Extract live range calculations from SplitKit.

SplitKit will soon need two copies of these data structures, and the
algorithms will also be useful when LiveIntervalAnalysis becomes
independent of LiveVariables.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@139572 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 226 insertions, 0 deletions

diff --git a/lib/CodeGen/LiveRangeCalc.h b/lib/CodeGen/LiveRangeCalc.h
new file mode 100644
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+++ b/lib/CodeGen/LiveRangeCalc.h
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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.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef LLVM_CODEGEN_LIVERANGECALC_H
+#define LLVM_CODEGEN_LIVERANGECALC_H
+
+#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*);
+
+public:
+  //===--------------------------------------------------------------------===//
+  // 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) {
+    Seen.set(MBB->getNumber());
+    LiveOut[MBB] = LiveOutPair(VNI, 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
+
+#endif