Turn a 2-address instruction into a 3-address one when it's profitable even if...

Turn a 2-address instruction into a 3-address one when it's profitable even if the two-address operand is killed.
e.g.
%reg1024<def> = MOV r1
%reg1025<def> = ADD %reg1024, %reg1026
r0            = MOV %reg1025

If it's not possible / profitable to commute ADD, then turning ADD into a LEA saves a copy.

llvm-svn: 68065