Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: patrikhuber at gmail dot com
Target Milestone: ---
Hello,
I noticed today what may look like quite a large performance regression
with Eigen (3.3.4) matrix multiplication. It only seems to
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84280
--- Comment #3 from Patrik Huber ---
@Richard: I'm not 100% sure what you mean with "preprocessed source" but I
googled and you probably mean the output of compiling with "-c -save-temps".
Please see attached.
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84280
--- Comment #4 from Patrik Huber ---
Created attachment 43363
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=43363&action=edit
gcc5_gemm_test.s
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84280
--- Comment #5 from Patrik Huber ---
Created attachment 43364
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=43364&action=edit
gcc7_gemm_test.s
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84280
--- Comment #6 from Patrik Huber ---
I could also upload you the .ii files but they are 5 MB, which the bugtracker
doesn't allow (1 MB limit).
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84280
--- Comment #7 from Patrik Huber ---
Created attachment 43365
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=43365&action=edit
gemm_test.cpp
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84280
--- Comment #8 from Patrik Huber ---
Created attachment 43366
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=43366&action=edit
full_log.txt
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84280
--- Comment #10 from Patrik Huber ---
Created attachment 43367
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=43367&action=edit
gcc5_gemm_test.ii
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84280
--- Comment #11 from Patrik Huber ---
Created attachment 43368
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=43368&action=edit
gcc7_gemm_test.ii
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84280
--- Comment #13 from Patrik Huber ---
>> Did you try with FDO? (-fprofile-generate, run, -fprofile-use)
I just tried this with g++-7. It didn't help, the final executable has the same
slower run time as in the attached log without the FDO.
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=84280
--- Comment #14 from Patrik Huber ---
It even seems a few percent slower after the FDO stuff. But the `
-fprofile-use` is a bit weird. If there is no .gcda file, it doesn't complain.
If you give it a file that doesn't exist (e.g. -fprofile-use=fo
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