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Arm64Emitter: Simplify LogicalImm further

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h/t @dougallj
This commit is contained in:
Merry 2022-07-07 23:04:56 +01:00
parent 20ccc38f0f
commit 0d947ed6fe
1 changed files with 12 additions and 26 deletions

38
Source/Core/Common/Arm64Emitter.h

@ -538,38 +538,26 @@ struct LogicalImm
value |= value >> kWRegSizeInBits; value |= value >> kWRegSizeInBits;
} }
// Identify the smallest repeating element size. if (value == 0 || (~value) == 0)
size_t esize = 0;
for (size_t i = 64; i > 1; i /= 2)
{
if (value != Common::RotateRight(value, i / 2))
{
esize = i;
break;
}
}
if (value == 0 || (~value) == 0 || esize == 0 || esize > width)
{ {
valid = false; valid = false;
return; return;
} }
const u64 emask = (~u64{0}) >> (64 - esize); // Normalize value, rotating it such that the LSB is 1:
// Extract the repeating element, rotating it such that the LSB is 1:
// If LSB is already one, we mask away the trailing sequence of ones and // If LSB is already one, we mask away the trailing sequence of ones and
// pick the next sequence of ones. This ensures we get a complete element // pick the next sequence of ones. This ensures we get a complete element
// that has not been cut-in-half due to rotation across the word boundary. // that has not been cut-in-half due to rotation across the word boundary.
const u64 inverse_mask_from_trailing_ones = ~value | (value + 1); const size_t rotation = Common::CountTrailingZeros(value & (value + 1));
const size_t rotation = Common::LeastSignificantSetBit(value & inverse_mask_from_trailing_ones); const u64 normalized = Common::RotateRight(value, rotation);
const u64 element = Common::RotateRight(value, rotation) & emask;
// In order to be a valid element of an AArch64 logical immediate, it must const size_t element_size = Common::CountTrailingZeros(normalized & (normalized + 1));
// be contiguous. const size_t ones = Common::CountTrailingZeros(~normalized);
if (!Common::IsValidLowMask(element)) // Check the value is repeating; also ensures element size is a power of two.
if (Common::RotateRight(value, element_size) != value)
{ {
valid = false; valid = false;
return; return;
@ -579,11 +567,9 @@ struct LogicalImm
// it gives both the number of set bits and the length of the repeated // it gives both the number of set bits and the length of the repeated
// segment. // segment.
const size_t tmp = ((~esize + 1) << 1) | (Common::CountSetBits(element) - 1); r = static_cast<u8>((element_size - rotation) & (element_size - 1));
s = (((~element_size + 1) << 1) | (ones - 1)) & 0x3f;
r = static_cast<u8>((esize - rotation) & (esize - 1)); n = (element_size >> 6) & 1;
s = tmp & 0x3f;
n = (~tmp >> 6) & 1;
valid = true; valid = true;
} }