Merge r353031 from stable/12:

Merge r353031 from stable/12:

Pull in r357528 from upstream llvm trunk (by Craig Topper):

  [X86] Check MI.isConvertibleTo3Addr() before calling
  convertToThreeAddress in X86FixupLEAs.

  X86FixupLEAs just assumes convertToThreeAddress will return nullptr
  for any instruction that isn't convertible.

  But the code in convertToThreeAddress for X86 assumes that any
  instruction coming in has at least 2 operands and that the second one
  is a register. But those properties aren't guaranteed of all
  instructions. We should check the instruction property first.

Pull in r365720 from upstream llvm trunk (by Craig Topper):

  [X86] Don't convert 8 or 16 bit ADDs to LEAs on Atom in FixupLEAPass.

  We use the functions that convert to three address to do the
  conversion, but changing an 8 or 16 bit will cause it to create a
  virtual register. This can't be done after register allocation where
  this pass runs.

  I've switched the pass completely to a white list of instructions
  that can be converted to LEA instead of a blacklist that was
  incorrect. This will avoid surprises if we enhance the three address
  conversion function to include additional instructions in the future.

  Fixes PR42565.

This should fix assertions/segfaults when compiling certain ports with
CPUTYPE=atom.

Approved by:	re (kib)
PR:		240928