[Intrinsic] Signed Saturation Addition Intrinsic

Add an intrinsic that takes 2 integers and perform saturation addition on them.

This is a part of implementing fixed point arithmetic in clang where some of
the more complex operations will be implemented as intrinsics.

Differential Revision: https://reviews.llvm.org/D53053

llvm-svn: 344629
diff --git a/llvm/lib/CodeGen/TargetLoweringBase.cpp b/llvm/lib/CodeGen/TargetLoweringBase.cpp
index b785fdc..03a29a3 100644
--- a/llvm/lib/CodeGen/TargetLoweringBase.cpp
+++ b/llvm/lib/CodeGen/TargetLoweringBase.cpp
@@ -608,6 +608,7 @@
     setOperationAction(ISD::UMIN, VT, Expand);
     setOperationAction(ISD::UMAX, VT, Expand);
     setOperationAction(ISD::ABS, VT, Expand);
+    setOperationAction(ISD::SADDSAT, VT, Expand);
 
     // Overflow operations default to expand
     setOperationAction(ISD::SADDO, VT, Expand);