The two 3c LEA cases:
lea D(base, index,1) -> lea D(,index,2)
lea D(r13/rbp, index) -> lea D(,r13/rbp,2) // D maybe zero
Current take 2 instructions to transform. We can do a bit better by
using LEA w.o a base if base == index and scale == 1.
Reviewed By: pengfei
Differential Revision: https://reviews.llvm.org/D141980