Jit64: Optimize fsel a bit more #9127
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For the non-packed variant of this instruction, a MOVSD instruction was generated to copy only the lower 64 bits of XMM1 to the destination register. This was done in order to keep the destination register's upper half intact. However, when register c and the destination register are the same, there is no need for this copy. Because the registers match and due to the way the mask is generated, VBLENDVPD will end up taking the upper half from the destination register, as intended. Before: 66 0F 57 C0 xorpd xmm0,xmm0 F2 41 0F C2 C6 06 cmpnlesd xmm0,xmm14 C4 C3 09 4B CA 00 vblendvpd xmm1,xmm14,xmm10,xmm0 F2 44 0F 10 F1 movsd xmm14,xmm1 After: 66 0F 57 C0 xorpd xmm0,xmm0 F2 41 0F C2 C6 06 cmpnlesd xmm0,xmm14 C4 43 09 4B F2 00 vblendvpd xmm14,xmm14,xmm10,xmm0
For the non-packed variant of this instruction, a MOVSD instruction was generated to copy only the lower 64 bits of XMM1 to the destination register. This was done in order to keep the destination register's upper half intact. However, when register c and the destination register are the same, there is no need for this copy. Because the registers match and due to the way the mask is generated, BLENDVPD will end up taking the upper half from the destination register, as intended. Additionally, the MOVAPS to copy Rc into XMM1 can also be skipped. Before: 66 0F 57 C0 xorpd xmm0,xmm0 F2 41 0F C2 C6 06 cmpnlesd xmm0,xmm14 41 0F 28 CE movaps xmm1,xmm14 66 41 0F 38 15 CA blendvpd xmm1,xmm10,xmm0 F2 44 0F 10 F1 movsd xmm14,xmm1 After: 66 0F 57 C0 xorpd xmm0,xmm0 F2 41 0F C2 C6 06 cmpnlesd xmm0,xmm14 66 45 0F 38 15 F2 blendvpd xmm14,xmm10,xmm0
lioncash
approved these changes
Oct 19, 2020
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This PR builds upon optimizations introduced in pull request #8992, which were only applied to the packed variant of this instruction. As it turns out, these optimizations can also be applied to the non-packed variant when the destination register and a specific input register match. Luckily, according to my testing, this happens to be the case most of the time in games that use this instruction.
fsel (AVX)
Before:
After:
fsel (SSE4.1)
Before:
After: