Thanks to magumagu's softfp experiments, we know a lot more about the Wii's
strange floating point unit than we used to. In particular, when doing a
single-precision floating point multiply (fmulsx), it rounds the right hand
side's mantissa so as to lose the low 28 bits (of the 53-bit mantissa).
Emulating this behavior in Dolphin fixes a bunch of issues with games that
require extremely precise emulation of floating point hardware, especially
game replays. Fortunately, we can do this with rather little CPU cost; just ~5
extra instructions per multiply, instead of the vast load of a pure-software
float implementation.
This doesn't make floating-point behavior at all perfect. I still suspect
fmadd rounding might not be quite right, since the Wii uses fused instructions
and Dolphin doesn't, and NaN/infinity/exception handling is probably off in
various ways... but it's definitely way better than before.
This appears to fix replays in Mario Kart Wii, Mario Kart Double Dash, and
Super Smash Brothers Brawl. I wouldn't be surprised if it fixes a bunch of
other stuff too.
The changes to instructions other than fmulsx may not be strictly necessary,
but I included them for completeness, since it feels wrong to fix some
instructions but not others, since some games we didn't test might rely on
them.
(1) Rename ABI_ALL_CALLEE_SAVED to ABI_ALL_CALLER_SAVED, because that's
what it was actually defined as (and used as). Derp.
(2) RegistersInUse is always used for the purpose of saving registers
before calling a C++ function in the middle of a JIT block (without
flushing). There is no need to save callee-saved registers in this
case. Change the name to CallerSavedRegistersInUse and mask with
ABI_ALL_CALLER_SAVED.
Nothing obvious broke when starting up a Melee game. (I added a test
for anything actually being masked out; it happens, but in this
particular case seemed to occur at most a few dozen times per second, so
the actual performance benefit is probably negligible.)
The PPC_FP conversion code can be made a lot simpler with the observation
that the only values that need to be sent through the slow x87 path are
denormals.
A whole bunch faster: 708->678 seconds on POV-RAY.
Updates gameinis for various us wiiware titles. How to Train Your Dragon
2 (wii), Opoona (wii), The Legend of Zelda: Collector's Edition (gc),
Super Mario Sunshine (gc), Super Monkey Ball 2 (gc) updated.
Fixes issues 7491, 7447 and 7581.
Pierre Bourdon