Add the llvm.frameallocate and llvm.recoverframeallocation intrinsics

These intrinsics allow multiple functions to share a single stack
allocation from one function's call frame. The function with the
allocation may only perform one allocation, and it must be in the entry
block.

Functions accessing the allocation call llvm.recoverframeallocation with
the function whose frame they are accessing and a frame pointer from an
active call frame of that function.

These intrinsics are very difficult to inline correctly, so the
intention is that they be introduced rarely, or at least very late
during EH preparation.

Reviewers: echristo, andrew.w.kaylor

Differential Revision: http://reviews.llvm.org/D6493

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@225746 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/ISDOpcodes.h

@@ -72,6 +72,11 @@ namespace ISD {
     /// the parent's frame or return address, and so on.
     FRAMEADDR, RETURNADDR,
 
+    /// RECOVER_FRAME_ALLOC - Represents the llvm.recoverframeallocation
+    /// intrinsic. Materializes the offset from the frame pointer of another
+    /// function to the result of llvm.frameallocate.
+    RECOVER_FRAME_ALLOC,
+
     /// READ_REGISTER, WRITE_REGISTER - This node represents llvm.register on
     /// the DAG, which implements the named register global variables extension.
     READ_REGISTER,