[Bug rtl-optimization/49936] [4.7 Regression] IRA handles CANNOT_CHANGE_MODE_CLASS poorly, + spills to memory on 4.7

[vmakarov at redhat dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49936

--- Comment #2 from Vladimir Makarov <vmakarov at redhat dot com> 2011-08-16 02:05:02 UTC ---
After thorough investigation of the problem I came to a conclusion that fixing
it in IRA requires to form regions on pseudo mode usage too (besides just
register pressure).  Allocnos for the pseudo in question should get a different
classes (FP class inside loop and INT outside).

The problem is that IRA were written on assumption that register class of all
allocnos for a pseudo is the same.  It needs a lot of changes besides a new
code for forming regions on the mode base.

I'll try to do this but it will take long time.

If it does not work, I could try to restore 4.6 behaviour (assigning INT class
instead of memory).