x64: Add shuffle specialization for palignr
#5999
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| (xmm_rm_r_imm (SseOpcode.Palignr) | ||
| src1 | ||
| src2 | ||
| imm | ||
| size)) | ||
| (rule 1 (x64_palignr src1 src2 imm size) | ||
| (OperandSize.Size32))) |
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Why this change? Why always 32?
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I guess it was always passed 32, but I'm still a little confused why it was like that.
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@abrown do you perhaps remember why palignr was always generated with OperandSize.Size32? I'll admit I don't fully understand how OperandSize maps to instructions all the time but I naively figured that it could be "constant folded" into the palignr constructor, but a double-check would be good.
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Ah I remember now actually, this has to do with the rex flags when encoding where a 64-bit size forces the W bit to be set and otherwise W is unset. I believe the encoding of the palignr instruction forces this to "unset" so for palignr it should always be a non-64-bit size.
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Yeah, I think that sounds right. The OperandSize isn't my invention and I recall having to work around it--I think things would be more clear if we hid OperandSize completely or alternately surfaced it as REX.W, which is more direct.
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This commit adds specializations for the `palignr` instruction to the x64 backend to specialize some more patterns of byte shuffles.
This commit adds specializations for the
palignrinstruction to the x64 backend to specialize some more patterns of byte shuffles.