Allow overlaps between virtreg and physreg live ranges.
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
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