Collector is the base class for garbage collection code generators.

This version enhances the previous patch to add root initialization
as discussed here:

http://lists.cs.uiuc.edu/pipermail/llvm-commits/Week-of-Mon-20070910/053455.html

Collector gives its subclasses control over generic algorithms:

  unsigned NeededSafePoints; //< Bitmask of required safe points.
  bool CustomReadBarriers;   //< Default is to insert loads.
  bool CustomWriteBarriers;  //< Default is to insert stores.
  bool CustomRoots;          //< Default is to pass through to backend.
  bool InitRoots;            //< If set, roots are nulled during lowering.

It also has callbacks which collectors can hook:

  /// If any of the actions are set to Custom, this is expected to
  /// be overriden to create a transform to lower those actions to
  /// LLVM IR.
  virtual Pass *createCustomLoweringPass() const;

  /// beginAssembly/finishAssembly - Emit module metadata as
  /// assembly code.
  virtual void beginAssembly(Module &M, std::ostream &OS,
                             AsmPrinter &AP,
                             const TargetAsmInfo &TAI) const;
  virtual void finishAssembly(Module &M,
                              CollectorModuleMetadata &CMM,
                              std::ostream &OS, AsmPrinter &AP,
                              const TargetAsmInfo &TAI) const;  

Various other independent algorithms could be implemented, but were
not necessary for the initial two collectors. Some examples are
listed here:

http://llvm.org/docs/GarbageCollection.html#collector-algos


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@42466 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/CodeGen/Collector.h

@@ -0,0 +1,133 @@
+//===-- llvm/CodeGen/Collector.h - Garbage collection -----------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file was developed by Gordon Henriksen and is distributed under
+// the University of Illinois Open Source License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// GCInfo records sufficient information about a machine function to enable
+// accurate garbage collectors. Specifically:
+// 
+// - Safe points
+//   Garbage collection is only possible at certain points in code. Code
+//   generators should record points:
+//
+//     - At and after any call to a subroutine
+//     - Before returning from the current function
+//     - Before backwards branches (loops)
+// 
+// - Roots
+//   When a reference to a GC-allocated object exists on the stack, it must be
+//   stored in an alloca registered with llvm.gcoot.
+//
+// This generic information should used by ABI-specific passes to emit support
+// tables for the runtime garbage collector.
+//
+// GCSafePointPass identifies the GC safe points in the machine code. (Roots are
+// identified in SelectionDAGISel.)
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_COLLECTOR_H
+#define LLVM_CODEGEN_COLLECTOR_H
+
+#include "llvm/CodeGen/CollectorMetadata.h"
+#include <iosfwd>
+
+namespace llvm {
+  
+  class AsmPrinter;
+  class FunctionPassManager;
+  class PassManager;
+  class TargetAsmInfo;
+  
+  
+  /// Collector describes a garbage collector's code generation requirements,
+  /// and provides overridable hooks for those needs which cannot be abstractly
+  /// described.
+  class Collector {
+  protected:
+    unsigned NeededSafePoints; //< Bitmask of required safe points.
+    bool CustomReadBarriers;   //< Default is to insert loads.
+    bool CustomWriteBarriers;  //< Default is to insert stores.
+    bool CustomRoots;          //< Default is to pass through to backend.
+    bool InitRoots;            //< If set, roots are nulled during lowering.
+    
+    /// If any of the actions are set to Custom, this is expected to be
+    /// overriden to create a transform to lower those actions to LLVM IR.
+    virtual Pass *createCustomLoweringPass() const;
+    
+  public:
+    Collector();
+    
+    virtual ~Collector();
+    
+    
+    /// True if this collector requires safe points of any kind. By default,
+    /// none are recorded.
+    bool needsSafePoints() const { return NeededSafePoints != 0; }
+    
+    /// True if the collector requires the given kind of safe point. By default,
+    /// none are recorded.
+    bool needsSafePoint(GC::PointKind Kind) const {
+      return (NeededSafePoints & 1 << Kind) != 0;
+    }
+    
+    /// By default, write barriers are replaced with simple store instructions.
+    /// If true, then addPassesToCustomLowerIntrinsics must instead process
+    /// them.
+    bool customWriteBarrier() const { return CustomWriteBarriers; }
+    
+    /// By default, read barriers are replaced with simple load instructions.
+    /// If true, then addPassesToCustomLowerIntrinsics must instead process
+    /// them.
+    bool customReadBarrier() const { return CustomReadBarriers; }
+    
+    /// By default, roots are left for the code generator. If Custom, then 
+    /// addPassesToCustomLowerIntrinsics must add passes to delete them.
+    bool customRoots() const { return CustomRoots; }
+    
+    /// If set, gcroot intrinsics should initialize their allocas to null. This
+    /// is necessary for most collectors.
+    bool initializeRoots() const { return InitRoots; }
+    
+    
+    /// Adds LLVM IR transforms to handle collection intrinsics. By default,
+    /// read- and write barriers are replaced with direct memory accesses, and
+    /// roots are passed on to the code generator.
+    void addLoweringPasses(FunctionPassManager &PM) const;
+    
+    /// Same as addLoweringPasses(FunctionPassManager &), except uses a
+    /// PassManager for compatibility with unusual backends (such as MSIL or
+    /// CBackend).
+    void addLoweringPasses(PassManager &PM) const;
+    
+    /// Adds target-independent MachineFunction pass to mark safe points. This 
+    /// is added very late during code generation, just prior to output, and
+    /// importantly after all CFG transformations (like branch folding).
+    void addGenericMachineCodePass(FunctionPassManager &PM,
+                                   const TargetMachine &TM, bool Fast) const;
+    
+    /// beginAssembly/finishAssembly - Emit module metadata as assembly code.
+    virtual void beginAssembly(Module &M, std::ostream &OS, AsmPrinter &AP,
+                               const TargetAsmInfo &TAI) const;
+    virtual void finishAssembly(Module &M, CollectorModuleMetadata &CMM,
+                                std::ostream &OS, AsmPrinter &AP,
+                                const TargetAsmInfo &TAI) const;
+    
+  private:
+    bool NeedsDefaultLoweringPass() const;
+    bool NeedsCustomLoweringPass() const;
+    
+  };
+  
+  
+  /// If set, the code generator should generate garbage collection as specified
+  /// by the collector properties.
+  extern const Collector *TheCollector;  // FIXME: Find a better home!
+  
+}
+
+#endif