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JitArm64_Integer: cmp - Subtract shifted 12-bit constant

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You can encode a shifted 12-bit immediate in a SUB instruction on ARM64.
Constants in this range do not need to be sign extended, so we can
exploit this to avoid materializing the immediate.

This approach saves an instruction if it does not need to be
materialized in a register afterwards. Otherwise, we just materialize
it later and the total number of instructions stays the same.

Before:
0x52a00099   mov    w25, #0x40000             ; =262144
0x93407f7a   sxtw   x26, w27
0xcb39c35a   sub    x26, x26, w25, sxtw

After:
0x93407f7a   sxtw   x26, w27
0xd141035a   sub    x26, x26, #0x40, lsl #12  ; =0x40000
This commit is contained in:
Sintendo 2025-02-01 16:57:40 +01:00
parent 4a29e0e4f4
commit 352cbc4772
1 changed files with 5 additions and 0 deletions
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5
Source/Core/Core/PowerPC/JitArm64/JitArm64_Integer.cpp
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@ -658,6 +658,11 @@ void JitArm64::cmp(UGeckoInstruction inst)
if (const u32 imm = gpr.GetImm(b); imm != 0)
SUB(CR, CR, imm);
}
else if (gpr.IsImm(b) && (gpr.GetImm(b) & 0xFFF000) == gpr.GetImm(b))
{
SXTW(CR, gpr.R(a));
SUB(CR, CR, gpr.GetImm(b) >> 12, true);
}
else
{
ARM64Reg RA = gpr.R(a);