//===- LiveRangeCalc.h - Calculate live ranges -----------------*- C++ -*-===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// The LiveRangeCalc class can be used to implement the computation of
// 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.
//
//===----------------------------------------------------------------------===//
#ifndef LLVM_CODEGEN_LIVERANGECALC_H
#define LLVM_CODEGEN_LIVERANGECALC_H
#include "llvm/ADT/ArrayRef.h"
#include "llvm/ADT/BitVector.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/IndexedMap.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/CodeGen/LiveInterval.h"
#include "llvm/CodeGen/MachineBasicBlock.h"
#include "llvm/CodeGen/SlotIndexes.h"
#include <utility>
namespace llvm {
template <class NodeT> class DomTreeNodeBase;
class MachineDominatorTree;
class MachineFunction;
class MachineRegisterInfo;
using MachineDomTreeNode = DomTreeNodeBase<MachineBasicBlock>;
class LiveRangeCalc {
const MachineFunction *MF = nullptr;
const MachineRegisterInfo *MRI = nullptr;
SlotIndexes *Indexes = nullptr;
MachineDominatorTree *DomTree = nullptr;
VNInfo::Allocator *Alloc = nullptr;
/// LiveOutPair - A value and the block that defined it. The domtree node is
/// redundant, it can be computed as: MDT[Indexes.getMBBFromIndex(VNI->def)].
using LiveOutPair = std::pair<VNInfo *, MachineDomTreeNode *>;
/// LiveOutMap - Map basic blocks to the value leaving the block.
using LiveOutMap = IndexedMap<LiveOutPair, MBB2NumberFunctor>;
/// 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;
/// Map LiveRange to sets of blocks (represented by bit vectors) that
/// in the live range are defined on entry and undefined on entry.
/// A block is defined on entry if there is a path from at least one of
/// the defs in the live range to the entry of the block, and conversely,
/// a block is undefined on entry, if there is no such path (i.e. no
/// definition reaches the entry of the block). A single LiveRangeCalc
/// object is used to track live-out information for multiple registers
/// in live range splitting (which is ok, since the live ranges of these
/// registers do not overlap), but the defined/undefined information must
/// be kept separate for each individual range.
/// By convention, EntryInfoMap[&LR] = { Defined, Undefined }.
using EntryInfoMap = DenseMap<LiveRange *, std::pair<BitVector, BitVector>>;
EntryInfoMap EntryInfos;
/// 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 Map;
/// 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 {
// The live range set that is live-in to this block. The algorithms can
// handle multiple non-overlapping live ranges simultaneously.
LiveRange &LR;
// 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 = nullptr;
LiveInBlock(LiveRange &LR, MachineDomTreeNode *node, SlotIndex kill)
: LR(LR), DomNode(node), Kill(kill) {}
};
/// 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;
/// Check if the entry to block @p MBB can be reached by any of the defs
/// in @p LR. Return true if none of the defs reach the entry to @p MBB.
bool isDefOnEntry(LiveRange &LR, ArrayRef<SlotIndex> Undefs,
MachineBasicBlock &MBB, BitVector &DefOnEntry,
BitVector &UndefOnEntry);
/// Find the set of defs that can reach @p Kill. @p Kill must belong to
/// @p UseMBB.
///
/// If exactly one def can reach @p UseMBB, and the def dominates @p Kill,
/// all paths from the def to @p UseMBB are added to @p LR, and the function
/// returns true.
///
/// If multiple values can reach @p UseMBB, the blocks that need @p LR to be
/// live in are added to the LiveIn array, and the function returns false.
///
/// The array @p Undef provides the locations where the range @p LR becomes
/// undefined by <def,read-undef> operands on other subranges. If @p Undef
/// is non-empty and @p Kill is jointly dominated only by the entries of
/// @p Undef, the function returns false.
///
/// PhysReg, when set, is used to verify live-in lists on basic blocks.
bool findReachingDefs(LiveRange &LR, MachineBasicBlock &UseMBB, SlotIndex Use,
unsigned PhysReg, ArrayRef<SlotIndex> Undefs);
/// 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();
/// Transfer information from the LiveIn vector to the live ranges and update
/// the given @p LiveOuts.
void updateFromLiveIns();
protected:
/// Some getters to expose in a read-only way some private fields to
/// subclasses.
const MachineFunction *getMachineFunction() { return MF; }
const MachineRegisterInfo *getRegInfo() const { return MRI; }
SlotIndexes *getIndexes() { return Indexes; }
MachineDominatorTree *getDomTree() { return DomTree; }
VNInfo::Allocator *getVNAlloc() { return Alloc; }
/// Reset Map and Seen fields.
void resetLiveOutMap();
public:
LiveRangeCalc() = default;
//===--------------------------------------------------------------------===//
// 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, SlotIndexes *SI,
MachineDominatorTree *MDT, VNInfo::Allocator *VNIA);
//===--------------------------------------------------------------------===//
// Mid-level interface.
//===--------------------------------------------------------------------===//
//
// Modify existing live ranges.
//
/// Extend the live range of @p LR to reach @p Use.
///
/// The existing values in @p LR must be live so they jointly dominate @p Use.
/// If @p Use is not dominated by a single existing value, PHI-defs are
/// inserted as required to preserve SSA form.
///
/// PhysReg, when set, is used to verify live-in lists on basic blocks.
void extend(LiveRange &LR, SlotIndex Use, unsigned PhysReg,
ArrayRef<SlotIndex> Undefs);
//===--------------------------------------------------------------------===//
// 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) {
Seen.set(MBB->getNumber());
Map[MBB] = LiveOutPair(VNI, nullptr);
}
/// 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 LR 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(LiveRange &LR, MachineDomTreeNode *DomNode,
SlotIndex Kill = SlotIndex()) {
LiveIn.push_back(LiveInBlock(LR, 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();
/// A diagnostic function to check if the end of the block @p MBB is
/// jointly dominated by the blocks corresponding to the slot indices
/// in @p Defs. This function is mainly for use in self-verification
/// checks.
LLVM_ATTRIBUTE_UNUSED
static bool isJointlyDominated(const MachineBasicBlock *MBB,
ArrayRef<SlotIndex> Defs,
const SlotIndexes &Indexes);
};
} // end namespace llvm
#endif // LLVM_CODEGEN_LIVERANGECALC_H