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Re: swap (a, b) - test

To: Eric Buddington <eric at sparrow dot vgernet dot net>
Subject: Re: swap (a, b) - test
From: Richard Henderson <rth at cygnus dot com>
Date: Sun, 4 Jan 1998 22:15:27 -0800
Cc: egcs at cygnus dot com
References: <19980103181123.28803@sparrow.vgernet.net> <19980103201251.06123@dot.cygnus.com> <19980104135749.39120@sparrow.vgernet.net>
Reply-To: Richard Henderson <rth at cygnus dot com>

On Sun, Jan 04, 1998 at 01:57:49PM -0500, Eric Buddington wrote:
> However, a quick test now is now running slower with the XOR swap. I
> don't see why three XOR operations on two ints would be slower
> than three assignments among three ints...

Ideally the register allocator can elide the swap altogether by
logically swapping what register it believes a value to reside in.

Certainly it would not be possible all of the time, and I think
things are in practice hindered by the fact that pseudos are 
currently allocated (or not) a single register for their entire 
life span.  

r~

References:
- swap (a, b) suggestion
  - From: Eric Buddington
- Re: swap (a, b) suggestion
  - From: Richard Henderson
- Re: swap (a, b) - test
  - From: Eric Buddington

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