[X86FixupLEAs] Transform the sequence LEA/SUB to SUB/SUB
This patch transforms the sequence
lea (reg1, reg2), reg3 sub reg3, reg4
to two sub instructions
sub reg1, reg4 sub reg2, reg4
Similar optimization can also be applied to LEA/ADD sequence.
The modifications to TwoAddressInstructionPass is to ensure the operands of ADD
instruction has expected order (the dest register of LEA should be src register of ADD).
Differential Revision: https://reviews.llvm.org/D101970