[release-branch.go1.10] cmd/compile: prevent overflow in walkinrange
In the compiler frontend, walkinrange indiscriminately calls Int64()
on const CTINT nodes, even though Int64's return value is undefined
for anything over 2⁶³ (in practise, it'll return a negative number).
This causes the introduction of bad constants during rewrites of
unsigned expressions, which make the compiler reject valid Go
programs.
This change introduces a preliminary check that Int64() is safe to
call on the consts on hand. If it isn't, walkinrange exits without
doing any rewrite.
Fixes #27247
Change-Id: I2017073cae65468a521ff3262d4ea8ab0d7098d9
Reviewed-on: https://go-review.googlesource.com/130735
Run-TryBot: Josh Bleecher Snyder <josharian@gmail.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
(cherry picked from commit
42cc4ca30a7729a4c6d1bb0bbbc3e4a736ef91c8)
Reviewed-on: https://go-review.googlesource.com/c/131595
Run-TryBot: Dmitri Shuralyov <dmitshur@golang.org>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>