[llvm-commits] [llvm-gcc-4.2] r97989 - /llvm-gcc-4.2/trunk/gcc/llvm-types.cpp

[Duncan Sands]

Hi Dan,

>     // If this function returns via a shadow argument, the dest loc is passed
> -  // in as a pointer.  Mark that pointer as struct-ret and noalias.
> +  // in as a pointer.  Mark that pointer as struct-ret.
> +  //
> +  // It's tempting to want NoAlias here too, however even though llvm-gcc
> +  // itself currently always passes a dedicated alloca as the actual argument,
> +  // this isn't mandated by the ABI. There are other compilers which don't
> +  // always pass a dedicated alloca. Using NoAlias here would make code which
> +  // isn't interoperable with that of other compilers.
>     if (ABIConverter.isShadowReturn())
>       Attrs.push_back(AttributeWithIndex::get(ArgTys.size(),
> -                                    Attribute::StructRet | Attribute::NoAlias));
> +                                    Attribute::StructRet));

what does the ABI say exactly?  Is it really valid to pass something which may
get "accidentally" altered when the callee (for example) writes to a global or
to some other argument?

Ciao,

Duncan.