Hi!
On Tue, Oct 29, 2019 at 01:34:15PM -0600, Jeff Law wrote:
> That needs to turn into a define_insn_and_split. The idea is the form
> above is what's seen prior to register allocation and reloading. After
> reloading we turn it into a form with an attached clobber. We achieve
> this by rewriting the pattern into a define_insn_and_split like this:
>
> > (define_insn_and_split "*addsi_h8300"
> > [(set (match_operand:SI 0 "register_operand" "=r,r")
> > (plus:SI (match_operand:SI 1 "register_operand" "%0,0")
> > (match_operand:SI 2 "h8300_src_operand" "n,r")))]
> > "TARGET_H8300"
> > "#"
> > "reload_completed"
> > [(parallel [(set (match_dup 0) (plus:SI (match_dup 1) (match_dup 2)))
> > (clobber (reg:CC CC_REG))])])
>
> We added the "#" which indicates the pattern has to be split and will
> never generate assembly code in and of itself.
It is important to note that this indication is mostly a comment, and
nothing more. The split condition ("reload_completed", here) is the only
thing that determines if something is split or not.
The exception is that final.c *does* look if the template is "#", and
splits while outputting to asm. Normally though everything is split
earlier already (there is a split pass almost immediately before final,
one of the two that is run at -O0 as well).
It's great to always write "#" here, it is nice documentation ("this insn
is always split"), but you still need to get your split condition correct.
Segher
