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Date: Sat, 25 Dec 2004 21:57:00 -0000
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From: "schlie at comcast dot net" <gcc-bugzilla@gcc.gnu.org>
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Reply-To: gcc-bugzilla@gcc.gnu.org
Subject: [Bug middle-end/19154] miss-optimization of (x & pow2C) avr conditionals returning bool equivalent values
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X-SW-Source: 2004-12/txt/msg03535.txt.bz2
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------- Additional Comments From schlie at comcast dot net  2004-12-25 21:56 -------
Subject: Re:  miss-optimization of (x & pow2C) avr
 conditionals returning bool equivalent values

I apologize, I'm confused, what are you comparing to what?

(are you using 4.0, which to my knowledge only builds with my
recent proposed patches, unless the problem was fixed otherwise?)

- to my understanding, (x & C) should never result in ((x >> C') & 1)
  presented to the backend, as it's purely a target specific optimization.


> From: pinskia at gcc dot gnu dot org <gcc-bugzilla@gcc.gnu.org>
> ------- Additional Comments From pinskia at gcc dot gnu dot org  2004-12-25
> 20:57 -------
> Take:
> char g(char c)
> {
> return (c & (1 << 3)) != 0;
> }
> 
> (insn 8 4 30 (set (reg:HI 24 r24 [orig:44 c ] [44])
>         (sign_extend:HI (reg:QI 24 r24 [ c ]))) 81 {extendqihi2} (nil)
>     (nil))
> 
> (insn 30 8 11 (parallel [
>             (set (reg:HI 24 r24 [orig:44 c ] [44])
>                 (lshiftrt:HI (reg:HI 24 r24 [orig:44 c ] [44])
>                     (const_int 3 [0x3])))
>             (clobber (reg:QI 19 r19))
>         ]) 70 {*lshrhi3_const} (nil)
>     (expr_list:REG_UNUSED (reg:QI 19 r19)
>         (expr_list:REG_UNUSED (reg:QI 25 r25)
>             (nil))))
> 
> (insn 11 30 12 (set (reg:HI 24 r24 [46])
>         (sign_extend:HI (reg:QI 24 r24 [47]))) 81 {extendqihi2}
> (insn_list:REG_DEP_TRUE 10 (nil))
>     (nil))
> (insn 19 16 25 (parallel [
>             (set (reg/i:HI 24 r24 [ <result> ])
>                 (and:HI (reg:HI 24 r24 [46])
>                     (const_int 1 [0x1])))
>             (clobber (scratch:QI))
>         ]) 47 {andhi3} (insn_list:REG_DEP_TRUE 11 (nil))
>     (expr_list:REG_UNUSED (scratch:QI)
>         (nil)))
> 
> 
> Which looks good if the rtl matches up one to one per instruction but since
> avr is not like that we get a
> werid interaction.
> 
> -- 
>            What    |Removed                     |Added
> ----------------------------------------------------------------------------
>              Status|UNCONFIRMED                 |NEW
>      Ever Confirmed|                            |1
>    Last reconfirmed|0000-00-00 00:00:00         |2004-12-25 20:57:17
>                date|                            |
> 
> 
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19154
> 
> ------- You are receiving this mail because: -------
> You reported the bug, or are watching the reporter.




-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19154