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Keith Randall 585c9e8412 cmd/compile: implement shifts by signed amounts
Allow shifts by signed amounts. Panic if the shift amount is negative.

TODO: We end up doing two compares per shift, see Ian's comment
https://github.com/golang/go/issues/19113#issuecomment-443241799 that
we could do it with a single comparison in the normal case.

The prove pass mostly handles this code well. For instance, it removes the
<0 check for cases like this:
    if s >= 0 { _ = x << s }
    _ = x << len(a)

This case isn't handled well yet:
    _ = x << (y & 0xf)
I'll do followon CLs for unhandled cases as needed.

Update #19113

R=go1.13

Change-Id: I839a5933d94b54ab04deb9dd5149f32c51c90fa1
Reviewed-on: https://go-review.googlesource.com/c/158719
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Josh Bleecher Snyder <josharian@gmail.com>
2019-02-15 23:13:09 +00:00
.github .github: don't render author-facing text in ISSUE_TEMPLATE 2018-11-02 04:47:34 +00:00
api api: add os.(*File).SyscallConn to go1.12.txt 2019-01-02 21:21:53 +00:00
doc doc/go1.12: note that Go 1.12 is the last release to include godoc 2019-02-13 23:16:39 +00:00
lib/time lib/time: update tzdata to 2018i 2019-01-07 20:14:03 +00:00
misc cmd/cgo: don't copy a simple variable x in &x[0] 2019-02-04 06:53:49 +00:00
src cmd/compile: implement shifts by signed amounts 2019-02-15 23:13:09 +00:00
test cmd/compile: implement shifts by signed amounts 2019-02-15 23:13:09 +00:00
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