cmd/compile: recognize integer ranges in switch statements
Consider a switch statement like:
switch x {
case 1:
// ...
case 2, 3, 4, 5, 6:
// ...
case 5:
// ...
}
Prior to this CL, the generated code treated
2, 3, 4, 5, and 6 independently in a binary search.
With this CL, the generated code checks whether
2 <= x && x <= 6.
walkinrange then optimizes that range check
into a single unsigned comparison.
Experiments suggest that the best min range size
is 2, using binary size as a proxy for optimization.
Binary sizes before/after this CL:
cmd/compile:
14209728 /
14165360
cmd/go:
9543100 /
9539004
Change-Id: If2f7fb97ca80468fa70351ef540866200c4c996c
Reviewed-on: https://go-review.googlesource.com/26770
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Matthew Dempsky <mdempsky@google.com>