Add a 'v8_optimized_debug' option to the build flags

PATCH ABANDONED ... see https://codereview.chromium.org/19384011/

Add a 'v8_optimized_debug' option to the build flags

This allows us to do a build with the DEBUG macros enabled and
with all of the compiler optimizations still happening. This provides
a speedup of 3x - 4x when running the layout tests in chromium/blink (this makes the debug builds only 3x-4x slower than Release, as opposed to 10x-11x slower).

R=danno@chromium.org
BUG=https://code.google.com/p/chromium/issues/detail?id=254188

[Michael Achenbach, 2013-07-10 13:19:31]

I cannot get the code to compile with gcc under linux64. I get weird array
bounds warnings, which are recognized as errors. With only using -O1 it works
fine and gives a quite good speedup as well.

I copied most of this CL into the similar CL I was working on
(https://codereview.chromium.org/18516012/), which we will land with just the O1
optimization for now.

[Dirk Pranke, 2013-07-10 17:00:13]

On 2013/07/10 13:19:31, machenbach wrote:
> I cannot get the code to compile with gcc under linux64. I get weird array
> bounds warnings, which are recognized as errors. With only using -O1 it works
> fine and gives a quite good speedup as well.
> 
> I copied most of this CL into the similar CL I was working on
> (https://codereview.chromium.org/18516012/), which we will land with just the
O1
> optimization for now.

Odd. I was running this on both mac and linux64 and it seemed to be fine. I will
try again today and also compare it with the -O1 change and report back.

[Michael Achenbach, 2013-07-10 18:48:40]

On 2013/07/10 17:00:13, Dirk Pranke wrote:
> On 2013/07/10 13:19:31, machenbach wrote:
> > I cannot get the code to compile with gcc under linux64. I get weird array
> > bounds warnings, which are recognized as errors. With only using -O1 it
works
> > fine and gives a quite good speedup as well.
> > 
> > I copied most of this CL into the similar CL I was working on
> > (https://codereview.chromium.org/18516012/), which we will land with just
the
> O1
> > optimization for now.
> 
> Odd. I was running this on both mac and linux64 and it seemed to be fine. I
will
> try again today and also compare it with the -O1 change and report back.

My gcc version is 4.6.3. My compiler errors might have been spurious warnings
issued by the array bounds check. We saw this also on several bots today and
issued a change to suppress it https://codereview.chromium.org/19009003/. Would
be great if we could get to the bottom of this.

[Michael Achenbach, 2013-07-12 09:58:16]

We are building debug now with the -O1 optimization. See also last comment in
crbug.com/238095