Re: Loop unrolling and asm

[Joern Rennecke <amylaar at cygnus dot co dot uk>]

> Hi folks,
> 
> While trying out egcs-1.0.2-prerelease, I compiled the
> new XFree86-3.3.2 on a Linux 2.1.88 (RH 5.0) PPro box.
> binutils-2.8.(...).21 is installed.
> 
> I used -O2 -march=i686 -funroll-loops to compile XFree.
> I encountered a small problem where a loop containing asm
> was unrolled.  The asm included labels (.label00, .label01, ...)
> and the assembler died because of multiple definitions of
> the labels.
> 
> The problem, of course, went away when I recompiled the incriminated
> file without loop unrolling.
> 
> XFree seems to run fine.
> 
> Now the question: how do you go about including an asm with labels
> in a loop that will be unrolled?

There are two ways to do this:

- local labels
  Not all assemblers support these, but at least gnu as does.  You define
  a local label as <digit>: , and reference it as <digit>b for a backwards
  reference, or <digit>f for a forwards reference.  E.g.:
  0:
   add -1,r0
   bne 0b

- using "%=" in the assembler template.  This will expand to a number
  which is unique to the template as seen by final_scan_insn.  That is,
  for each copy that final_scan_insn created, you will get a different
  number.