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thirdparty/clang/include/llvm/CodeGen/GCStrategy.h

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+//===-- llvm/CodeGen/GCStrategy.h - Garbage collection ----------*- C++ -*-===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
+// GCStrategy coordinates code generation algorithms and implements some itself
+// in order to generate code compatible with a target code generator as
+// specified in a function's 'gc' attribute. Algorithms are enabled by setting
+// flags in a subclass's constructor, and some virtual methods can be
+// overridden.
+// 
+// When requested, the GCStrategy will be populated with data about each
+// function which uses it. Specifically:
+// 
+// - Safe points
+//   Garbage collection is generally only possible at certain points in code.
+//   GCStrategy can request that the collector insert such 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 information can used to emit the metadata tables which are required by
+// the target garbage collector runtime.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_GCSTRATEGY_H
+#define LLVM_CODEGEN_GCSTRATEGY_H
+
+#include "llvm/CodeGen/GCMetadata.h"
+#include "llvm/CodeGen/MachineFunction.h"
+#include "llvm/Support/Registry.h"
+#include <string>
+
+namespace llvm {
+  
+  class GCStrategy;
+  
+  /// The GC strategy registry uses all the defaults from Registry.
+  /// 
+  typedef Registry<GCStrategy> GCRegistry;
+  
+  /// GCStrategy describes a garbage collector algorithm's code generation
+  /// requirements, and provides overridable hooks for those needs which cannot
+  /// be abstractly described.
+  class GCStrategy {
+  public:
+    typedef std::vector<GCFunctionInfo*> list_type;
+    typedef list_type::iterator iterator;
+    
+  private:
+    friend class GCModuleInfo;
+    const Module *M;
+    std::string Name;
+    
+    list_type Functions;
+    
+  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 CustomSafePoints;     ///< Default is to use NeededSafePoints
+                               ///< to find safe points.
+    bool InitRoots;            ///< If set, roots are nulled during lowering.
+    bool UsesMetadata;         ///< If set, backend must emit metadata tables.
+    
+  public:
+    GCStrategy();
+    
+    virtual ~GCStrategy();
+    
+    
+    /// getName - The name of the GC strategy, for debugging.
+    /// 
+    const std::string &getName() const { return Name; }
+
+    /// getModule - The module within which the GC strategy is operating.
+    /// 
+    const Module &getModule() const { return *M; }
+
+    /// needsSafePoitns - True if safe points of any kind are required. By
+    //                    default, none are recorded.
+    bool needsSafePoints() const {
+      return CustomSafePoints || NeededSafePoints != 0;
+    }
+    
+    /// needsSafePoint(Kind) - True if the given kind of safe point is
+    //                          required. By default, none are recorded.
+    bool needsSafePoint(GC::PointKind Kind) const {
+      return (NeededSafePoints & 1 << Kind) != 0;
+    }
+    
+    /// customWriteBarrier - By default, write barriers are replaced with simple
+    ///                      store instructions. If true, then
+    ///                      performCustomLowering must instead lower them.
+    bool customWriteBarrier() const { return CustomWriteBarriers; }
+    
+    /// customReadBarrier - By default, read barriers are replaced with simple
+    ///                     load instructions. If true, then
+    ///                     performCustomLowering must instead lower them.
+    bool customReadBarrier() const { return CustomReadBarriers; }
+    
+    /// customRoots - By default, roots are left for the code generator so it
+    ///               can generate a stack map. If true, then
+    //                performCustomLowering must delete them.
+    bool customRoots() const { return CustomRoots; }
+
+    /// customSafePoints - By default, the GC analysis will find safe
+    ///                    points according to NeededSafePoints. If true,
+    ///                    then findCustomSafePoints must create them.
+    bool customSafePoints() const { return CustomSafePoints; }
+    
+    /// initializeRoots - If set, gcroot intrinsics should initialize their
+    //                    allocas to null before the first use. This is
+    //                    necessary for most GCs and is enabled by default.
+    bool initializeRoots() const { return InitRoots; }
+    
+    /// usesMetadata - If set, appropriate metadata tables must be emitted by
+    ///                the back-end (assembler, JIT, or otherwise).
+    bool usesMetadata() const { return UsesMetadata; }
+    
+    /// begin/end - Iterators for function metadata.
+    /// 
+    iterator begin() { return Functions.begin(); }
+    iterator end()   { return Functions.end();   }
+
+    /// insertFunctionMetadata - Creates metadata for a function.
+    /// 
+    GCFunctionInfo *insertFunctionInfo(const Function &F);
+
+    /// initializeCustomLowering/performCustomLowering - If any of the actions
+    /// are set to custom, performCustomLowering must be overriden to transform
+    /// the corresponding actions to LLVM IR. initializeCustomLowering is
+    /// optional to override. These are the only GCStrategy methods through
+    /// which the LLVM IR can be modified.
+    virtual bool initializeCustomLowering(Module &F);
+    virtual bool performCustomLowering(Function &F);
+    virtual bool findCustomSafePoints(GCFunctionInfo& FI, MachineFunction& MF);
+  };
+  
+}
+
+#endif