not only "debug symbols" that binary will contain, it will also contain code within some #ifdef's; yet some -Oxxx are disabled

Let's RTFS a bit -- following is an excerpt from ./win32/makefile.mk (same for linux build, I guess)

#
# uncomment next line if you want debug version of perl (big,slow)
# If not enabled, we automatically try to use maximum optimization
# with all compilers that are known to have a working optimizer.
#
#CFG        *= Debug
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