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Re: [PATCH 6/6] combine: allow combining two insns into two in some cases (PR52714)

From: Jeff Law <law at redhat dot com>
To: Segher Boessenkool <segher at kernel dot crashing dot org>, gcc-patches at gcc dot gnu dot org
Date: Mon, 01 Dec 2014 10:39:58 -0700
Subject: Re: [PATCH 6/6] combine: allow combining two insns into two in some cases (PR52714)
Authentication-results: sourceware.org; auth=none
References: <cover dot 1417135737 dot git dot segher at kernel dot crashing dot org> <5030840454fd7bbd071e868121a946eaa3e03338 dot 1417135738 dot git dot segher at kernel dot crashing dot org>

On 11/27/14 18:44, Segher Boessenkool wrote:

If one of the resulting insns is a noop set it is safe to allow the
combination, for it will never lead to a loop: any following combination
using that noop will delete it.  In fact, in most cases combine deletes
the noop immediately; for cc0 targets it does not in some cases, but it
deletes another insn in that case (a following jump insn).

This fixes PR52714.


2014-11-27  Segher Boessenkool  <segher@kernel.crashing.org>

gcc/
	PR rtl-optimization/52714
	* combine.c (try_combine): Allow combining two insns into two
	new insns if at least one of those is a noop.

Also OK with a testcase. I'd recommend just using the one from 52714,make it m68k specific. Not sure if it's best to scan the assembly or.combine dump -- your call.


jeff

Follow-Ups:
- Re: [PATCH 6/6] combine: allow combining two insns into two in some cases (PR52714)
  - From: Segher Boessenkool

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