llvm-6502/lib/CodeGen/SplitKit.h
Jakob Stoklund Olesen 5881799d0c Delete dead code after rematerializing.
LiveRangeEdit::eliminateDeadDefs() will eventually be used by coalescing,
splitting, and spilling for dead code elimination. It can delete chains of dead
instructions as long as there are no dependency loops.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@127287 91177308-0d34-0410-b5e6-96231b3b80d8
2011-03-08 22:46:11 +00:00

350 lines
13 KiB
C++

//===-------- SplitKit.h - Toolkit for splitting live ranges ----*- C++ -*-===//
//
// The LLVM Compiler Infrastructure
//
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
//
//===----------------------------------------------------------------------===//
//
// This file contains the SplitAnalysis class as well as mutator functions for
// live range splitting.
//
//===----------------------------------------------------------------------===//
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/IndexedMap.h"
#include "llvm/ADT/IntervalMap.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/CodeGen/SlotIndexes.h"
namespace llvm {
class ConnectedVNInfoEqClasses;
class LiveInterval;
class LiveIntervals;
class LiveRangeEdit;
class MachineInstr;
class MachineLoopInfo;
class MachineRegisterInfo;
class TargetInstrInfo;
class TargetRegisterInfo;
class VirtRegMap;
class VNInfo;
class raw_ostream;
/// At some point we should just include MachineDominators.h:
class MachineDominatorTree;
template <class NodeT> class DomTreeNodeBase;
typedef DomTreeNodeBase<MachineBasicBlock> MachineDomTreeNode;
/// SplitAnalysis - Analyze a LiveInterval, looking for live range splitting
/// opportunities.
class SplitAnalysis {
public:
const MachineFunction &MF;
const VirtRegMap &VRM;
const LiveIntervals &LIS;
const MachineLoopInfo &Loops;
const TargetInstrInfo &TII;
// Instructions using the the current register.
typedef SmallPtrSet<const MachineInstr*, 16> InstrPtrSet;
InstrPtrSet UsingInstrs;
// Sorted slot indexes of using instructions.
SmallVector<SlotIndex, 8> UseSlots;
// The number of instructions using CurLI in each basic block.
typedef DenseMap<const MachineBasicBlock*, unsigned> BlockCountMap;
BlockCountMap UsingBlocks;
/// Additional information about basic blocks where the current variable is
/// live. Such a block will look like one of these templates:
///
/// 1. | o---x | Internal to block. Variable is only live in this block.
/// 2. |---x | Live-in, kill.
/// 3. | o---| Def, live-out.
/// 4. |---x o---| Live-in, kill, def, live-out.
/// 5. |---o---o---| Live-through with uses or defs.
/// 6. |-----------| Live-through without uses. Transparent.
///
struct BlockInfo {
MachineBasicBlock *MBB;
SlotIndex Start; ///< Beginining of block.
SlotIndex Stop; ///< End of block.
SlotIndex FirstUse; ///< First instr using current reg.
SlotIndex LastUse; ///< Last instr using current reg.
SlotIndex Kill; ///< Interval end point inside block.
SlotIndex Def; ///< Interval start point inside block.
/// Last possible point for splitting live ranges.
SlotIndex LastSplitPoint;
bool Uses; ///< Current reg has uses or defs in block.
bool LiveThrough; ///< Live in whole block (Templ 5. or 6. above).
bool LiveIn; ///< Current reg is live in.
bool LiveOut; ///< Current reg is live out.
// Per-interference pattern scratch data.
bool OverlapEntry; ///< Interference overlaps entering interval.
bool OverlapExit; ///< Interference overlaps exiting interval.
};
/// Basic blocks where var is live. This array is parallel to
/// SpillConstraints.
SmallVector<BlockInfo, 8> LiveBlocks;
private:
// Current live interval.
const LiveInterval *CurLI;
// Sumarize statistics by counting instructions using CurLI.
void analyzeUses();
/// calcLiveBlockInfo - Compute per-block information about CurLI.
bool calcLiveBlockInfo();
/// canAnalyzeBranch - Return true if MBB ends in a branch that can be
/// analyzed.
bool canAnalyzeBranch(const MachineBasicBlock *MBB);
public:
SplitAnalysis(const VirtRegMap &vrm, const LiveIntervals &lis,
const MachineLoopInfo &mli);
/// analyze - set CurLI to the specified interval, and analyze how it may be
/// split.
void analyze(const LiveInterval *li);
/// clear - clear all data structures so SplitAnalysis is ready to analyze a
/// new interval.
void clear();
/// getParent - Return the last analyzed interval.
const LiveInterval &getParent() const { return *CurLI; }
/// hasUses - Return true if MBB has any uses of CurLI.
bool hasUses(const MachineBasicBlock *MBB) const {
return UsingBlocks.lookup(MBB);
}
/// isOriginalEndpoint - Return true if the original live range was killed or
/// (re-)defined at Idx. Idx should be the 'def' slot for a normal kill/def,
/// and 'use' for an early-clobber def.
/// This can be used to recognize code inserted by earlier live range
/// splitting.
bool isOriginalEndpoint(SlotIndex Idx) const;
typedef SmallPtrSet<const MachineBasicBlock*, 16> BlockPtrSet;
// Print a set of blocks with use counts.
void print(const BlockPtrSet&, raw_ostream&) const;
/// getMultiUseBlocks - Add basic blocks to Blocks that may benefit from
/// having CurLI split to a new live interval. Return true if Blocks can be
/// passed to SplitEditor::splitSingleBlocks.
bool getMultiUseBlocks(BlockPtrSet &Blocks);
};
/// SplitEditor - Edit machine code and LiveIntervals for live range
/// splitting.
///
/// - Create a SplitEditor from a SplitAnalysis.
/// - Start a new live interval with openIntv.
/// - Mark the places where the new interval is entered using enterIntv*
/// - Mark the ranges where the new interval is used with useIntv*
/// - Mark the places where the interval is exited with exitIntv*.
/// - Finish the current interval with closeIntv and repeat from 2.
/// - Rewrite instructions with finish().
///
class SplitEditor {
SplitAnalysis &SA;
LiveIntervals &LIS;
VirtRegMap &VRM;
MachineRegisterInfo &MRI;
MachineDominatorTree &MDT;
const TargetInstrInfo &TII;
const TargetRegisterInfo &TRI;
/// Edit - The current parent register and new intervals created.
LiveRangeEdit *Edit;
/// Index into Edit of the currently open interval.
/// The index 0 is used for the complement, so the first interval started by
/// openIntv will be 1.
unsigned OpenIdx;
typedef IntervalMap<SlotIndex, unsigned> RegAssignMap;
/// Allocator for the interval map. This will eventually be shared with
/// SlotIndexes and LiveIntervals.
RegAssignMap::Allocator Allocator;
/// RegAssign - Map of the assigned register indexes.
/// Edit.get(RegAssign.lookup(Idx)) is the register that should be live at
/// Idx.
RegAssignMap RegAssign;
typedef DenseMap<std::pair<unsigned, unsigned>, VNInfo*> ValueMap;
/// Values - keep track of the mapping from parent values to values in the new
/// intervals. Given a pair (RegIdx, ParentVNI->id), Values contains:
///
/// 1. No entry - the value is not mapped to Edit.get(RegIdx).
/// 2. Null - the value is mapped to multiple values in Edit.get(RegIdx).
/// Each value is represented by a minimal live range at its def.
/// 3. A non-null VNInfo - the value is mapped to a single new value.
/// The new value has no live ranges anywhere.
ValueMap Values;
typedef std::pair<VNInfo*, MachineDomTreeNode*> LiveOutPair;
typedef IndexedMap<LiveOutPair, MBB2NumberFunctor> LiveOutMap;
// LiveOutCache - Map each basic block where a new register is live out to the
// live-out value and its defining block.
// One of these conditions shall be true:
//
// 1. !LiveOutCache.count(MBB)
// 2. LiveOutCache[MBB].second.getNode() == MBB
// 3. forall P in preds(MBB): LiveOutCache[P] == LiveOutCache[MBB]
//
// This is only a cache, the values can be computed as:
//
// VNI = Edit.get(RegIdx)->getVNInfoAt(LIS.getMBBEndIdx(MBB))
// Node = mbt_[LIS.getMBBFromIndex(VNI->def)]
//
// The cache is also used as a visited set by extendRange(). It can be shared
// by all the new registers because at most one is live out of each block.
LiveOutMap LiveOutCache;
// LiveOutSeen - Indexed by MBB->getNumber(), a bit is set for each valid
// entry in LiveOutCache.
BitVector LiveOutSeen;
/// defValue - define a value in RegIdx from ParentVNI at Idx.
/// Idx does not have to be ParentVNI->def, but it must be contained within
/// ParentVNI's live range in ParentLI. The new value is added to the value
/// map.
/// Return the new LI value.
VNInfo *defValue(unsigned RegIdx, const VNInfo *ParentVNI, SlotIndex Idx);
/// markComplexMapped - Mark ParentVNI as complex mapped in RegIdx regardless
/// of the number of defs.
void markComplexMapped(unsigned RegIdx, const VNInfo *ParentVNI);
/// defFromParent - Define Reg from ParentVNI at UseIdx using either
/// rematerialization or a COPY from parent. Return the new value.
VNInfo *defFromParent(unsigned RegIdx,
VNInfo *ParentVNI,
SlotIndex UseIdx,
MachineBasicBlock &MBB,
MachineBasicBlock::iterator I);
/// extendRange - Extend the live range of Edit.get(RegIdx) so it reaches Idx.
/// Insert PHIDefs as needed to preserve SSA form.
void extendRange(unsigned RegIdx, SlotIndex Idx);
/// updateSSA - Insert PHIDefs as necessary and update LiveOutCache such that
/// Edit.get(RegIdx) is live-in to all the blocks in LiveIn.
/// Return the value that is eventually live-in to IdxMBB.
VNInfo *updateSSA(unsigned RegIdx,
SmallVectorImpl<MachineDomTreeNode*> &LiveIn,
SlotIndex Idx,
const MachineBasicBlock *IdxMBB);
/// transferSimpleValues - Transfer simply defined values to the new ranges.
/// Return true if any complex ranges were skipped.
bool transferSimpleValues();
/// extendPHIKillRanges - Extend the ranges of all values killed by original
/// parent PHIDefs.
void extendPHIKillRanges();
/// rewriteAssigned - Rewrite all uses of Edit.getReg() to assigned registers.
void rewriteAssigned(bool ExtendRanges);
/// rewriteComponents - Rewrite all uses of Intv[0] according to the eq
/// classes in ConEQ.
/// This must be done when Intvs[0] is styill live at all uses, before calling
/// ConEq.Distribute().
void rewriteComponents(const SmallVectorImpl<LiveInterval*> &Intvs,
const ConnectedVNInfoEqClasses &ConEq);
/// deleteRematVictims - Delete defs that are dead after rematerializing.
void deleteRematVictims();
public:
/// Create a new SplitEditor for editing the LiveInterval analyzed by SA.
/// Newly created intervals will be appended to newIntervals.
SplitEditor(SplitAnalysis &SA, LiveIntervals&, VirtRegMap&,
MachineDominatorTree&);
/// reset - Prepare for a new split.
void reset(LiveRangeEdit&);
/// Create a new virtual register and live interval.
void openIntv();
/// enterIntvBefore - Enter the open interval before the instruction at Idx.
/// If the parent interval is not live before Idx, a COPY is not inserted.
/// Return the beginning of the new live range.
SlotIndex enterIntvBefore(SlotIndex Idx);
/// enterIntvAtEnd - Enter the open interval at the end of MBB.
/// Use the open interval from he inserted copy to the MBB end.
/// Return the beginning of the new live range.
SlotIndex enterIntvAtEnd(MachineBasicBlock &MBB);
/// useIntv - indicate that all instructions in MBB should use OpenLI.
void useIntv(const MachineBasicBlock &MBB);
/// useIntv - indicate that all instructions in range should use OpenLI.
void useIntv(SlotIndex Start, SlotIndex End);
/// leaveIntvAfter - Leave the open interval after the instruction at Idx.
/// Return the end of the live range.
SlotIndex leaveIntvAfter(SlotIndex Idx);
/// leaveIntvBefore - Leave the open interval before the instruction at Idx.
/// Return the end of the live range.
SlotIndex leaveIntvBefore(SlotIndex Idx);
/// leaveIntvAtTop - Leave the interval at the top of MBB.
/// Add liveness from the MBB top to the copy.
/// Return the end of the live range.
SlotIndex leaveIntvAtTop(MachineBasicBlock &MBB);
/// overlapIntv - Indicate that all instructions in range should use the open
/// interval, but also let the complement interval be live.
///
/// This doubles the register pressure, but is sometimes required to deal with
/// register uses after the last valid split point.
///
/// The Start index should be a return value from a leaveIntv* call, and End
/// should be in the same basic block. The parent interval must have the same
/// value across the range.
///
void overlapIntv(SlotIndex Start, SlotIndex End);
/// closeIntv - Indicate that we are done editing the currently open
/// LiveInterval, and ranges can be trimmed.
void closeIntv();
/// finish - after all the new live ranges have been created, compute the
/// remaining live range, and rewrite instructions to use the new registers.
void finish();
/// dump - print the current interval maping to dbgs().
void dump() const;
// ===--- High level methods ---===
/// splitSingleBlocks - Split CurLI into a separate live interval inside each
/// basic block in Blocks.
void splitSingleBlocks(const SplitAnalysis::BlockPtrSet &Blocks);
};
}