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From: "ubizjak at gmail dot com" <gcc-bugzilla@gcc.gnu.org> To: gcc-bugs@gcc.gnu.org Subject: [Bug target/23322] [4.1/4.2/4.3 regression] performance regression, possibly related to caching Date: Thu, 13 Dec 2007 14:10:00 -0000 [thread overview] Message-ID: <20071213141026.15089.qmail@sourceware.org> (raw) In-Reply-To: <bug-23322-10914@http.gcc.gnu.org/bugzilla/> ------- Comment #9 from ubizjak at gmail dot com 2007-12-13 14:10 ------- Reduced c++ testcase that is the cause of the runtime difference: --cut here-- #include <iostream> extern double *dpb; void s000005m_test(void) { double result = 0.0; for (int n = 0; n < 2000; ++n) result += dpb[n]; #ifdef FUBAR std::cerr << "Blah" << result << std::endl; #else std::cerr << result << std::endl; #endif } --cut here-- g++ -O2: ... .LCFI8: movl dpb, %edx # dpb, dpb.68 fldz .L4: faddl (%edx,%eax,8) #* dpb.68 addl $1, %eax #, n cmpl $2000, %eax #, n jne .L4 #, fstpl 4(%esp) # movl $_ZSt4cerr, (%esp) #, call _ZNSo9_M_insertIdEERSoT_ # ... g++ -O2 -DFUBAR: ... .LCFI8: movl dpb, %edx # dpb, dpb.68 fldz fstpl -288(%ebp) # result .p2align 4,,7 .p2align 3 .L4: fldl -288(%ebp) # result faddl (%edx,%eax,8) #* dpb.68 addl $1, %eax #, n cmpl $2000, %eax #, n fstpl -288(%ebp) # result jne .L4 #, movl $4, 8(%esp) #, movl $.LC1, 4(%esp) #, movl $_ZSt4cerr, (%esp) #, call _ZSt16__ostream_insertIcSt11char_traitsIcEERSt13basic_ostreamIT_T0_ES6_PKS3_i # movl $_ZSt4cerr, (%esp) #, fldl -288(%ebp) # result fstpl 4(%esp) # call _ZNSo9_M_insertIdEERSoT_ # ... Please see what happens to "result" variable in -DFUBAR case. Similar effect happens for -mfpmath=sse, but postreload gcse eliminates the load (but not the store) from the loop (stack regs are not gcse'd after reload by design). IMO, this is not target dependant, but pure RA problem. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23322
next prev parent reply other threads:[~2007-12-13 14:10 UTC|newest] Thread overview: 35+ messages / expand[flat|nested] mbox.gz Atom feed top [not found] <bug-23322-10914@http.gcc.gnu.org/bugzilla/> 2005-10-31 4:49 ` [Bug target/23322] [4.1 " mmitchel at gcc dot gnu dot org 2006-02-24 0:30 ` [Bug target/23322] [4.1/4.2 " mmitchel at gcc dot gnu dot org 2006-05-25 2:34 ` mmitchel at gcc dot gnu dot org 2006-08-27 18:46 ` pinskia at gcc dot gnu dot org 2007-02-14 9:06 ` [Bug target/23322] [4.1/4.2/4.3 " mmitchel at gcc dot gnu dot org 2007-12-13 14:10 ` ubizjak at gmail dot com [this message] 2007-12-13 14:13 ` ubizjak at gmail dot com 2007-12-13 14:24 ` ubizjak at gmail dot com 2007-12-13 14:36 ` rguenth at gcc dot gnu dot org 2007-12-13 14:43 ` rguenth at gcc dot gnu dot org 2007-12-13 14:54 ` rguenth at gcc dot gnu dot org 2007-12-13 15:00 ` rguenth at gcc dot gnu dot org 2007-12-13 15:42 ` [Bug target/23322] [4.1/4.2/4.3 regression] performance regression: global regalloc doesn't split live ranges ubizjak at gmail dot com 2008-02-05 16:19 ` hubicka at gcc dot gnu dot org 2008-02-05 16:25 ` [Bug target/23322] [4.1/4.2/4.3 regression] performance regression hubicka at gcc dot gnu dot org 2008-02-05 18:26 ` ubizjak at gmail dot com 2008-02-05 22:51 ` hubicka at gcc dot gnu dot org 2008-02-05 23:54 ` hubicka at gcc dot gnu dot org 2008-02-06 6:52 ` ubizjak at gmail dot com 2008-02-06 9:01 ` steven at gcc dot gnu dot org 2008-02-06 11:27 ` hubicka at gcc dot gnu dot org 2008-02-06 11:31 ` hubicka at gcc dot gnu dot org 2008-02-06 11:43 ` steven at gcc dot gnu dot org 2008-02-06 11:55 ` hubicka at gcc dot gnu dot org 2008-02-06 15:10 ` hubicka at gcc dot gnu dot org 2008-02-08 14:55 ` hubicka at gcc dot gnu dot org 2008-02-11 9:24 ` hubicka at gcc dot gnu dot org 2008-07-04 20:02 ` [Bug target/23322] [4.2/4.3/4.4 " jsm28 at gcc dot gnu dot org 2009-02-03 16:16 ` bonzini at gnu dot org 2009-02-03 16:16 ` bonzini at gnu dot org 2009-02-08 11:32 ` hubicka at gcc dot gnu dot org 2009-02-12 13:43 ` ubizjak at gmail dot com 2009-03-31 18:55 ` [Bug target/23322] [4.3/4.4/4.5 " jsm28 at gcc dot gnu dot org 2009-04-16 16:22 ` [Bug target/23322] [4.3 " pinskia at gcc dot gnu dot org 2009-04-22 15:11 ` rguenth at gcc dot gnu dot org
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