Implement a complete type inference system for dag patterns, based on the

constraints defined in the DAG node definitions in the .td files.  This
allows us to infer (and check!) the types for all nodes in the current
ppc .td file.  For example, instead of:

Inst pattern EQV:       (set GPRC:i32:$rT, (xor (xor GPRC:i32:$rA, GPRC:i32:$rB), (imm)<<Predicate_immAllOnes>>))

we now fully infer:

Inst pattern EQV:       (set:void GPRC:i32:$rT, (xor:i32 (xor:i32 GPRC:i32:$rA, GPRC:i32:$rB), (imm:i32)<<Predicate_immAllOnes>>))

from:  (set GPRC:$rT, (not (xor GPRC:$rA, GPRC:$rB)))
llvm-svn: 23284