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cmd/internal/obj/arm64: ARM assembly rotational right shift of a register with @> syntax causes compile error #57662

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dadrian opened this issue Jan 6, 2023 · 3 comments
Closed

cmd/internal/obj/arm64: ARM assembly rotational right shift of a register with @> syntax causes compile error #57662

dadrian opened this issue Jan 6, 2023 · 3 comments
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@dadrian
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dadrian commented Jan 6, 2023

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

$ go version 
go1.19.4 darwin/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="/Users/dadrian/Library/Caches/go-build"
GOENV="/Users/dadrian/Library/Application Support/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="arm64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/dadrian/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="darwin"
GOPATH="/Users/dadrian/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/opt/homebrew/Cellar/go/1.19.4/libexec"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/opt/homebrew/Cellar/go/1.19.4/libexec/pkg/tool/darwin_arm64"
GOVCS=""
GOVERSION="go1.19.4"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/Users/dadrian/src/github.com/dadrian/go-bugs/go.mod"
GOWORK=""
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -arch arm64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/7_/yc9s7tp94lq83r7fmlncg58c0000gn/T/go-build2852821403=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

Compiled Go assembly for arm that uses a rotation right shift with the @> syntax.

ADD R0@>16, ZR, R0

I pushed a minimal test case here: https://github.com/dadrian/go-bugs/tree/main/arm-ror

What did you expect to see?

Successful compilation

What did you see instead?

asm: unsupported shift operator: 00016 (/Users/dadrian/src/github.com/dadrian/go-bugs/arm-ror/function_arm64.s:3)       ADDR0@>16, ZR, R0
@cespare
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cespare commented Jan 6, 2023

@dadrian is ROR a valid shift type for ADD?

If I look at the ADD docs I see

Is the optional shift type to be applied to the second source operand, defaulting to LSL, and can be one of LSL, LSR, or ASR.

whereas if I look at, for example, EOR I see

Is the optional shift to be applied to the final source, defaulting to LSL, and can be one of LSL, LSR, ASR, or ROR.

(I'm an arm64 newbie so maybe I'm mistaken.)

@dadrian
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dadrian commented Jan 6, 2023

I actually first ran into this on an EOR and dumbed it down to ADD for the repro. You're absolutely correct.

That being said, it does work on EOR but only on the first argument, not the second. Not sure if that's intentional (I'm also an ARM newbie).

@dadrian dadrian closed this as completed Jan 6, 2023
@greatroar
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greatroar commented Jan 6, 2023 •
edited

it does work on EOR but only on the first argument, not the second.

This is a feature/limitation of the architecture.

@golang golang locked and limited conversation to collaborators Jan 7, 2024
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@cespare @dadrian @gopherbot @greatroar