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Re: copyprop_hardreg_forward removes division
- From: Jan Hubicka <jh at suse dot cz>
- To: Lars Brinkhoff <lars dot spam at nocrew dot org>
- Cc: gcc at gcc dot gnu dot org
- Date: Fri, 15 Feb 2002 19:10:04 +0100
- Subject: Re: copyprop_hardreg_forward removes division
- References: <85u1sibync.fsf@junk.nocrew.org>
> I have a problem with a dissapearing division instruction. Before
> copyprop_hardreg_forward in regrename.c is called, the situation looks
> like this:
>
> (insn 47 39 19 (set (reg:SI 3 3)
> (reg:SI 3 3)) -1 (nil)
> (nil))
>
> ;; This instruction divides (reg:SI 3) by (const_int 3), and puts
> ;; the quotient in (reg:SI 3) and the remainder in the next register,
> ;; (reg:SI 4).
> (insn 19 47 24 (parallel[
> (set (subreg:SI (reg:DI 3 3 [30]) 0)
> (div:SI (reg:SI 3 3)
> (const_int 3 [0x3])))
> (set (subreg:SI (reg:DI 3 3 [30]) 4)
> (mod:SI (reg:SI 3 3)
> (const_int 3 [0x3])))
> ] ) 107 {IDIV} (insn_list 18 (nil))
> (expr_list:REG_UNUSED (reg:SI 4 4)
> (nil)))
It looks like you are having same problem as I had. copyprop_hardreg misses
the stores to subregs. I've commited fix to that so hope it is OK in the
tree (see kill_value).
Honza
>
> (note 24 19 27 NOTE_INSN_FUNCTION_END)
>
> (insn 27 24 30 (set (reg/i:SI 1 1)
> (reg:SI 3 3 [29])) 74 {*movsi_cache} (insn_list 19 (nil))
> (expr_list:REG_DEAD (reg:SI 3 3 [29])
> (nil)))
>
> However, when copyprop_hardreg_forward_1 is called from
> copyprop_hardreg_forward, it will change (reg:SI 3) in insns 47 and 27
> to (reg:SI 2), but not in insn 19:
>
> (insn 47 39 19 (set (reg:SI 3 3)
> (reg:SI 2 2 [3])) 74 {*movsi_cache} (nil)
> (nil))
>
> (insn 19 47 24 (parallel[
> (set (subreg:SI (reg:DI 3 3 [30]) 0)
> (div:SI (reg:SI 3 3)
> (const_int 3 [0x3])))
> (set (subreg:SI (reg:DI 3 3 [30]) 4)
> (mod:SI (reg:SI 3 3)
> (const_int 3 [0x3])))
> ] ) 107 {IDIV} (insn_list 18 (nil))
> (expr_list:REG_UNUSED (reg:SI 4 4)
> (nil)))
>
> (note 24 19 27 NOTE_INSN_FUNCTION_END)
>
> (insn 27 24 30 (set (reg/i:SI 1 1)
> (reg:SI 2 2 [29])) 74 {*movsi_cache} (insn_list 19 (nil))
> (expr_list:REG_DEAD (reg:SI 3 3 [29])
> (nil)))
>
> update_life_info will then happily remove the unnecessary insn 19.
>
> How can I avoid this?
>
> --
> Lars Brinkhoff http://lars.nocrew.org/ Linux, GCC, PDP-10,
> Brinkhoff Consulting http://www.brinkhoff.se/ HTTP programming