cmd/compile: bad mpint length: 65 > 64

[j-mnr]

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

$ go version
go version go1.19 linux/amd64

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="amd64"
GOBIN="/home/jay/.local/bin"
GOCACHE="/home/jay/.cache/go-build"
GOENV="/home/jay/.config/go/env"
GOEXE=""
GOEXPERIMENT=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOINSECURE=""
GOMODCACHE="/home/jay/.local/share/go/pkg/mod"
GONOPROXY=""
GONOSUMDB=""
GOOS="linux"
GOPATH="/home/jay/.local/share/go"
GOPRIVATE=""
GOPROXY="https://proxy.golang.org,direct"
GOROOT="/usr/lib/go"
GOSUMDB="sum.golang.org"
GOTMPDIR=""
GOTOOLDIR="/usr/lib/go/pkg/tool/linux_amd64"
GOVCS=""
GOVERSION="go1.19"
GCCGO="gccgo"
GOAMD64="v1"
AR="ar"
CC="gcc"
CXX="g++"
CGO_ENABLED="1"
GOMOD="/home/jay/src/go/playground/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 -m64 -pthread -Wl,--no-gc-sections -fmessage-length=0 -fdebug-prefix-map=/tmp/go-build1919621165=/tmp/go-build -gno-record-gcc-switches"

What did you do?

https://go.dev/play/p/_jct1xi435j

What did you expect to see?

Nothing, I was just exploring untyped constants

What did you see instead?

# playtime
./main.go:10:13: internal compiler error: bad mpint length: 65 > 64 (type untyped int, value 912345678901234567890123456789012345678901234567890912345678901234567890123456789012345678901234567890912345678901234567890123456789012345678901234567890912)

Please file a bug report including a short program that triggers the error.
https://go.dev/issue/new

This could be a false alarm, I'm just following what the toolchain asked me to do.

[mknyszek]

CC @golang/compiler

Optimistically assigning to @griesemer but giving it a low priority since this case doesn't seem like it would come up much in practice. Seems like it could just use a better error message. @griesemer Please feel free to unassign!

[mdempsky]

The crash is actually happening in iexport, but the issue is that the integer constant requires more than 64 bytes (512 bits) to represent.

I think the issue is that types2 rejects arithmetic that overflows 512 bits, but evidently it doesn't check that constant literals themselves fit into 512 bits. If I change the declaration of BIG to include + 0, then types2 reports "constant addition overflow" even though it represents the same value.

[gopherbot]

Change https://go.dev/cl/424055 mentions this issue: go/types, types2: check integer constant literal overflow