cmd/compile: archsimd load isn't treated as read only for string → []byte elision

Go version

go version go1.28-devel_9ea81f5213 Tue Aug 25 00:07:53 2026 -0700 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='/home/hugo/go/bin'
GOCACHE='/tmp/go-build/'
GOCACHEPROG=''
GODEBUG=''
GOENV='/home/hugo/.config/go/env'
GOEXE=''
GOEXPERIMENT='simd'
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build661455473=/tmp/go-build -gno-record-gcc-switches'
GOHOSTARCH='amd64'
GOHOSTOS='linux'
GOINSECURE=''
GOMOD='/home/hugo/k/go/src/go.mod'
GOMODCACHE='/home/hugo/go/pkg/mod'
GONOPROXY=''
GONOSUMDB=''
GOOS='linux'
GOPACKAGESDRIVER=''
GOPATH='/home/hugo/go'
GOPRIVATE=''
GOPROXY='https://proxy.golang.org,direct'
GOROOT='/home/hugo/k/go'
GOSUMDB='sum.golang.org'
GOTELEMETRY='local'
GOTELEMETRYDIR='/home/hugo/.config/go/telemetry'
GOTMPDIR=''
GOTOOLCHAIN='local'
GOTOOLDIR='/home/hugo/k/go/pkg/tool/linux_amd64'
GOVCS=''
GOVERSION='go1.28-devel_9ea81f5213 Tue Aug 25 00:07:53 2026 -0700'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

Compile:

package a

import "simd/archsimd"

func f(x string) archsimd.Uint8x16 {
	return archsimd.LoadUint8x16([]byte(x))
}

What did you see happen?

Call to stringtoslicebyte

What did you expect to see?

An XMM load from the string's backing array.

Note I'm not asking for intrinsics that load from a string.
I am trying to use this in the encoding/hex package (see CL 795820), sadly this patch adds a heap allocation in the DecodeString function:

func DecodeString(s string) ([]byte, error) {
	dst := make([]byte, DecodedLen(len(s)))
	n, err := Decode(dst, []byte(s))
	return dst[:n], err
}

If I had intrinsics to load from a string it would be painful to use since it adds color to the SIMD routines.

Related Issues

simd/archsimd: archsimd.LoadUint8x32Slice() emits nops #76968 (closed)
cmd/compile: memcombine should learn allignement of byte slices - easy mode - types #71778 (closed)
cmd/compile: memcombine should learn alignment of byte slices - hard mode - arithmetic #71780
cmd/compile: internal compiler error using `archsimd.Int8x16` as type parameter #77444 (closed)
cmd/compile: unsafe conversion from slice to struct pointer generates worse code on amd64 than on 386 #65330
cmd/compile: simd operations not marked as hoistable #79984
cmd/objdump: disassembly of AVX instructions generated by archsimd produces nonsense. #78065 (closed)
simd: bridge.LoadFloat32sPart ... are not shape types #80689
cmd/compile: missing inlining and/or SROA for SIMD code #79322
cmd/compile: stringtoslicebytetmp optimization broken #14973 (closed)

_{(Emoji vote if this was helpful or unhelpful; more detailed feedback welcome in this discussion.)}

Change https://go.dev/cl/822404 mentions this issue: [release-branch.go1.27] cmd: vendor changes for "go fix"

@golang/compiler

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cmd/compile: archsimd load isn't treated as read only for string → []byte elision #81097

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Output of `go env` in your module/workspace:

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What did you see happen?

What did you expect to see?

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cmd/compile: archsimd load isn't treated as read only for string → []byte elision #81097

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Go version

Output of go env in your module/workspace:

What did you do?

What did you see happen?

What did you expect to see?

Activity

Jorropo commented on Aug 25, 2026

gabyhelp commented on Aug 25, 2026

gopherbot commented on Aug 26, 2026

dr2chase commented on Aug 28, 2026

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Output of `go env` in your module/workspace: