Georg-Johann Lay <avr@xxxxxxxx> writes:
> When calculate_needs_all_insns runs on the insn the insn looks like
> this (other insn numbers than above as I proceed my very work
> regardless of the possible bug)
>
> calculate_needs_all_insns[__kernel_rem_pio2:greg(180)]: (insn:HI 409
> 438 400 17 k_rem_pio2.c:816 (set (reg:SI 566)
> (lshiftrt:SI (reg:SI 0 d0 [565])
> (const_int 8 [0x8]))) 22 {lshrsi3} (expr_list:REG_EQUIV
> (const_int 16777215 [0xffffff])
> (expr_list:REG_DEAD (reg:SI 0 d0 [565])
>
> Someone already replaced #1 with d0, a reg of the right class
> "d". Maybe a function parameter or return value is propagated.
>
> However, calculate_needs_all_insns decides that there are no reloads
> needed. reload1.c:1554 reads:
>
> /* Skip insns that only set an equivalence. */
> if (set && REG_P (SET_DEST (set))
> && reg_renumber[REGNO (SET_DEST (set))] < 0
> && (reg_equiv_constant[REGNO (SET_DEST (set))]
> || (reg_equiv_invariant[REGNO (SET_DEST (set))]))
> && reg_equiv_init[REGNO (SET_DEST (set))])
> continue;
>
> Before lreg, the insn is tagged REG_EQUAL but lreg then retags it as
> REG_EQUIV.
>
> So is the problem in lreg because it says REG_EQUIV?
> Or is it wrong to omit REG_EQUIV insns from reload?
Neither is the problem.
This case happens when a pseudo-register which is equivalent to a
constant or a memory location is not given a hard register. Reload is
supposed to replace every use of the register with the constant. The
insn would then normally be deleted. I don't know why it wasn't deleted
in your case.
One way to address this would probably be to define
LEGITIMATE_CONSTANT_P such that it rejects 0xffffff. If you don't do
that--if LEGITIMATE_CONSTANT_P accepts 0xffffff--then you need to ensure
that your movsi insn will handle 0xffffff directly, without using any
pseudo-registers when can_create_pseudo_p returns false.
Ian
