FMA instruction set: Difference between revisions

* ”’February 2017”’ The first generation of AMD [[AMD Ryzen|Ryzen]] processors officially supports FMA3, but not FMA4 according to the [[CPUID]] instruction.{{cite web | url=http://www.agner.org/optimize/microarchitecture.pdf | title=The microarchitecture of Intel, AMD and VIA CPUs An optimization guide for assembly programmers and compiler makers | access-date=2017-05-02}} There has been confusion regarding whether FMA4 was implemented or not on this processor due to errata in the initial patch to the [[GNU Binutils]] package that has since been rectified.{{Cite web |last=Gopalasubramanian |first=Ganesh |url=https://sourceware.org/ml/binutils/2015-03/msg00078.html |title=[PATCH] add znver1 processor. |date=2015-03-10 |access-date=2022-05-01}}{{Cite web |last=Pawar |first=Amit |url=https://sourceware.org/ml/binutils/2015-08/msg00039.html |title=[PATCH] Remove CpuFMA4 from Znver1 CPU Flags |date=2015-08-07 |access-date=2022-05-01}} One unconfirmed report of wrong results{{cite web|url=https://www.reddit.com/r/Amd/comments/68s4bj/ryzen_has_undocumented_support_for_fma4/dh0y353/|title=Discussion – Ryzen has undocumented support for FMA4|access-date=2017-05-10}} led to some doubt, but Mysticial (Alexander Yee, developer of y-cruncher) debunked it{{cite web|url=https://web.archive.org/web/20190822063407/https://stackoverflow.com/questions/57055756/arbitrary-position-2-input-shuffling-using-sse#comment100649361_57057094|title=Stack Overflow comment by Mysticial|date=2019-07-19|access-date=2023-09-01}}: FMA4 worked for bit-exact bignum calculations on his Zen 1 system for years, and the one report on reddit never had any followup investigation to rule out mistakes in the testing software before being widely repeated. The initial Ryzen CPUs could be crashed by a particular sequence of FMA3 instructions, but updated CPU microcode fixes the problem.{{cite web|url=https://www.techpowerup.com/231536/amd-ryzen-machine-crashes-to-a-sequence-of-fma3-instructions|title=AMD Ryzen Machine Crashes to a Sequence of FMA3 Instructions|date=16 March 2017 |access-date=2017-09-10}}