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Re: GCC floating point usage
On Wed, Oct 16, 2002 at 03:36:45PM -0700, Zack Weinberg wrote:
> > You're going to need the front/middle-end to indicate whether
> > "floating point has been used", and if not, hide *all* existance
> > of the fp registers from the register allocators. Nothing less
> > gives you assurance they won't be used.
>
> Okay. Care to suggest how this should be accomplished?
For the second part?
Arrange for REG_CLASS_FROM_LETTER to return NO_REGS for 'f'
when appropriate would be one way. Mistakes here would result
in reload aborts, since reload would fail to find a way to
move data between, into, or out of the FP regs.
Marking the fp registers to be fixed for the duration of the
function would be another way, though it would seem that you'd
need a new hook run from rest_of_compilation, somewhere before
regclass/reload, in order to make this work.
r~