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Re: RFC: [PATCH] X86: Add pseudo prefixes to control encoding
On 11/11/2016 10:24 PM, H.J. Lu wrote:
Sure, but I think the instruction length specification would still be *very*
useful in some cases to lock things down (and document the length
Instruction length can a vague constraint:
0: c4 e1 78 28 50 00 vmovaps 0x0(%rax),%xmm2
6: 62 f1 7c 08 28 10 vmovaps (%rax),%xmm2
Both instructions with the same length do the same thing.
But one is AVX and the other is AVX512.
c: c4 e1 78 28 10 vmovaps (%rax),%xmm2
11: c5 f8 28 50 00 vmovaps 0x0(%rax),%xmm2
These 2 are AVX. Majority of programmers don't care how
an instruction is encoded. If they want specific instruction
length, they can experiment with pseudo prefixes to get
exactly what they need.
Oh, I didn't intend this as a replacement, just as an additional