[LLVMdev] "Ran out of registers during register allocation" bug affecting ffmpeg

[Eli Friedman]

See http://llvm.org/bugs/show_bug.cgi?id=4668 and
http://llvm.org/bugs/show_bug.cgi?id=5010.  The basic description of
the issue (from http://llvm.org/bugs/show_bug.cgi?id=4668#c5): "The
fundamental problem is we can't spill a register once it's fixed to a
physical register."

>From discussion on IRC:

[17:14]	<_sabre_>	efriedma: sounds like a RA bug in linscan
[17:14]	<_sabre_>	unfortunately, it is a fairly well known bug that is
difficult to fix
[17:14]	<_sabre_>	it would be worth bringing up on llvmdev, there may
be a good approach since I stopped looking at the regalloc
[17:14]	<_sabre_>	in any case, its worth surfacing the issue so that
Jakob can keep it in mind as he's building the new RA infrastructure

-Eli