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cmd/asm: ARM64 VLD1 from pseudo-register FP results in asm: illegal combination #41183

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paultag opened this issue Sep 2, 2020 · 3 comments
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cmd/asm: ARM64 VLD1 from pseudo-register FP results in asm: illegal combination #41183

paultag opened this issue Sep 2, 2020 · 3 comments
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@paultag
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paultag commented Sep 2, 2020 •
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What version of Go are you using (go version)?

$ go version
go version go1.15.1 linux/arm64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

go env Output
$ go env
GO111MODULE=""
GOARCH="arm64"
GOBIN=""
GOCACHE="/home/ubuntu/.cache/go-build"
GOENV="/home/ubuntu/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="arm64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/ubuntu/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/ubuntu/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/opt/golang/go-1.15"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/opt/golang/go-1.15/pkg/tool/linux_arm64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/home/ubuntu/go/src/hz.tools/sdr/go.mod"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build634724932=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Using the VLD1 instruction with a pseudo register such as FP results in an asm: illegal combination.

For instance, when I try and load the [4]float32 as a S4, I get an asm: illegal combination even though the variant using the actual registers works fine.

// func x([4]float32, []float32)
TEXT ·x(SB), $0-40
    VLD1 f+0(FP), [V2.S4]

What did you expect to see?

My data in V2 as an S4

What did you see instead?

asm: illegal combination: 00000 (.s:27)	VLD1	a+16(FP), [V2.S4] PSAUTO_8 NONE NONE LIST, 3 13
asm: illegal combination: 00000 (.s:27)	VLD1	a+16(FP), [V2.S4] PSAUTO_8 NONE NONE LIST, 3 13
asm: illegal combination: 00000 (.s:27)	VLD1	a+16(FP), [V2.S4] PSAUTO_8 NONE NONE LIST, 3 13
asm: illegal combination: 00000 (.s:27)	VLD1	a+16(FP), [V2.S4] PSAUTO_8 NONE NONE LIST, 3 13
asm: assembly failed
@paultag paultag changed the title cmd/asm: ARM64 VLD1 from psuedo-register FP results in asm: illegal combination cmd/asm: ARM64 VLD1 from pseudo-register FP results in asm: illegal combination Sep 2, 2020
@paultag
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paultag commented Sep 2, 2020

My workaround for this, for my fellow nerds who stumble upon this, is to change [4]float32 to a *[4]float32, MOVD that to a register, then do a VLD (R1), [V2.S4]. Not ideal, but it beats having to work out how to do this by hand :)

@cherrymui
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VLD1 instruction doesn't take an offset for the source, so it must be (Rx) instead of something like 16(Rx), also not a symbolic offset like f+0(FP).

You don't have to change the signature of the function. You could MOVD the address of the argument to a register, then VLD1 from there, like MOVD $f+0(FP), R1; VLD1 (R1), [V2.S4].

@paultag
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paultag commented Sep 2, 2020

Thanks, @cherrymui !

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@paultag @gopherbot @cherrymui