[PATCH] LOAD_EXTEND_OP only applies to (subreg (mem ...))

[Hans-Peter Nilsson]

On Tue, 9 Jul 2002, Roger Sayle wrote:
> I originally came up with this patch over a week ago, but wasn't
> sure it was the correct solution until now.  Whilst working on an
> possible alternate fix to the problem, I came across the comment
> at about line 11,000 of combine.c (in simplify_comparison).  This
> page long description of the semantics of SUBREGs is the best
> documentation I've come across so far, and has confirmed my belief
> that LOAD_EXTEND_OP should not apply to SUB_REGs of REGs.

Heh, that comment was derived from patches and arguments from
several gcc seniors, found while spelunking the mail archive
when fixing another paradoxical subreg bug. The mailing list
archive is your friend at times like that.

  You're in a maze of buggy RTL, all shared.  It's pitch dark.
  You're likely to be eaten by a paradoxical subreg.

brgds, H-P