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Re: x86 code generation question
- From: Bernd Jendrissek <berndj at prism dot co dot za>
- To: Paul Koning <pkoning at equallogic dot com>
- Cc: vadim at cs dot washington dot edu, gcc at gcc dot gnu dot org
- Date: Fri, 30 Apr 2004 08:34:04 +0200
- Subject: Re: x86 code generation question
- References: <16529.28055.229626.658780@gargle.gargle.HOWL>
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On Thu, Apr 29, 2004 at 05:03:19PM -0400, Paul Koning wrote:
> That isn't straight line code. The reason is that the x86 doesn't
> have instructions that turn comparisons into the integers 0 and 1. So
Oh but it does! And it doesn't even need anything beyond bog-standard
8086 code.
cmp ax,bx
sbb dx,dx
; dx is now 0 if ax >= bx, -1 if ax < bx
neg dx
Have you used superopt? It finds some pretty surprising sequences to do
some nifty stuff. AFAIK some of GCC's sequences are inspired by
superopt, which, in fact, (and again, IIRC) was written precisely to
find such beyond-humanly clever sequences for GCC.
- --
http://voyager.abite.co.za/~berndj/ (up again for now - yay!)
bernd's stupid blog: http://voyager.abite.co.za/~berndj/blog.php
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