forked from OSchip/llvm-project
106 lines
4.1 KiB
C++
106 lines
4.1 KiB
C++
//===-- 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 placeSpills() which is 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/CodeGen/MachineFunctionPass.h"
|
|
|
|
namespace llvm {
|
|
|
|
class BitVector;
|
|
class EdgeBundles;
|
|
class MachineBasicBlock;
|
|
class MachineLoopInfo;
|
|
template <typename> class SmallVectorImpl;
|
|
|
|
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 placeSpills
|
|
// caller.
|
|
BitVector *ActiveNodes;
|
|
|
|
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.
|
|
};
|
|
|
|
/// placeSpills - 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.
|
|
/// @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.
|
|
/// @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.
|
|
/// @return True if a perfect solution was found, allowing the variable to be
|
|
/// in a register through all relevant bundles.
|
|
bool placeSpills(const SmallVectorImpl<BlockConstraint> &LiveBlocks,
|
|
BitVector &RegBundles);
|
|
|
|
private:
|
|
virtual bool runOnMachineFunction(MachineFunction&);
|
|
virtual void getAnalysisUsage(AnalysisUsage&) const;
|
|
virtual void releaseMemory();
|
|
|
|
void activate(unsigned);
|
|
float getBlockFrequency(const MachineBasicBlock*);
|
|
void prepareNodes(const SmallVectorImpl<BlockConstraint>&);
|
|
void iterate(const SmallVectorImpl<unsigned>&);
|
|
};
|
|
|
|
} // end namespace llvm
|
|
|
|
#endif
|