diff --git a/include/llvm/CodeGen/IntrinsicLowering.h b/include/llvm/CodeGen/IntrinsicLowering.h
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+++ b/include/llvm/CodeGen/IntrinsicLowering.h
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+//===-- llvm/CodeGen/IntrinsicLowering.h - Intrinsic Lowering ---*- C++ -*-===//
+// 
+//                     The LLVM Compiler Infrastructure
+//
+// This file was developed by the LLVM research group and is distributed under
+// the University of Illinois Open Source License. See LICENSE.TXT for details.
+// 
+//===----------------------------------------------------------------------===//
+// 
+// This file defines the IntrinsicLowering interface.  This interface allows
+// addition of domain-specific or front-end specific intrinsics to LLVM without
+// having to modify all of the target-machines to support the new intrinsic.
+// Later, as desired, code generators can incrementally add support for
+// particular intrinsic functions, as desired, to generate better code.
+//
+// If a code generator cannot handle or does not know about an intrinsic
+// function, it will use the intrinsic lowering interface to change an intrinsic
+// function name into a concrete function name which can be used to implement
+// the functionality of the intrinsic.  For example, llvm.acos can be
+// implemented as a call to the math library 'acos' function if the target
+// doesn't have hardware support for the intrinsic, or if it has not yet been
+// implemented yet.
+//
+// Another use for this interface is the addition of domain-specific intrinsics.
+// The default implementation of this interface would then lower the intrinsics
+// to noop calls, allowing the direct execution of programs with instrumentation
+// or other hooks placed in them.  When a specific tool or flag is used, a
+// different implementation of these interfaces may be used, which activates the
+// intrinsics in some way.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_INTRINSICLOWERING_H
+#define LLVM_CODEGEN_INTRINSICLOWERING_H
+
+namespace llvm {
+  class CallInst;
+  
+  struct IntrinsicLowering {
+
+    /// LowerIntrinsicCall - This method returns the LLVM function which should
+    /// be used to implement the specified intrinsic function call.  If an
+    /// intrinsic function must be implemented by the code generator (such as
+    /// va_start), this function should print a message and abort.
+    ///
+    /// Otherwise, if an intrinsic function call can be lowered, the code to
+    /// implement it (often a call to a non-intrinsic function) is inserted
+    /// _after_ the call instruction and the call is deleted.  The caller must
+    /// be capable of handling this kind of change.
+    ///
+    virtual void LowerIntrinsicCall(CallInst *CI) = 0;
+  };
+
+  /// DefaultIntrinsicLower - This is the default intrinsic lowering pass which
+  /// is used if no other one is specified.  Custom intrinsic lowering
+  /// implementations should pass any unhandled intrinsics to this
+  /// implementation to allow for future extensibility.
+  struct DefaultIntrinsicLowering : public IntrinsicLowering {
+    virtual void LowerIntrinsicCall(CallInst *CI);    
+  };
+}
+
+#endif