[llvm-dev] analyzePhysReg question

[JF Bastien via llvm-dev]

On Fri, Dec 4, 2015 at 2:22 PM, Smith, Kevin B <kevin.b.smith at intel.com>
wrote:

> Ø  It would be good to check that this maps correctly onto
> computeRegisterLiveness: there's a bug in analyzePhysReg and I think other
> parts of the code base are slightly wrong or will become slightly wrong as
> well :-(
>
>
>
> Yes, I agree.  I will also have to look into all other users of
> analyzePhysReg as well.  There are surprisingly few users of either
> computeRegisterLiveness
>
> or analyzePhysReg.  The other thing that I am trying to think about would
> be a way to comprehensively test the correctness of these, both as they
> stand,
>
> and after changes.
>

Great, thanks! I'd be happy to review this, I just don't have much time to
tackle the problem myself.

This code should also be fixed at the same time:
http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20140317/209514.html

I am curious, does anyone know how do get this kind of Machine IR to be
> created from LLVM:
>
>
>
> xor eax, eax
>
> movw ax, mem
>
> read eax
>
>
>
> where the actual intent is for the xor, and the sub-register def in the
> movw to create form of zero-extension, and then to have full uses of eax? I
> know this isn't very desirable
>
> code for X86, but these kinds of unusual machine IR are what would stress
> the implementations of these routines.
>

I'm not sure, sorry. You could play tricks with asm and clobbers?
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