[Hexagon] Implement bit-tracking facility with specifics for Hexagon

This includes code that is intended to be target-independent as well
as the Hexagon-specific details. This is just the framework without
any users.

llvm-svn: 241595

lib/Target/Hexagon/BitTracker.h

@@ -0,0 +1,455 @@
+//===--- BitTracker.h -----------------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef BITTRACKER_H
+#define BITTRACKER_H
+
+#include "llvm/ADT/SetVector.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/CodeGen/MachineFunction.h"
+
+#include <map>
+#include <queue>
+#include <set>
+
+namespace llvm {
+  class ConstantInt;
+  class MachineRegisterInfo;
+  class MachineBasicBlock;
+  class MachineInstr;
+  class MachineOperand;
+  class raw_ostream;
+}
+
+struct BitTracker {
+  struct BitRef;
+  struct RegisterRef;
+  struct BitValue;
+  struct BitMask;
+  struct RegisterCell;
+  struct MachineEvaluator;
+
+  typedef llvm::SetVector<const llvm::MachineBasicBlock*> BranchTargetList;
+
+  struct CellMapType : public std::map<unsigned,RegisterCell> {
+    bool has(unsigned Reg) const;
+  };
+
+  BitTracker(const MachineEvaluator &E, llvm::MachineFunction &F);
+  ~BitTracker();
+
+  void run();
+  void trace(bool On = false) { Trace = On; }
+  bool has(unsigned Reg) const;
+  const RegisterCell &lookup(unsigned Reg) const;
+  RegisterCell get(RegisterRef RR) const;
+  void put(RegisterRef RR, const RegisterCell &RC);
+  void subst(RegisterRef OldRR, RegisterRef NewRR);
+  bool reached(const llvm::MachineBasicBlock *B) const;
+
+private:
+  void visitPHI(const llvm::MachineInstr *PI);
+  void visitNonBranch(const llvm::MachineInstr *MI);
+  void visitBranchesFrom(const llvm::MachineInstr *BI);
+  void visitUsesOf(unsigned Reg);
+  void reset();
+
+  typedef std::pair<int,int> CFGEdge;
+  typedef std::set<CFGEdge> EdgeSetType;
+  typedef std::set<const llvm::MachineInstr*> InstrSetType;
+  typedef std::queue<CFGEdge> EdgeQueueType;
+
+  EdgeSetType EdgeExec;       // Executable flow graph edges.
+  InstrSetType InstrExec;     // Executable instructions.
+  EdgeQueueType FlowQ;        // Work queue of CFG edges.
+  bool Trace;                 // Enable tracing for debugging.
+
+  const MachineEvaluator &ME;
+  llvm::MachineFunction &MF;
+  llvm::MachineRegisterInfo &MRI;
+  CellMapType &Map;
+};
+
+
+// Abstraction of a reference to bit at position Pos from a register Reg.
+struct BitTracker::BitRef {
+  BitRef(unsigned R = 0, uint16_t P = 0) : Reg(R), Pos(P) {}
+  BitRef(const BitRef &BR) : Reg(BR.Reg), Pos(BR.Pos) {}
+  bool operator== (const BitRef &BR) const {
+    // If Reg is 0, disregard Pos.
+    return Reg == BR.Reg && (Reg == 0 || Pos == BR.Pos);
+  }
+  unsigned Reg;
+  uint16_t Pos;
+};
+
+
+// Abstraction of a register reference in MachineOperand.  It contains the
+// register number and the subregister index.
+struct BitTracker::RegisterRef {
+  RegisterRef(unsigned R = 0, unsigned S = 0)
+    : Reg(R), Sub(S) {}
+  RegisterRef(const llvm::MachineOperand &MO)
+    : Reg(MO.getReg()), Sub(MO.getSubReg()) {}
+  unsigned Reg, Sub;
+};
+
+
+// Value that a single bit can take.  This is outside of the context of
+// any register, it is more of an abstraction of the two-element set of
+// possible bit values.  One extension here is the "Ref" type, which
+// indicates that this bit takes the same value as the bit described by
+// RefInfo.
+struct BitTracker::BitValue {
+  enum ValueType {
+    Top,    // Bit not yet defined.
+    Zero,   // Bit = 0.
+    One,    // Bit = 1.
+    Ref     // Bit value same as the one described in RefI.
+    // Conceptually, there is no explicit "bottom" value: the lattice's
+    // bottom will be expressed as a "ref to itself", which, in the context
+    // of registers, could be read as "this value of this bit is defined by
+    // this bit".
+    // The ordering is:
+    //   x <= Top,
+    //   Self <= x, where "Self" is "ref to itself".
+    // This makes the value lattice different for each virtual register
+    // (even for each bit in the same virtual register), since the "bottom"
+    // for one register will be a simple "ref" for another register.
+    // Since we do not store the "Self" bit and register number, the meet
+    // operation will need to take it as a parameter.
+    //
+    // In practice there is a special case for values that are not associa-
+    // ted with any specific virtual register. An example would be a value
+    // corresponding to a bit of a physical register, or an intermediate
+    // value obtained in some computation (such as instruction evaluation).
+    // Such cases are identical to the usual Ref type, but the register
+    // number is 0. In such case the Pos field of the reference is ignored.
+    //
+    // What is worthy of notice is that in value V (that is a "ref"), as long
+    // as the RefI.Reg is not 0, it may actually be the same register as the
+    // one in which V will be contained.  If the RefI.Pos refers to the posi-
+    // tion of V, then V is assumed to be "bottom" (as a "ref to itself"),
+    // otherwise V is taken to be identical to the referenced bit of the
+    // same register.
+    // If RefI.Reg is 0, however, such a reference to the same register is
+    // not possible.  Any value V that is a "ref", and whose RefI.Reg is 0
+    // is treated as "bottom".
+  };
+  ValueType Type;
+  BitRef RefI;
+
+  BitValue(ValueType T = Top) : Type(T) {}
+  BitValue(bool B) : Type(B ? One : Zero) {}
+  BitValue(const BitValue &V) : Type(V.Type), RefI(V.RefI) {}
+  BitValue(unsigned Reg, uint16_t Pos) : Type(Ref), RefI(Reg, Pos) {}
+
+  bool operator== (const BitValue &V) const {
+    if (Type != V.Type)
+      return false;
+    if (Type == Ref && !(RefI == V.RefI))
+      return false;
+    return true;
+  }
+  bool operator!= (const BitValue &V) const {
+    return !operator==(V);
+  }
+  bool is(unsigned T) const {
+    assert(T == 0 || T == 1);
+    return T == 0 ? Type == Zero
+                  : (T == 1 ? Type == One : false);
+  }
+
+  // The "meet" operation is the "." operation in a semilattice (L, ., T, B):
+  // (1)  x.x = x
+  // (2)  x.y = y.x
+  // (3)  x.(y.z) = (x.y).z
+  // (4)  x.T = x  (i.e. T = "top")
+  // (5)  x.B = B  (i.e. B = "bottom")
+  //
+  // This "meet" function will update the value of the "*this" object with
+  // the newly calculated one, and return "true" if the value of *this has
+  // changed, and "false" otherwise.
+  // To prove that it satisfies the conditions (1)-(5), it is sufficient
+  // to show that a relation
+  //   x <= y  <=>  x.y = x
+  // defines a partial order (i.e. that "meet" is same as "infimum").
+  bool meet(const BitValue &V, const BitRef &Self) {
+    // First, check the cases where there is nothing to be done.
+    if (Type == Ref && RefI == Self)    // Bottom.meet(V) = Bottom (i.e. This)
+      return false;
+    if (V.Type == Top)                  // This.meet(Top) = This
+      return false;
+    if (*this == V)                     // This.meet(This) = This
+      return false;
+
+    // At this point, we know that the value of "this" will change.
+    // If it is Top, it will become the same as V, otherwise it will
+    // become "bottom" (i.e. Self).
+    if (Type == Top) {
+      Type = V.Type;
+      RefI = V.RefI;  // This may be irrelevant, but copy anyway.
+      return true;
+    }
+    // Become "bottom".
+    Type = Ref;
+    RefI = Self;
+    return true;
+  }
+
+  // Create a reference to the bit value V.
+  static BitValue ref(const BitValue &V);
+  // Create a "self".
+  static BitValue self(const BitRef &Self = BitRef());
+
+  bool num() const {
+    return Type == Zero || Type == One;
+  }
+  operator bool() const {
+    assert(Type == Zero || Type == One);
+    return Type == One;
+  }
+
+  friend llvm::raw_ostream &operator<< (llvm::raw_ostream &OS,
+                                        const BitValue &BV);
+};
+
+
+// This operation must be idempotent, i.e. ref(ref(V)) == ref(V).
+inline BitTracker::BitValue
+BitTracker::BitValue::ref(const BitValue &V) {
+  if (V.Type != Ref)
+    return BitValue(V.Type);
+  if (V.RefI.Reg != 0)
+    return BitValue(V.RefI.Reg, V.RefI.Pos);
+  return self();
+}
+
+
+inline BitTracker::BitValue
+BitTracker::BitValue::self(const BitRef &Self) {
+  return BitValue(Self.Reg, Self.Pos);
+}
+
+
+// A sequence of bits starting from index B up to and including index E.
+// If E < B, the mask represents two sections: [0..E] and [B..W) where
+// W is the width of the register.
+struct BitTracker::BitMask {
+  BitMask() : B(0), E(0) {}
+  BitMask(uint16_t b, uint16_t e) : B(b), E(e) {}
+  uint16_t first() const { return B; }
+  uint16_t last() const { return E; }
+private:
+  uint16_t B, E;
+};
+
+
+// Representation of a register: a list of BitValues.
+struct BitTracker::RegisterCell {
+  RegisterCell(uint16_t Width = DefaultBitN) : Bits(Width) {}
+
+  uint16_t width() const {
+    return Bits.size();
+  }
+  const BitValue &operator[](uint16_t BitN) const {
+    assert(BitN < Bits.size());
+    return Bits[BitN];
+  }
+  BitValue &operator[](uint16_t BitN) {
+    assert(BitN < Bits.size());
+    return Bits[BitN];
+  }
+
+  bool meet(const RegisterCell &RC, unsigned SelfR);
+  RegisterCell &insert(const RegisterCell &RC, const BitMask &M);
+  RegisterCell extract(const BitMask &M) const;  // Returns a new cell.
+  RegisterCell &rol(uint16_t Sh);    // Rotate left.
+  RegisterCell &fill(uint16_t B, uint16_t E, const BitValue &V);
+  RegisterCell &cat(const RegisterCell &RC);  // Concatenate.
+  uint16_t cl(bool B) const;
+  uint16_t ct(bool B) const;
+
+  bool operator== (const RegisterCell &RC) const;
+  bool operator!= (const RegisterCell &RC) const {
+    return !operator==(RC);
+  }
+
+  const RegisterCell &operator=(const RegisterCell &RC) {
+    Bits = RC.Bits;
+    return *this;
+  }
+
+  // Generate a "ref" cell for the corresponding register. In the resulting
+  // cell each bit will be described as being the same as the corresponding
+  // bit in register Reg (i.e. the cell is "defined" by register Reg).
+  static RegisterCell self(unsigned Reg, uint16_t Width);
+  // Generate a "top" cell of given size.
+  static RegisterCell top(uint16_t Width);
+  // Generate a cell that is a "ref" to another cell.
+  static RegisterCell ref(const RegisterCell &C);
+
+private:
+  // The DefaultBitN is here only to avoid frequent reallocation of the
+  // memory in the vector.
+  static const unsigned DefaultBitN = 32;
+  typedef llvm::SmallVector<BitValue,DefaultBitN> BitValueList;
+  BitValueList Bits;
+
+  friend llvm::raw_ostream &operator<< (llvm::raw_ostream &OS,
+                                        const RegisterCell &RC);
+};
+
+
+inline bool BitTracker::has(unsigned Reg) const {
+  return Map.find(Reg) != Map.end();
+}
+
+
+inline const BitTracker::RegisterCell&
+BitTracker::lookup(unsigned Reg) const {
+  CellMapType::const_iterator F = Map.find(Reg);
+  assert(F != Map.end());
+  return F->second;
+}
+
+
+inline BitTracker::RegisterCell
+BitTracker::RegisterCell::self(unsigned Reg, uint16_t Width) {
+  RegisterCell RC(Width);
+  for (uint16_t i = 0; i < Width; ++i)
+    RC.Bits[i] = BitValue::self(BitRef(Reg, i));
+  return RC;
+}
+
+
+inline BitTracker::RegisterCell
+BitTracker::RegisterCell::top(uint16_t Width) {
+  RegisterCell RC(Width);
+  for (uint16_t i = 0; i < Width; ++i)
+    RC.Bits[i] = BitValue(BitValue::Top);
+  return RC;
+}
+
+
+inline BitTracker::RegisterCell
+BitTracker::RegisterCell::ref(const RegisterCell &C) {
+  uint16_t W = C.width();
+  RegisterCell RC(W);
+  for (unsigned i = 0; i < W; ++i)
+    RC[i] = BitValue::ref(C[i]);
+  return RC;
+}
+
+
+inline bool BitTracker::CellMapType::has(unsigned Reg) const {
+  return find(Reg) != end();
+}
+
+
+// A class to evaluate target's instructions and update the cell maps.
+// This is used internally by the bit tracker.  A target that wants to
+// utilize this should implement the evaluation functions (noted below)
+// in a subclass of this class.
+struct BitTracker::MachineEvaluator {
+  MachineEvaluator(const llvm::TargetRegisterInfo &T,
+        llvm::MachineRegisterInfo &M) : TRI(T), MRI(M) {}
+  virtual ~MachineEvaluator() {}
+
+  uint16_t getRegBitWidth(const RegisterRef &RR) const;
+
+  RegisterCell getCell(const RegisterRef &RR, const CellMapType &M) const;
+  void putCell(const RegisterRef &RR, RegisterCell RC, CellMapType &M) const;
+  // A result of any operation should use refs to the source cells, not
+  // the cells directly. This function is a convenience wrapper to quickly
+  // generate a ref for a cell corresponding to a register reference.
+  RegisterCell getRef(const RegisterRef &RR, const CellMapType &M) const {
+    RegisterCell RC = getCell(RR, M);
+    return RegisterCell::ref(RC);
+  }
+
+  // Helper functions.
+  // Check if a cell is an immediate value (i.e. all bits are either 0 or 1).
+  bool isInt(const RegisterCell &A) const;
+  // Convert cell to an immediate value.
+  uint64_t toInt(const RegisterCell &A) const;
+
+  // Generate cell from an immediate value.
+  RegisterCell eIMM(int64_t V, uint16_t W) const;
+  RegisterCell eIMM(const llvm::ConstantInt *CI) const;
+
+  // Arithmetic.
+  RegisterCell eADD(const RegisterCell &A1, const RegisterCell &A2) const;
+  RegisterCell eSUB(const RegisterCell &A1, const RegisterCell &A2) const;
+  RegisterCell eMLS(const RegisterCell &A1, const RegisterCell &A2) const;
+  RegisterCell eMLU(const RegisterCell &A1, const RegisterCell &A2) const;
+
+  // Shifts.
+  RegisterCell eASL(const RegisterCell &A1, uint16_t Sh) const;
+  RegisterCell eLSR(const RegisterCell &A1, uint16_t Sh) const;
+  RegisterCell eASR(const RegisterCell &A1, uint16_t Sh) const;
+
+  // Logical.
+  RegisterCell eAND(const RegisterCell &A1, const RegisterCell &A2) const;
+  RegisterCell eORL(const RegisterCell &A1, const RegisterCell &A2) const;
+  RegisterCell eXOR(const RegisterCell &A1, const RegisterCell &A2) const;
+  RegisterCell eNOT(const RegisterCell &A1) const;
+
+  // Set bit, clear bit.
+  RegisterCell eSET(const RegisterCell &A1, uint16_t BitN) const;
+  RegisterCell eCLR(const RegisterCell &A1, uint16_t BitN) const;
+
+  // Count leading/trailing bits (zeros/ones).
+  RegisterCell eCLB(const RegisterCell &A1, bool B, uint16_t W) const;
+  RegisterCell eCTB(const RegisterCell &A1, bool B, uint16_t W) const;
+
+  // Sign/zero extension.
+  RegisterCell eSXT(const RegisterCell &A1, uint16_t FromN) const;
+  RegisterCell eZXT(const RegisterCell &A1, uint16_t FromN) const;
+
+  // Extract/insert
+  // XTR R,b,e:  extract bits from A1 starting at bit b, ending at e-1.
+  // INS R,S,b:  take R and replace bits starting from b with S.
+  RegisterCell eXTR(const RegisterCell &A1, uint16_t B, uint16_t E) const;
+  RegisterCell eINS(const RegisterCell &A1, const RegisterCell &A2,
+                    uint16_t AtN) const;
+
+  // User-provided functions for individual targets:
+
+  // Return a sub-register mask that indicates which bits in Reg belong
+  // to the subregister Sub. These bits are assumed to be contiguous in
+  // the super-register, and have the same ordering in the sub-register
+  // as in the super-register. It is valid to call this function with
+  // Sub == 0, in this case, the function should return a mask that spans
+  // the entire register Reg (which is what the default implementation
+  // does).
+  virtual BitMask mask(unsigned Reg, unsigned Sub) const;
+  // Indicate whether a given register class should be tracked.
+  virtual bool track(const llvm::TargetRegisterClass *RC) const {
+    return true;
+  }
+  // Evaluate a non-branching machine instruction, given the cell map with
+  // the input values. Place the results in the Outputs map. Return "true"
+  // if evaluation succeeded, "false" otherwise.
+  virtual bool evaluate(const llvm::MachineInstr *MI,
+        const CellMapType &Inputs, CellMapType &Outputs) const;
+  // Evaluate a branch, given the cell map with the input values. Fill out
+  // a list of all possible branch targets and indicate (through a flag)
+  // whether the branch could fall-through. Return "true" if this information
+  // has been successfully computed, "false" otherwise.
+  virtual bool evaluate(const llvm::MachineInstr *BI,
+        const CellMapType &Inputs, BranchTargetList &Targets,
+        bool &FallsThru) const = 0;
+
+  const llvm::TargetRegisterInfo &TRI;
+  llvm::MachineRegisterInfo &MRI;
+};
+
+#endif
+

lib/Target/Hexagon/CMakeLists.txt

@@ -12,7 +12,9 @@ tablegen(LLVM HexagonGenSubtargetInfo.inc -gen-subtarget)
 add_public_tablegen_target(HexagonCommonTableGen)
 
 add_llvm_target(HexagonCodeGen
+  BitTracker.cpp
   HexagonAsmPrinter.cpp
+  HexagonBitTracker.cpp
   HexagonCFGOptimizer.cpp
   HexagonCopyToCombine.cpp
   HexagonExpandCondsets.cpp

lib/Target/Hexagon/HexagonBitTracker.h

@@ -0,0 +1,66 @@
+//===--- HexagonBitTracker.h ----------------------------------------------===//
+//
+//                     The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+
+#ifndef HEXAGONBITTRACKER_H
+#define HEXAGONBITTRACKER_H
+
+#include "BitTracker.h"
+#include "llvm/ADT/DenseMap.h"
+
+namespace llvm {
+  class HexagonInstrInfo;
+  class HexagonRegisterInfo;
+}
+
+struct HexagonEvaluator : public BitTracker::MachineEvaluator {
+  typedef BitTracker::CellMapType CellMapType;
+  typedef BitTracker::RegisterRef RegisterRef;
+  typedef BitTracker::RegisterCell RegisterCell;
+  typedef BitTracker::BranchTargetList BranchTargetList;
+
+  HexagonEvaluator(const llvm::HexagonRegisterInfo &tri,
+        llvm::MachineRegisterInfo &mri, const llvm::HexagonInstrInfo &tii,
+        llvm::MachineFunction &mf);
+
+  virtual bool evaluate(const llvm::MachineInstr *MI,
+        const CellMapType &Inputs, CellMapType &Outputs) const;
+  virtual bool evaluate(const llvm::MachineInstr *BI,
+        const CellMapType &Inputs, BranchTargetList &Targets,
+        bool &FallsThru) const;
+
+  virtual BitTracker::BitMask mask(unsigned Reg, unsigned Sub) const;
+
+  llvm::MachineFunction &MF;
+  llvm::MachineFrameInfo &MFI;
+  const llvm::HexagonInstrInfo &TII;
+
+private:
+  bool evaluateLoad(const llvm::MachineInstr *MI, const CellMapType &Inputs,
+        CellMapType &Outputs) const;
+  bool evaluateFormalCopy(const llvm::MachineInstr *MI,
+        const CellMapType &Inputs, CellMapType &Outputs) const;
+
+  unsigned getNextPhysReg(unsigned PReg, unsigned Width) const;
+  unsigned getVirtRegFor(unsigned PReg) const;
+
+  // Type of formal parameter extension.
+  struct ExtType {
+    enum { SExt, ZExt };
+    char Type;
+    uint16_t Width;
+    ExtType() : Type(0), Width(0) {}
+    ExtType(char t, uint16_t w) : Type(t), Width(w) {}
+  };
+  // Map VR -> extension type.
+  typedef llvm::DenseMap<unsigned,ExtType> RegExtMap;
+  RegExtMap VRX;
+};
+
+#endif
+