bug in PEXTRW instruction

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CandyMan

Joined: 04 Sep 2009
Posts: 414
Location: film "CandyMan" directed through Bernard Rose OR Candy Shop

CandyMan 17 Jan 2017, 11:22

Code:

pextrw eax,xmm2,1

is assembled as avx512 instruction instead of sse41 (66 0F 3A 15 /r ib PEXTRW m16/r32,xmm,ib)

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17 Jan 2017, 11:22

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8392
Location: Kraków, Poland

Tomasz Grysztar 17 Jan 2017, 11:48

Please provide more context, what version of fasm does this concern, what is the entire source tested, what are the generated bytes, etc.
I have tested this single line with both the fasm 1.71.58 and the latest fasmg macros and they both assemble this instruction as "66 0F C5 C2 01", which is neither SSE4 nor AVX, but plain old SSE2.

17 Jan 2017, 11:48

CandyMan

Joined: 04 Sep 2009
Posts: 414
Location: film "CandyMan" directed through Bernard Rose OR Candy Shop

CandyMan 17 Jan 2017, 12:08

fasm version 1.71.57

Code:

pextrw [rax],xmm1,1 ;"66 0F 3A 15 08 01" OK
pextrw eax,xmm2,1   ;why not "66 0F 3A 15 D0 01" but "66 0F C5 C2 01" ?

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smaller is better

17 Jan 2017, 12:08

Tomasz Grysztar

Joined: 16 Jun 2003
Posts: 8392
Location: Kraków, Poland

Tomasz Grysztar 17 Jan 2017, 12:25

CandyMan wrote:

Code:

pextrw eax,xmm2,1   ;why not "66 0F 3A 15 D0 01" but "66 0F C5 C2 01" ?

Because "66 0F C5 C2 01" requires only SSE2 to run and also is shorter.

17 Jan 2017, 12:25

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