Massive performance regression from switching to gcc 4.5

[Jan Hubicka]

> > > Jan Hubicka wrote:
> > >>> On Fri, 25 Jun 2010, it was written:
> > >>> There sure is something in 4.5. I've seen a 1-10% slowdown at the GiNaC
> > >>> (a computer algebra library) benchmark suite after switching from 4.4 to
> > >>> 4.5 on x86_64 when compiling with -O2. And there hasn't been a measurable
> > >>> performance differences between 4.3 and 4.4.
> > >>
> > >> FP intensive code could be also affected by:
> > >
> > > This code isn't using floating-point.
> > 
> > Hmm, building ginac with current 4.5 branch I get:
> > /bin/sh ../libtool --tag=CXX   --mode=compile /abuild/jh/gcc-4.5-nopatch/bin/g++ -DHAVE_CONFIG_H -I. -I../../ginac -I../config   -I/usr/local/include    -g -O2 -MT function.lo -MD -MP -MF .deps/function.Tpo -c -o function.lo ../../ginac/function.cpp
> > libtool: compile:  /abuild/jh/gcc-4.5-nopatch/bin/g++ -DHAVE_CONFIG_H -I. -I../../ginac -I../config -I/usr/local/include -g -O2 -MT function.lo -MD -MP -MF .deps/function.Tpo -c ../../ginac/function.cpp  -fPIC -DPIC -o .libs/function.o
> > ../../ginac/function.cpp: In member function Ă˘Â€Â˜GiNaC::ex GiNaC::function::power(const GiNaC::ex&) const’:
> > ../../ginac/function.cpp:1800:15: error: expected type-specifier
> > ../../ginac/function.cpp:1800:15: error: expected Ă˘Â€Â˜)’
> > ../../ginac/function.cpp:1801:72: error: conversion from Ă˘Â€Â˜int*’ to Ă˘Â€Â˜GiNaC::ex’ is ambiguous
> > ../../ginac/ex.h:279:1: note: candidates are: GiNaC::ex::ex(long unsigned int) <near match>
> > ../../ginac/ex.h:273:1: note:                 GiNaC::ex::ex(long int) <near match>
> > ../../ginac/ex.h:267:1: note:                 GiNaC::ex::ex(unsigned int) <near match>
> > ../../ginac/ex.h:261:1: note:                 GiNaC::ex::ex(int) <near match>
> 
> Hi,
> I got arround by just replacing the offending line by abort() that seems to get me far enough
> to build the testsuite.  One thing I noticed is that compile time prolonged excessively to about
> 10 minutes.  It seems to be var tracking
> 
> 39609    11.3093  cc1plus                  canonicalize_values_star
> 33469     9.5562  cc1plus                  loc_cmp
> 22206     6.3403  cc1plus                  set_slot_part
> 15798     4.5107  cc1plus                  rtx_equal_p
> 14479     4.1341  cc1plus                  htab_find_with_hash
> 10461     2.9869  cc1plus                  htab_find_slot_with_hash
> 7268      2.0752  cc1plus                  find_loc_in_1pdv
> 6718      1.9181  cc1plus                  cselib_expand_value_rtx_1
> 6619      1.8899  libc-2.11.1.so           strcmp
> 6193      1.7682  cc1plus                  htab_expand
> 6020      1.7188  cc1plus                  check_changed_vars_0
> 5797      1.6552  cc1plus                  htab_traverse_noresize
> 5615      1.6032  cc1plus                  htab_find_with_hash
> 4757      1.3582  cc1plus                  vt_expand_loc_callback
> 4529      1.2931  libginac-1.5.so.0.1.2    GiNaC::basic::compare(GiNaC::basic const&) const
> 4497      1.2840  libc-2.11.1.so           _int_malloc
> 3879      1.1075  as                       /usr/bin/as
> 3703      1.0573  cc1plus                  variable_htab_eq
> 3698      1.0559  cc1plus                  insert_into_intersection
> 3287      0.9385  cc1plus                  emit_note_insn_var_location

(it is regression at 4.5 branch, forgot to mention)

Honza
> 
> Honza