Change the utils WhichPowerOf2 function to use a simpler algorithm.

Fix a potential error in Add() macro-instruction on ARM.

Committed: http://code.google.com/p/v8/source/detail?r=5769

[William Hesse, 2010-11-03 14:19:34]

A fun review for you.

[Mads Ager (chromium), 2010-11-03 14:36:21]

Cute. One question below.

http://codereview.chromium.org/4247004/diff/1/3
File src/utils.h (right):

http://codereview.chromium.org/4247004/diff/1/3#newcode53
src/utils.h:53: static inline int WhichPowerOf2(T x) {
Do we only ever use this on 32-bit integers? It is a template methods so nothing
prevents us from calling it with an intptr_t on 64-bit.

If we only use this on 32-bit integers could we just change the type to int to
reflect that.

[William Hesse, 2010-11-03 16:18:20]

Unfortunately, checking the single place this function is used showed a
potential bug there, which is now also fixed in the CL.  A relocatable immediate
that looked like a mask could have been encoded in the instruction.

[Mads Ager (chromium), 2010-11-03 17:05:06]

LGTM

[William Hesse, 2010-11-04 15:32:20]

The function is only used in one place, which is on the ARM platform, it is
barely ever hit, and the old version is faster on ARM.  

Only fixing the ARM bug.

On 2010/11/03 17:05:06, Mads Ager wrote:
> LGTM