[PATCH] [x86] Make the x86 PACKSSWB, PACKSSDW, PACKUSWB, and PACKUSDW instructions available as synthetic SDNodes PACKSS and PACKUS that will select to the correct instruction variants based on the return type.

[Jim Grosbach]

This looks really good. Am I correct in assuming we already have testcases for codegen of these intrinsics and assembly/disassembly of all of the instructions modified?

A bit more in the commit message about why the instruction definitions are being split out from the multiclasses they currently use would be good. It looks like that's just a convenience thing due to them needing a different DAG node to match against. Is that right?

================
Comment at: lib/Target/X86/X86InstrSSE.td:4421
@@ -4434,1 +4420,3 @@
 //===---------------------------------------------------------------------===//
+// SSE - Packed Integer Pack Instructions
+//===---------------------------------------------------------------------===//
----------------
Nipick. These define far more than just the SSE2 instructions. Perhaps update the comment(s) to better reflect modern reality?

http://reviews.llvm.org/D4016