Clean up regexp code gen a little

Clean up regexp code gen a little

R=yangguo@chromium.org
BUG=

Committed: https://code.google.com/p/v8/source/detail?r=23958

[Erik Corry, 2014-09-12 07:06:24]

WIth this change, the EmitChoices method doesn't have any flag that depends on
whether we are emitting a "greedy loop" (actually a fixed-length loop that can
be backtracked without unwinding any other state than a constant step backwards
in the input).

Tested on a very large number of regexps.  Emits almost the same code, but very
very occasionally emits a jump to the next instruction that wasn't there in the
previous version. This will happen if the thing immediately following the greedy
loop cannot match, eg if you search for .*€ in a latin1 string.  Perhaps we
should have a peephole optimizer to catch this more generally.

[Yang, 2014-09-15 08:52:47]

On 2014/09/12 07:06:24, Erik Corry wrote:
> WIth this change, the EmitChoices method doesn't have any flag that depends on
> whether we are emitting a "greedy loop" (actually a fixed-length loop that can
> be backtracked without unwinding any other state than a constant step
backwards
> in the input).
> 
> Tested on a very large number of regexps.  Emits almost the same code, but
very
> very occasionally emits a jump to the next instruction that wasn't there in
the
> previous version. This will happen if the thing immediately following the
greedy
> loop cannot match, eg if you search for .*€ in a latin1 string.  Perhaps we
> should have a peephole optimizer to catch this more generally.

lgtm.

[Erik Corry, 2014-09-15 08:54:52]

The CQ bit was checked by erik.corry@gmail.com

[commit-bot: I haz the power, 2014-09-15 08:54:59]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patchset/565043003/1

[commit-bot: I haz the power, 2014-09-15 08:54:59]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-09-15 08:55:00]

No LGTM from a valid reviewer yet. Only full committers are accepted.
Even if an LGTM may have been provided, it was from a non-committer or
a provisional committer, _not_ a full super star committer.
See http://www.chromium.org/getting-involved/become-a-committer
Note that this has nothing to do with OWNERS files.

[Erik Corry, 2014-09-16 07:09:54]

Committed patchset #1 (id:1) manually as 23958 (presubmit successful).