Re: [RFA] New pass for sign/zero extension elimination

[Oleg Endo <oleg.endo@t-online.de>]

On Sun, 2023-11-19 at 19:51 -0700, Jeff Law wrote:
> 
> On 11/19/23 18:22, Oleg Endo wrote:
> > 
> > On Sun, 2023-11-19 at 17:47 -0700, Jeff Law wrote:
> > > This is work originally started by Joern @ Embecosm.
> > > 
> > > There's been a long standing sense that we're generating too many
> > > sign/zero extensions on the RISC-V port.  REE is useful, but it's really
> > > focused on a relatively narrow part of the extension problem.
> > > 
> > > What Joern's patch does is introduce a new pass which tracks liveness of
> > > chunks of pseudo regs.  Specifically it tracks bits 0..7, 8..15, 16..31
> > > and 32..63.
> > > 
> > > If it encounters a sign/zero extend that sets bits that are never read,
> > > then it replaces the sign/zero extension with a narrowing subreg.  The
> > > narrowing subreg usually gets eliminated by subsequent passes (it's just
> > > a copy after all).
> > > 
> > 
> > Have you tried it on SH, too?  (and if so any numbers?)


> Just bootstrap with C regression testing on sh4/sh4eb.  No data on 
> improvements.
> 

Alright.  I'll check what it does for SH once it's in.

Cheers,
Oleg