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Re: Validity of SUBREG+AND-imm transformations

From: Richard Henderson <rth at redhat dot com>
To: Jeff Law <law at redhat dot com>, Kyrill Tkachov <kyrylo dot tkachov at foss dot arm dot com>, Richard Biener <richard dot guenther at gmail dot com>, Segher Boessenkool <segher at kernel dot crashing dot org>
Cc: "gcc at gcc dot gnu dot org" <gcc at gcc dot gnu dot org>
Date: Tue, 8 Mar 2016 13:49:00 -0500
Subject: Re: Validity of SUBREG+AND-imm transformations
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References: <56D055C6 dot 6040800 at foss dot arm dot com> <56D0C2A1 dot 1070501 at redhat dot com> <56D422AC dot 2000703 at foss dot arm dot com> <20160304115946 dot GA20650 at gate dot crashing dot org> <56D99E93 dot 70209 at foss dot arm dot com> <56D9A035 dot 2010902 at foss dot arm dot com> <54FB3F2C-EEE0-49E7-BFE5-BF17209B449C at gmail dot com> <56D9B627 dot 2040807 at redhat dot com> <56D9B8E9 dot 4050802 at foss dot arm dot com> <56DA742C dot 1050602 at redhat dot com> <56DD5B86 dot 5080007 at foss dot arm dot com> <56DDDB3F dot 8010106 at redhat dot com>

On 03/07/2016 02:49 PM, Jeff Law wrote:

On 03/07/2016 03:44 AM, Kyrill Tkachov wrote:


The RTL documentation for ASHIFT and friends says that the shift amount
must be:
"a fixed-point mode or be a constant with mode @code{VOIDmode}; which
mode is determined by the mode called for in the machine description
entry for the left-shift instruction". For example, on the VAX, the mode
of @var{c} is @code{QImode} regardless of @var{m}.

Use QImode in the named pattern/expander and use the other modes in an
unnamed/anonymous pattern.

I thought the same thing you did. But I tried it out on the aarch64 port andit didn't work. Combine kept coming back to the QImode pattern.

I didn't want to look into it any farther than that, lest I fall down a rabbithole, but there's more to it than just tweaking the patterns.

r~

Follow-Ups:
- Re: Validity of SUBREG+AND-imm transformations
  - From: Jeff Law

References:
- Re: Validity of SUBREG+AND-imm transformations
  - From: Segher Boessenkool
- Re: Validity of SUBREG+AND-imm transformations
  - From: Kyrill Tkachov
- Re: Validity of SUBREG+AND-imm transformations
  - From: Kyrill Tkachov
- Re: Validity of SUBREG+AND-imm transformations
  - From: Richard Biener
- Re: Validity of SUBREG+AND-imm transformations
  - From: Jeff Law
- Re: Validity of SUBREG+AND-imm transformations
  - From: Kyrill Tkachov
- Re: Validity of SUBREG+AND-imm transformations
  - From: Jeff Law
- Re: Validity of SUBREG+AND-imm transformations
  - From: Kyrill Tkachov
- Re: Validity of SUBREG+AND-imm transformations
  - From: Jeff Law

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