[PATCH] Support invoking the patchpoint intrinsic

[Philip Reames]

I think patchpoints should be invokable.  I like the general direction, but have not reviewed the details of the patchpoint lowering changes.

================
Comment at: lib/CodeGen/SelectionDAG/SelectionDAGBuilder.cpp:2023
@@ -2020,1 +2022,3 @@
+    visitPatchpoint(ImmutableCallSite(&I));
+  } else if (Fn && Fn->isIntrinsic()) {
     assert(Fn->getIntrinsicID() == Intrinsic::donothing);
----------------
Extremely minor, but a code pattern of:
if ( is intrinsic) 
  switch(intrinsic_id) {
  case patchpoint, patchpoint_void:
     handPatchpoint(); 
     break
  case do_nothing: break;
  default: assert...
  }

Would be more idiomatic and easier to extend.

http://reviews.llvm.org/D5572