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//===---- LiveRangeCalc.h - Calculate live ranges ---------------*- C++ -*-===//
// The LLVM Compiler Infrastructure
// This file is distributed under the University of Illinois Open Source
// License. See LICENSE.TXT for details.
// The LiveRangeCalc class can be used to compute live ranges from scratch. It
// caches information about values in the CFG to speed up repeated operations
// on the same live range. The cache can be shared by non-overlapping live
// ranges. SplitKit uses that when computing the live range of split products.
// A low-level interface is available to clients that know where a variable is
// live, but don't know which value it has as every point. LiveRangeCalc will
// propagate values down the dominator tree, and even insert PHI-defs where
// needed. SplitKit uses this faster interface when possible.
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/IndexedMap.h"
#include "llvm/CodeGen/LiveInterval.h"
namespace llvm {
/// Forward declarations for MachineDominators.h:
class MachineDominatorTree;
template <class NodeT> class DomTreeNodeBase;
typedef DomTreeNodeBase<MachineBasicBlock> MachineDomTreeNode;
class LiveRangeCalc {
/// Seen - Bit vector of active entries in LiveOut, also used as a visited
/// set by findReachingDefs. One entry per basic block, indexed by block
/// number. This is kept as a separate bit vector because it can be cleared
/// quickly when switching live ranges.
BitVector Seen;
/// LiveOutPair - A value and the block that defined it. The domtree node is
/// redundant, it can be computed as: MDT[Indexes.getMBBFromIndex(VNI->def)].
typedef std::pair<VNInfo*, MachineDomTreeNode*> LiveOutPair;
/// LiveOutMap - Map basic blocks to the value leaving the block.
typedef IndexedMap<LiveOutPair, MBB2NumberFunctor> LiveOutMap;
/// LiveOut - Map each basic block where a live range is live out to the
/// live-out value and its defining block.
/// For every basic block, MBB, one of these conditions shall be true:
/// 1. !Seen.count(MBB->getNumber())
/// Blocks without a Seen bit are ignored.
/// 2. LiveOut[MBB].second.getNode() == MBB
/// The live-out value is defined in MBB.
/// 3. forall P in preds(MBB): LiveOut[P] == LiveOut[MBB]
/// The live-out value passses through MBB. All predecessors must carry
/// the same value.
/// The domtree node may be null, it can be computed.
/// The map can be shared by multiple live ranges as long as no two are
/// live-out of the same block.
LiveOutMap LiveOut;
/// LiveInBlock - Information about a basic block where a live range is known
/// to be live-in, but the value has not yet been determined.
struct LiveInBlock {
// LI - The live range that is live-in to this block. The algorithms can
// handle multiple non-overlapping live ranges simultaneously.
LiveInterval *LI;
// DomNode - Dominator tree node for the block.
// Cleared when the final value has been determined and LI has been updated.
MachineDomTreeNode *DomNode;
// Position in block where the live-in range ends, or SlotIndex() if the
// range passes through the block. When the final value has been
// determined, the range from the block start to Kill will be added to LI.
SlotIndex Kill;
// Live-in value filled in by updateSSA once it is known.
VNInfo *Value;
LiveInBlock(LiveInterval *li, MachineDomTreeNode *node, SlotIndex kill)
: LI(li), DomNode(node), Kill(kill), Value(0) {}
/// LiveIn - Work list of blocks where the live-in value has yet to be
/// determined. This list is typically computed by findReachingDefs() and
/// used as a work list by updateSSA(). The low-level interface may also be
/// used to add entries directly.
SmallVector<LiveInBlock, 16> LiveIn;
/// findReachingDefs - Assuming that LI is live-in to KillMBB and killed at
/// Kill, search for values that can reach KillMBB. All blocks that need LI
/// to be live-in are added to LiveIn. If a unique reaching def is found,
/// its value is returned, if Kill is jointly dominated by multiple values,
/// NULL is returned.
VNInfo *findReachingDefs(LiveInterval *LI,
MachineBasicBlock *KillMBB,
SlotIndex Kill,
SlotIndexes *Indexes,
MachineDominatorTree *DomTree);
/// updateSSA - Compute the values that will be live in to all requested
/// blocks in LiveIn. Create PHI-def values as required to preserve SSA form.
/// Every live-in block must be jointly dominated by the added live-out
/// blocks. No values are read from the live ranges.
void updateSSA(SlotIndexes *Indexes,
MachineDominatorTree *DomTree,
VNInfo::Allocator *Alloc);
/// updateLiveIns - Add liveness as specified in the LiveIn vector, using VNI
/// as a wildcard value for LiveIn entries without a value.
void updateLiveIns(VNInfo *VNI, SlotIndexes*);
// High-level interface.
// Calculate live ranges from scratch.
/// reset - Prepare caches for a new set of non-overlapping live ranges. The
/// caches must be reset before attempting calculations with a live range
/// that may overlap a previously computed live range, and before the first
/// live range in a function. If live ranges are not known to be
/// non-overlapping, call reset before each.
void reset(const MachineFunction *MF);
/// calculate - Calculate the live range of a virtual register from its defs
/// and uses. LI must be empty with no values.
void calculate(LiveInterval *LI,
MachineRegisterInfo *MRI,
SlotIndexes *Indexes,
VNInfo::Allocator *Alloc);
// Mid-level interface.
// Modify existing live ranges.
/// extend - Extend the live range of LI to reach Kill.
/// The existing values in LI must be live so they jointly dominate Kill. If
/// Kill is not dominated by a single existing value, PHI-defs are inserted
/// as required to preserve SSA form. If Kill is known to be dominated by a
/// single existing value, Alloc may be null.
void extend(LiveInterval *LI,
SlotIndex Kill,
SlotIndexes *Indexes,
MachineDominatorTree *DomTree,
VNInfo::Allocator *Alloc);
/// extendToUses - Extend the live range of LI to reach all uses.
/// All uses must be jointly dominated by existing liveness. PHI-defs are
/// inserted as needed to preserve SSA form.
void extendToUses(LiveInterval *LI,
MachineRegisterInfo *MRI,
SlotIndexes *Indexes,
MachineDominatorTree *DomTree,
VNInfo::Allocator *Alloc);
// Low-level interface.
// These functions can be used to compute live ranges where the live-in and
// live-out blocks are already known, but the SSA value in each block is
// unknown.
// After calling reset(), add known live-out values and known live-in blocks.
// Then call calculateValues() to compute the actual value that is
// live-in to each block, and add liveness to the live ranges.
/// setLiveOutValue - Indicate that VNI is live out from MBB. The
/// calculateValues() function will not add liveness for MBB, the caller
/// should take care of that.
/// VNI may be null only if MBB is a live-through block also passed to
/// addLiveInBlock().
void setLiveOutValue(MachineBasicBlock *MBB, VNInfo *VNI) {
LiveOut[MBB] = LiveOutPair(VNI, (MachineDomTreeNode *)0);
/// addLiveInBlock - Add a block with an unknown live-in value. This
/// function can only be called once per basic block. Once the live-in value
/// has been determined, calculateValues() will add liveness to LI.
/// @param LI The live range that is live-in to the block.
/// @param DomNode The domtree node for the block.
/// @param Kill Index in block where LI is killed. If the value is
/// live-through, set Kill = SLotIndex() and also call
/// setLiveOutValue(MBB, 0).
void addLiveInBlock(LiveInterval *LI,
MachineDomTreeNode *DomNode,
SlotIndex Kill = SlotIndex()) {
LiveIn.push_back(LiveInBlock(LI, DomNode, Kill));
/// calculateValues - Calculate the value that will be live-in to each block
/// added with addLiveInBlock. Add PHI-def values as needed to preserve SSA
/// form. Add liveness to all live-in blocks up to the Kill point, or the
/// whole block for live-through blocks.
/// Every predecessor of a live-in block must have been given a value with
/// setLiveOutValue, the value may be null for live-trough blocks.
void calculateValues(SlotIndexes *Indexes,
MachineDominatorTree *DomTree,
VNInfo::Allocator *Alloc);
} // end namespace llvm