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cmd/compile: float64 to int64 conversion gives different result between amd64 and arm64 on overflows #45588

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@aderouineau

Description

@aderouineau

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

$ go version
go version go1.16.3 darwin/amd64

$ go version
go version go1.16.3 linux/arm64

Does this issue reproduce with the latest release?

Yes

What operating system and processor architecture are you using (go env)?

go env Output (amd64)
$ go env
GO111MODULE=""
GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/derouin/Library/Caches/go-build"
GOENV="/Users/derouin/Library/Application Support/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOINSECURE=""
GOMODCACHE="/Users/derouin/go/pkg/mod"
GONOPROXY="*"
GONOSUMDB="*"
GOOS="darwin"
GOPATH="/Users/derouin/go"
GOPRIVATE="*"
GOPROXY="direct"
GOROOT="/usr/local/Cellar/go/1.16.3/libexec"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/local/Cellar/go/1.16.3/libexec/pkg/tool/darwin_amd64"
GOVCS=""
GOVERSION="go1.16.3"
GCCGO="gccgo"
AR="ar"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD="/dev/null"
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 x86_64 -m64 -pthread -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/2m/168135fn6l73g8k7h7rmzdsc_h4s04/T/go-build1167711572=/tmp/go-build -gno-record-gcc-switches -fno-common"
go env Output (arm64)
$ go env
GO111MODULE=""
GOARCH="arm64"
GOBIN=""
GOCACHE="/home/derouin/.cache/go-build"
GOENV="/home/derouin/.config/go/env"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="arm64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/derouin/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/derouin/go"
GOPRIVATE=""
GOPROXY="direct"
GOROOT="/local/home/derouin/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/local/home/derouin/go/pkg/tool/linux_arm64"
GOVCS=""
GOVERSION="go1.16.3"
GCCGO="gccgo"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/dev/null"
CGO_CFLAGS="-g -O2"
CGO_CPPFLAGS=""
CGO_CXXFLAGS="-g -O2"
CGO_FFLAGS="-g -O2"
CGO_LDFLAGS="-g -O2"
PKG_CONFIG="pkg-config"
GOGCCFLAGS="-fPIC -pthread -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build70387541=/tmp/go-build -gno-record-gcc-switches"

What did you do?

Run the following small program on amd64 and arm64: https://play.golang.org/p/8nY1Dwgq-BU

What did you expect to see?

Same result on both platforms.

What did you see instead?

-9223372036854775808 on amd64 and 9223372036854775807 on arm64.

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