Add support for building the compactiontable for bytecode files. This shrinks

the bytecode file for 176.gcc by about 200K (10%), and 254.gap by about 167K,
a 25% reduction.  There is still a lot of room for improvement in the encoding
of the compaction table.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@10913 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Bytecode/Writer/SlotCalculator.cpp

@@ -36,6 +36,7 @@ using namespace llvm;
 
 SlotCalculator::SlotCalculator(const Module *M, bool buildBytecodeInfo) {
   BuildBytecodeInfo = buildBytecodeInfo;
+  ModuleContainsAllFunctionConstants = false;
   TheModule = M;
 
   // Preload table... Make sure that all of the primitive types are in the table
@@ -53,6 +54,7 @@ SlotCalculator::SlotCalculator(const Module *M, bool buildBytecodeInfo) {
 
 SlotCalculator::SlotCalculator(const Function *M, bool buildBytecodeInfo) {
   BuildBytecodeInfo = buildBytecodeInfo;
+  ModuleContainsAllFunctionConstants = false;
   TheModule = M ? M->getParent() : 0;
 
   // Preload table... Make sure that all of the primitive types are in the table
@@ -70,6 +72,17 @@ SlotCalculator::SlotCalculator(const Function *M, bool buildBytecodeInfo) {
   incorporateFunction(M);         // Start out in incorporated state
 }
 
+unsigned SlotCalculator::getGlobalSlot(const Value *V) const {
+  assert(!CompactionTable.empty() &&
+         "This method can only be used when compaction is enabled!");
+  if (const ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(V))
+    V = CPR->getValue();
+  std::map<const Value*, unsigned>::const_iterator I = NodeMap.find(V);
+  assert(I != NodeMap.end() && "Didn't find entry!");
+  return I->second;
+}
+
+
 
 // processModule - Process all of the module level function declarations and
 // types that are available.
@@ -127,23 +140,36 @@ void SlotCalculator::processModule() {
     }
   }
   
-#if 0
-  // FIXME: Empirically, this causes the bytecode files to get BIGGER, because
-  // it explodes the operand size numbers to be bigger than can be handled
-  // compactly, which offsets the ~40% savings in constant sizes.  Whoops.
-
   // If we are emitting a bytecode file, scan all of the functions for their
   // constants, which allows us to emit more compact modules.  This is optional,
   // and is just used to compactify the constants used by different functions
   // together.
+  //
+  // This functionality is completely optional for the bytecode writer, but
+  // tends to produce smaller bytecode files.  This should not be used in the
+  // future by clients that want to, for example, build and emit functions on
+  // the fly.  For now, however, it is unconditionally enabled when building
+  // bytecode information.
+  //
   if (BuildBytecodeInfo) {
+    ModuleContainsAllFunctionConstants = true;
+
     SC_DEBUG("Inserting function constants:\n");
     for (Module::const_iterator F = TheModule->begin(), E = TheModule->end();
-         F != E; ++F)
+         F != E; ++F) {
-      for_each(constant_begin(F), constant_end(F),
+      for (const_inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I){
-               bind_obj(this, &SlotCalculator::getOrCreateSlot));
+        for (unsigned op = 0, e = I->getNumOperands(); op != e; ++op)
+          if (isa<Constant>(I->getOperand(op)))
+            getOrCreateSlot(I->getOperand(op));
+        getOrCreateSlot(I->getType());
+        if (const VANextInst *VAN = dyn_cast<VANextInst>(*I))
+          getOrCreateSlot(VAN->getArgType());
+      }
+      processSymbolTableConstants(&F->getSymbolTable());
+    }
+
+
   }
-#endif
 
   // Insert constants that are named at module level into the slot pool so that
   // the module symbol table can refer to them...
@@ -220,24 +246,29 @@ void SlotCalculator::incorporateFunction(const Function *F) {
 
   SC_DEBUG("begin processFunction!\n");
 
+  // If we emitted all of the function constants, build a compaction table.
+  if (BuildBytecodeInfo && ModuleContainsAllFunctionConstants)
+    buildCompactionTable(F);
+  else {
     // Save the Table state before we process the function...
-  for (unsigned i = 0; i < Table.size(); ++i)
+    for (unsigned i = 0, e = Table.size(); i != e; ++i)
       ModuleLevel.push_back(Table[i].size());
-
+  }
-  SC_DEBUG("Inserting function arguments\n");
 
   // Iterate over function arguments, adding them to the value table...
   for(Function::const_aiterator I = F->abegin(), E = F->aend(); I != E; ++I)
     getOrCreateSlot(I);
 
-  // Iterate over all of the instructions in the function, looking for constant
+  if (BuildBytecodeInfo &&              // Assembly writer does not need this!
-  // values that are referenced.  Add these to the value pools before any
+      !ModuleContainsAllFunctionConstants) {
-  // nonconstant values.  This will be turned into the constant pool for the
+    // Iterate over all of the instructions in the function, looking for
-  // bytecode writer.
+    // constant values that are referenced.  Add these to the value pools
+    // before any nonconstant values.  This will be turned into the constant
+    // pool for the bytecode writer.
     //
-  if (BuildBytecodeInfo) {                // Assembly writer does not need this!
+    
-    // Emit all of the constants that are being used by the instructions in the
+    // Emit all of the constants that are being used by the instructions in
-    // function...
+    // the function...
     for_each(constant_begin(F), constant_end(F),
              bind_obj(this, &SlotCalculator::getOrCreateSlot));
     
@@ -271,14 +302,16 @@ void SlotCalculator::purgeFunction() {
 
   SC_DEBUG("begin purgeFunction!\n");
 
-  // First, remove values from existing type planes
+  // First, free the compaction map if used.
-  for (unsigned i = 0; i < NumModuleTypes; ++i) {
+  CompactionNodeMap.clear();
+
+  // Next, remove values from existing type planes
+  for (unsigned i = 0; i != NumModuleTypes; ++i)
+    if (i >= CompactionTable.size() || CompactionTable[i].empty()) {
       unsigned ModuleSize = ModuleLevel[i];// Size of plane before function came
       TypePlane &CurPlane = Table[i];
-    //SC_DEBUG("Processing Plane " <<i<< " of size " << CurPlane.size() <<"\n");
       
       while (CurPlane.size() != ModuleSize) {
-      //SC_DEBUG("  Removing [" << i << "] Value=" << CurPlane.back() << "\n");
         std::map<const Value *, unsigned>::iterator NI =
           NodeMap.find(CurPlane.back());
         assert(NI != NodeMap.end() && "Node not in nodemap?");
@@ -290,7 +323,12 @@ void SlotCalculator::purgeFunction() {
   // We don't need this state anymore, free it up.
   ModuleLevel.clear();
 
-  // Next, remove any type planes defined by the function...
+  if (!CompactionTable.empty()) {
+    CompactionTable.clear();
+  } else {
+    //  FIXME: this will require adjustment when we don't compact everything.
+
+    // Finally, remove any type planes defined by the function...
     while (NumModuleTypes != Table.size()) {
       TypePlane &Plane = Table.back();
       SC_DEBUG("Removing Plane " << (Table.size()-1) << " of size "
@@ -302,11 +340,131 @@ void SlotCalculator::purgeFunction() {
       
       Table.pop_back();                    // Nuke the plane, we don't like it.
     }
-
+  }
   SC_DEBUG("end purgeFunction!\n");
 }
 
+static inline bool hasNullValue(unsigned TyID) {
+  return TyID != Type::LabelTyID && TyID != Type::TypeTyID &&
+         TyID != Type::VoidTyID;
+}
+
+/// getOrCreateCompactionTableSlot - This method is used to build up the initial
+/// approximation of the compaction table.
+unsigned SlotCalculator::getOrCreateCompactionTableSlot(const Value *V) {
+  std::map<const Value*, unsigned>::iterator I =
+    CompactionNodeMap.lower_bound(V);
+  if (I != CompactionNodeMap.end() && I->first == V)
+    return I->second;  // Already exists?
+
+  // Make sure the type is in the table.
+  unsigned Ty = getOrCreateCompactionTableSlot(V->getType());
+  if (CompactionTable.size() <= Ty)
+    CompactionTable.resize(Ty+1);
+
+  assert(!isa<Type>(V) || ModuleLevel.empty());
+
+  TypePlane &TyPlane = CompactionTable[Ty];
+
+  // Make sure to insert the null entry if the thing we are inserting is not a
+  // null constant.
+  if (TyPlane.empty() && hasNullValue(V->getType()->getPrimitiveID())) {
+    Value *ZeroInitializer = Constant::getNullValue(V->getType());
+    if (V != ZeroInitializer) {
+      TyPlane.push_back(ZeroInitializer);
+      CompactionNodeMap[ZeroInitializer] = 0;
+    }
+  }
+
+  unsigned SlotNo = TyPlane.size();
+  TyPlane.push_back(V);
+  CompactionNodeMap.insert(std::make_pair(V, SlotNo));
+  return SlotNo;
+}
+
+
+/// buildCompactionTable - Since all of the function constants and types are
+/// stored in the module-level constant table, we don't need to emit a function
+/// constant table.  Also due to this, the indices for various constants and
+/// types might be very large in large programs.  In order to avoid blowing up
+/// the size of instructions in the bytecode encoding, we build a compaction
+/// table, which defines a mapping from function-local identifiers to global
+/// identifiers.
+void SlotCalculator::buildCompactionTable(const Function *F) {
+  assert(CompactionNodeMap.empty() && "Compaction table already built!");
+  // First step, insert the primitive types.
+  CompactionTable.resize(Type::TypeTyID+1);
+  for (unsigned i = 0; i != Type::FirstDerivedTyID; ++i) {
+    const Type *PrimTy = Type::getPrimitiveType((Type::PrimitiveID)i);
+    CompactionTable[Type::TypeTyID].push_back(PrimTy);
+    CompactionNodeMap[PrimTy] = i;
+  }
+
+  // Next, include any types used by function arguments.
+  for (Function::const_aiterator I = F->abegin(), E = F->aend(); I != E; ++I)
+    getOrCreateCompactionTableSlot(I->getType());
+
+  // Next, find all of the types and values that are referred to by the
+  // instructions in the program.
+  for (const_inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I) {
+    getOrCreateCompactionTableSlot(I->getType());
+    for (unsigned op = 0, e = I->getNumOperands(); op != e; ++op)
+      if (isa<Constant>(I->getOperand(op)) ||
+          isa<GlobalValue>(I->getOperand(op)))
+        getOrCreateCompactionTableSlot(I->getOperand(op));
+    if (const VANextInst *VAN = dyn_cast<VANextInst>(*I))
+      getOrCreateCompactionTableSlot(VAN->getArgType());
+  }
+
+  const SymbolTable &ST = F->getSymbolTable();
+  for (SymbolTable::const_iterator I = ST.begin(), E = ST.end(); I != E; ++I)
+    for (SymbolTable::type_const_iterator TI = I->second.begin(), 
+	   TE = I->second.end(); TI != TE; ++TI)
+      if (isa<Constant>(TI->second) || isa<Type>(TI->second) ||
+          isa<GlobalValue>(TI->second))
+	getOrCreateCompactionTableSlot(TI->second);
+
+  // Now that we have all of the values in the table, and know what types are
+  // referenced, make sure that there is at least the zero initializer in any
+  // used type plane.  Since the type was used, we will be emitting instructions
+  // to the plane even if there are no constants in it.
+  CompactionTable.resize(CompactionTable[Type::TypeTyID].size());
+  for (unsigned i = 0, e = CompactionTable.size(); i != e; ++i)
+    if (CompactionTable[i].empty() && i != Type::VoidTyID &&
+        i != Type::LabelTyID) {
+      const Type *Ty = cast<Type>(CompactionTable[Type::TypeTyID][i]);
+      getOrCreateCompactionTableSlot(Constant::getNullValue(Ty));
+    }
+  
+  // Okay, now at this point, we have a legal compaction table.  Since we want
+  // to emit the smallest possible binaries, we delete planes that do not NEED
+  // to be compacted, starting with the type plane.
+
+
+  // If decided not to compact anything, do not modify ModuleLevels.
+  if (CompactionTable.empty())
+    // FIXME: must update ModuleLevel.
+    return;
+
+  // Finally, for any planes that we have decided to compact, update the
+  // ModuleLevel entries to be accurate.
+
+  // FIXME: This does not yet work for partially compacted tables.
+  ModuleLevel.resize(CompactionTable.size());
+  for (unsigned i = 0, e = CompactionTable.size(); i != e; ++i)
+    ModuleLevel[i] = CompactionTable[i].size();
+}
+
 int SlotCalculator::getSlot(const Value *V) const {
+  // If there is a CompactionTable active...
+  if (!CompactionNodeMap.empty()) {
+    std::map<const Value*, unsigned>::const_iterator I =
+      CompactionNodeMap.find(V);
+    if (I != CompactionNodeMap.end())
+      return (int)I->second;
+    return -1;
+  }
+
   std::map<const Value*, unsigned>::const_iterator I = NodeMap.find(V);
   if (I != NodeMap.end())
     return (int)I->second;
@@ -327,8 +485,11 @@ int SlotCalculator::getOrCreateSlot(const Value *V) {
   if (const ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(V))
     return getOrCreateSlot(CPR->getValue());
 
-  if (!isa<GlobalValue>(V))
+  if (!isa<GlobalValue>(V))  // Initializers for globals are handled explicitly
     if (const Constant *C = dyn_cast<Constant>(V)) {
+      assert(CompactionNodeMap.empty() &&
+             "All needed constants should be in the compaction map already!");
+
       // If we are emitting a bytecode file, do not index the characters that
       // make up constant strings.  We emit constant strings as special
       // entities that don't require their individual characters to be emitted.
@@ -358,6 +519,17 @@ int SlotCalculator::insertValue(const Value *D, bool dontIgnore) {
   assert(D && "Can't insert a null value!");
   assert(getSlot(D) == -1 && "Value is already in the table!");
 
+  // If we are building a compaction map, and if this plane is being compacted,
+  // insert the value into the compaction map, not into the global map.
+  if (!CompactionNodeMap.empty()) {
+    if (D->getType() == Type::VoidTy) return -1;  // Do not insert void values
+    assert(!isa<Type>(D) && !isa<Constant>(D) && !isa<GlobalValue>(D) &&
+           "Types, constants, and globals should be in global SymTab!");
+
+    // FIXME: this does not yet handle partially compacted tables yet!
+    return getOrCreateCompactionTableSlot(D);
+  }
+
   // If this node does not contribute to a plane, or if the node has a 
   // name and we don't want names, then ignore the silly node... Note that types
   // do need slot numbers so that we can keep track of where other values land.
@@ -406,11 +578,6 @@ int SlotCalculator::insertValue(const Value *D, bool dontIgnore) {
   return doInsertValue(D);
 }
 
-static inline bool hasNullValue(unsigned TyID) {
-  return TyID != Type::LabelTyID && TyID != Type::TypeTyID &&
-         TyID != Type::VoidTyID;
-}
-
 // doInsertValue - This is a small helper function to be called only
 // be insertValue.
 //

lib/VMCore/SlotCalculator.cpp

@@ -36,6 +36,7 @@ using namespace llvm;
 
 SlotCalculator::SlotCalculator(const Module *M, bool buildBytecodeInfo) {
   BuildBytecodeInfo = buildBytecodeInfo;
+  ModuleContainsAllFunctionConstants = false;
   TheModule = M;
 
   // Preload table... Make sure that all of the primitive types are in the table
@@ -53,6 +54,7 @@ SlotCalculator::SlotCalculator(const Module *M, bool buildBytecodeInfo) {
 
 SlotCalculator::SlotCalculator(const Function *M, bool buildBytecodeInfo) {
   BuildBytecodeInfo = buildBytecodeInfo;
+  ModuleContainsAllFunctionConstants = false;
   TheModule = M ? M->getParent() : 0;
 
   // Preload table... Make sure that all of the primitive types are in the table
@@ -70,6 +72,17 @@ SlotCalculator::SlotCalculator(const Function *M, bool buildBytecodeInfo) {
   incorporateFunction(M);         // Start out in incorporated state
 }
 
+unsigned SlotCalculator::getGlobalSlot(const Value *V) const {
+  assert(!CompactionTable.empty() &&
+         "This method can only be used when compaction is enabled!");
+  if (const ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(V))
+    V = CPR->getValue();
+  std::map<const Value*, unsigned>::const_iterator I = NodeMap.find(V);
+  assert(I != NodeMap.end() && "Didn't find entry!");
+  return I->second;
+}
+
+
 
 // processModule - Process all of the module level function declarations and
 // types that are available.
@@ -127,23 +140,36 @@ void SlotCalculator::processModule() {
     }
   }
   
-#if 0
-  // FIXME: Empirically, this causes the bytecode files to get BIGGER, because
-  // it explodes the operand size numbers to be bigger than can be handled
-  // compactly, which offsets the ~40% savings in constant sizes.  Whoops.
-
   // If we are emitting a bytecode file, scan all of the functions for their
   // constants, which allows us to emit more compact modules.  This is optional,
   // and is just used to compactify the constants used by different functions
   // together.
+  //
+  // This functionality is completely optional for the bytecode writer, but
+  // tends to produce smaller bytecode files.  This should not be used in the
+  // future by clients that want to, for example, build and emit functions on
+  // the fly.  For now, however, it is unconditionally enabled when building
+  // bytecode information.
+  //
   if (BuildBytecodeInfo) {
+    ModuleContainsAllFunctionConstants = true;
+
     SC_DEBUG("Inserting function constants:\n");
     for (Module::const_iterator F = TheModule->begin(), E = TheModule->end();
-         F != E; ++F)
+         F != E; ++F) {
-      for_each(constant_begin(F), constant_end(F),
+      for (const_inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I){
-               bind_obj(this, &SlotCalculator::getOrCreateSlot));
+        for (unsigned op = 0, e = I->getNumOperands(); op != e; ++op)
+          if (isa<Constant>(I->getOperand(op)))
+            getOrCreateSlot(I->getOperand(op));
+        getOrCreateSlot(I->getType());
+        if (const VANextInst *VAN = dyn_cast<VANextInst>(*I))
+          getOrCreateSlot(VAN->getArgType());
+      }
+      processSymbolTableConstants(&F->getSymbolTable());
+    }
+
+
   }
-#endif
 
   // Insert constants that are named at module level into the slot pool so that
   // the module symbol table can refer to them...
@@ -220,24 +246,29 @@ void SlotCalculator::incorporateFunction(const Function *F) {
 
   SC_DEBUG("begin processFunction!\n");
 
+  // If we emitted all of the function constants, build a compaction table.
+  if (BuildBytecodeInfo && ModuleContainsAllFunctionConstants)
+    buildCompactionTable(F);
+  else {
     // Save the Table state before we process the function...
-  for (unsigned i = 0; i < Table.size(); ++i)
+    for (unsigned i = 0, e = Table.size(); i != e; ++i)
       ModuleLevel.push_back(Table[i].size());
-
+  }
-  SC_DEBUG("Inserting function arguments\n");
 
   // Iterate over function arguments, adding them to the value table...
   for(Function::const_aiterator I = F->abegin(), E = F->aend(); I != E; ++I)
     getOrCreateSlot(I);
 
-  // Iterate over all of the instructions in the function, looking for constant
+  if (BuildBytecodeInfo &&              // Assembly writer does not need this!
-  // values that are referenced.  Add these to the value pools before any
+      !ModuleContainsAllFunctionConstants) {
-  // nonconstant values.  This will be turned into the constant pool for the
+    // Iterate over all of the instructions in the function, looking for
-  // bytecode writer.
+    // constant values that are referenced.  Add these to the value pools
+    // before any nonconstant values.  This will be turned into the constant
+    // pool for the bytecode writer.
     //
-  if (BuildBytecodeInfo) {                // Assembly writer does not need this!
+    
-    // Emit all of the constants that are being used by the instructions in the
+    // Emit all of the constants that are being used by the instructions in
-    // function...
+    // the function...
     for_each(constant_begin(F), constant_end(F),
              bind_obj(this, &SlotCalculator::getOrCreateSlot));
     
@@ -271,14 +302,16 @@ void SlotCalculator::purgeFunction() {
 
   SC_DEBUG("begin purgeFunction!\n");
 
-  // First, remove values from existing type planes
+  // First, free the compaction map if used.
-  for (unsigned i = 0; i < NumModuleTypes; ++i) {
+  CompactionNodeMap.clear();
+
+  // Next, remove values from existing type planes
+  for (unsigned i = 0; i != NumModuleTypes; ++i)
+    if (i >= CompactionTable.size() || CompactionTable[i].empty()) {
       unsigned ModuleSize = ModuleLevel[i];// Size of plane before function came
       TypePlane &CurPlane = Table[i];
-    //SC_DEBUG("Processing Plane " <<i<< " of size " << CurPlane.size() <<"\n");
       
       while (CurPlane.size() != ModuleSize) {
-      //SC_DEBUG("  Removing [" << i << "] Value=" << CurPlane.back() << "\n");
         std::map<const Value *, unsigned>::iterator NI =
           NodeMap.find(CurPlane.back());
         assert(NI != NodeMap.end() && "Node not in nodemap?");
@@ -290,7 +323,12 @@ void SlotCalculator::purgeFunction() {
   // We don't need this state anymore, free it up.
   ModuleLevel.clear();
 
-  // Next, remove any type planes defined by the function...
+  if (!CompactionTable.empty()) {
+    CompactionTable.clear();
+  } else {
+    //  FIXME: this will require adjustment when we don't compact everything.
+
+    // Finally, remove any type planes defined by the function...
     while (NumModuleTypes != Table.size()) {
       TypePlane &Plane = Table.back();
       SC_DEBUG("Removing Plane " << (Table.size()-1) << " of size "
@@ -302,11 +340,131 @@ void SlotCalculator::purgeFunction() {
       
       Table.pop_back();                    // Nuke the plane, we don't like it.
     }
-
+  }
   SC_DEBUG("end purgeFunction!\n");
 }
 
+static inline bool hasNullValue(unsigned TyID) {
+  return TyID != Type::LabelTyID && TyID != Type::TypeTyID &&
+         TyID != Type::VoidTyID;
+}
+
+/// getOrCreateCompactionTableSlot - This method is used to build up the initial
+/// approximation of the compaction table.
+unsigned SlotCalculator::getOrCreateCompactionTableSlot(const Value *V) {
+  std::map<const Value*, unsigned>::iterator I =
+    CompactionNodeMap.lower_bound(V);
+  if (I != CompactionNodeMap.end() && I->first == V)
+    return I->second;  // Already exists?
+
+  // Make sure the type is in the table.
+  unsigned Ty = getOrCreateCompactionTableSlot(V->getType());
+  if (CompactionTable.size() <= Ty)
+    CompactionTable.resize(Ty+1);
+
+  assert(!isa<Type>(V) || ModuleLevel.empty());
+
+  TypePlane &TyPlane = CompactionTable[Ty];
+
+  // Make sure to insert the null entry if the thing we are inserting is not a
+  // null constant.
+  if (TyPlane.empty() && hasNullValue(V->getType()->getPrimitiveID())) {
+    Value *ZeroInitializer = Constant::getNullValue(V->getType());
+    if (V != ZeroInitializer) {
+      TyPlane.push_back(ZeroInitializer);
+      CompactionNodeMap[ZeroInitializer] = 0;
+    }
+  }
+
+  unsigned SlotNo = TyPlane.size();
+  TyPlane.push_back(V);
+  CompactionNodeMap.insert(std::make_pair(V, SlotNo));
+  return SlotNo;
+}
+
+
+/// buildCompactionTable - Since all of the function constants and types are
+/// stored in the module-level constant table, we don't need to emit a function
+/// constant table.  Also due to this, the indices for various constants and
+/// types might be very large in large programs.  In order to avoid blowing up
+/// the size of instructions in the bytecode encoding, we build a compaction
+/// table, which defines a mapping from function-local identifiers to global
+/// identifiers.
+void SlotCalculator::buildCompactionTable(const Function *F) {
+  assert(CompactionNodeMap.empty() && "Compaction table already built!");
+  // First step, insert the primitive types.
+  CompactionTable.resize(Type::TypeTyID+1);
+  for (unsigned i = 0; i != Type::FirstDerivedTyID; ++i) {
+    const Type *PrimTy = Type::getPrimitiveType((Type::PrimitiveID)i);
+    CompactionTable[Type::TypeTyID].push_back(PrimTy);
+    CompactionNodeMap[PrimTy] = i;
+  }
+
+  // Next, include any types used by function arguments.
+  for (Function::const_aiterator I = F->abegin(), E = F->aend(); I != E; ++I)
+    getOrCreateCompactionTableSlot(I->getType());
+
+  // Next, find all of the types and values that are referred to by the
+  // instructions in the program.
+  for (const_inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I) {
+    getOrCreateCompactionTableSlot(I->getType());
+    for (unsigned op = 0, e = I->getNumOperands(); op != e; ++op)
+      if (isa<Constant>(I->getOperand(op)) ||
+          isa<GlobalValue>(I->getOperand(op)))
+        getOrCreateCompactionTableSlot(I->getOperand(op));
+    if (const VANextInst *VAN = dyn_cast<VANextInst>(*I))
+      getOrCreateCompactionTableSlot(VAN->getArgType());
+  }
+
+  const SymbolTable &ST = F->getSymbolTable();
+  for (SymbolTable::const_iterator I = ST.begin(), E = ST.end(); I != E; ++I)
+    for (SymbolTable::type_const_iterator TI = I->second.begin(), 
+	   TE = I->second.end(); TI != TE; ++TI)
+      if (isa<Constant>(TI->second) || isa<Type>(TI->second) ||
+          isa<GlobalValue>(TI->second))
+	getOrCreateCompactionTableSlot(TI->second);
+
+  // Now that we have all of the values in the table, and know what types are
+  // referenced, make sure that there is at least the zero initializer in any
+  // used type plane.  Since the type was used, we will be emitting instructions
+  // to the plane even if there are no constants in it.
+  CompactionTable.resize(CompactionTable[Type::TypeTyID].size());
+  for (unsigned i = 0, e = CompactionTable.size(); i != e; ++i)
+    if (CompactionTable[i].empty() && i != Type::VoidTyID &&
+        i != Type::LabelTyID) {
+      const Type *Ty = cast<Type>(CompactionTable[Type::TypeTyID][i]);
+      getOrCreateCompactionTableSlot(Constant::getNullValue(Ty));
+    }
+  
+  // Okay, now at this point, we have a legal compaction table.  Since we want
+  // to emit the smallest possible binaries, we delete planes that do not NEED
+  // to be compacted, starting with the type plane.
+
+
+  // If decided not to compact anything, do not modify ModuleLevels.
+  if (CompactionTable.empty())
+    // FIXME: must update ModuleLevel.
+    return;
+
+  // Finally, for any planes that we have decided to compact, update the
+  // ModuleLevel entries to be accurate.
+
+  // FIXME: This does not yet work for partially compacted tables.
+  ModuleLevel.resize(CompactionTable.size());
+  for (unsigned i = 0, e = CompactionTable.size(); i != e; ++i)
+    ModuleLevel[i] = CompactionTable[i].size();
+}
+
 int SlotCalculator::getSlot(const Value *V) const {
+  // If there is a CompactionTable active...
+  if (!CompactionNodeMap.empty()) {
+    std::map<const Value*, unsigned>::const_iterator I =
+      CompactionNodeMap.find(V);
+    if (I != CompactionNodeMap.end())
+      return (int)I->second;
+    return -1;
+  }
+
   std::map<const Value*, unsigned>::const_iterator I = NodeMap.find(V);
   if (I != NodeMap.end())
     return (int)I->second;
@@ -327,8 +485,11 @@ int SlotCalculator::getOrCreateSlot(const Value *V) {
   if (const ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(V))
     return getOrCreateSlot(CPR->getValue());
 
-  if (!isa<GlobalValue>(V))
+  if (!isa<GlobalValue>(V))  // Initializers for globals are handled explicitly
     if (const Constant *C = dyn_cast<Constant>(V)) {
+      assert(CompactionNodeMap.empty() &&
+             "All needed constants should be in the compaction map already!");
+
       // If we are emitting a bytecode file, do not index the characters that
       // make up constant strings.  We emit constant strings as special
       // entities that don't require their individual characters to be emitted.
@@ -358,6 +519,17 @@ int SlotCalculator::insertValue(const Value *D, bool dontIgnore) {
   assert(D && "Can't insert a null value!");
   assert(getSlot(D) == -1 && "Value is already in the table!");
 
+  // If we are building a compaction map, and if this plane is being compacted,
+  // insert the value into the compaction map, not into the global map.
+  if (!CompactionNodeMap.empty()) {
+    if (D->getType() == Type::VoidTy) return -1;  // Do not insert void values
+    assert(!isa<Type>(D) && !isa<Constant>(D) && !isa<GlobalValue>(D) &&
+           "Types, constants, and globals should be in global SymTab!");
+
+    // FIXME: this does not yet handle partially compacted tables yet!
+    return getOrCreateCompactionTableSlot(D);
+  }
+
   // If this node does not contribute to a plane, or if the node has a 
   // name and we don't want names, then ignore the silly node... Note that types
   // do need slot numbers so that we can keep track of where other values land.
@@ -406,11 +578,6 @@ int SlotCalculator::insertValue(const Value *D, bool dontIgnore) {
   return doInsertValue(D);
 }
 
-static inline bool hasNullValue(unsigned TyID) {
-  return TyID != Type::LabelTyID && TyID != Type::TypeTyID &&
-         TyID != Type::VoidTyID;
-}
-
 // doInsertValue - This is a small helper function to be called only
 // be insertValue.
 //