Ilya Leoshkevich <i...@linux.ibm.com> writes:
> On Thu, 2021-01-21 at 10:49 +0000, Richard Sandiford wrote:
>> What prevents combine from handling this? Are the instructions in
>> different blocks?
>
> I wanted to do this before combine, because in __ieee754_sqrtl case
> fwprop turns this (example from the commit message + the insn after
> it):
>
> (set (reg:TF 63) (mem:TF (reg:DI 62)))
> (set (reg:FPRX2 66) (subreg:FPRX2 (reg:TF 63) 0))
> (set (reg:FPRX2 65)
> (asm_operands:FPRX2 ("sqxbr %0,%1") ("=f") 0
> [(reg:FPRX2 66)]
> [(asm_input:FPRX2 ("f"))]
> []))
>
> into this:
>
> (set (reg:TF 63) (mem:TF (reg:DI 62)))
> (set (reg:FPRX2 65)
> (asm_operands:FPRX2 ("sqxbr %0,%1") ("=f") 0
> [(subreg:FPRX2 (reg:TF 63) 0)]
> [(asm_input:FPRX2 ("f"))]
> []))
>
> by propagating (reg:FPRX2 66), and there is not much combine can do
> about this anymore:
>
> (set (reg:FPRX2 65)
> (asm_operands:FPRX2 ("sqxbr %0,%1") ("=f") 0
> [(mem:FPRX2 (reg:DI 62))]
> [(asm_input:FPRX2 ("f"))]
> []))
>
> is not a valid insn.
Ah, yeah, that's unfortunate. I guess a combine-ish way of fixing
that would be to do a 2-2 split, but there's no support for doing
that on asms.
Thanks,
Richard
