Adding more arithmetic operators to MMX. This is an almost exact copy of
the addition. Please let me know if you have suggestions.

llvm-svn: 35055
diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 2ab5e08..4fecb70 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -331,6 +331,10 @@
     setOperationAction(ISD::ADD,                MVT::v4i16, Legal);
     setOperationAction(ISD::ADD,                MVT::v2i32, Legal);
 
+    setOperationAction(ISD::SUB,                MVT::v8i8,  Legal);
+    setOperationAction(ISD::SUB,                MVT::v4i16, Legal);
+    setOperationAction(ISD::SUB,                MVT::v2i32, Legal);
+
     setOperationAction(ISD::LOAD,               MVT::v8i8,  Promote);
     AddPromotedToType (ISD::LOAD,               MVT::v8i8,  MVT::v2i32);
     setOperationAction(ISD::LOAD,               MVT::v4i16, Promote);