On 3/12/06, Richard Guenther <[EMAIL PROTECTED]> wrote: > On 3/12/06, Nickolay Kolchin <[EMAIL PROTECTED]> wrote: > > During "bashmark" memory benchmark perfomance analyze, I found 100x > > perfomance > > regression between gcc 3.4.5 and gcc 4.X. > > > > ------ test_cmd.cpp (simplified bashmark memory RW test) ------- > > #include <stdint.h> > > #include <cstring> > > > > template <const uint8_t Block_Size, const uint32_t Loops> > > static void int_membench(uint8_t* mb1, uint8_t* mb2) > > { > > for(uint32_t i = 0; i < Loops; i+=1) > > { > > #define T memcpy(mb1, mb2, Block_Size); memset(mb2, i, Block_Size); > > T T T T T > > T T T T T > > #undef T > > } > > } > > > > template <const uint32_t Buf_Size, const uint32_t Loops> > > static void membench() > > { > > static uint8_t mb1[Buf_Size]; > > static uint8_t mb2[Buf_Size]; > > for(uint32_t i = 0; i < 10000; i+=1) > > int_membench<Buf_Size, Loops>(mb1, mb2); > > } > > > > int main() > > { > > membench<128, 4000>(); > > return 0; > > } > > > > --------------------------------------------------------------- > > GCC 3.4.5: 0.43user 0.00system 0:00.44elapsed > > GCC 4.0.2: 34.83user 0.68system 0:36.09elapsed > > GCC 4.1.0: 33.86user 0.58system 0:34.96elapsed > > > > Compiler options: > > -march=athlon-xp > > -O3 > > -fomit-frame-pointer > > -mfpmath=sse -msse > > -ftracer -fweb > > -maccumulate-outgoing-args > > -ffast-math > > > > I've played with various settings (-O2, -O1, without march, without tracer > > and > > web, etc) without any serious difference. I.e. GCC4 is always many times > > slower > > than GCC 3.4.5. > > > > Lurking inside assembler generation showed that GCC4 don't inline memcpy and > > memset calls. > > > > ------ test.c (uber simplified problem demonstration) --------- > > #include <string.h> > > > > char* f(char* b) > > { > > static char a[64]; > > memcpy(a, b, 64); > > memset(a, 0, 64); > > return a; > > } > > ---------------------------------------------------------------- > > > > GCC4 will generate calls to memcpy and memset in this example. GCC3 will > > inline > > all calls. > > > > So, it looks like GCC4 inliner is broken at some point. > > Inlining of memcpy/memset is architecture dependent (I see calls > on ppc for gcc 3.4, too). This is a stupid benchmark and as such > not worth optimizing for. >
bashmark (http://bashmark.coders-net.de/ ) is a benchmark. My code is just a test to demonstrate problem and as such can't be stupid. :) Situation when compiler generates code from simple test that run 100 times slower, than code from previous compiler version is not normal anyway. (and GCC3 generates smaller code, too) I thought that this regression was caused by different "max-inline-*" params setting in 4.X. In any case: memcpy/memset inlining is broken in current GCC at least on athlon arch. -- Nickolay