Rpcs3: PPU Accurate FMA default setting of "true" has performance hit on older CPU (i7-3770)

[greentop]

OS: Ubuntu 18.04
CPU: Intel i7-3770
RPCS3 build: Master 72c0aed

PPU Accurate FMA: true (default setting)
This setting on the i7-3770 cpu results in a random fps drop by roughly 12 fps or greater in some areas while playing games. Setting this value within the config & custom config files to "false" removes the performance hit.

[dio-gh]

That is the correct behaviour.

[greentop]

This is a performance regression that was introduced in commit 92f821a -
Games that were performing at a stable 30 fps before that commit are now dipping to a noticeable fps crawl. Manually setting PPU Accurate FMA to "false" returns the games back to their previous stable 30 fps performance.

[Yahfz]

Old cpus that doesn't support FMA natively now require the accurate FMA option set to false. So again, like dio said that is the correct behavior.

[AniLeo]

Note: All CPUs in the recommended specifications have the FMA extension

It doesn't make any sense to make the inaccurate version default since there won't be a performance hit on any of the recommended CPUs provided LLVM is generating code that uses the native FMA instructions. Setting is there precisely so people with old CPUs can disable it if they want.

[AniLeo]

Closing since this is the correct behavior, accurate FMA on CPUs without support for the FMA instruction set will be slower as expected

[greentop]

An CPU auto detection for this setting and/or a GUI configuration option with notes about its setting would be helpful.

[AniLeo]

Automatically forcing inaccurate mode on older CPUs doesn't make sense since some games need it to be accurate in order to process logic properly
Adding to GUI is already being done on #7915