[PATCH] Add support for ARM modified immediate syntax

[Tim Northover]

Hi Mihai,

I think the approach is interesting, but a dead end. It cements the
duplicated instructions rather than moving towards unification.

http://llvm-reviews.chandlerc.com/D1432 *does* move that way (and also
converts "add r0, #0, #0" back into "add r0, #0" automatically).

That said, I did have a look at the code and spotted this:

+  static inline bool isSOImmCanonical(unsigned Val, unsigned Rot) {
+    if (Rot == 0) return true;
+    if (Val == 0 && Rot != 0) return false;
+    return (Val % 4) != 0;
+  }

This isn't quite right. "#1, #30" is not canonical, for example (I
only know this because I made the same mistake in my patch at first).

Cheers.

Tim.