[PATCH] D20179: Fail early on unknown appending linkage variables

[Duncan P. N. Exon Smith via llvm-commits]

The patch LGTM with an update to LangRef.  Has this been discussed on
llvm-dev though?  It seems like an IR change, since whether or not the
old behaviour was a good idea, it was certainly tested for...

> On 2016-May-11, at 12:13, Rafael Ávila de Espíndola <rafael.espindola at gmail.com> wrote:
> 
> rafael created this revision.
> rafael added a reviewer: dexonsmith.
> rafael added a subscriber: llvm-commits.
> 
> In practice only a few well known appending linkage variables work.
> 
> Currently if codegen sees an unknown appending linkage variable it will just print it as a regular global. That is wrong as the symbol in the produced object file has different semantics as the one provided by the appending linkage.
> 
> This just errors early instead of producing a broken .o.
> 
> http://reviews.llvm.org/D20179
> 
> Files:
>  lib/CodeGen/AsmPrinter/AsmPrinter.cpp
>  test/CodeGen/X86/2007-08-13-AppendingLinkage.ll
>  test/CodeGen/X86/AppendingLinkage.ll
> 
> Index: test/CodeGen/X86/AppendingLinkage.ll
> ===================================================================
> --- /dev/null
> +++ test/CodeGen/X86/AppendingLinkage.ll
> @@ -0,0 +1,4 @@
> +; RUN: not llc < %s -march=x86 2>&1 | FileCheck %s
> +
> +; CHECK: unknown special variable
> + at foo = appending constant [1 x i32 ]zeroinitializer
> Index: test/CodeGen/X86/2007-08-13-AppendingLinkage.ll
> ===================================================================
> --- test/CodeGen/X86/2007-08-13-AppendingLinkage.ll
> +++ /dev/null
> @@ -1,12 +0,0 @@
> -; RUN: llc < %s -march=x86 | not grep drectve
> -; PR1607
> -
> -%hlvm_programs_element = type { i8*, i32 (i32, i8**)* }
> - at hlvm_programs = appending constant [1 x %hlvm_programs_element]
> -zeroinitializer
> -
> -define %hlvm_programs_element* @hlvm_get_programs() {
> -entry:
> -  ret %hlvm_programs_element* getelementptr([1 x %hlvm_programs_element], [1 x %hlvm_programs_element]*  
> -                                            @hlvm_programs, i32 0, i32 0)
> -}
> Index: lib/CodeGen/AsmPrinter/AsmPrinter.cpp
> ===================================================================
> --- lib/CodeGen/AsmPrinter/AsmPrinter.cpp
> +++ lib/CodeGen/AsmPrinter/AsmPrinter.cpp
> @@ -318,17 +318,14 @@
>       OutStreamer->EmitSymbolAttribute(GVSym, MCSA_Weak);
>     }
>     return;
> -  case GlobalValue::AppendingLinkage:
> -    // FIXME: appending linkage variables should go into a section of
> -    // their name or something.  For now, just emit them as external.
>   case GlobalValue::ExternalLinkage:
> -    // If external or appending, declare as a global symbol.
> -    // .globl _foo
> +    // If external, declare as a global symbol: .globl _foo
>     OutStreamer->EmitSymbolAttribute(GVSym, MCSA_Global);
>     return;
>   case GlobalValue::PrivateLinkage:
>   case GlobalValue::InternalLinkage:
>     return;
> +  case GlobalValue::AppendingLinkage:
>   case GlobalValue::AvailableExternallyLinkage:
>   case GlobalValue::ExternalWeakLinkage:
>     llvm_unreachable("Should never emit this");
> @@ -1562,7 +1559,7 @@
>     return true;
>   }
> 
> -  return false;
> +  report_fatal_error("unknown special variable");
> }
> 
> /// EmitLLVMUsedList - For targets that define a MAI::UsedDirective, mark each
> 
> 
> <D20179.56948.patch>