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Re: Possible CSE quirk involving SUBREG on the i386
- To: Richard Henderson <rth at cygnus dot com>
- Subject: Re: Possible CSE quirk involving SUBREG on the i386
- From: Jeffrey A Law <law at cygnus dot com>
- Date: Wed, 01 Jul 1998 23:50:31 -0600
- cc: John Wehle <john at feith dot com>, egcs at cygnus dot com, egcs-patches at cygnus dot com
- Reply-To: law at cygnus dot com
In message <19980701033305.A23054@dot.cygnus.com>you write:
> Ho hum. The explanation is simple here -- MODES_TIEABLE_P.
>
> I believe that we can do slightly better for this; while only
> the first four int regs can hold QImode values, all of them
> can hold HImode values.
>
> This happens to cure this exact problem, but the same problem
> will occur with unsigned char, and I don't see that we can do
> anything about it.
>
>
> r~
>
>
> * i386.h (HARD_REGNO_MODE_OK): Kill spurrious test.
> (MODES_TIEABLE_P): Tie SImode and HImode.
Patch seems reasonble. I think you should install it.
I think we're still trying to decide if we can relax MODES_TIEABLE_P's
need to be symmetric. :-) That might help the char problem in some
cases.
jeff