What happens when -O1 flag is used?

[Segher Boessenkool]

>    1)Are -O and -O1 flags  equal?

Yes.

>    2) What happens internally when -O1/-O flag is
> used?

Lots of stuff, read the source code; gcc/opts.c is a
good starting point.  The "optimize" variable is set
to the optimisation level.

>       I have been searching gcc internal manuals. But
> I could not locate.

The internals manual is not a replacement for the source
code; the manual is meant to help understanding and modifying
the source code.

Have fun and good luck,


Segher