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//===-- SpillPlacement.h - Optimal Spill Code Placement --------*- C++ -*--===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This analysis computes the optimal spill code placement between basic blocks.
//
// The runOnMachineFunction() method only precomputes some profiling information
// about the CFG. The real work is done by prepare(), addConstraints(), and
// finish() which are called by the register allocator.
//
// Given a variable that is live across multiple basic blocks, and given
// constraints on the basic blocks where the variable is live, determine which
// edge bundles should have the variable in a register and which edge bundles
// should have the variable in a stack slot.
//
// The returned bit vector can be used to place optimal spill code at basic
// block entries and exits. Spill code placement inside a basic block is not
// considered.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_CODEGEN_SPILLPLACEMENT_H
#define LLVM_CODEGEN_SPILLPLACEMENT_H
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/CodeGen/MachineFunctionPass.h"
namespace llvm {
class BitVector;
class EdgeBundles;
class MachineBasicBlock;
class MachineLoopInfo;
class SpillPlacement : public MachineFunctionPass {
struct Node;
const MachineFunction *MF;
const EdgeBundles *bundles;
const MachineLoopInfo *loops;
Node *nodes;
// Nodes that are active in the current computation. Owned by the prepare()
// caller.
BitVector *ActiveNodes;
// The number of active nodes with a positive bias.
unsigned PositiveNodes;
// Block frequencies are computed once. Indexed by block number.
SmallVector<float, 4> BlockFrequency;
public:
static char ID; // Pass identification, replacement for typeid.
SpillPlacement() : MachineFunctionPass(ID), nodes(0) {}
~SpillPlacement() { releaseMemory(); }
/// BorderConstraint - A basic block has separate constraints for entry and
/// exit.
enum BorderConstraint {
DontCare, ///< Block doesn't care / variable not live.
PrefReg, ///< Block entry/exit prefers a register.
PrefSpill, ///< Block entry/exit prefers a stack slot.
MustSpill ///< A register is impossible, variable must be spilled.
};
/// BlockConstraint - Entry and exit constraints for a basic block.
struct BlockConstraint {
unsigned Number; ///< Basic block number (from MBB::getNumber()).
BorderConstraint Entry : 8; ///< Constraint on block entry.
BorderConstraint Exit : 8; ///< Constraint on block exit.
};
/// prepare - Reset state and prepare for a new spill placement computation.
/// @param RegBundles Bit vector to receive the edge bundles where the
/// variable should be kept in a register. Each bit
/// corresponds to an edge bundle, a set bit means the
/// variable should be kept in a register through the
/// bundle. A clear bit means the variable should be
/// spilled. This vector is retained.
void prepare(BitVector &RegBundles);
/// addConstraints - Add constraints and biases. This method may be called
/// more than once to accumulate constraints.
/// @param LiveBlocks Constraints for blocks that have the variable live in or
/// live out. DontCare/DontCare means the variable is live
/// through the block. DontCare/X means the variable is live
/// out, but not live in.
void addConstraints(ArrayRef<BlockConstraint> LiveBlocks);
/// getPositiveNodes - Return the total number of graph nodes with a positive
/// bias after adding constraints.
unsigned getPositiveNodes() const { return PositiveNodes; }
/// finish - Compute the optimal spill code placement given the
/// constraints. No MustSpill constraints will be violated, and the smallest
/// possible number of PrefX constraints will be violated, weighted by
/// expected execution frequencies.
/// The selected bundles are returned in the bitvector passed to prepare().
/// @return True if a perfect solution was found, allowing the variable to be
/// in a register through all relevant bundles.
bool finish();
/// getBlockFrequency - Return the estimated block execution frequency per
/// function invocation.
float getBlockFrequency(unsigned Number) const {
return BlockFrequency[Number];
}
private:
virtual bool runOnMachineFunction(MachineFunction&);
virtual void getAnalysisUsage(AnalysisUsage&) const;
virtual void releaseMemory();
void activate(unsigned);
void iterate(const SmallVectorImpl<unsigned>&);
};
} // end namespace llvm
#endif
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