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Subject: Re: [PATCH][ARM] PR target/70566 Check that condition register is dead in tst-imm -> lsls-imm Thumb2 peepholes
To: Kyrill Tkachov <kyrylo.tkachov@foss.arm.com>, GCC Patches <gcc-patches@gcc.gnu.org>
References: <570673FB.7020803@foss.arm.com>
Cc: Ramana Radhakrishnan <ramana.radhakrishnan@arm.com>
From: "Richard Earnshaw (lists)" <Richard.Earnshaw@arm.com>
Message-ID: <57077A47.2070100@arm.com>
Date: Fri, 08 Apr 2016 09:31:00 -0000
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On 07/04/16 15:51, Kyrill Tkachov wrote:
> Hi all,
> 
> In this wrong-code PR we have a Thumb2 peephole transforming:
>     tst    r3, #2
>     bne    .L3
>     beq    .L6
> 
> into:
>     lsls    r3, r3, #30  // LSLS is shorter than TST in Thumb2
>     bmi    .L3
>     beq    .L6
> 
> that is, the branch following the extract+compare has its condition
> properly changed but the
> following branch doesn't get updated to check the opposite condition of
> MI (PL).
> Since the peepholes in thumb2.md only see the compare and a single
> branch the solution,
> suggested by Richard, is to guard those peepholes on the condition that
> the condition register
> is dead after the first branch. This patch does that and with it we no
> longer perform the transformation
> on the testcase. I've checked manually that we still perform the
> peephole when the condition register
> is indeed dead after the sequence.
> 
> Bootstrapped and tested on on arm-none-linux-gnueabihf with
> --with-mode=thumb as this affects only
> Thumb2 codegen.
> 
> Ok for trunk?
> 
> This PR also affects GCC 5 and 4.9 so I'll be testing the patch there as
> well.
> 
> Thanks,
> Kyrill
> 
> 
> 2016-04-07  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
> 
>     PR target/70566
>     * config/arm/thumb2.md (tst + branch-> lsls + branch
>     peephole below *orsi_not_shiftsi_si): Require that condition
>     register is dead after the peephole.
>     (second peephole after the above): Likewise.
> 
> 2016-04-07  Kyrylo Tkachov  <kyrylo.tkachov@arm.com>
> 
>     PR target/70566
>     * gcc.c-torture/execute/pr70566.c: New test.


OK.

R.