Use-and-clobber insns and some ancient combine.c code

[Michael Matz]

Hi,

On Thu, 17 Jun 2004, Ulrich Weigand wrote:

> I had not been aware of this interpretation of CLOBBER.  This is
> unfortunate, as it appears to make the use of use-and-clobber
> type patterns unfeasible ...

Yes.  A CLOBBER without any constraints is implicitely an early-clobber, 
and yes that's unfortunate.  The way I was working around this issue in 
some local patches was to implement a kind of non-early-clobber, which is 
simply a SET with an UNSPEC source:

  parallel([
    (set X Y)
    (set Y (unspec blabla)) ])


Ciao,
Michael.