------- 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 <[EMAIL PROTECTED]>
> ------- 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
>
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--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=19154
