Coverage Report

Created: 2019-07-24 05:18

/Users/buildslave/jenkins/workspace/clang-stage2-coverage-R/llvm/lib/CodeGen/SpillPlacement.h
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//===- SpillPlacement.h - Optimal Spill Code Placement ---------*- 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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// This analysis computes the optimal spill code placement between basic blocks.
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//
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// The runOnMachineFunction() method only precomputes some profiling information
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// about the CFG. The real work is done by prepare(), addConstraints(), and
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// finish() which are called by the register allocator.
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//
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// Given a variable that is live across multiple basic blocks, and given
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// constraints on the basic blocks where the variable is live, determine which
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// edge bundles should have the variable in a register and which edge bundles
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// should have the variable in a stack slot.
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//
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// The returned bit vector can be used to place optimal spill code at basic
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// block entries and exits. Spill code placement inside a basic block is not
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// considered.
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//
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//===----------------------------------------------------------------------===//
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#ifndef LLVM_LIB_CODEGEN_SPILLPLACEMENT_H
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#define LLVM_LIB_CODEGEN_SPILLPLACEMENT_H
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#include "llvm/ADT/ArrayRef.h"
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#include "llvm/ADT/SmallVector.h"
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#include "llvm/ADT/SparseSet.h"
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#include "llvm/CodeGen/MachineFunctionPass.h"
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#include "llvm/Support/BlockFrequency.h"
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namespace llvm {
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class BitVector;
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class EdgeBundles;
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class MachineBlockFrequencyInfo;
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class MachineFunction;
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class MachineLoopInfo;
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class SpillPlacement : public MachineFunctionPass {
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  struct Node;
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  const MachineFunction *MF;
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  const EdgeBundles *bundles;
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  const MachineLoopInfo *loops;
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  const MachineBlockFrequencyInfo *MBFI;
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  Node *nodes = nullptr;
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  // Nodes that are active in the current computation. Owned by the prepare()
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  // caller.
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  BitVector *ActiveNodes;
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  // Nodes with active links. Populated by scanActiveBundles.
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  SmallVector<unsigned, 8> Linked;
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  // Nodes that went positive during the last call to scanActiveBundles or
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  // iterate.
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  SmallVector<unsigned, 8> RecentPositive;
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  // Block frequencies are computed once. Indexed by block number.
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  SmallVector<BlockFrequency, 8> BlockFrequencies;
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  /// Decision threshold. A node gets the output value 0 if the weighted sum of
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  /// its inputs falls in the open interval (-Threshold;Threshold).
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  BlockFrequency Threshold;
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  /// List of nodes that need to be updated in ::iterate.
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  SparseSet<unsigned> TodoList;
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public:
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  static char ID; // Pass identification, replacement for typeid.
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33.5k
  SpillPlacement() : MachineFunctionPass(ID) {}
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33.4k
  ~SpillPlacement() override { releaseMemory(); }
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  /// BorderConstraint - A basic block has separate constraints for entry and
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  /// exit.
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  enum BorderConstraint {
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    DontCare,  ///< Block doesn't care / variable not live.
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    PrefReg,   ///< Block entry/exit prefers a register.
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    PrefSpill, ///< Block entry/exit prefers a stack slot.
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    PrefBoth,  ///< Block entry prefers both register and stack.
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    MustSpill  ///< A register is impossible, variable must be spilled.
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  };
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  /// BlockConstraint - Entry and exit constraints for a basic block.
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  struct BlockConstraint {
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    unsigned Number;            ///< Basic block number (from MBB::getNumber()).
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    BorderConstraint Entry : 8; ///< Constraint on block entry.
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    BorderConstraint Exit : 8;  ///< Constraint on block exit.
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    /// True when this block changes the value of the live range. This means
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    /// the block has a non-PHI def.  When this is false, a live-in value on
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    /// the stack can be live-out on the stack without inserting a spill.
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    bool ChangesValue;
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  };
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  /// prepare - Reset state and prepare for a new spill placement computation.
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  /// @param RegBundles Bit vector to receive the edge bundles where the
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  ///                   variable should be kept in a register. Each bit
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  ///                   corresponds to an edge bundle, a set bit means the
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  ///                   variable should be kept in a register through the
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  ///                   bundle. A clear bit means the variable should be
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  ///                   spilled. This vector is retained.
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  void prepare(BitVector &RegBundles);
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  /// addConstraints - Add constraints and biases. This method may be called
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  /// more than once to accumulate constraints.
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  /// @param LiveBlocks Constraints for blocks that have the variable live in or
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  ///                   live out.
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  void addConstraints(ArrayRef<BlockConstraint> LiveBlocks);
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  /// addPrefSpill - Add PrefSpill constraints to all blocks listed.  This is
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  /// equivalent to calling addConstraint with identical BlockConstraints with
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  /// Entry = Exit = PrefSpill, and ChangesValue = false.
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  ///
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  /// @param Blocks Array of block numbers that prefer to spill in and out.
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  /// @param Strong When true, double the negative bias for these blocks.
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  void addPrefSpill(ArrayRef<unsigned> Blocks, bool Strong);
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  /// addLinks - Add transparent blocks with the given numbers.
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  void addLinks(ArrayRef<unsigned> Links);
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  /// scanActiveBundles - Perform an initial scan of all bundles activated by
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  /// addConstraints and addLinks, updating their state. Add all the bundles
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  /// that now prefer a register to RecentPositive.
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  /// Prepare internal data structures for iterate.
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  /// Return true is there are any positive nodes.
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  bool scanActiveBundles();
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  /// iterate - Update the network iteratively until convergence, or new bundles
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  /// are found.
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  void iterate();
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  /// getRecentPositive - Return an array of bundles that became positive during
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  /// the previous call to scanActiveBundles or iterate.
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16.9M
  ArrayRef<unsigned> getRecentPositive() { return RecentPositive; }
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  /// finish - Compute the optimal spill code placement given the
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  /// constraints. No MustSpill constraints will be violated, and the smallest
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  /// possible number of PrefX constraints will be violated, weighted by
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  /// expected execution frequencies.
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  /// The selected bundles are returned in the bitvector passed to prepare().
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  /// @return True if a perfect solution was found, allowing the variable to be
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  ///         in a register through all relevant bundles.
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  bool finish();
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  /// getBlockFrequency - Return the estimated block execution frequency per
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  /// function invocation.
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47.4M
  BlockFrequency getBlockFrequency(unsigned Number) const {
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47.4M
    return BlockFrequencies[Number];
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  }
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private:
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  bool runOnMachineFunction(MachineFunction &mf) override;
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  void getAnalysisUsage(AnalysisUsage &AU) const override;
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  void releaseMemory() override;
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  void activate(unsigned n);
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  void setThreshold(const BlockFrequency &Entry);
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  bool update(unsigned n);
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};
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} // end namespace llvm
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#endif // LLVM_LIB_CODEGEN_SPILLPLACEMENT_H