Register Allocation

[Vladimir N. Makarov]

John Lu wrote:

>Hi,
>
>I've been working on a port based on gcc-3.3 and I've noticed that
>better assembly code is generated if the C source has
>separate variables declared for distinct live ranges.
>
>  
>
Pesudo-register renaming is made by -fweb.  It was written by Jan 
Hubicka.  Probably, this option should be set up by default (although 
there is no practically improvement for SPECInt2000 for P4, some tests 
are really faster).  Another positive thing of usage this option is 
better scheduling because of less anti-dependences.

Different live ranges of a varaible sometimes has less conflicts and 
never more.  Therefore there is more probablility that varaible values 
will be in registers.  New ra works on webs (it is definitions and 
usages of pseudo-register which can have different names).  So it should 
work for new ra too.  But there are a lot factors which could prevent 
generates a better code.

Vlad

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