optimization problems, how to obtain "processed source"?

[Daniel Franke]

Hi all.

This is a somewhat stupid question, but the manpages are no help here
(or I can't identify what is needed).

I try to hunt down a problem with optimization. From my tests, it is
to assume that a variable gets optimized away, that shouldn't. The
main problem is, that adding WRITEs changes the behaviour of the
compiled code, therefore I can't use them to debug. My ability to
decipher assembler is limited, therefore I would like to obtain
"processed source" as it sometimes added to PRs, e.g. PR29101, comment
#1 [1]. How can I obtain such "processed sources"? (Is there a proper
name for this stuff?)

Thanks in advance!
     Daniel

[1] http://gcc.gnu.org/bugzilla/show_bug.cgi?id=29101#c1