cmd/compile: add memory operand ADC and SBB to `AMD64.rules`

[Jorropo]

Go version

go version go1.27-devel_a129840779 Mon Jul 13 14:06:37 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=''
GOFIPS140='off'
GOFLAGS=''
GOGCCFLAGS='-fPIC -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -ffile-prefix-map=/tmp/go-build784687367=/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='go1.27-devel_a129840779 Mon Jul 13 14:06:37 2026 -0700'
GOWORK=''
PKG_CONFIG='pkg-config'

What did you do?

Compile:

package carry

import "math/bits"

func AddUseCarry(a, b [2]uint64, s uint64) uint64 {
	_, c := bits.Add64(a[0], b[0], 0)
	_, c2 := bits.Add64(a[1], b[1], c)
	return s + c2 // carry consumed by a plain add
}

What did you see happen?

TEXT command-line-arguments.AddUseCarry(SB), ABIInternal
    MOVQ command-line-arguments.a(SP), CX
    MOVQ command-line-arguments.b+16(SP), DX
    MOVQ command-line-arguments.a+8(SP), BX
    MOVQ command-line-arguments.b+24(SP), SI
    ADDQ CX, DX
    ADCQ SI, BX
    ADCQ $0, AX
    RET

What did you expect to see?

TEXT command-line-arguments.AddUseCarry(SB), ABIInternal
    MOVQ command-line-arguments.b+16(SP), DX
    MOVQ command-line-arguments.a+8(SP), BX
    ADDQ command-line-arguments.a(SP), DX
    ADCQ command-line-arguments.b+24(SP), BX
    ADCQ $0, AX
    RET

[Jorropo]

There is also modify and constmodify encoding modes we aren't currently supporting.

Everything added in this issue will also have to be added to the addressing modes pass for displacement and scale encoding.

[gabyhelp]

Related Issues

• cmd/compile: amd64 carry flag spilling uses SBBQ + NEGQ instead of SETCS #68961
• cmd/compile: materialized bits.Add64/Sub64 carries no longer fold into consumers on amd64 (regression from CL 778140) #80399
• cmd/compile: on `AMD64` slow instruction sequence to Zext a < register size instruction output #76066
• cmd/compile: suboptimal arm64 output #43145
• cmd/compile: memcombine should learn alignment of byte slices - hard mode - arithmetic #71780
• cmd/compile: ADCQ and SBBQ rules no longer eat `InvertFlags` leading to ICE sometimes #79887 (closed)

Related Code Changes

• cmd/compile: intrinsify math/bits.Add64 for arm64
• cmd/compile: intrinsify math/bits.Add on amd64
• cmd/compile: intrinsify math/bits.{Sub32|Add32} for arm64
• cmd/compile: intrinsify math/bits.Sub on amd64

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

[gopherbot]

Change https://go.dev/cl/804506 mentions this issue: cmd/compile: use memory operands in AMD64 carry chains