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Re: RFA: cache enabled attribute by insn code
- From: Jakub Jelinek <jakub at redhat dot com>
- To: Richard Earnshaw <rearnsha at arm dot com>
- Cc: Christophe Lyon <christophe dot lyon at linaro dot org>, Jeff Law <law at redhat dot com>, "gcc-patches at gcc dot gnu dot org" <gcc-patches at gcc dot gnu dot org>, rsandifo at linux dot vnet dot ibm dot com
- Date: Tue, 27 May 2014 17:27:26 +0200
- Subject: Re: RFA: cache enabled attribute by insn code
- Authentication-results: sourceware.org; auth=none
- References: <87k39gkgq0 dot fsf at talisman dot default> <537B95E9 dot 1010203 at redhat dot com> <87iop0i13e dot fsf at talisman dot default> <537F9126 dot 5080904 at redhat dot com> <CAKdteOaYVgFZg5aUWUj9K7LPgmiGoT3iFiiaVbc-eSUKv22HCQ at mail dot gmail dot com> <87zji31fh7 dot fsf at sandifor-thinkpad dot stglab dot manchester dot uk dot ibm dot com> <5384AC23 dot 40701 at arm dot com>
- Reply-to: Jakub Jelinek <jakub at redhat dot com>
On Tue, May 27, 2014 at 04:15:47PM +0100, Richard Earnshaw wrote:
> On 27/05/14 15:08, Richard Sandiford wrote:
> > Hmm, is this because of "insn_enabled"? If so, how did that work before
> > the patch? LRA already assumed that the "enabled" attribute didn't depend
> > on the operands.
>
> Huh! "enabled" can be applied to each alternative. Alternatives are
> selected based on the operands. If LRA can't cope with that we have a
> serious problem. In fact, a pattern that matches but has no enabled
> alternatives is meaningless and guaranteed to cause problems during
> register allocation.
This is not LRA fault, but the backend misusing the "enabled" attribute
for something it wasn't designed for, and IMHO against the documentation
of the attribute too.
Just look at the original submission why it has been added.
Jakub