Improve Hydrogen code for accessing undefined/null/Infinity.

Improve Hydrogen code for accessing undefined/null/Infinity.

In some special (but probably very common) cases we can do better than loading
from a global cell for these global properties by emitting the corresponding
constant directly. This opens up opportunities for further improvements, coming
in a separate CL...

[Steven, 2011-09-22 13:57:23]

LGTM.

http://codereview.chromium.org/7992002/diff/7/src/factory.h
File src/factory.h (right):

http://codereview.chromium.org/7992002/diff/7/src/factory.h#newcode448
src/factory.h:448: // a null handle when the given name is unknown.
Add a comment that those properties of the global object are not 'configurable'
and not 'writable', i.e. they are really global constants.

http://codereview.chromium.org/7992002/diff/7/src/heap.h
File src/heap.h (right):

http://codereview.chromium.org/7992002/diff/7/src/heap.h#newcode234
src/heap.h:234: V(infinity_symbol, "Infinity")
The runtime functions contain multiple calls of the form
isolate->heap()->
  AllocateStringFromAscii(CStrVector("Infinity"));
Can you replace them by using the infinity_symbol instead? Same for NaN and
-Infinity for which you would have to introduce another symbol.

[Sven Panne, 2011-09-23 07:59:48]

http://codereview.chromium.org/7992002/diff/7/src/factory.h
File src/factory.h (right):

http://codereview.chromium.org/7992002/diff/7/src/factory.h#newcode448
src/factory.h:448: // a null handle when the given name is unknown.
On 2011/09/22 13:57:23, Steven wrote:
> Add a comment that those properties of the global object are not
'configurable'
> and not 'writable', i.e. they are really global constants.

Done.

http://codereview.chromium.org/7992002/diff/7/src/heap.h
File src/heap.h (right):

http://codereview.chromium.org/7992002/diff/7/src/heap.h#newcode234
src/heap.h:234: V(infinity_symbol, "Infinity")
On 2011/09/22 13:57:23, Steven wrote:
> The runtime functions contain multiple calls of the form
> isolate->heap()->
>   AllocateStringFromAscii(CStrVector("Infinity"));
> Can you replace them by using the infinity_symbol instead? Same for NaN and
> -Infinity for which you would have to introduce another symbol.

Done. And I've just seen that the related Ctrl-C/Ctrl-V-generated parts of
runtime.cc *really* need a cleanup, but not in this CL...