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[Bug tree-optimization/54116] suboptimal code for tight loops
- From: "neleai at seznam dot cz" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: Sun, 29 Jul 2012 10:30:46 +0000
- Subject: [Bug tree-optimization/54116] suboptimal code for tight loops
- Auto-submitted: auto-generated
- References: <bug-54116-4@http.gcc.gnu.org/bugzilla/>
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54116
--- Comment #2 from Ondrej Bilka <neleai at seznam dot cz> 2012-07-29 10:30:46 UTC ---
On Sun, Jul 29, 2012 at 10:13:41AM +0000, pinskia at gcc dot gnu.org wrote:
> http://gcc.gnu.org/bugzilla/show_bug.cgi?id=54116
>
> --- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> 2012-07-29 10:13:41 UTC ---
> The tree level looks correct:
> <bb 4>:
> # ivtmp.23_69 = PHI <ivtmp.23_68(5), ivtmp.23_66(3)>
> D.1771_65 = (void *) ivtmp.23_69;
> D.1717_6 = MEM[base: D.1771_65, offset: 0B];
> D.1722_10 = MEM[base: D.1771_65, offset: 4B];
> D.1723_11 = D.1722_10 | D.1717_6;
> D.1727_15 = MEM[base: D.1771_65, offset: 8B];
> D.1731_19 = MEM[base: D.1771_65, offset: 12B];
> D.1732_20 = D.1731_19 | D.1727_15;
> D.1733_21 = D.1732_20 | D.1723_11;
> ivtmp.23_68 = ivtmp.23_69 + 16;
> if (D.1733_21 != 0)
> goto <bb 6>;
> else
> goto <bb 5>;
>
> <bb 5>:
> goto <bb 4>;
>
> <bb 6>:
> # D.1723_22 = PHI <D.1723_11(4), D.1723_36(2)>
> # D.1732_23 = PHI <D.1732_20(4), D.1732_45(2)>
> D.1737_25 = D.1723_22 * D.1732_23;
> return D.1737_25;
>
>
> --- CUT ----
> Are you trying to say GCC should copy the loop header in this case?
> Or keeping around x[i]|x[i+1] and x[i+2]|x[i+3] result increases register
> pressure and exposes issues with 2-operand machines in some cases?
Increases register pressure.
>
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