https://gcc.gnu.org/bugzilla/show_bug.cgi?id=108922
--- Comment #6 from Uroš Bizjak <ubizjak at gmail dot com> --- (In reply to Uroš Bizjak from comment #5) > (In reply to Alexander Monakov from comment #3) > > I guess Uros' claim was based on what Intel and AMD manuals specify rather > > than observed behavior of CPUs. > > As a "committer", I really don't remember the reason to disable the > patterns, but there is some analysis in the corresponding e-mail. Please see Table 3-31 (and Table 3-32) in SDM [1]. If 'x' (AKA st(0)) is infinity, no return is specified, since invalid arith operand exception is generated. In the above case, the SDM declares output as *undefined*, but c99 specifies NaN. [1] https://www.intel.com/content/www/us/en/developer/articles/technical/intel-sdm.html
