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Re: register move costs broken
- To: Jeffrey A Law <law at redhat dot com>
- Subject: Re: register move costs broken
- From: Alan Modra <alan at linuxcare dot com dot au>
- Date: Wed, 14 Feb 2001 17:41:19 +1100 (EST)
- cc: jh at suse dot cz, gcc-bugs at gcc dot gnu dot org
On Tue, 13 Feb 2001, Jeffrey A Law wrote:
> In message <Pine.LNX.4.21.0102141611450.32094-100000@front.linuxcare.com.au>y
> ou write:
> > serial.c: In function `change_speed':
> > serial.c:1803: Insn does not satisfy its constraints:
> > (insn 1409 1406 649 (set (reg:DI 60 SAR [269])
> > (mem:DI (plus:DI (reg/f:DI 30 %r30)
> > (const_int -248 [0xffffff08])) 0)) 123 {*pa.md:3157} (nil)
> > (nil))
> > serial.c:1803: confused by earlier errors, bailing out
> Note there's a bug either in the PA backend or reload which is closely
> related to this failure.
>
> In particular if we have a multiply which is then used as a shift count
> in a variable shift instruction, then we can end up in a situation where
> we need to copy from an FP register into the SAR register.
In this case it wasn't later used in a variable shift.
lreg dump showed every register class cost at 20000 for register 269, then
;; Register 269 in 60.
which is SAR unless I'm mistaken.
All costs the same looked highly irregular to me, which is why I decided
to investigate the effect of backing out Jan's patch.
Alan
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