We were running bench++ looking for cases that perform worse
with g++-4.x than they do with g++-2.95 .
We posted a related mail to the gcc list
http://gcc.gnu.org/ml/gcc/2005-08/msg00197.html
There seems to be an interesting regression, exhibited by
more than one test, that is related to the inliner.
For example, the test s000005a, when compiled with g++-4.0.1
runs faster when compiled with -O2 than it does
when compiled with -O2 -finline-functions, or with -O3 .
Specifically, the slowdown is in the order of x2.5
If g++-2.95.3 is used with the same flags, the
slowdown does not occur.
Interestingly, if a *dead* function is commented
out, or a *dead* call to cerr, the regression goes away.
If g++-410_0723 is used, the regression appears as
with g++-4.0.1 (when -O2 -finline, or -O3 is used),
but it does *not* go away when then dead function
is commented out. It only goes away when the dead
cerr is commented out.
--
Summary: Inlining related regression for gcc-4.x
Product: gcc
Version: 4.0.1
Status: UNCONFIRMED
Severity: normal
Priority: P2
Component: rtl-optimization
AssignedTo: unassigned at gcc dot gnu dot org
ReportedBy: danalis at cis dot udel dot edu
CC: gcc-bugs at gcc dot gnu dot org
GCC target triplet: i686-linux
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=23305
