Re: rfa (x86): 387<=>sse moves

[Dale Johannesen <dalej at apple dot com>]

On Jul 26, 2005, at 12:51 AM, Paolo Bonzini wrote:
> Dale Johannesen wrote:
> > With -march=pentium4 -mfpmath=sse -O2, we get an extra move for code 
> > like
> >     double d = atof(foo);
> >     int i = d;
> >         call    atof
> >         fstpl   -8(%ebp)
> >         movsd   -8(%ebp), %xmm0
> >         cvttsd2si       %xmm0, %eax
> > (This is Linux, Darwin is similar.)  I think the difficulty is that 
> > for
>
> > (set (reg/v:DF 58 [ d ]) (reg:DF 8 st)) 64 {*movdf_nointeger}

> Try the attached patch.  It gave a 3% speedup on -mfpmath=sse for 
> tramp3d.  Richard Henderson asked for SPEC testing, then it may go in.

Thanks.  That's progress; the cost computation in regclass now figures 
out that memory
is that fastest place to put R58:

  Register 58 costs: AD_REGS:87000 Q_REGS:87000 NON_Q_REGS:87000
INDEX_REGS:87000 LEGACY_REGS:87000 GENERAL_REGS:87000 FP_TOP_REG:49000
FP_SECOND_REG:50000 FLOAT_REGS:50000 SSE_REGS:50000 
FP_TOP_SSE_REGS:75000
FP_SECOND_SSE_REGS:75000 FLOAT_SSE_REGS:75000 FLOAT_INT_REGS:87000
INT_SSE_REGS:91000 FLOAT_INT_SSE_REGS:91000
ALL_REGS:91000 MEM:40000

Unfortunately local-alloc insists on putting in a register anyway 
(ST(0) instead of an XMM,
but the end codegen is unchanged):

;; Register 58 in 8.

I think the RA may be missing the concept that memory might be faster 
than any possible register....
will dig further.