cmd/compile: typeparams: ++ operator doesn't instantiate correctly

[randall77]

package main

type C interface {
	int32
}

func inc[T C](x T) T {
	x++
	return x
}
func main() {
	println(inc(int32(5)))
}

$ go run -gcflags=-G=3 ~/gowork/tmp2.go
# command-line-arguments
../../../gowork/tmp2.go:8:3: invalid operation: x + 1 (mismatched types int32 and int)
../../../gowork/tmp2.go:12:13: invalid operation: x + 1 (mismatched types int32 and int)

I think the 1 introduced by ++ needs to have the type of the LHS.

Not sure why there are two errors also.

@danscales

[randall77]

x+=1 and x=x+1 both work fine.

[gopherbot]

Change https://golang.org/cl/336009 mentions this issue: [dev.typeparams] cmd/compile: handle ++/-- in noder2 for expression with generic type

[randall77]

@gopherbot didn't close this one either. Methinks it isn't closing issues when fixes are checked into dev.typeparams.