Add an I64Regs register class for 64-bit registers.

Add an I64Regs register class for 64-bit registers.

We are going to use the same registers for 32-bit and 64-bit values, but
in two different register classes. The I64Regs register class has a
larger spill size and alignment.

The addition of an i64 register class confuses TableGen's type
inference, so it is necessary to clarify the type of some immediates and
the G0 register.

In 64-bit mode, pointers are i64 and should use the I64Regs register
class. Implement getPointerRegClass() to dynamically provide the pointer
register class depending on the subtarget. Use ptr_rc and iPTR for
memory operands.

Finally, add the i64 type to the IntRegs register class. This register
class is not used to hold i64 values, I64Regs is for that. The type is
required to appease TableGen's type checking in output patterns like this:

  def : Pat<(add i64:$a, i64:$b), (ADDrr $a, $b)>;

SPARC v9 uses the same ADDrr instruction for i32 and i64 additions, and
TableGen doesn't know to check the type of register sub-classes.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@178522 91177308-0d34-0410-b5e6-96231b3b80d8