Optimize icmp involving addition better

Optimize icmp involving addition better

Allows LLVM to optimize sequences like the following:

%add = add nsw i32 %x, 1
%cmp = icmp sgt i32 %add, %y

into:

%cmp = icmp sge i32 %x, %y

as well as:

%add1 = add nsw i32 %x, 20
%add2 = add nsw i32 %y, 57
%cmp = icmp sge i32 %add1, %add2

into:

%add = add nsw i32 %y, 37
%cmp = icmp sle i32 %cmp, %x

llvm-svn: 179316