http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53533
Bug #: 53533
Summary: [4.7 regression] loop unrolling as measured by Adobe's
C++Benchmark is twice as slow versus 4.4-4.6
Classification: Unclassified
Product: gcc
Version: 4.7.1
Status: UNCONFIRMED
Severity: major
Priority: P3
Component: middle-end
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: m...@use.net
Comparing GCC versions, branches, and optimization levels on Adobe's
C++Benchmark suite, I discovered that 4.7 has a major regression with their
loop unrolling tests. I have captures the data here:
https://docs.google.com/spreadsheet/ccc?key=0Amu19eOay72HdE1xYVRPUTFYWU1TSld3Y2FEOEt5LXc
All compilers were fresh checkouts by me from their trunk revisions as of a few
days ago. My configure command line:
/u/mhargett/src/gcc-4_7-branch/configure --program-suffix=-4.7
--prefix=/u/mhargett --enable-languages=c,c++,lto --enable-lto
--with-build-config=bootstrap-lto --with-fpmath=sse --disable-libmudflap
--disable-libssp --enable-build-with-cxx --enable-gold=yes
--with-mpc=/u/mhargett --with-cloog=/u/mhargett/ --with-ppl=/u/mhargett/
--with-gmp=/u/mhargett/ --with-mpfr=/u/mhargett/ --enable-cloog-backend=isl
--disable-cloog-version-check CC=gcc-4.7 CXX=g++-4.7
The 4.6 and 4.7 versions were both build against the same Cloog, ppl, mpfr,
etc.
Going from "-O3 -floop-block -floop-strip-mine -floop-interchange
-mtune=amdfam10" to "-Ofast -funsafe-loop-optimizations -funroll-loops
-floop-block -floop-strip-mine -floop-interchange" didn't help.
Attached is a tar ball of the 4.6 and 4.7 -O3 optimized builds. 'make report'
re-runs the tests, 'make clean && make' rebuilds.
