Re: [PATCH, ARM] Avoid using VFP registers for SImode

[Daniel Jacobowitz <drow at false dot org>]

On Wed, Jan 05, 2005 at 11:30:54AM +0000, Richard Earnshaw wrote:
> Not sure if this really counts as a bug, but VFP support is new in
> gcc-4, so this can't introduce a regression.
> 
> On ARM processors with VFP floating point, using the VFP registers for
> integer values (except when we are about to convert them into floating
> point values) is a bad idea.  However, GCC is far too keen to try this
> when register pressure starts to increase.  This patch fixes this by
> hiding the VFP register classes from the register preferencing pass.
> 
> Tested on arm-elf with VFP enabled.

Ah, that's a fix I hadn't thought of...

I noticed a similar case at -O0 last week.  The reason in my testcase that
regclass is so eager to try this is here:

enum reg_class
{
  NO_REGS,
  FPA_REGS,
  CIRRUS_REGS,
  VFP_REGS,
  ...

At -O0 regclass uses the cheapest class for "best" and the first class
it sees that is better than memory for "alt", so "alt" is almost always
VFP_REGS.  Maybe the costs need adjustment if memry should be preferred
to VFP_REGS.

-- 
Daniel Jacobowitz