binary compiled with -O1 and w/ individual optimization flags are not the same

[CSights <csights@fastmail.fm>]

Hi,
	I'm trying to debug some mismatching results from a program compiled with 
O1,2,3) and without (-O0 or nothing) optimization flags.
	My thought was to individually turn on optimization flags and see which one 
changes the program's output.
	Unfortunately for this plan, the binaries produced using -O1 and those flags 
said to be turned on by g++ in the manual (-fdefer-pop -fdelayed-branch
-fguess-branch-probability -fcprop-registers -fif-conversion -fif-conversion2 
-ftree-ccp -ftree-dce -ftree-dominator-opts -ftree-dse -ftree-ter -ftree-lrs 
-ftree-sra -ftree-copyrename -ftree-fre -ftree-ch -funit-at-a-time -fmerge-constants) 
do not match.  I also tried without -fdelayed-branch b/c it is not supported 
on my architectures (i386: athlon xp, core duo) and with -fomit-frame-pointer 
in case that was the difference.
	I've tried this with g++ versions
g++ (GCC) 4.2.3 (Debian 4.2.3-1) 
and
i686-apple-darwin8-g++-4.0.1 (GCC) 4.0.1 (Apple Computer, Inc. build 5363)
	Is there a way to have g++ tell me which flags it is actually using when 
compiling a program.  E.g. expand -O1 to the individual optimization flags at 
run time?
	Anyone have any other suggestions?

Thanks much,
	C.