Store sub-class lists as a bit vector.

This uses less memory and it reduces the complexity of sub-class
operations:

- hasSubClassEq() and friends become O(1) instead of O(N).

- getCommonSubClass() becomes O(N) instead of O(N^2).

In the future, TableGen will infer register classes.  This makes it
cheap to add them.

llvm-svn: 140898

llvm/include/llvm/Target/TargetRegisterInfo.h

@@ -40,17 +40,17 @@ public:
 private:
   const MCRegisterClass *MC;
   const vt_iterator VTs;
-  const sc_iterator SubClasses;
+  const unsigned *SubClassMask;
   const sc_iterator SuperClasses;
   const sc_iterator SubRegClasses;
   const sc_iterator SuperRegClasses;
 public:
   TargetRegisterClass(const MCRegisterClass *MC, const EVT *vts,
-                      const TargetRegisterClass * const *subcs,
+                      const unsigned *subcm,
                       const TargetRegisterClass * const *supcs,
                       const TargetRegisterClass * const *subregcs,
                       const TargetRegisterClass * const *superregcs)
-    : MC(MC), VTs(vts), SubClasses(subcs), SuperClasses(supcs),
+    : MC(MC), VTs(vts), SubClassMask(subcm), SuperClasses(supcs),
       SubRegClasses(subregcs), SuperRegClasses(superregcs) {}
 
   virtual ~TargetRegisterClass() {}     // Allow subclasses
@@ -159,59 +159,44 @@ public:
   }
 
   /// hasSubClass - return true if the specified TargetRegisterClass
-  /// is a proper subset of this TargetRegisterClass.
-  bool hasSubClass(const TargetRegisterClass *cs) const {
-    for (int i = 0; SubClasses[i] != NULL; ++i)
-      if (SubClasses[i] == cs)
-        return true;
-    return false;
+  /// is a proper sub-class of this TargetRegisterClass.
+  bool hasSubClass(const TargetRegisterClass *RC) const {
+    return RC != this && hasSubClassEq(RC);
   }
 
-  /// hasSubClassEq - Returns true if RC is a subclass of or equal to this
+  /// hasSubClassEq - Returns true if RC is a sub-class of or equal to this
   /// class.
   bool hasSubClassEq(const TargetRegisterClass *RC) const {
-    return RC == this || hasSubClass(RC);
-  }
-
-  /// subclasses_begin / subclasses_end - Loop over all of the classes
-  /// that are proper subsets of this register class.
-  sc_iterator subclasses_begin() const {
-    return SubClasses;
-  }
-
-  sc_iterator subclasses_end() const {
-    sc_iterator I = SubClasses;
-    while (*I != NULL) ++I;
-    return I;
+    unsigned ID = RC->getID();
+    return (SubClassMask[ID / 32] >> (ID % 32)) & 1;
   }
 
   /// hasSuperClass - return true if the specified TargetRegisterClass is a
-  /// proper superset of this TargetRegisterClass.
-  bool hasSuperClass(const TargetRegisterClass *cs) const {
-    for (int i = 0; SuperClasses[i] != NULL; ++i)
-      if (SuperClasses[i] == cs)
-        return true;
-    return false;
+  /// proper super-class of this TargetRegisterClass.
+  bool hasSuperClass(const TargetRegisterClass *RC) const {
+    return RC->hasSubClass(this);
   }
 
-  /// hasSuperClassEq - Returns true if RC is a superclass of or equal to this
+  /// hasSuperClassEq - Returns true if RC is a super-class of or equal to this
   /// class.
   bool hasSuperClassEq(const TargetRegisterClass *RC) const {
-    return RC == this || hasSuperClass(RC);
+    return RC->hasSubClassEq(this);
   }
 
-  /// superclasses_begin / superclasses_end - Loop over all of the classes
-  /// that are proper supersets of this register class.
-  sc_iterator superclasses_begin() const {
+  /// getSubClassMask - Returns a bit vector of subclasses, including this one.
+  /// The vector is indexed by class IDs, see hasSubClassEq() above for how to
+  /// use it.
+  const unsigned *getSubClassMask() const {
+    return SubClassMask;
+  }
+
+  /// getSuperClasses - Returns a NULL terminated list of super-classes.  The
+  /// classes are ordered by ID which is also a topological ordering from large
+  /// to small classes.  The list does NOT include the current class.
+  sc_iterator getSuperClasses() const {
     return SuperClasses;
   }
 
-  sc_iterator superclasses_end() const {
-    sc_iterator I = SuperClasses;
-    while (*I != NULL) ++I;
-    return I;
-  }
-
   /// isASubClass - return true if this TargetRegisterClass is a subset
   /// class of at least one other TargetRegisterClass.
   bool isASubClass() const {

llvm/lib/Target/ARM/ARMBaseRegisterInfo.cpp

@@ -353,7 +353,7 @@ const TargetRegisterClass*
 ARMBaseRegisterInfo::getLargestLegalSuperClass(const TargetRegisterClass *RC)
                                                                          const {
   const TargetRegisterClass *Super = RC;
-  TargetRegisterClass::sc_iterator I = RC->superclasses_begin();
+  TargetRegisterClass::sc_iterator I = RC->getSuperClasses();
   do {
     switch (Super->getID()) {
     case ARM::GPRRegClassID:

llvm/lib/Target/TargetRegisterInfo.cpp

@@ -100,42 +100,23 @@ BitVector TargetRegisterInfo::getAllocatableSet(const MachineFunction &MF,
 const TargetRegisterClass *
 TargetRegisterInfo::getCommonSubClass(const TargetRegisterClass *A,
                                       const TargetRegisterClass *B) const {
-  // First take care of the trivial cases
+  // First take care of the trivial cases.
   if (A == B)
     return A;
   if (!A || !B)
     return 0;
 
-  // If B is a subclass of A, it will be handled in the loop below
-  if (B->hasSubClass(A))
-    return A;
+  // Register classes are ordered topologically, so the largest common
+  // sub-class it the common sub-class with the smallest ID.
+  const unsigned *SubA = A->getSubClassMask();
+  const unsigned *SubB = B->getSubClassMask();
 
-  const TargetRegisterClass *Best = 0;
-  for (TargetRegisterClass::sc_iterator I = A->subclasses_begin();
-       const TargetRegisterClass *X = *I; ++I) {
-    if (X == B)
-      return B;                 // B is a subclass of A
+  // We could start the search from max(A.ID, B.ID), but we are only going to
+  // execute 2-3 iterations anyway.
+  for (unsigned Base = 0, BaseE = getNumRegClasses(); Base < BaseE; Base += 32)
+    if (unsigned Common = *SubA++ & *SubB++)
+      return getRegClass(Base + CountTrailingZeros_32(Common));
 
-    // X must be a common subclass of A and B
-    if (!B->hasSubClass(X))
-      continue;
-
-    // A superclass is definitely better.
-    if (!Best || Best->hasSuperClass(X)) {
-      Best = X;
-      continue;
-    }
-
-    // A subclass is definitely worse
-    if (Best->hasSubClass(X))
-      continue;
-
-    // Best and *I have no super/sub class relation - pick the larger class, or
-    // the smaller spill size.
-    int nb = std::distance(Best->begin(), Best->end());
-    int ni = std::distance(X->begin(), X->end());
-    if (ni>nb || (ni==nb && X->getSize() < Best->getSize()))
-      Best = X;
-  }
-  return Best;
+  // No common sub-class exists.
+  return NULL;
 }

llvm/lib/Target/X86/X86RegisterInfo.cpp

@@ -235,7 +235,7 @@ X86RegisterInfo::getMatchingSuperRegClass(const TargetRegisterClass *A,
 const TargetRegisterClass*
 X86RegisterInfo::getLargestLegalSuperClass(const TargetRegisterClass *RC) const{
   const TargetRegisterClass *Super = RC;
-  TargetRegisterClass::sc_iterator I = RC->superclasses_begin();
+  TargetRegisterClass::sc_iterator I = RC->getSuperClasses();
   do {
     switch (Super->getID()) {
     case X86::GR8RegClassID:

llvm/utils/TableGen/RegisterInfoEmitter.cpp

@@ -622,26 +622,9 @@ RegisterInfoEmitter::runTargetDesc(raw_ostream &OS, CodeGenTarget &Target,
       // Give the register class a legal C name if it's anonymous.
       std::string Name = RC.TheDef->getName();
 
-      OS << "  // " << Name
-         << " Register Class sub-classes...\n"
-         << "  static const TargetRegisterClass* const "
-         << Name << "Subclasses[] = {\n    ";
-
-      bool Empty = true;
-      for (unsigned rc2 = 0, e2 = RegisterClasses.size(); rc2 != e2; ++rc2) {
-        const CodeGenRegisterClass &RC2 = *RegisterClasses[rc2];
-
-        // Sub-classes are used to determine if a virtual register can be used
-        // as an instruction operand, or if it must be copied first.
-        if (rc == rc2 || !RC.hasSubClass(&RC2)) continue;
-
-        if (!Empty) OS << ", ";
-        OS << "&" << getQualifiedName(RC2.TheDef) << "RegClass";
-        Empty = false;
-      }
-
-      OS << (!Empty ? ", " : "") << "NULL";
-      OS << "\n  };\n\n";
+      OS << "  static const unsigned " << Name << "SubclassMask[] = { ";
+      printBitVectorAsHex(OS, RC.getSubClasses(), 32);
+      OS << "};\n\n";
     }
 
     // Emit NULL terminated super-class lists.
@@ -668,7 +651,7 @@ RegisterInfoEmitter::runTargetDesc(raw_ostream &OS, CodeGenTarget &Target,
          << Target.getName() << "MCRegisterClasses["
          << RC.getName() + "RegClassID" << "], "
          << RC.getName() + "VTs" << ", "
-         << RC.getName() + "Subclasses" << ", ";
+         << RC.getName() + "SubclassMask" << ", ";
       if (RC.getSuperClasses().empty())
         OS << "NullRegClasses, ";
       else