For completeness, generalize the (X + Y) - Y -> X transform and add X - (X + 1) -> -1.

These were not recommended by my auto-simplifier since they don't fire often enough.
However they do fire from time to time, for example they remove one subtraction from
the final bitcode for 483.xalancbmk.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@123755 91177308-0d34-0410-b5e6-96231b3b80d8

test/Transforms/InstSimplify/2010-12-20-Reassociate.ll

@@ -70,3 +70,23 @@ define i32 @sub1(i32 %x, i32 %y) {
   ret i32 %r
 ; CHECK: ret i32 %y
 }
+
+define i32 @sub2(i32 %x) {
+; CHECK: @sub2
+; X - (X + 1) -> -1
+  %xp1 = add i32 %x, 1
+  %r = sub i32 %x, %xp1
+  ret i32 %r
+; CHECK: ret i32 -1
+}
+
+define i32 @sub3(i32 %x, i32 %y) {
+; CHECK: @sub3
+; ((X + 1) + Y) - (Y + 1) -> X
+  %xp1 = add i32 %x, 1
+  %lhs = add i32 %xp1, %y
+  %rhs = add i32 %y, 1
+  %r = sub i32 %lhs, %rhs
+  ret i32 %r
+; CHECK: ret i32 %x
+}