Add a bit IsUndef to MachineOperand. This indicates the def / use register operand is defined by an implicit_def. That means it can def / use any register and passes (e.g. register scavenger) can feel free to ignore them.

The register allocator, when it allocates a register to a virtual register defined by an implicit_def, can allocate any physical register without worrying about overlapping live ranges. It should mark all of operands of the said virtual register so later passes will do the right thing.

This is not the best solution. But it should be a lot less fragile to having the scavenger try to track what is defined by implicit_def.

llvm-svn: 74518

llvm-svn: 72880

Fix for PR4225: When rewriter reuse a value in a physical register , it clear the register kill operand marker and its kill ops information. However, the cleared operand may be a def of a super-register. Clear the kill ops info for the super-register's sub-registers as well.

llvm-svn: 72758

llvm-svn: 72729

llvm-svn: 71848

llvm-svn: 71606

llvm-svn: 71057