cmd/compile: panic when shadowing builtin function

[GreenHorse]

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

reproduce on darwin with go1.11 darwin/amd64, go1.11 linux/amd64 and go1.11.1 darwin/amd64

The bug does NOT reproduce with
go1.9.7 darwin/amd64 nor go1.10.4 darwin/amd64

Does this issue reproduce with the latest release?

Yes

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

GOARCH="amd64"
GOBIN=""
GOCACHE="/Users/greenhorse/Library/Caches/go-build"
GOEXE=""
GOFLAGS=""
GOHOSTARCH="amd64"
GOHOSTOS="darwin"
GOOS="darwin"
GOPATH="/Users/greenhorse/Project/go"
GOPROXY=""
GORACE=""
GOROOT="/usr/local/Cellar/go/1.11.1/libexec"
GOTMPDIR=""
GOTOOLDIR="/usr/local/Cellar/go/1.11.1/libexec/pkg/tool/darwin_amd64"
GCCGO="gccgo"
CC="clang"
CXX="clang++"
CGO_ENABLED="1"
GOMOD=""
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 -fno-caret-diagnostics -Qunused-arguments -fmessage-length=0 -fdebug-prefix-map=/var/folders/l6/9928hprx3yxcpv22q12s28bw0000gn/T/go-build692282058=/tmp/go-build -gno-record-gcc-switches -fno-common"

What did you do?

package main

func main() {
	var len int
	len("azerty")
}

I shadow len and then try to use it as a function.

The error doesn't happened on the playground.
https://play.golang.org/p/ixHH7fbdpHO

What did you expect to see?

main.go:5:5: cannot call non-function len (type int)

What did you see instead?

# github.com/somehere/mypackage
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x70 pc=0x177c96e]

goroutine 1 [running]:
cmd/compile/internal/gc.typecheck1(0xc000340180, 0x1, 0xc000340080)
	/usr/local/Cellar/go/1.11.1/libexec/src/cmd/compile/internal/gc/typecheck.go:1270 +0x3ece
cmd/compile/internal/gc.typecheck(0xc000340180, 0x1, 0xc000340080)
	/usr/local/Cellar/go/1.11.1/libexec/src/cmd/compile/internal/gc/typecheck.go:238 +0x6ad
cmd/compile/internal/gc.typecheckslice(0xc000334220, 0x3, 0x4, 0x1)
	/usr/local/Cellar/go/1.11.1/libexec/src/cmd/compile/internal/gc/typecheck.go:68 +0x50
cmd/compile/internal/gc.Main(0x18c1300)
	/usr/local/Cellar/go/1.11.1/libexec/src/cmd/compile/internal/gc/main.go:518 +0x2059
main.main()
	/usr/local/Cellar/go/1.11.1/libexec/src/cmd/compile/main.go:51 +0x96

[agnivade]

Dup of #27356. Fixed in tip. Will be backported.

Thanks for reporting.