Re: [PATCH, rs6000] Eliminate TARGET_CTZ,TARGET_FCTIDZ,FCTIWUZ defines

[will schmidt <will_schmidt@vnet.ibm.com>]

On Tue, 2022-09-20 at 16:14 -0500, Segher Boessenkool wrote:
> Hi!
> 
> On Mon, Sep 19, 2022 at 06:19:15PM -0500, will schmidt wrote:
> >   This is the first of a batch of changes that eliminate a number
> > of define TARGET_foo entries we have collected over time.
> 
> Good good :-)
> 
> > TARGET_CTZ is defined as TARGET_MODULO, and has a low number
> > of uses.  References to TARGET_CTZ should be safe to replace
> > with TARGET_MODULO throughout.
> 
> No, please don't.  This has nothing to with "modulo".  If you want to
> say this is just whether we have ISA 3.0 or p9, make a new target
> macro
> for *that* and use that everywhere.
> 
> This is a general issue, that will make the code much more sane if
> you
> can fix it!

> 
> > TARGET_FCTIDZ is entirely unused, and safe to remove.
> 
> Please make separate patches for separate issues.  This makes it much
> easier to review, and MUCH easier for all other ways we need to
> handle
> it (backports, reverts, everything else).  With Git it is *easier* to
> keep separate patches separate than it is to lump it all
> together.  So,
> the trick is to keep things in separate commits during development
> already (and you will find more benefits doing that, too!)

Yup, I actually developed these three (plus a bunch more) separately,
but combined the first three for posting.   I'll split them back out
and repost after a bit. 

> 
> TARGET_FCTIDZ was never used, it always used TARGET_FCFID directly.
> 
> The original PEM mistakenly said this insn is "64-bit only".  This
> was
> fixed in ISA 2.01 .
> 
> > TARGET_FCTIWUZ has a low number of uses, and can be directly
> > replaced with TARGET_POPCNTD.
> 
> It is a p7 (ISA 2.06) insn.  Please make a TARGET_P7 or such?


Yes.  I do have a change later in the (unposted) series to replace
POPCNTD with POWER7, at a glance thats #17 down the line. In review I
agree with your comment that the in-between changes aren't the best
choices. I'll see about skipping the in-between values and going
straight for POPCNTD->POWER7.

I am looking at the TARGET_POWER10 notation as the target style, versus
TARGET_P7, but I can go that direction if we think that would be
preferred.   Maybe it is since this is a retro-fix versus new. :-)


> 
> In the current situation target macros like TARGET_POPCNTD are abused
> to
> mean either "can we use the popcntd insn", or to mean "can we use
> insn
> new on p7".  Or sometimes something in between, or something in this
> general neighbourhood.  It is never clear which is meant, which makes
> it
> very hard to untangle this.  But thanks for trying!  :-)
>
> (Don't let me dicsourage you btw, most is pretty straightforward).

Absolutely..   I do have this mostly covered locally, I just need to
refine a few parts.  :-)

> 
> 
> >             * config/rs6000/rs6000.h (TARGET_CTZ): Replace with
> >             TARGET_MODULO.
> 
> Changelogs are indented with tabs, and this fits on one line.
> 
> So, please make TARGET_P7 and such, and OPTION_MASKs for those in
> rs6000-cpus.def?

willdo, 
thanks
-Will


> 
> 
> Segher