Simplify double to number convertion.

Simplify double to number convertion.


Committed: http://code.google.com/p/v8/source/detail?r=4550

[Søren Thygesen Gjesse, 2010-04-26 10:57:48]

The existing code all used NewNumberFromDouble which allocates  new heap number.
As far as I can see there was no use of SmiOrNumberFromDouble with argument
new_object set to false. I am not sure whether returning a pre-allocated heap
number is a good idea as we can generate code which overwrites heap numbers.
This might not be hit for values returned from %NumberDiv and %NumberMod right
now, but I think that always allocating a new heap number is the right thing to
do.

http://codereview.chromium.org/1694004/diff/10001/11001
File src/heap.cc (right):

http://codereview.chromium.org/1694004/diff/10001/11001#newcode1832
src/heap.cc:1832: if (rep.bits == plus_zero.bits) return Smi::FromInt(0);  //
not uncommon
Start comment with uppercase and end with dot.

[Oleg Eterevsky, 2010-04-26 11:18:28]

The current code used NewNumberFromDouble only in a couple of places and
NumberFromDouble in 20 or so places.

http://codereview.chromium.org/1694004/diff/10001/11001
File src/heap.cc (right):

http://codereview.chromium.org/1694004/diff/10001/11001#newcode1832
src/heap.cc:1832: if (rep.bits == plus_zero.bits) return Smi::FromInt(0);  //
not uncommon
On 2010/04/26 10:57:48, Søren Gjesse wrote:
> Start comment with uppercase and end with dot.

I'm removing the checks, according to your advice.

[Mads Ager (chromium), 2010-04-28 07:06:35]

http://codereview.chromium.org/1694004/diff/17001/18001
File src/heap.cc (right):

http://codereview.chromium.org/1694004/diff/17001/18001#newcode1830
src/heap.cc:1830: return minus_zero_value();
This means that we will never allocate a new heap number for minus zero in this
function. This seems dangerous in combination with our heap-number overwriting
for nested binary ops.

If you cannot measure any performance gain by avoiding allocation in certain
situations, you should return a new heap number for minus zero.

http://codereview.chromium.org/1694004/diff/17001/18001#newcode1833
src/heap.cc:1833: int int_value = static_cast<int>(value);
Do you have a good reason for not using FastD2I and FastI2D as we do in the old
code and in the rest of the system?

[Oleg Eterevsky, 2010-04-28 15:22:39]

I've changed the return value to newly allocated HeapNumber.

[Mads Ager (chromium), 2010-04-29 07:31:10]

LGTM if you change to use FastD2I and FastI2D as in the rest of the code.

http://codereview.chromium.org/1694004/diff/24001/25001
File src/heap.cc (right):

http://codereview.chromium.org/1694004/diff/24001/25001#newcode1832
src/heap.cc:1832: int int_value = static_cast<int>(value);
FastD2I(value) and FastI2D(int_value)?