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cmd/internal: AVX2 instruction VPSHUFD failed to compile #16499

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aead opened this issue Jul 26, 2016 · 5 comments
Closed

cmd/internal: AVX2 instruction VPSHUFD failed to compile #16499

aead opened this issue Jul 26, 2016 · 5 comments
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Go1.8

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@aead
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aead commented Jul 26, 2016 •
edited

  1. What version of Go are you using (go version)?
    1.7-beta2, 1.7-beta3
  2. What operating system and processor architecture are you using (go env)?
GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GORACE=""
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0"
CXX="g++"
CGO_ENABLED="1"

What did you do?
The AVX2 instruction VPSHUFD $0x39, Y1, Y1 and VPSHUFD $0x78, Y1, Y1
compile, but VPSHUFD $0x93, Y0, Y0 e.g. fails with:

asm: invalid instruction: 03087 VPSHUFD $147, Y1, Y1

If I use the plain byte representation,
in my case BYTE $0xC5; BYTE $0xFD; BYTE $0x70; BYTE $0xC9; BYTE $0x93
everything is fine...

For reproducing:

TEXT ·foo(SB),4,$0-8
         VPSHUFD $0x39, Y1, Y1
         VPSHUFD $0x93, Y1, Y1
         RET
@aead
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aead commented Jul 27, 2016

VPSHUFD seems to accept only a 7 bit constant:
VPSHUFD $127, Y1, Y1 compiles, but VPSHUFD $128, Y1, Y1 does not....

@aead
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aead commented Jul 28, 2016

Okay, VPSHUFD accepts either a positive or negative 7 bit shuffle constant...
Semantically these two lines are equal:
VPSHUFD $147, Y1, Y1 and VPSHUFD $-109, Y1, Y1
but only the second one compile without an error

@randall77
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@TocarIP

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CL https://golang.org/cl/25383 mentions this issue.

@TocarIP
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TocarIP commented Aug 1, 2016

CL25383 makes VPSHUFD consistent with PSHUFD and only allows non-negative arguments.
Gnu as allows both (e. g. -6 and 0xFA). It may make sense to add signed form, but that should be done for all instructions at once.

@quentinmit quentinmit added this to the Go1.8 milestone Aug 1, 2016
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@quentinmit @randall77 @gopherbot @TocarIP @aead