[LLVMdev] Why do X86_32TargetMachine and X86_64TargetMachine classes exist?

[Jim Grosbach]

Hi David,

AFAIK, the answer is basically “because it’s always been that way.” I seem to recall there were some things that were different (data layout string and such), but that could also be parameterized if it hasn’t been already by the recent refactorings, I suppose.

-Jim

(inline comment below)

On Jan 6, 2014, at 7:18 AM, David Woodhouse <dwmw2 at infradead.org> wrote:

> These two subclasses of X86TargetMachine are basically identical.
> 
> The *only* thing that's different is the constructor. And that *only*
> differs in the is64Bit argument that it passes to the X86TargetMachine
> constructor. Replacing the hard-coded 'true' or 'false' with
> 'Triple(TT).getArch()==Triple::x86_64' makes them *actually* identical.
> 
> Can we just ditch the subclasses, move the fields and methods that they
> share into the X86TargetMachine class, and use that instead? Or am I
> missing something?
> 
> In the patch I'm about to post to llvm-commits, I *stop* using the
> X86_64TargetMachine subclass entirely, and use X86_32TargetMachine for
> the 64-bit target. And the 16-bit target too. And nothing seems to have
> broken AFAICT...
> 
> --- a/lib/Target/X86/X86TargetMachine.cpp
> +++ b/lib/Target/X86/X86TargetMachine.cpp
> @@ -24,8 +24,9 @@ using namespace llvm;
> 
> extern "C" void LLVMInitializeX86Target() {
>   // Register the target.
> +  RegisterTargetMachine<X86_32TargetMachine> W(TheX86_16Target);
>   RegisterTargetMachine<X86_32TargetMachine> X(TheX86_32Target);
> -  RegisterTargetMachine<X86_64TargetMachine> Y(TheX86_64Target);
> +  RegisterTargetMachine<X86_32TargetMachine> Y(TheX86_64Target);
> }
> @@ -74,7 +75,7 @@ X86_32TargetMachine::X86_32TargetMachine(const Target &T, Stri
>                                          const TargetOptions &Options,
>                                          Reloc::Model RM, CodeModel::Model CM,
>                                          CodeGenOpt::Level OL)
> -  : X86TargetMachine(T, TT, CPU, FS, Options, RM, CM, OL, false),
> +  : X86TargetMachine(T, TT, CPU, FS, Options, RM, CM, OL, Triple(TT).getArch())

Think this is missing a "==Triple::x86_64” at the end, yes?

>     DL(computeDataLayout(*getSubtargetImpl())),
>     InstrInfo(*this),
> 
> 
> -- 
> David Woodhouse                            Open Source Technology Centre
> David.Woodhouse at intel.com                              Intel Corporation
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