Skip to content

cmd/compile: division of uint8 by 128 emits a divw instruction on atleast 386 and amd64 arch #74485

Open
@renthraysk

Description

@renthraysk

Go version

go version go1.24.4 linux/amd64

Output of go env in your module/workspace:

AR='ar'
CC='gcc'
CGO_CFLAGS='-O2 -g'
CGO_CPPFLAGS=''
CGO_CXXFLAGS='-O2 -g'
CGO_ENABLED='1'
CGO_FFLAGS='-O2 -g'
CGO_LDFLAGS='-O2 -g'
CXX='g++'
GCCGO='gccgo'
GO111MODULE=''
GOAMD64='v3'
GOARCH='amd64'
GOAUTH='netrc'
GOBIN=''
GOCACHE='/home/ren/.cache/go-build'
GOCACHEPROG=''
GODEBUG=''
GOENV='/home/ren/.config/go/env'
GOEXE=''
GOEXPERIMENT=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build3297555499=/tmp/go-build -gno-record-gcc-switches'
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMOD='/home/ren/dev/junk/bugXXX/go.mod'
GOMODCACHE='/home/ren/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPATH='/home/ren/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/usr/local/go'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/home/ren/.config/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='auto'
GOTOOLDIR='/usr/local/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.24.4'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

package main

func f(b uint8) uint8 {
	return b / 128
}

What did you see happen?

MOVBLZX	AL, AX
MOVL	$-128, CX
MOVBLZX	CL, CX
XORL	DX, DX
DIVW	CX
RET

What did you expect to see?

SHRB	$7, AL

Metadata

Metadata

Assignees

No one assigned

    Labels

    ImplementationIssues describing a semantics-preserving change to the Go implementation.NeedsFixThe path to resolution is known, but the work has not been done.Performancecompiler/runtimeIssues related to the Go compiler and/or runtime.

    Type

    No type

    Projects

    Status

    No status

    Relationships

    None yet

    Development

    No branches or pull requests

    Issue actions