[Bug rtl-optimization/66790] Invalid uninitialized register handling in REE

[bernds at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66790

--- Comment #18 from Bernd Schmidt <bernds at gcc dot gnu.org> ---
FWIW I did some googling to refresh my memory, and this may be helpful:

www.seas.harvard.edu/courses/cs252/2011sp/slides/Lec02-Dataflow.pdf

It looks like you want exactly the available expressions problem from page 26.
Maybe that's better terminology than must-initialized? (I'm not sure, but I'd
never heard the latter term before.)

I think I'm coming to the conclusion that df_live really does want what it
currently uses, which is the guarantee that there is _any_ def that reaches a
use. The commentary could use updating though, I think it clearly isn't
computing a "must" problem.

When updating the patch please ensure that all new parameters are documented
before the function.