Coverage Report

Created: 2019-02-20 00:17

/Users/buildslave/jenkins/workspace/clang-stage2-coverage-R/llvm/include/llvm/CodeGen/GCStrategy.h
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//===- llvm/CodeGen/GCStrategy.h - Garbage collection -----------*- C++ -*-===//
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//
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// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
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// See https://llvm.org/LICENSE.txt for license information.
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// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
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//
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//===----------------------------------------------------------------------===//
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//
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// GCStrategy coordinates code generation algorithms and implements some itself
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// in order to generate code compatible with a target code generator as
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// specified in a function's 'gc' attribute. Algorithms are enabled by setting
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// flags in a subclass's constructor, and some virtual methods can be
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// overridden.
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//
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// GCStrategy is relevant for implementations using either gc.root or
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// gc.statepoint based lowering strategies, but is currently focused mostly on
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// options for gc.root.  This will change over time.
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//
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// When requested by a subclass of GCStrategy, the gc.root implementation will
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// populate GCModuleInfo and GCFunctionInfo with that about each Function in
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// the Module that opts in to garbage collection.  Specifically:
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//
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// - Safe points
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//   Garbage collection is generally only possible at certain points in code.
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//   GCStrategy can request that the collector insert such points:
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//
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//     - At and after any call to a subroutine
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//     - Before returning from the current function
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//     - Before backwards branches (loops)
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//
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// - Roots
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//   When a reference to a GC-allocated object exists on the stack, it must be
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//   stored in an alloca registered with llvm.gcoot.
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//
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// This information can used to emit the metadata tables which are required by
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// the target garbage collector runtime.
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//
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// When used with gc.statepoint, information about safepoint and roots can be
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// found in the binary StackMap section after code generation.  Safepoint
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// placement is currently the responsibility of the frontend, though late
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// insertion support is planned.  gc.statepoint does not currently support
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// custom stack map formats; such can be generated by parsing the standard
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// stack map section if desired.
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//
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// The read and write barrier support can be used with either implementation.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_CODEGEN_GCSTRATEGY_H
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#define LLVM_CODEGEN_GCSTRATEGY_H
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#include "llvm/ADT/None.h"
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#include "llvm/ADT/Optional.h"
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#include "llvm/Support/Registry.h"
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#include <string>
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namespace llvm {
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class Type;
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/// GCStrategy describes a garbage collector algorithm's code generation
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/// requirements, and provides overridable hooks for those needs which cannot
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/// be abstractly described.  GCStrategy objects must be looked up through
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/// the Function.  The objects themselves are owned by the Context and must
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/// be immutable.
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class GCStrategy {
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private:
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  friend class GCModuleInfo;
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  std::string Name;
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protected:
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  bool UseStatepoints = false; /// Uses gc.statepoints as opposed to gc.roots,
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                               /// if set, none of the other options can be
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                               /// anything but their default values.
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  bool NeededSafePoints = false;    ///< if set, calls are inferred to be safepoints
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  bool UsesMetadata = false;     ///< If set, backend must emit metadata tables.
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public:
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  GCStrategy();
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  virtual ~GCStrategy() = default;
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  /// Return the name of the GC strategy.  This is the value of the collector
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  /// name string specified on functions which use this strategy.
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  const std::string &getName() const { return Name; }
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  /// Returns true if this strategy is expecting the use of gc.statepoints,
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  /// and false otherwise.
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  bool useStatepoints() const { return UseStatepoints; }
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  /** @name Statepoint Specific Properties */
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  ///@{
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  /// If the type specified can be reliably distinguished, returns true for
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  /// pointers to GC managed locations and false for pointers to non-GC
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  /// managed locations.  Note a GCStrategy can always return 'None' (i.e. an
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  /// empty optional indicating it can't reliably distinguish.
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  virtual Optional<bool> isGCManagedPointer(const Type *Ty) const {
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    return None;
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  }
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  ///@}
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  /** @name GCRoot Specific Properties
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   * These properties and overrides only apply to collector strategies using
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   * GCRoot.
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   */
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  ///@{
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  /// True if safe points need to be inferred on call sites
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  bool needsSafePoints() const { return NeededSafePoints; }
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  /// If set, appropriate metadata tables must be emitted by the back-end
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  /// (assembler, JIT, or otherwise). For statepoint, this method is
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  /// currently unsupported.  The stackmap information can be found in the
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  /// StackMap section as described in the documentation.
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  bool usesMetadata() const { return UsesMetadata; }
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  ///@}
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};
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/// Subclasses of GCStrategy are made available for use during compilation by
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/// adding them to the global GCRegistry.  This can done either within the
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/// LLVM source tree or via a loadable plugin.  An example registeration
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/// would be:
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/// static GCRegistry::Add<CustomGC> X("custom-name",
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///        "my custom supper fancy gc strategy");
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///
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/// Note that to use a custom GCMetadataPrinter w/gc.roots, you must also
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/// register your GCMetadataPrinter subclass with the
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/// GCMetadataPrinterRegistery as well.
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using GCRegistry = Registry<GCStrategy>;
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} // end namespace llvm
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#endif // LLVM_CODEGEN_GCSTRATEGY_H