What is `-fsee` in GCC?

Question

I was surprised to find that this flag gave no error:

g++ -fsee foo.cpp

whereas -fasdf, as well as any other unknown flag gives an error. I'm unable to find it in man gcc as well as the online manual. Try online for GCC 6.1.0 and 4.8. It also works on 5.3.1 (my machine).

It has a -fno-see counterpart like most flags.

Does anyone know what this flag does or where I can find documentation for it?

Answer 1

From here

-fsee Eliminate redundant sign extension instructions and move the non-redundant ones to optimal placement using lazy code motion ( LCM ).

Other options imply the letters stand for "sign extension elimination":

-fdump-rtl-see Dump after sign extension elimination.