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Re: Gcc 3.1 performance regressions with respect to 2.95.3
> > And in addition to the decrease in the performance of the stepanov tests
> > there is a substantial decrease in the performance for processing
> > complex numbers (S000004a).
>
> This looks like aliasing bug. Gcc generates a lot of reloading from
> stack:
> (insn 274 22 27 (set (reg/v:DF 60)
> (mem/u/f:DF (symbol_ref/u:SI ("*.LC3")) [0 S8 A64])) 95 {*movdf_integer} (nil)
> (expr_list:REG_EQUIV (const_double:DF 0 [0x0] 0 [0x0] 1073643520 [0x3ffe8000] 0 [0x0] 0 [0x0])
> (nil)))
>
> (insn 27 274 273 (set (mem/s/j:DF (plus:SI (reg/f:SI 20 frame)
> (const_int -16 [0xfffffff0])) [0 <variable>.re+0 S8 A32])
> (reg/v:DF 60)) 95 {*movdf_integer} (insn_list 19 (nil))
> (expr_list:REG_DEAD (reg/v:DF 60)
> (nil)))
>
> ... later ...
>
> (insn 249 41 252 (set (reg/v:SI 102)
> (mem/s:SI (plus:SI (reg/f:SI 20 frame)
> (const_int -16 [0xfffffff0])) [0 factor+0 S4 A128])) 45 {*movsi_1} (nil)
> (nil))
>
>
> All memory references in a way are explicit and really should not invalidate
> the reference. I have no slightest idea why this happends, but we should
> investigate it.
Futher investigation shows that it is not cse guilty. Actually there
is loop boundary in a way and our local CSE has been never able to get this.
It is probably work for load/store motion if it wasn't that inefective
as it is right now. However this is not gcc 2.95 regression.
WHat maked this testcase run slower is overactive GCSE allowing
overactive invariant code motion.
With stronger alias analysis we now identify more invariant memory location
(about 8), move them outside of loop and run out of registers later.
I have not idea what to do until we get better reincarnation in the
register allocation pass.
Honza
>
> Honza
> >
> > It looks that there are some flaws in the -O2 optimizer passes. Is
> > there a chance that this is fixed for the upcoming gcc 3.1 release?
> >
> > Hope this helps,
> >
> > Peter Schmid
> >
> >
> >
> > RELATIVE TIMES ..........
> > TEST NAME Pentium II, 350 MHz Pentium II, 350 MHz
> > gcc 3.1 gcc 3.1
> > -O -O2
> > --------- ------------------- -------------------
> > A000091 1.00 1.00
> > A000092 1.00 0.99
> > A000094a 1.00 1.08
> > A000094b 1.00 0.87
> > A000094c 1.00 1.00
> >
> > A000094d 1.00 0.67
> > A000094e 1.00 0.67
> > A000094f 1.00 0.95
> > A000094g 1.00 0.98
> > A000094h 1.00 0.83
> >
> > A000094i 1.00 0.68
> > A000094j 1.00 0.96
> > A000094k 1.00 0.44
> > B000002b 1.00 1.02 *
> > B000003b 1.00 1.02 *
> >
> > B000004b 1.00 1.01 *
> > B000010 1.00 0.98
> > B000011 1.00 0.99
> > B000013 1.00 0.81
> > D000001 1.00 0.99
> >
> > D000002 1.00 1.01 *
> > D000003 1.00 0.99
> > D000004 1.00 1.01 *
> > D000005 1.00 1.16 *
> > D000006 1.00 1.00
> >
> > E000001 1.00 0.98
> > E000002 1.00 0.98
> > E000003 1.00 0.68
> > E000004 1.00 0.59
> > E000007 1.00 1.00
> >
> > E000008 1.00 1.07
> > F000001 1.00 1.44 *
> > F000002 1.00 1.44 *
> > F000003 1.00 0.37
> > F000004 1.00 0.55
> >
> > F000005 1.00 0.59
> > F000006 1.00 0.70
> > F000007 1.00 0.88
> > F000008 1.00 1.14 *
> > G000001 1.00 0.95
> >
> > G000002 1.00 0.99
> > G000003 1.00 1.05 *
> > G000004 1.00 1.01 *
> > G000005 1.00 0.92
> > G000006 1.00 1.05 *
> >
> > G000007 1.00 1.03 *
> > H000001 1.00 1.01 *
> > H000002 1.00 1.00
> > H000003 1.00 0.90
> > H000004 1.00 0.88
> >
> > H000005 1.00 0.00
> > H000006 1.00 0.88
> > H000007 1.00 0.99
> > H000008 1.00 0.76
> > H000009 1.00 0.99
> >
> > L000001 1.00 1.21 *
> > L000002 1.00 1.16 *
> > L000003 1.00 1.38 *
> > L000004 1.00 2.00 *
> > O000001a 1.00 0.82
> >
> > O000001b 1.00 0.83
> > O000002a 1.00 0.94
> > O000002b 1.00 1.00
> > O000003a 1.00 1.09 *
> > O000003b 1.00 0.96
> >
> > O000004a 1.00 1.05 *
> > O000004b 1.00 1.05 *
> > O000005a 1.00 1.01 *
> > O000005b 1.00 0.85
> > O000006a 1.00 0.94
> >
> > O000006b 1.00 0.86
> > O000007a 1.00 1.15 *
> > O000007b 1.00 1.26 *
> > O000008a 1.00 1.08 *
> > O000008b 1.00 0.95
> >
> > O000009a 1.00 0.84
> > O000009b 1.00 0.85
> > O000010a 1.00 0.99
> > O000010b 1.00 1.07 *
> > O000011a 1.00 0.93
> >
> > O000011b 1.00 1.05 *
> > O000012a 1.00 1.00
> > O000012b 1.00 0.99
> > P000001 1.00 0.61
> > P000002 1.00 0.72
> >
> > P000003 1.00 0.65
> > P000004 1.00 0.00
> > P000005 1.00 1.43 *
> > P000006 1.00 1.14 *
> > P000007 1.00 1.10
> >
> > P000008 1.00 1.21 *
> > P000010 1.00 0.76
> > P000011 1.00 0.98
> > P000012 1.00 1.11 *
> > P000013 1.00 1.00
> >
> > P000020 1.00 0.93
> > P000021 1.00 0.59
> > P000022 1.00 0.59
> > P000023 1.00 1.12 *
> > S000001a 1.00 0.93
> >
> > S000001b 1.00 1.17 *
> > S000002a 1.00 0.53
> > S000002b 1.00 0.59
> > S000003a 1.00 0.63
> > S000003b 1.00 1.02 *
> >
> > S000004a 1.00 1.47 *
> > S000004b 1.00 0.99
> > S000005a 1.00 1.03 *
> > S000005b 1.00 0.97
> > S000005c 1.00 1.03 *
> >
> > S000005d 1.00 0.97
> > S000005e 1.00 1.18 *
> > S000005f 1.00 0.98
> > S000005g 1.00 1.12 *
> > S000005h 1.00 0.98
> >
> > S000005i 1.00 1.03 *
> > S000005j 1.00 0.97
> > S000005k 1.00 1.01 *
> > S000005l 1.00 0.98
> > S000005m 1.00 1.00
> >