http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50969
Bug #: 50969
Summary: 17% degradation in 168.wupwise for interleave via
permutation
Classification: Unclassified
Product: gcc
Version: 4.7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: pthau...@gcc.gnu.org
CC: berg...@gcc.gnu.org, r...@gcc.gnu.org
Host: powerpc64-linux
Target: powerpc64-linux
Build: powerpc64-linux
Created attachment 25694
--> http://gcc.gnu.org/bugzilla/attachment.cgi?id=25694
benchmark file
Revision 180450 (along with 180567 to fix the ICE) causes a large degradation
in cpu2000 benchmark wupwise. Additional loops are now being vectorized but
result in worse performance, not sure it that means a cost issue or what. Based
on prior observations the degradation is most likely due to the permute
instructions being used which are restricted to a single VSU pipe, so two of
them can't be executed in parallel.
Attatched file zaxpy.f is just one of the files containing a function that
degraded (zscal.f is another). The second loop is where the time is spent in
the function. Following degradations (compared to revision 180449) were
observed with oprofile.
-m64 -O3 -mcpu=power7
zaxpy : -24%
zscal : -79%
-m64 -O3 -mcpu=power7 -funroll-loops
zaxpy : -65%
zscal : -61%
