1. Helper function sameVarOrReg() also needs to return true if the two physical registers alias or overlap.  Otherwise advanced phi lowering may pick an incorrect ordering.

2. With -asm-verbose, redundant truncation assignments expressed as _mov instructions, like "mov cl, ecx", need to have their register use counts updated properly, so that the LIVEEND= annotations are correct.

3. The register allocator should consider suitably typed aliases when choosing a register preference.

4. When evicting a variable, the register allocator should decrement the use count of all aliases.

5. When saving/restoring callee-save registers in the prolog/epilog, map each register to its "canonical" register (e.g. %bl --> %ebx) and make sure each canonical register is only considered once.

6. Remove some unnecessary Variable::setMustHaveReg() calls.

7. When assigning bool results as a constant 0 or 1, use an 8-bit constant instead of 32-bit so that only the 8-bit register gets assigned.

BUG= none
TEST= make check, plus spec2k -asm-verbose output is unchanged
R=kschimpf@google.com

Review URL: https://codereview.chromium.org/1405643003 .