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JitArm64_Integer: subfex - Explicitly handle a == b

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Number of instructions stays the same, but we remove the false
dependency on the input registers.

Before:
0x7a1b037a   sbcs   w26, w27, w27

After:
0x5a9f23fa   csetm  w26, lo
This commit is contained in:
Sintendo 2025-07-30 22:08:38 +02:00
commit ed5cea2635
1 changed files with 18 additions and 6 deletions
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24
Source/Core/Core/PowerPC/JitArm64/JitArm64_Integer.cpp
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@ -1306,13 +1306,10 @@ void JitArm64::subfex(UGeckoInstruction inst)
JITDISABLE(bJITIntegerOff); JITDISABLE(bJITIntegerOff);
FALLBACK_IF(inst.OE); FALLBACK_IF(inst.OE);
bool mex = inst.SUBOP10 & 32; const bool mex = inst.SUBOP10 & 32;
int a = inst.RA, b = inst.RB, d = inst.RD; const int a = inst.RA, b = inst.RB, d = inst.RD;
if (gpr.IsImm(a) && (mex || gpr.IsImm(b))) const auto handle_imm = [&](const u32 i, const u32 j) {
{
const u32 i = gpr.GetImm(a);
const u32 j = mex ? -1 : gpr.GetImm(b);
const u32 imm = ~i + j; const u32 imm = ~i + j;
const bool is_zero = imm == 0; const bool is_zero = imm == 0;
const bool is_all_ones = imm == 0xFFFFFFFF; const bool is_all_ones = imm == 0xFFFFFFFF;
@ -1385,6 +1382,21 @@ void JitArm64::subfex(UGeckoInstruction inst)
{ {
ComputeCarry(false); ComputeCarry(false);
} }
};
if (!mex && a == b)
{
// Special case: subfe A, B, B is a common compiler idiom to copy the carry
// flag to a register.
// We handle this as-if we're dealing with two identical immediate values.
// The exact values used here don't matter. We use zeroes.
handle_imm(0, 0);
}
else if (gpr.IsImm(a) && (mex || gpr.IsImm(b)))
{
const u32 i = gpr.GetImm(a);
const u32 j = mex ? -1 : gpr.GetImm(b);
handle_imm(i, j);
} }
else else
{ {