cmd/compile: real and imag don't produce untyped results for untyped constant arguments

[griesemer]

package main
const _ int = real(10i)

=>

$ go build x.go
# command-line-arguments
./x.go:2: cannot use real(10i) (type float64) as type int in const initializer

(same for use of imag instead of real).

It appears that real and imag always produce a float32 or float64 constant respectively, for untyped constant arguments. The spec is not explicit about this, but this behavior violates the invariant

z == complex(real(z), imag(z))

for untyped constants z because real and imag won't work if the complex arguments have untyped constant components outside the float64 domain (see also #11540 ).

Both gc, and go/types accept this code. Both gc and go/types produce an untyped floating-point constant for untyped constant arguments.

[gopherbot]

CL https://golang.org/cl/12860 mentions this issue.

[gopherbot]

CL https://golang.org/cl/45076 mentions this issue.

[gopherbot]

CL https://golang.org/cl/45081 mentions this issue.