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Re: Defining constraint for registers tuple

From: Ian Lance Taylor <iant at google dot com>
To: Kirill Yukhin <kirill dot yukhin at gmail dot com>
Cc: gcc at gcc dot gnu dot org
Date: Fri, 29 Jul 2011 05:44:30 -0700
Subject: Re: Defining constraint for registers tuple
References: <CAGs3Rfth_Ds57WT8-Wg0=c3tFEvwkUE3Hg4nJ=kx-+fvxEtrvQ@mail.gmail.com>

Kirill Yukhin <kirill.yukhin@gmail.com> writes:

> I'm working on implementation of `mulx` (which is part of BMI2). One
> of improvements compared generic `mul` is that it allows to specify
> destination registers.
> For `mul` we have `A` constraint, which stands for AX:DX pair.
> So, is there a possibility to relax such cinstraint and allow any pair
> of registers as destination?

Don't change the constraint, just add an alternative.  Or use a
different insn with an insn predicate.

Ian

References:
- Defining constraint for registers tuple
  - From: Kirill Yukhin

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