https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51119
--- Comment #34 from Jerry DeLisle <jvdelisle at gcc dot gnu.org> --- Created attachment 39987 --> https://gcc.gnu.org/bugzilla/attachment.cgi?id=39987&action=edit A test program Just ran some tests comparing reference results and results using -Ofast. -Ofast does reorder execution.. Using kind=8 DELTA = (reference - result) and looking at the ranges of minval and maxval with several random matrices one sees (4 cases): Using some smaller matrices. see attachment for test program. delta minval delta maxval -2.2204460492503131E-016 2.2204460492503131E-016 -4.4408920985006262E-016 4.4408920985006262E-016 -2.2204460492503131E-016 2.2204460492503131E-016 -4.4408920985006262E-016 2.2204460492503131E-016 So the wiggling one gets in the least significant bits may matter to some. With larger arrays (error amplification): 1000 x 1000 -1.0231815394945443E-012 8.8107299234252423E-013 2000 x 2000 -2.7284841053187847E-012 2.6716406864579767E-012 Compiling the test program with -Ofast so that the reference method has the same optimization as MATMUL, one gets. 2000 x 2000 0.0000000000000000 0.0000000000000000 Opinions welcome.
