Add new interface that allows removal of some code from the code generators,

provides for future extensibility, might help the LLVA project avoid having to
hack their own LLI, and provides support required for the experimental Venus
project.

llvm-svn: 10620

include/llvm/CodeGen/IntrinsicLowering.h

@@ -0,0 +1,63 @@
+//===-- 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