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JitArm64: MultiplyImmediate - Handle -(2^n) + 1

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Let's take advantage of ARM64's input register shifting one last time,
shall we?

Before:
0x1280005b   mov    w27, #-0x3
0x1b1b7f18   mul    w24, w24, w27

After:
0x4b180b18   sub    w24, w24, w24, lsl #2
This commit is contained in:
Bram Speeckaert 2022-11-02 21:41:03 +01:00
parent 7073a135c6
commit 274e34ddf1
1 changed files with 10 additions and 0 deletions
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10
Source/Core/Core/PowerPC/JitArm64/JitArm64_Integer.cpp
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@ -927,6 +927,16 @@ bool JitArm64::MultiplyImmediate(u32 imm, int a, int d, bool rc)
if (rc) if (rc)
ComputeRC0(gpr.R(d)); ComputeRC0(gpr.R(d));
} }
else if (MathUtil::IsPow2(~imm + 2))
{
// Multiplication by a negative power of two plus one (-(2^n) + 1).
const int shift = IntLog2(~imm + 2);
gpr.BindToRegister(d, d == a);
SUB(gpr.R(d), gpr.R(a), gpr.R(a), ArithOption(gpr.R(a), ShiftType::LSL, shift));
if (rc)
ComputeRC0(gpr.R(d));
}
else else
{ {
// Immediate did not match any known special cases. // Immediate did not match any known special cases.