Crankshaft: Recognize (i >>> 0) === i for integer32 inputs and replace

Crankshaft: Recognize (i >>> 0) === i for integer32 inputs and replace
with i >= 0, with no bailout.

[Jakob Kummerow, 2013-04-23 11:09:23]

DBC.

https://codereview.chromium.org/14211009/diff/1/src/hydrogen.cc
File src/hydrogen.cc (right):

https://codereview.chromium.org/14211009/diff/1/src/hydrogen.cc#newcode10052
src/hydrogen.cc:10052:
compare->set_observed_input_representation(Representation::Integer32(),
Manually setting observed input representations is a hack. Please harvest i's
representation from the >>> operation instead.

https://codereview.chromium.org/14211009/diff/1/src/hydrogen.cc#newcode10090
src/hydrogen.cc:10090: if (!right->representation().IsInteger32()) return false;
You can't rely on representations at graph construction time. For most
instructions, they're not set at all, and they can change later during the
representation inference phase.

I think replacement operations like this belong in the Canonicalization pass.

[erikcorry, 2013-04-23 14:27:04]

I'm abandoning the change.  The latest uploaded version does the change in
Canonicalize as recommended, but that is too late, because at that point the
HSimulate instruction is a user of the HShr, so it is not eliminated, and nor is
the bailout.  That makes the change pointless.

[erikcorry, 2013-04-23 14:28:57]

OK, patch upload failed due to some borkage in gcl, but I have the diff here if
anyone wants to see it.

[Jakob Kummerow, 2015-11-28 15:21:16]

Description was changed from

==========
Crankshaft: Recognize (i >>> 0) === i for integer32 inputs and replace
with i >= 0, with no bailout.
==========

to

==========
Crankshaft: Recognize (i >>> 0) === i for integer32 inputs and replace
with i >= 0, with no bailout.
==========