From: Jeff Law <law@redhat.com>
To: gcc-patches@gcc.gnu.org, richard.sandiford@arm.com
Subject: Re: [PATCH 0/5] Fix handling of word subregs of wide registers
Date: Fri, 19 Sep 2014 06:14:00 -0000 [thread overview]
Message-ID: <541BC9A2.2030309@redhat.com> (raw)
In-Reply-To: <87ppetnsxd.fsf@e105548-lin.cambridge.arm.com>
On 09/18/14 04:07, Richard Sandiford wrote:
> This series is a cleaned-up version of:
>
> https://gcc.gnu.org/ml/gcc/2014-03/msg00163.html
>
> The underlying problem is that the semantics of subregs depend on the
> word size. You can't have a subreg for byte 2 of a 4-byte word, say,
> but you can have a subreg for word 2 of a 4-word value (as well as lowpart
> subregs of that word, etc.). This causes problems when an architecture has
> wider-than-word registers, since the addressability of a word can then depend
> on which register class is used.
>
> The register allocators need to fix up cases where a subreg turns out to
> be invalid for a particular class. This is really an extension of what
> we need to do for CANNOT_CHANGE_MODE_CLASS.
>
> Tested on x86_64-linux-gnu, powerpc64-linux-gnu and aarch64_be-elf.
I thought we fixed these problems long ago with the change to subreg_byte?!?
Clearly I missed something.
jeff
next prev parent reply other threads:[~2014-09-19 6:14 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-09-18 10:07 Richard Sandiford
2014-09-18 10:09 ` [PATCH 1/5] Allow *_HARD_REG_SET arguments to be const Richard Sandiford
2014-09-19 6:14 ` Jeff Law
2014-09-18 10:10 ` [PATCH 2/5] Tweak subreg_get_info documentation Richard Sandiford
2014-09-19 6:16 ` Jeff Law
2014-09-18 10:13 ` [PATCH 3/5] Use simplify_subreg_regno in combine.c:subst Richard Sandiford
2014-09-19 6:17 ` Jeff Law
2014-09-18 10:25 ` [PATCH 4/5] Generalise invalid_mode_change_p Richard Sandiford
2014-09-19 17:53 ` Jeff Law
2014-09-22 7:34 ` Richard Sandiford
2014-09-22 16:29 ` Jeff Law
2014-09-18 10:26 ` [PATCH 5/5] Remove CANNOT_CHANGE_MODE_CLASS workaround in i386.c Richard Sandiford
2014-09-19 17:54 ` Jeff Law
2014-09-19 6:14 ` Jeff Law [this message]
2014-09-19 7:24 ` [PATCH 0/5] Fix handling of word subregs of wide registers Richard Sandiford
2014-09-19 15:59 ` Jeff Law
2014-09-19 17:14 ` Jeff Law
2014-09-22 7:23 ` Richard Sandiford
2014-09-22 10:49 ` Ajit Kumar Agarwal
2014-09-22 11:26 ` Richard Sandiford
2014-09-22 12:07 ` Ajit Kumar Agarwal
2014-09-22 9:00 ` Andrew Pinski
2014-09-22 11:29 ` Richard Sandiford
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