question about -ffast-math implementation

[Mike Izbicki <mike dot izbicki at gmail dot com>]

I'm trying to copy gcc's behavior with the -ffast-math compiler flag
into haskell's ghc compiler.  The only documentation I can find about
it is at:

https://gcc.gnu.org/onlinedocs/gcc/Optimize-Options.html

I understand how floating point operations work and have come up with
a reasonable list of optimizations to perform.  But I doubt it is
exhaustive.

My question is: where can I find all the gory details about what gcc
will do with this flag?  I'm perfectly willing to look at source code
if that's what it takes.

Also, are there any optimizations that you wish -ffast-math could
perform, but for various architectural reasons they don't fit into
gcc?