The RegisterCoalescer understands overlapping live ranges where one
register is defined as a copy of the other. With this change, register
allocators using LiveRegMatrix can do the same, at least for copies
between physical and virtual registers.

When a physreg is defined by a copy from a virtreg, allow those live
ranges to overlap:

  %CL<def> = COPY %vreg11:sub_8bit; GR32_ABCD:%vreg11
  %vreg13<def,tied1> = SAR32rCL %vreg13<tied0>, %CL<imp-use,kill>

We can assign %vreg11 to %ECX, overlapping the live range of %CL.

llvm-svn: 163336

Calling checkRegMaskInterference(VirtReg) checks if VirtReg crosses any
regmask operands, regardless of the registers they clobber.

llvm-svn: 158563

The LiveRegMatrix represents the live range of assigned virtual
registers in a Live interval union per register unit. This is not
fundamentally different from the interference tracking in RegAllocBase
that both RABasic and RAGreedy use.

The important differences are:

- LiveRegMatrix tracks interference per register unit instead of per
  physical register. This makes interference checks cheaper and
  assignments slightly more expensive. For example, the ARM D7 reigster
  has 24 aliases, so we would check 24 physregs before assigning to one.
  With unit-based interference, we check 2 units before assigning to 2
  units.

- LiveRegMatrix caches regmask interference checks. That is currently
  duplicated functionality in RABasic and RAGreedy.

- LiveRegMatrix is a pass which makes it possible to insert
  target-dependent passes between register allocation and rewriting.
  Such passes could tweak the register assignments with interference
  checking support from LiveRegMatrix.

Eventually, RABasic and RAGreedy will be switched to LiveRegMatrix.

llvm-svn: 158255