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Re: [PATCH] Fix optimization regression in constant folder

From: kenner at vlsi1 dot ultra dot nyu dot edu (Richard Kenner)
To: richard dot guenther at gmail dot com
Cc: ebotcazou at adacore dot com, gcc-patches at gcc dot gnu dot org, iant at google dot com, mark at codesourcery dot com, matz at suse dot de
Date: Sun, 14 Oct 2007 22:22:31 EDT
Subject: Re: [PATCH] Fix optimization regression in constant folder
References: <200709171539.26653.ebotcazou@adacore.com> <10710120240.AA03734@vlsi1.ultra.nyu.edu> <m3wsttymh6.fsf@localhost.localdomain> <200710141225.08559.ebotcazou@adacore.com> <84fc9c000710140331t5b1bf94cr3a19b395c19faa22@mail.gmail.com> <m3bqb1r972.fsf@localhost.localdomain> <84fc9c000710140901x53b621cbhb453eb148925f6f9@mail.gmail.com>

> It looks like giving sizetype mode_for_size (GET_MODE_SIZE
> (Pmode)) (or similar) while raising its precision to cover the full
> 2 * HWI could do the right thing for constants and expansion.

I'm not sure what you mean.  That mode has a lower precision, but if
you use that wider precision it become VERY expensive do all
arithmetic at run time in that wider precision.  sizetype needs to be
at least as wide as needed for correctness purposes but no wider than
needed for efficiency purposes.

References:
- Re: [PATCH] Fix optimization regression in constant folder
  - From: Richard Kenner
- Re: [PATCH] Fix optimization regression in constant folder
  - From: Ian Lance Taylor
- Re: [PATCH] Fix optimization regression in constant folder
  - From: Eric Botcazou
- Re: [PATCH] Fix optimization regression in constant folder
  - From: Richard Guenther
- Re: [PATCH] Fix optimization regression in constant folder
  - From: Ian Lance Taylor
- Re: [PATCH] Fix optimization regression in constant folder
  - From: Richard Guenther

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