r189218 - Simplify now that -O4 just maps to -O3 and -O is an alias of -O2.

[Rafael Espíndola]

>> This is something Chris requested, IIRC. I'm not sure I remember the
>> motivation beyond that.
>
> Two reasons:
>
> 1) -O1 doesn't actually mean anything.  It is the optimization level least understood by both the GCC folks and us.  Recently (last 5 years?) there has been a move to try to make this "optimize without messing up debug info", but this is a new movement.

Another thing that is making -O1 better defined is asan. It is the
optimization level that makes asan fast but still provides useful
backtraces :-)

> 2) Users who specify -O generally don't know it maps onto -O1.  They almost certainly don't want whatever -O1 provides.  In my experience, most are coming from Sun, HP or other compilers, where -O was a generally useful flag.
>
> 3) There are some benchmarks that pass -O (because of #2), which is ridiculous, but reflects some reality that people use -O.  I don't recall what these benchmarks were.
>
> These are reasons that I suggested the change.  I really don't like -O1 :-)

I haven't seen -O being used in wild, so I OK with keeping it mapping to -O2.

> -Chris

Thanks,
Rafael