Simple elimination of redundant array-hole checks.

Simple elimination of redundant array-hole checks.

If the result of an fast elements load is converted to an untagged
representation we can omit the hole check if the value is not used
anywhere else except for HChange instructions converting it to
an untagged representation since those will deoptimize for the hole
value anyway.
Committed: http://code.google.com/p/v8/source/detail?r=7827

[Kevin Millikin (Chromium), 2011-05-09 14:59:54]

LGTM.

http://codereview.chromium.org/6964012/diff/1/src/hydrogen-instructions.h
File src/hydrogen-instructions.h (right):

http://codereview.chromium.org/6964012/diff/1/src/hydrogen-instructions.h#new...
src/hydrogen-instructions.h:3258: bool check_hole_value() const;
This should probably have a CamelCase name.  I'd also like it to sound more
obviously like a predicate.  ShouldCheckHoleValue?  MustCheckHoleValue?