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Re: [PATCH][ARM] Restrict MAX_CONDITIONAL_EXECUTE when -mrestrict-it is in place

From: Ramana Radhakrishnan <ramana dot radhakrishnan at foss dot arm dot com>
To: Kyrill Tkachov <kyrylo dot tkachov at foss dot arm dot com>, GCC Patches <gcc-patches at gcc dot gnu dot org>
Cc: Richard Earnshaw <Richard dot Earnshaw at arm dot com>
Date: Thu, 11 Jun 2015 10:55:50 +0100
Subject: Re: [PATCH][ARM] Restrict MAX_CONDITIONAL_EXECUTE when -mrestrict-it is in place
Authentication-results: sourceware.org; auth=none
References: <5559BE41 dot 8040909 at foss dot arm dot com> <55659BA5 dot 5010709 at foss dot arm dot com>



On 27/05/15 11:25, Kyrill Tkachov wrote:

Ping.

Here is the rebased (and retested) patch after Christian's series.

Thanks,
Kyrill

On 18/05/15 11:26, Kyrill Tkachov wrote:

Hi all,

When using the short Thumb2 IT blocks we want to also restrict ifcvt so that it will not end up generating a number of back-to-back cond_execs
that will later end up being back to back single-instruction IT blocks. Branching over them should be a better choice.

This patch implements that by setting max_insns_skipped to 1 when arm_restrict_it.

With this patch, I've seen GCC replace a number of sequences in places like SPEC2006 from:
       it    eq
       moveq    r1, r5
       it    ne
       movne    r1, r10
       it    eq
       moveq    r8, r4

to a branch over them.

Bootstrapped and tested on arm.
Ok for trunk?


Bah, opened the wrong message - yes this is OK.

Ramana


Thanks,
Kyrill

2015-05-18  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>

       * config/arm/arm.c (arm_option_params_internal): When optimising
       for speed set max_insns_skipped when arm_restrict_it.

2015-05-18  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>

       * gcc.target/arm/short-it-ifcvt-1.c: New test.
       * gcc.target/arm/short-it-ifcvt-2.c: Likewise.

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