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JitArm64_Integer: cmp - Skip sign extension if possible

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While we cannot always avoid materializing immediates, we can still
inspect the most significant bit and potentially skip sign extension.
This can sometimes save an instruction.

Before:
0x5280003a   mov    w26, #0x1                 ; =1
0x93407f5b   sxtw   x27, w26
0xcb38c37b   sub    x27, x27, w24, sxtw

After:
0x5280003a   mov    w26, #0x1                 ; =1
0xcb38c35b   sub    x27, x26, w24, sxtw

Before:
0x52a20018   mov    w24, #0x10000000          ; =268435456
0x93407f79   sxtw   x25, w27
0xcb38c339   sub    x25, x25, w24, sxtw

After:
0x52a20018   mov    w24, #0x10000000          ; =268435456
0x93407f79   sxtw   x25, w27
0xcb180339   sub    x25, x25, x24
This commit is contained in:
Sintendo 2025-02-01 18:18:32 +01:00
parent 075c35602f
commit c5870ed0c7
1 changed files with 26 additions and 2 deletions
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28
Source/Core/Core/PowerPC/JitArm64/JitArm64_Integer.cpp
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@ -675,11 +675,35 @@ void JitArm64::cmp(UGeckoInstruction inst)
}
else
{
// If we're dealing with immediates, check their most significant bit to
// see if we can skip sign extension.
const auto should_sign_extend = [&](u32 reg) -> bool {
return !gpr.IsImm(reg) || (gpr.GetImm(reg) & (1U << 31));
};
bool sign_extend_a = should_sign_extend(a);
bool sign_extend_b = should_sign_extend(b);
ARM64Reg RA = gpr.R(a);
ARM64Reg RB = gpr.R(b);
SXTW(CR, RA);
SUB(CR, CR, RB, ArithOption(RB, ExtendSpecifier::SXTW));
if (sign_extend_a)
{
SXTW(CR, RA);
RA = CR;
}
else
{
RA = EncodeRegTo64(RA);
}
auto opt = ArithOption(RB, ExtendSpecifier::SXTW);
if (!sign_extend_b)
{
opt = ArithOption(CR, ShiftType::LSL, 0);
RB = EncodeRegTo64(RB);
}
SUB(CR, RA, RB, opt);
}
}