cmd/compile: improve floating point constant propagation
Add generic rules to propagate floating point constants through
comparisons and integer conversions. These new rules seldom trigger
in the standard library so there is no performance change, however
I think it is worth adding them anyway for completeness.
Change-Id: I9db5222746508a2996f1cafb72f4e0cf2541de07
Reviewed-on: https://go-review.googlesource.com/63795
Run-TryBot: Michael Munday <mike.munday@ibm.com>
TryBot-Result: Gobot Gobot <gobot@golang.org> Reviewed-by: Keith Randall <khr@golang.org>