[llvm-commits] CVS: llvm/lib/VMCore/ConstantFolding.cpp

[Chris Lattner]

Reid,

On Nov 30, 2006, at 4:25 PM, Anton Korobeynikov wrote:
> Introducing external weak linkage. Darwin codegen should be added  
> later.
>
> Index: llvm/lib/VMCore/ConstantFolding.cpp
> diff -u llvm/lib/VMCore/ConstantFolding.cpp:1.100 llvm/lib/VMCore/ 
> ConstantFolding.cpp:1.101
> --- llvm/lib/VMCore/ConstantFolding.cpp:1.100	Sun Nov 26 19:05:10 2006
> +++ llvm/lib/VMCore/ConstantFolding.cpp	Thu Nov 30 18:25:12 2006
> @@ -894,11 +894,8 @@
>
>    case Instruction::PtrToInt:
>      // Cast of a global address to boolean is always true.
> -    if (isa<GlobalValue>(V)) {
> -      if (DestTy == Type::BoolTy)
> -        // FIXME: When we support 'external weak' references, we  
> have to
> -        // prevent this transformation from happening.  This code  
> will need
> -        // to be updated to ignore external weak symbols when we  
> support it.
> +    if (const GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
> +      if (DestTy == Type::BoolTy && !GV->hasExternalWeakLinkage())
>          return ConstantBool::getTrue();
>

This code is wrong, but it's not anton's fault.  This is fallout from  
the cast patch.  ptrtoint(&GV, bool) is not guaranteed to be true,  
even with non-extern-weak symbols, as the ptrtoint truncates, it  
doesn't compare to null any more.

This code should be removed, and code should be added to  
ConstantFolding.cpp in the setne(&GV, null)/seteq(&GV, null) codepath  
to handle this.

Thanks,

-Chris