Re: [PATCH 1/2] powerpc: rewrite LOAD_REG_IMMEDIATE() as an intelligent macro

[Christophe Leroy]

Le 14/08/2019 Ã 04:08, Paul Mackerras a ÃcritÂ:
> On Tue, Aug 13, 2019 at 09:59:35AM +0000, Christophe Leroy wrote:
>
> [snip]
>
> > +.macro __LOAD_REG_IMMEDIATE r, x
> > +	.if \x & ~0xffffffff != 0
> > +		__LOAD_REG_IMMEDIATE_32 \r, (\x) >> 32
> > +		rldicr	\r, \r, 32, 31
> > +		.if (\x) & 0xffff0000 != 0
> > +			oris \r, \r, (\x)@__AS_ATHIGH
> > +		.endif
> > +		.if (\x) & 0xffff != 0
> > +			oris \r, \r, (\x)@l
> > +		.endif
> > +	.else
> > +		__LOAD_REG_IMMEDIATE_32 \r, \x
> > +	.endif
> > +.endm
>
> Doesn't this force all negative constants, even small ones, to use
> the long sequence?  For example, __LOAD_REG_IMMEDIATE r3, -1 will
> generate (as far as I can see):
>
> 	li	r3, -1
> 	rldicr	r3, r3, 32, 31
> 	oris	r3, r3, 0xffff
> 	ori	r3, r3, 0xffff
>
> which seems suboptimal.

Ah yes, thanks. And it is also buggy when \x is over 0x80000000 because 
lis is a signed ops

I'll send v2

Christophe