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Jit64: srawx - Handle constant zero input 

Shifting zero by any amount always gives zero.

Before:
41 B9 00 00 00 00    mov         r9d,0
41 8B CF             mov         ecx,r15d
49 C1 E1 20          shl         r9,20h
49 D3 F9             sar         r9,cl
49 C1 E9 20          shr         r9,20h

After:
Nothing, register is set to constant zero.

Before:
41 B8 00 00 00 00    mov         r8d,0
41 8B CF             mov         ecx,r15d
49 C1 E0 20          shl         r8,20h
49 D3 F8             sar         r8,cl
41 8B C0             mov         eax,r8d
49 C1 E8 20          shr         r8,20h
44 85 C0             test        eax,r8d
0F 95 45 58          setne       byte ptr [rbp+58h]

After:
C6 45 58 00          mov         byte ptr [rbp+58h],0

Occurs a bunch of times in Super Mario Sunshine. Since this is an
arithmetic shift a similar optimization can be done for constant -1
(0xFFFFFFFF), but I couldn't find any game where this happens.
This commit is contained in:
Sintendo 2020-12-13 12:36:07 +01:00
parent 10d65519f9
commit 67d2fa11f1
1 changed files with 5 additions and 0 deletions
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5
Source/Core/Core/PowerPC/Jit64/Jit_Integer.cpp
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@ -1983,6 +1983,11 @@ void Jit64::srawx(UGeckoInstruction inst)
FinalizeCarry(CC_NZ);
}
}
else if (gpr.IsImm(s) && gpr.Imm32(s) == 0)
{
gpr.SetImmediate32(a, 0);
FinalizeCarry(false);
}
else
{
RCX64Reg ecx = gpr.Scratch(ECX); // no register choice