https://gcc.gnu.org/bugzilla/show_bug.cgi?id=55212
--- Comment #309 from Kazumoto Kojima <kkojima at gcc dot gnu.org> ---
(In reply to Oleg Endo from comment #308)
> Thanks for confirming it. In this case, wouldn't it be better to explicitly
> mention the hard reg numbers everywhere, where they are involved? Otherwise
> the definitions are bara-bara all over the place. For example:
>
> (define_insn "block_lump_real"
> [(set (mem:BLK (match_operand:SI 2 "hard_reg_r4" "=r,r"))
Sure. hard_reg_r[456] sounds better.
> But actually, why are the register constraints "=r,r"? The insn only takes
> inputs, but those are declared as outputs. That looks wrong to me. Perhaps
> that's why the need for the seemingly superflous (use (reg:SI ... )?
If "=" is removed, it doesn't work, unfortunately. It compiles our tiny case to
foo:
mov.l r14,@-r15 ! 32 [c=4 l=2] movsi_ie/8
mov r4,r5 ! 23 [c=4 l=2] movsi_ie/1
sts.l pr,@-r15 ! 33 [c=4 l=2] movsi_ie/10
mov.w .L6,r1 ! 34 [c=10 l=2] *movhi/0
mov #31,r6 ! 11 [c=4 l=2] movsi_ie/2
mov.l .L4,r14 ! 29 [c=10 l=2] movsi_ie/0
mov #0,r7 ! 16 [c=4 l=2] movsi_ie/2
sub r1,r15 ! 35 [c=4 l=2] *subsi3_internal
mov r15,r4 ! 30 [c=4 l=2] movsi_ie/1
jsr @r14 ! 12 [c=1 l=2] block_lump_real_i4/0
add #4,r4 ! 31 [c=4 l=2] *addsi3_compact_lra/0
mov.l .L5,r1 ! 27 [c=10 l=2] movsi_ie/0
mov #0,r6 ! 17 [c=4 l=2] movsi_ie/2
mov.l r4,@r15 ! 14 [c=4 l=2] movsi_ie/8
which uses r4 as if it isn't clobbered.
As mentioned in c#276, I assume that LRA doesn't handle the clobber reg pattern
if that reg is recognized as the input reg, unless it's call_insn. It would
have been nice if the pattern in c#276 had worked.
