Re: [PATCH] [SH] Fix target/48596

[Oleg Endo <oleg dot endo at t-online dot de>]

On Thu, 2012-03-01 at 13:11 +0900, Kaz Kojima wrote:
> Hi,
> 
> The attached patch is to avoid PR target/48596 which is a 4.7
> regression on SH.  It seems that now IRA aggressively tried to
> use fp regs as the holder for memory addresses on this port.
> SH requires a special fpul register to move from the fp regs to
> the general regs which are legitimate for pointers and, in
> the problematic situation, fpul is already reserved for reload
> and the spill failure resulted for the reg equiv processing in RA.
> I guess that no other targets have such restrictions.  Perhaps
> if there eas a direct way to notify IRA that some register classes
> will be too costly for the addresses, SH port will utilize it,
> though it looks to be invasive.
> 
> The patch tries to work around the problem with increasing the move
> cost between fp and general registers for SImode.  The usual tests
> are done successfully on sh4-unknown-linux-gnu with no new failures.
> A bit surprisingly, there are no size/performance regressions and
> a few code size improvements with CSiBE tests I've done.
> I'd like to hear the suggestions from the experts before applying
> this work around.
> 

I was afraid that with this patch, in the following use case ...

int32_t float_as_int (float val)
{
  union { float f; int32_t i; } u;
  u.f = val;
  return u.i;
}

... the value would somehow get pushed/popped through the stack.
Luckily this is not the case, it still goes through the fpul register :)

__Z12float_as_intf:
	flds	fr5,fpul
	rts	
	sts	fpul,r0

(I've got a similar use case where it does go through the stack, but it
also happens without the patch...)

BTW, the patch also seems to fix PR 48806.

Cheers,
Oleg