https://gcc.gnu.org/bugzilla/show_bug.cgi?id=79291
Bug ID: 79291
Summary: r244397 introduces alias related performance issues
for daxpy on MIPS
Product: gcc
Version: 7.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: doug.gilmore at imgtec dot com
Target Milestone: ---
It appears that r244397 introduces pealing for DP daxpy, which per
bug 69710, introduces a performance degradation due to alias issues.
After IVOPTS before r244897 (use daxpy example from bug 69710):
ivtmp.20_36 = ivtmp.20_35 + 1;
ivtmp.21_24 = ivtmp.21_9 + 16;
ivtmp.24_3 = ivtmp.24_2 + 16;
After IVOPTS after r244897:
ivtmp.23_56 = ivtmp.23_24 + 1;
ivtmp.24_11 = ivtmp.24_9 + 16;
ivtmp.27_87 = ivtmp.27_86 + 16;
ivtmp.29_90 = ivtmp.29_89 + 16;
Thus after r244397 we have a problem in DP daxpy that we were
only seeing for SP daxpy (or saxpy) as shown in bug69710.
BTW: I have been investigating another IVOPTS related regression
on MIPS32R2 that is related to the generation of indexed
memory OPs:
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78176#c12
I'll be updating that report with more information on how to
fix the regression and how it relates to this issue.
Bin: I suspect this is also now broken on ARM, can
you check?
Thanks,
Doug
