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loop unrolling, flags and passes


Hello everyone

I have few questions regarding loop unrolling and the effect of flags
(provided at command line) on the execution of passes.

Is it possible to do loop unrolling without using -O3, -O2 and -O1?

The -Q -O3 --help=optimizers options provides us the list of enabled
and disabled optimizations at -O3 level. If I specify -O3 to compile
any file then the total number of passes executed are around 182. And
If I manually specify all the optimization which are enabled at -O3
(without specifying -O3 actually), we get the total number of passes
as 64. So, my question is that why is there a difference of passes
between these two cases?

And while specifying all enabled optimizations (at -O3) along with
-funroll-all-loops, I am unable to do the unrolling, while the same
program is unrolled if we specify -O3 along with -funroll-all-loops.

Best regards

Memon


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