This is the mail archive of the
gcc-patches@gcc.gnu.org
mailing list for the GCC project.
Re: [PATCH][RFA][PR target/15184] Partial fix for direct byte access on x86
- From: Jeff Law <law at redhat dot com>
- To: Segher Boessenkool <segher at kernel dot crashing dot org>
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Tue, 27 Jan 2015 13:53:34 -0700
- Subject: Re: [PATCH][RFA][PR target/15184] Partial fix for direct byte access on x86
- Authentication-results: sourceware.org; auth=none
- References: <54C700F1 dot 6080502 at redhat dot com> <20150127051101 dot GB9815 at gate dot crashing dot org> <54C7E6AA dot 6010703 at redhat dot com> <20150127203632 dot GA406 at gate dot crashing dot org>
On 01/27/15 13:36, Segher Boessenkool wrote:
I mean e.g. DI on a 32-bit target. My worry is that zero_extend:DI then
is more expensive -- if say, it is implemented as a split, combine itself
cannot get rid of the redundancy.
OK. Let me play with that a bit.
Okay, if there are actual real cases like that :-) All this code does
is cull cases that are not useful to try to combine, since without that
combining four insns is very expensive.
There are :-) It surprised me as well.
Does this do anything good for the "dec mem" thing on x86? That would
be a nice bonus :-)
It might, but I haven't tested for that specifically. If you've got
sample code or a PR in mind, pass it along and I'll take a look. I'd
think dec mem would generally be handled by 3->1 insn combination code
unless there's something else going on.
I do have a specific PR in mind, but I cannot currently find it. It was
about x86, dec mem and then using the flags... Must have sent 100 emails
in that thread... And cannot find it now!
Are you referring to 61225?
Jeff