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JitArm64: Make fcmpX with flush-to-zero enabled less bad

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See the added code comment for details. Fixes Pokémon Battle
Revolution not progressing past the title screen.
This commit is contained in:
JosJuice 2021-05-25 14:58:48 +02:00
parent 21ebc176fe
commit b6cc3c4b6e
1 changed files with 14 additions and 1 deletions
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15
Source/Core/Core/PowerPC/JitArm64/JitArm64_FloatingPoint.cpp
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@ -3,6 +3,7 @@
// Refer to the license.txt file included.
#include "Common/Arm64Emitter.h"
#include "Common/CPUDetect.h"
#include "Common/CommonTypes.h"
#include "Common/StringUtil.h"
@ -374,7 +375,19 @@ void JitArm64::fcmpX(UGeckoInstruction inst)
const u32 b = inst.FB;
const int crf = inst.CRFD;
const bool singles = fpr.IsSingle(a, true) && fpr.IsSingle(b, true);
// On the GC/Wii CPU, outputs are flushed to zero if FPSCR.NI is set, and inputs are never
// flushed to zero. Ideally we would emulate FPSCR.NI by setting FPCR.FZ and FPCR.AH, but
// unfortunately FPCR.AH is a very new feature that we can't rely on (as of 2021). For CPUs
// without FPCR.AH, the best we can do (without killing the performance by explicitly flushing
// outputs using bitwise operations) is to only set FPCR.FZ, which flushes both inputs and
// outputs. This may cause problems in some cases, and one such case is Pokémon Battle Revolution,
// which does not progress past the title screen if a denormal single compares equal to zero.
// Workaround: Perform the comparison using a double operation instead. This ensures that denormal
// singles behave correctly in comparisons, but we still have a problem with denormal doubles.
const bool input_ftz_workaround =
!cpu_info.bAFP && (!js.fpr_is_store_safe[a] || !js.fpr_is_store_safe[b]);
const bool singles = fpr.IsSingle(a, true) && fpr.IsSingle(b, true) && !input_ftz_workaround;
const RegType type = singles ? RegType::LowerPairSingle : RegType::LowerPair;
const auto reg_encoder = singles ? EncodeRegToSingle : EncodeRegToDouble;