp?rev=255371&r1=255370&r2=255371&view=diff
>     ==============================================================================
>     --- cfe/trunk/lib/Sema/SemaDecl.cpp (original)
>     +++ cfe/trunk/lib/Sema/SemaDecl.cpp Fri Dec 11 15:28:55 2015
>     @@ -2379,9 +2379,24 @@ void Sema::mergeDeclAttributes(NamedDecl
>         if (!Old->hasAttrs() && !New->hasAttrs())
>           return;
>
>     -  // attributes declared post-definition are currently ignored
>     +  // Attributes declared post-definition are currently ignored.
>         checkNewAttributesAfterDef(*this, New, Old);
>
>     +  if (AsmLabelAttr *NewA = New->getAttr<AsmLabelAttr>()) {
>     +    if (AsmLabelAttr *OldA = Old->getAttr<AsmLabelAttr>()) {
>     +      if (OldA->getLabel() != NewA->getLabel()) {
>     +        // This redeclaration changes __asm__ label.
>     +        Diag(New->getLocation(), diag::err_different_asm_label);
>     +        Diag(OldA->getLocation(), diag::note_previous_declaration);
>     +      }
>     +    } else if (Old->isUsed()) {
>     +      // This redeclaration adds an __asm__ label to a declaration
>     that has
>     +      // already been ODR-used.
>     +      Diag(New->getLocation(), diag::err_late_asm_label_name)
>     +        << isa<FunctionDecl>(Old) <<
>     New->getAttr<AsmLabelAttr>()->getRange();
>     +    }
>     +  }
>     +
>         if (!Old->hasAttrs())
>           return;
>
>
>     Added: cfe/trunk/test/Sema/asm-label.c
>     URL:
>     http://llvm.org/viewvc/llvm-project/cfe/trunk/test/Sema/asm-label.c?rev=255371&view=auto
>     ==============================================================================
>     --- cfe/trunk/test/Sema/asm-label.c (added)
>     +++ cfe/trunk/test/Sema/asm-label.c Fri Dec 11 15:28:55 2015
>     @@ -0,0 +1,30 @@
>     +// RUN: %clang_cc1 -verify %s
>     +
>     +void f();
>     +void f() __asm__("fish");
>     +void g();
>     +
>     +void f() {
>     +  g();
>     +}
>     +void g() __asm__("gold");  // expected-error{{cannot apply asm
>     label to function after its first use}}
>     +
>     +void h() __asm__("hose");  // expected-note{{previous declaration
>     is here}}
>     +void h() __asm__("hair");  // expected-error{{conflicting asm label}}
>     +
>     +int x;
>     +int x __asm__("xenon");
>     +int y;
>     +
>     +int test() { return y; }
>     +
>     +int y __asm__("yacht");  // expected-error{{cannot apply asm label
>     to variable after its first use}}
>     +
>     +int z __asm__("zebra");  // expected-note{{previous declaration is
>     here}}
>     +int z __asm__("zooms");  // expected-error{{conflicting asm label}}
>     +
>     +
>     +// No diagnostics on the following.
>     +void __real_readlink() __asm("readlink");
>     +void readlink() __asm("__protected_readlink");
>     +void readlink() { __real_readlink(); }
>
>
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