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Date: Mon, 28 Jan 2002 11:50:00 -0000
From: Richard Henderson <rth@redhat.com>
To: law@redhat.com
Cc: gcc@gcc.gnu.org
Subject: Re: paradoxical subreg problem
Message-ID: <20020128105031.D25844@redhat.com>
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In-Reply-To: <16350.1012242676@porcupine.cygnus.com>; from law@redhat.com on Mon, Jan 28, 2002 at 11:31:16AM -0700
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On Mon, Jan 28, 2002 at 11:31:16AM -0700, law@redhat.com wrote:
> I'll start simple.  On a big endian machine, can this expression be optimized
> into true/false at compile time, or must it be run-time computed?
> 
> (eq (subreg:SI (mem/s:QI (plus:SI (reg:SI 3 %r3)
>                 (const_int 15 [0xf])) 1) 0)
>     (mem/s:SI (plus:SI (reg:SI 3 %r3)
>             (const_int 12 [0xc])) 1))
> 
> 
> Think very very carefully about the semantics of a paradoxical subreg.

I'll remind you that we should only have subregs of memory during
reload (while pseudos are being replaced), and even then we don't
create paradoxical subregs of memory.

So this is a "shouldn't happen".


r~