From: Roger Sayle <roger@www.eyesopen.com>
To: David Edelsohn <dje@watson.ibm.com>
Cc: gcc@gcc.gnu.org
Subject: Re: Strange conditional jumps on the POWER4
Date: Sun, 06 Apr 2003 05:21:00 -0000 [thread overview]
Message-ID: <Pine.LNX.4.44.0304051833030.27022-100000@www.eyesopen.com> (raw)
In-Reply-To: <200304060211.VAA31048@makai.watson.ibm.com>
Hi David,
> It appears that you are not compiling the code with -mcpu=power4
> commandline option for GCC 3.4, because the branch hint mnemonics (+/-)
> would not be present without greater probabilities.
Indeed, I used exactly the flags described in the posting. Out of
interest, I've now also run Whetstone with "-mcpu=power4", hoping that
it would fix things. Not only does this not fix the N3 regression, it
actually does slightly worse overall.
With gcc-3.2 -O2 -ffast-math:
Loop content Result MFLOPS MOPS Seconds
N1 floating point -1.12475025653839111 157.257 0.588
N2 floating point -1.12274754047393799 130.235 4.970
N3 if then else 1.00000000000000000 488.682 1.020
N4 fixed point 12.00000000000000000 171.030 8.870
N5 sin,cos etc. 0.49904659390449524 32.550 12.310
N6 floating point 0.99999988079071045 58.826 44.160
N7 assignments 3.00000000000000000 92.323 9.640
N8 exp,sqrt etc. 0.75110864639282227 10.374 17.270
MWIPS 487.311 98.828
With gcc-3.4 -O2 -ffast-math:
Loop content Result MFLOPS MOPS Seconds
N1 floating point -1.12475013732910156 189.658 0.582
N2 floating point -1.12274742126464844 180.109 4.290
N3 if then else 1.00000000000000000 214.037 2.780
N4 fixed point 12.00000000000000000 186.310 9.720
N5 sin,cos etc. 0.49911010265350342 33.102 14.450
N6 floating point 0.99999982118606567 72.217 42.940
N7 assignments 3.00000000000000000 137.619 7.720
N8 exp,sqrt etc. 0.75110864639282227 16.008 13.360
MWIPS 599.841 95.842
With gcc-3.4 -O2 -ffast-math -mcpu=power4
Loop content Result MFLOPS MOPS Seconds
N1 floating point -1.12475013732910156 190.647 0.582
N2 floating point -1.12274742126464844 178.142 4.360
N3 if then else 1.00000000000000000 214.382 2.790
N4 fixed point 12.00000000000000000 204.308 8.910
N5 sin,cos etc. 0.49911010265350342 33.647 14.290
N6 floating point 0.99999982118606567 71.627 43.520
N7 assignments 3.00000000000000000 88.334 12.090
N8 exp,sqrt etc. 0.75110864639282227 15.819 13.590
MWIPS 577.138 100.132
So as you can see the situation isn't too bad at all. Overall gcc 3.4
is much faster than gcc 3.2. But you can see my concern over the slow
down of N3, and that adding "-mcpu=power4" doesn't resolve the issue.
Roger
--
next prev parent reply other threads:[~2003-04-06 2:47 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-04-05 21:26 Roger Sayle
2003-04-06 1:42 ` Zack Weinberg
2003-04-06 1:59 ` Roger Sayle
2003-04-06 3:33 ` David Edelsohn
2003-04-06 5:21 ` Roger Sayle [this message]
2003-04-06 16:49 ` Segher Boessenkool
2003-04-07 23:03 ` David Edelsohn
2003-04-06 15:14 ` David Edelsohn
[not found] <200304080131.VAA30506@makai.watson.ibm.com>
2003-04-08 15:50 ` Roger Sayle
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