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[Bug rtl-optimization/17088] New: poor optimisation at -O2/3 and -fnew-ra
- From: "jv244 at cam dot ac dot uk" <gcc-bugzilla at gcc dot gnu dot org>
- To: gcc-bugs at gcc dot gnu dot org
- Date: 18 Aug 2004 20:47:16 -0000
- Subject: [Bug rtl-optimization/17088] New: poor optimisation at -O2/3 and -fnew-ra
- Reply-to: gcc-bugzilla at gcc dot gnu dot org
GNU F95 version 3.5.0 20040818 (experimental) (i686-pc-linux-gnu)
compiled by GNU C version 3.5.0 20040818 (experimental).
the attached program (generated code to perform small matrix multiply)
illustrates interesting behaviour. The third number printed is the timing of
the MULT subroutine and is the one of interest (the other times the MATMUL
built-in and the first measures the numerical error).
ifc -O2 test.f90 : 0.38 ! reference
gfortran -O1 test.f90 : 0.26 ! nice, faster than intel
gfortran -O2 test.f90 : 0.50 ! 2x slower than -O1
gfortran -O3 test.f90 : 0.50 ! idem
gfortran -O2 -fnew-ra test.f90 : 7.78 ! 30x slower than -O1
I have no idea what the magical switch would be to good code at e.g. -O2
--
Summary: poor optimisation at -O2/3 and -fnew-ra
Product: gcc
Version: 3.5.0
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: rtl-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: jv244 at cam dot ac dot uk
CC: gcc-bugs at gcc dot gnu dot org
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=17088