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Re: RFC/RFA: Fix bug with REE optimization corrupting extended registers
- From: Eric Botcazou <ebotcazou at adacore dot com>
- To: Jeff Law <law at redhat dot com>
- Cc: gcc-patches at gcc dot gnu dot org, Nick Clifton <nickc at redhat dot com>, Bernd Schmidt <bschmidt at redhat dot com>
- Date: Fri, 20 Nov 2015 23:10:21 +0100
- Subject: Re: RFC/RFA: Fix bug with REE optimization corrupting extended registers
- Authentication-results: sourceware.org; auth=none
- References: <87d1v7v1g9 dot fsf at redhat dot com> <564EE5BE dot 4080409 at redhat dot com> <564F9841 dot 7080005 at redhat dot com>
> I would hazard a guess that the authors simply didn't consider the
> multi-hard reg case. Essentially if the original set reached an
> extension, then obviously the original set got there unharmed and the
> extended destination should reach as well -- except that doesn't apply
> to multi-word hard regs.
This pass started as a Zero-Extension Elimination pass for x86-64 and was only
considering implicit SI->DI extensions initially. The algorithm was tailored
to this specific pattern and I agree that the pass should be reimplemented.
--
Eric Botcazou