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Re: [patch] Fix PR rtl-optimization/78437
- From: Eric Botcazou <ebotcazou at adacore dot com>
- To: Uros Bizjak <ubizjak at gmail dot com>
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Wed, 23 Nov 2016 11:33:32 +0100
- Subject: Re: [patch] Fix PR rtl-optimization/78437
- Authentication-results: sourceware.org; auth=none
- References: <CAFULd4Yt4DMZZipnzio8S8VhKJSQqqHCZtYFE=CKObY44ntpeQ@mail.gmail.com>
> Please note that there is no guarantee that "(set (reg1:QI)
> (expression:QI))" will preserve high-order bits. This is guaranteed
> only when strict_low_part is used on the destination operand.
>
> C.f. *addqi_1 pattern, where QImode plus RTX can emit SImode ADDL insn
> vs. *addqi_1_slp, where QImode ADDQ insn is always emitted.
>
> So, the assumption in your last sentece is invalid, as far as x86 is
> concerned.
OK, thanks, if that's the consensus, I'll stick to version #1.
--
Eric Botcazou