[Bug 1753] Use -funroll-loops with umac.c

[bugzilla-daemon at mindrot.org]

https://bugzilla.mindrot.org/show_bug.cgi?id=1753

Michael Felt <aixtools at gmail.com> changed:

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--- Comment #3 from Michael Felt <aixtools at gmail.com> ---
As far as POWER goes (more specifically, AIX and xlc) there is a PDF
describing the optimization 'process' when using vac/xlc as a compiler.
The document # for VAC-v11 is SC27-2478-00 (or higher for the last two
digits - the revision number).

Here is a starting point for documentation:
http://www-01.ibm.com/support/knowledgecenter/SSGH2K_11.1.0/com.ibm.xlc111.aix.doc/conventions/compiler_pubs.html

On page (printed) page 47 (Chapter 7. Optimizing your applications) the
path of moving from -O2 to higher degrees of optimization is discussed.

On pages 48 and 49 it discusses -O3, -O4 and -O5 - and the bottom of
page 49 discusses only adding the a variation of the options -qhot to
act on loop transformations.

In summary, -funroll-loops is not a vac/xlc flag I am aware of - but
there is documentation to be had to help setup your own customization.
imho, anything beyond -O2 needs careful. At least for xlc/vac, unless
you specify -qstrict with -O3 and above you are permitting the compiler
to reorder code (blocks).

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