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JitArm64: MultiplyImmediate - Handle 2^n + 1

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By taking advantage of ARM64's ability to shift an input register by any
amount, we can calculate multiplication by a number that is one more
than a power of two with a single instruction.

Before:
0x52800838   mov    w24, #0x41
0x1b187f7b   mul    w27, w27, w24

After:
0x0b1b1b7b   add    w27, w27, w27, lsl #6
This commit is contained in:
Bram Speeckaert 2022-11-01 21:06:43 +01:00
parent 3aaf1a2b8b
commit c349875cdc
1 changed files with 9 additions and 0 deletions
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9
Source/Core/Core/PowerPC/JitArm64/JitArm64_Integer.cpp
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@ -904,6 +904,15 @@ 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 - 1))
{
const int shift = IntLog2(imm - 1);
gpr.BindToRegister(d, d == a);
ADD(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.