cmd/vet: false positives for FP assembly

[kortschak]

What version of Go are you using (go version)?

$ go version
go version go1.13.3 linux/amd64

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="on"
GOARCH="amd64"
GOBIN="/home/user/bin"
GOCACHE="/home/user/.cache/go-build"
GOENV="/home/user/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/user"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/home/user/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/home/user/go/pkg/tool/linux_amd64"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/home/user/src/gonum.org/v1/gonum/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 -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build952532343=/tmp/go-build -gno-record-gcc-switches"

What did you do?

git clone git@github.com:gonum/gonum.git
cd gonum.org/v1/gonum/internal/asm
go vet ./...

What did you expect to see?

No complaints.

What did you see instead?

# gonum.org/v1/gonum/internal/asm/c64
c64/axpyinc_amd64.s:53:1: [amd64] AxpyInc: invalid MOVSD of alpha+0(FP); complex64 is 8-byte value containing alpha_real+0(FP) and alpha_imag+4(FP)
c64/axpyincto_amd64.s:57:1: [amd64] AxpyIncTo: invalid MOVSD of alpha+40(FP); complex64 is 8-byte value containing alpha_real+40(FP) and alpha_imag+44(FP)
c64/axpyunitary_amd64.s:48:1: [amd64] AxpyUnitary: invalid MOVSD of alpha+0(FP); complex64 is 8-byte value containing alpha_real+0(FP) and alpha_imag+4(FP)
c64/axpyunitaryto_amd64.s:49:1: [amd64] AxpyUnitaryTo: invalid MOVSD of alpha+24(FP); complex64 is 8-byte value containing alpha_real+24(FP) and alpha_imag+28(FP)
c64/dotcinc_amd64.s:159:1: [amd64] DotcInc: invalid MOVSD of sum+88(FP); complex64 is 8-byte value containing sum_real+88(FP) and sum_imag+92(FP)
c64/dotcunitary_amd64.s:207:1: [amd64] DotcUnitary: invalid MOVSD of sum+48(FP); complex64 is 8-byte value containing sum_real+48(FP) and sum_imag+52(FP)
c64/dotuinc_amd64.s:147:1: [amd64] DotuInc: invalid MOVSD of sum+88(FP); complex64 is 8-byte value containing sum_real+88(FP) and sum_imag+92(FP)
c64/dotuunitary_amd64.s:196:1: [amd64] DotuUnitary: invalid MOVSD of sum+48(FP); complex64 is 8-byte value containing sum_real+48(FP) and sum_imag+52(FP)
# gonum.org/v1/gonum/internal/asm/f64
f64/sum_amd64.s:99:1: [amd64] Sum: unknown variable sum; offset 24 is ret+24(FP)
f64/sum_amd64.s:100:1: [amd64] Sum: RET without writing to 8-byte ret+24(FP)

See gonum/gonum#79.

[randall77]

I have a fix for the complex ones. We should allow a single instruction to load both parts of a complex value.

Those last two lines are intended. The name of the return value for an anonymous return value is "ret", not "sum". You can either change the assembly to use "ret", or change the prototype to:

func Sum(x []float64) (sum float64)

[gopherbot]

Change https://golang.org/cl/204537 mentions this issue: go/analyis/passes/asmdecl: allow loading both parts of a complex with one instruction

[gopherbot]

Change https://golang.org/cl/204538 mentions this issue: cmd/vet: add test for loading complex values with a single instruction

[kortschak]

Thanks, @randall77. I had thought I had tried that change in Sum. Clearly not.

[gopherbot]

Change https://golang.org/cl/205240 mentions this issue: cmd: vendor in new version of x/tools