[PATCH] [mips] Reserve $at and use it for frame pointer elimination.

[Daniel Sanders]

This patch unconditionally reserves a register in order to support the fairly rare case of a stack frame being larger than 64KB. My starting position is that this isn't the right thing to do

Why not create an emergency spill slot for the register scavenger to use when the stack frame is large? This should allow it to cope with this rare case without limiting the optimization of the common cases.

http://reviews.llvm.org/D6509