Moved this file to lib/Bytecode/Writer because its used there only.

llvm-svn: 13900

1 files changed, 786 insertions, 0 deletions

diff --git a/llvm/lib/Bytecode/Writer/SlotCalculator.cpp b/llvm/lib/Bytecode/Writer/SlotCalculator.cpp
new file mode 100644
index 00000000000..3408982c8d5
--- /dev/null
+++ b/llvm/lib/Bytecode/Writer/SlotCalculator.cpp
@@ -0,0 +1,786 @@
+//===-- SlotCalculator.cpp - Calculate what slots values land in ----------===//
+// 
+//                     The LLVM Compiler Infrastructure
+//
+// This file was developed by the LLVM research group and is distributed under
+// the University of Illinois Open Source License. See LICENSE.TXT for details.
+// 
+//===----------------------------------------------------------------------===//
+//
+// This file implements a useful analysis step to figure out what numbered slots
+// values in a program will land in (keeping track of per plane information).
+//
+// This is used when writing a file to disk, either in bytecode or assembly.
+//
+//===----------------------------------------------------------------------===//
+
+#include "llvm/Analysis/SlotCalculator.h"
+#include "llvm/Constants.h"
+#include "llvm/DerivedTypes.h"
+#include "llvm/iOther.h"
+#include "llvm/Module.h"
+#include "llvm/SymbolTable.h"
+#include "llvm/Analysis/ConstantsScanner.h"
+#include "Support/PostOrderIterator.h"
+#include "Support/STLExtras.h"
+#include <algorithm>
+using namespace llvm;
+
+#if 0
+#define SC_DEBUG(X) std::cerr << X
+#else
+#define SC_DEBUG(X)
+#endif
+
+SlotCalculator::SlotCalculator(const Module *M ) {
+  ModuleContainsAllFunctionConstants = false;
+  TheModule = M;
+
+  // Preload table... Make sure that all of the primitive types are in the table
+  // and that their Primitive ID is equal to their slot #
+  //
+  SC_DEBUG("Inserting primitive types:\n");
+  for (unsigned i = 0; i < Type::FirstDerivedTyID; ++i) {
+    assert(Type::getPrimitiveType((Type::PrimitiveID)i));
+    insertValue(Type::getPrimitiveType((Type::PrimitiveID)i), true);
+  }
+
+  if (M == 0) return;   // Empty table...
+  processModule();
+}
+
+SlotCalculator::SlotCalculator(const Function *M ) {
+  ModuleContainsAllFunctionConstants = false;
+  TheModule = M ? M->getParent() : 0;
+
+  // Preload table... Make sure that all of the primitive types are in the table
+  // and that their Primitive ID is equal to their slot #
+  //
+  SC_DEBUG("Inserting primitive types:\n");
+  for (unsigned i = 0; i < Type::FirstDerivedTyID; ++i) {
+    assert(Type::getPrimitiveType((Type::PrimitiveID)i));
+    insertValue(Type::getPrimitiveType((Type::PrimitiveID)i), true);
+  }
+
+  if (TheModule == 0) return;   // Empty table...
+
+  processModule();              // Process module level stuff
+  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 global slot entry!");
+  return I->second;
+}
+
+SlotCalculator::TypePlane &SlotCalculator::getPlane(unsigned Plane) {
+  unsigned PIdx = Plane;
+  if (CompactionTable.empty()) {                // No compaction table active?
+    // fall out
+  } else if (!CompactionTable[Plane].empty()) { // Compaction table active.
+    assert(Plane < CompactionTable.size());
+    return CompactionTable[Plane];
+  } else {
+    // Final case: compaction table active, but this plane is not
+    // compactified.  If the type plane is compactified, unmap back to the
+    // global type plane corresponding to "Plane".
+    if (!CompactionTable[Type::TypeTyID].empty()) {
+      const Type *Ty = cast<Type>(CompactionTable[Type::TypeTyID][Plane]);
+      std::map<const Value*, unsigned>::iterator It = NodeMap.find(Ty);
+      assert(It != NodeMap.end() && "Type not in global constant map?");
+      PIdx = It->second;
+    }
+  }
+
+  // Okay we are just returning an entry out of the main Table.  Make sure the
+  // plane exists and return it.
+  if (PIdx >= Table.size())
+    Table.resize(PIdx+1);
+  return Table[PIdx];
+}
+
+
+// processModule - Process all of the module level function declarations and
+// types that are available.
+//
+void SlotCalculator::processModule() {
+  SC_DEBUG("begin processModule!\n");
+
+  // Add all of the global variables to the value table...
+  //
+  for (Module::const_giterator I = TheModule->gbegin(), E = TheModule->gend();
+       I != E; ++I)
+    getOrCreateSlot(I);
+
+  // Scavenge the types out of the functions, then add the functions themselves
+  // to the value table...
+  //
+  for (Module::const_iterator I = TheModule->begin(), E = TheModule->end();
+       I != E; ++I)
+    getOrCreateSlot(I);
+
+  // Add all of the module level constants used as initializers
+  //
+  for (Module::const_giterator I = TheModule->gbegin(), E = TheModule->gend();
+       I != E; ++I)
+    if (I->hasInitializer())
+      getOrCreateSlot(I->getInitializer());
+
+  // Now that all global constants have been added, rearrange constant planes
+  // that contain constant strings so that the strings occur at the start of the
+  // plane, not somewhere in the middle.
+  //
+  TypePlane &Types = Table[Type::TypeTyID];
+  for (unsigned plane = 0, e = Table.size(); plane != e; ++plane) {
+    if (const ArrayType *AT = dyn_cast<ArrayType>(Types[plane]))
+      if (AT->getElementType() == Type::SByteTy ||
+	  AT->getElementType() == Type::UByteTy) {
+	TypePlane &Plane = Table[plane];
+	unsigned FirstNonStringID = 0;
+	for (unsigned i = 0, e = Plane.size(); i != e; ++i)
+	  if (isa<ConstantAggregateZero>(Plane[i]) ||
+	      cast<ConstantArray>(Plane[i])->isString()) {
+	    // Check to see if we have to shuffle this string around.  If not,
+	    // don't do anything.
+	    if (i != FirstNonStringID) {
+	      // Swap the plane entries....
+	      std::swap(Plane[i], Plane[FirstNonStringID]);
+	      
+	      // Keep the NodeMap up to date.
+	      NodeMap[Plane[i]] = i;
+	      NodeMap[Plane[FirstNonStringID]] = FirstNonStringID;
+	    }
+	    ++FirstNonStringID;
+	  }
+      }
+  }
+  
+  // 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.
+  //
+  ModuleContainsAllFunctionConstants = true;
+
+  SC_DEBUG("Inserting function constants:\n");
+  for (Module::const_iterator F = TheModule->begin(), E = TheModule->end();
+       F != E; ++F) {
+    for (const_inst_iterator I = inst_begin(F), E = inst_end(F); I != E; ++I){
+      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());
+  }
+
+  // Insert constants that are named at module level into the slot pool so that
+  // the module symbol table can refer to them...
+  SC_DEBUG("Inserting SymbolTable values:\n");
+  processSymbolTable(&TheModule->getSymbolTable());
+
+  // Now that we have collected together all of the information relevant to the
+  // module, compactify the type table if it is particularly big and outputting
+  // a bytecode file.  The basic problem we run into is that some programs have
+  // a large number of types, which causes the type field to overflow its size,
+  // which causes instructions to explode in size (particularly call
+  // instructions).  To avoid this behavior, we "sort" the type table so that
+  // all non-value types are pushed to the end of the type table, giving nice
+  // low numbers to the types that can be used by instructions, thus reducing
+  // the amount of explodage we suffer.
+  if (Table[Type::TypeTyID].size() >= 64) {
+    // Scan through the type table moving value types to the start of the table.
+    TypePlane *Types = &Table[Type::TypeTyID];
+    unsigned FirstNonValueTypeID = 0;
+    for (unsigned i = 0, e = Types->size(); i != e; ++i)
+      if (cast<Type>((*Types)[i])->isFirstClassType() ||
+          cast<Type>((*Types)[i])->isPrimitiveType()) {
+        // Check to see if we have to shuffle this type around.  If not, don't
+        // do anything.
+        if (i != FirstNonValueTypeID) {
+          assert(i != Type::TypeTyID && FirstNonValueTypeID != Type::TypeTyID &&
+                 "Cannot move around the type plane!");
+
+          // Swap the type ID's.
+          std::swap((*Types)[i], (*Types)[FirstNonValueTypeID]);
+
+          // Keep the NodeMap up to date.
+          NodeMap[(*Types)[i]] = i;
+          NodeMap[(*Types)[FirstNonValueTypeID]] = FirstNonValueTypeID;
+
+          // When we move a type, make sure to move its value plane as needed.
+          if (Table.size() > FirstNonValueTypeID) {
+            if (Table.size() <= i) Table.resize(i+1);
+            std::swap(Table[i], Table[FirstNonValueTypeID]);
+            Types = &Table[Type::TypeTyID];
+          }
+        }
+        ++FirstNonValueTypeID;
+      }
+  }
+
+  SC_DEBUG("end processModule!\n");
+}
+
+// processSymbolTable - Insert all of the values in the specified symbol table
+// into the values table...
+//
+void SlotCalculator::processSymbolTable(const SymbolTable *ST) {
+  // Do the types first.
+  for (SymbolTable::type_const_iterator TI = ST->type_begin(),
+       TE = ST->type_end(); TI != TE; ++TI )
+    getOrCreateSlot(TI->second);
+
+  // Now do the values.
+  for (SymbolTable::plane_const_iterator PI = ST->plane_begin(), 
+       PE = ST->plane_end(); PI != PE; ++PI)
+    for (SymbolTable::value_const_iterator VI = PI->second.begin(),
+	   VE = PI->second.end(); VI != VE; ++VI)
+      getOrCreateSlot(VI->second);
+}
+
+void SlotCalculator::processSymbolTableConstants(const SymbolTable *ST) {
+  // Do the types first
+  for (SymbolTable::type_const_iterator TI = ST->type_begin(),
+       TE = ST->type_end(); TI != TE; ++TI )
+    getOrCreateSlot(TI->second);
+
+  // Now do the constant values in all planes
+  for (SymbolTable::plane_const_iterator PI = ST->plane_begin(), 
+       PE = ST->plane_end(); PI != PE; ++PI)
+    for (SymbolTable::value_const_iterator VI = PI->second.begin(),
+	   VE = PI->second.end(); VI != VE; ++VI)
+      if (isa<Constant>(VI->second))
+	getOrCreateSlot(VI->second);
+}
+
+
+void SlotCalculator::incorporateFunction(const Function *F) {
+  assert(ModuleLevel.size() == 0 && "Module already incorporated!");
+
+  SC_DEBUG("begin processFunction!\n");
+
+  // If we emitted all of the function constants, build a compaction table.
+  if ( ModuleContainsAllFunctionConstants)
+    buildCompactionTable(F);
+
+  // Update the ModuleLevel entries to be accurate.
+  ModuleLevel.resize(getNumPlanes());
+  for (unsigned i = 0, e = getNumPlanes(); i != e; ++i)
+    ModuleLevel[i] = getPlane(i).size();
+
+  // 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);
+
+  if ( !ModuleContainsAllFunctionConstants ) {
+    // Iterate over all of the instructions in the function, looking for
+    // 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.
+    //
+    
+    // Emit all of the constants that are being used by the instructions in
+    // the function...
+    for_each(constant_begin(F), constant_end(F),
+             bind_obj(this, &SlotCalculator::getOrCreateSlot));
+    
+    // If there is a symbol table, it is possible that the user has names for
+    // constants that are not being used.  In this case, we will have problems
+    // if we don't emit the constants now, because otherwise we will get 
+    // symbol table references to constants not in the output.  Scan for these
+    // constants now.
+    //
+    processSymbolTableConstants(&F->getSymbolTable());
+  }
+
+  SC_DEBUG("Inserting Instructions:\n");
+
+  // Add all of the instructions to the type planes...
+  for (Function::const_iterator BB = F->begin(), E = F->end(); BB != E; ++BB) {
+    getOrCreateSlot(BB);
+    for (BasicBlock::const_iterator I = BB->begin(), E = BB->end(); I!=E; ++I) {
+      getOrCreateSlot(I);
+      if (const VANextInst *VAN = dyn_cast<VANextInst>(I))
+        getOrCreateSlot(VAN->getArgType());
+    }
+  }
+
+  // If we are building a compaction table, prune out planes that do not benefit
+  // from being compactified.
+  if (!CompactionTable.empty())
+    pruneCompactionTable();
+
+  SC_DEBUG("end processFunction!\n");
+}
+
+void SlotCalculator::purgeFunction() {
+  assert(ModuleLevel.size() != 0 && "Module not incorporated!");
+  unsigned NumModuleTypes = ModuleLevel.size();
+
+  SC_DEBUG("begin purgeFunction!\n");
+
+  // First, free the compaction map if used.
+  CompactionNodeMap.clear();
+
+  // Next, remove values from existing type planes
+  for (unsigned i = 0; i != NumModuleTypes; ++i) {
+    // Size of plane before function came
+    unsigned ModuleLev = getModuleLevel(i);
+    assert(int(ModuleLev) >= 0 && "BAD!");
+
+    TypePlane &Plane = getPlane(i);
+
+    assert(ModuleLev <= Plane.size() && "module levels higher than elements?");
+    while (Plane.size() != ModuleLev) {
+      assert(!isa<GlobalValue>(Plane.back()) &&
+             "Functions cannot define globals!");
+      NodeMap.erase(Plane.back());       // Erase from nodemap
+      Plane.pop_back();                  // Shrink plane
+    }
+  }
+
+  // We don't need this state anymore, free it up.
+  ModuleLevel.clear();
+
+  // Finally, remove any type planes defined by the function...
+  if (!CompactionTable.empty()) {
+    CompactionTable.clear();
+  } else {
+    while (Table.size() > NumModuleTypes) {
+      TypePlane &Plane = Table.back();
+      SC_DEBUG("Removing Plane " << (Table.size()-1) << " of size "
+               << Plane.size() << "\n");
+      while (Plane.size()) {
+        assert(!isa<GlobalValue>(Plane.back()) &&
+               "Functions cannot define globals!");
+        NodeMap.erase(Plane.back());   // Erase from nodemap
+        Plane.pop_back();              // Shrink plane
+      }
+      
+      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) {
+  if (const ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(V))
+    V = CPR->getValue();
+  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;
+  if (!CompactionTable[Type::TypeTyID].empty())
+    Ty = getOrCreateCompactionTableSlot(V->getType());
+  else    // If the type plane was decompactified, use the global plane ID
+    Ty = getSlot(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());
+  }
+
+  // Do the types in the symbol table
+  const SymbolTable &ST = F->getSymbolTable();
+  for (SymbolTable::type_const_iterator TI = ST.type_begin(),
+       TE = ST.type_end(); TI != TE; ++TI)
+    getOrCreateCompactionTableSlot(TI->second);
+
+  // Now do the constants and global values
+  for (SymbolTable::plane_const_iterator PI = ST.plane_begin(), 
+       PE = ST.plane_end(); PI != PE; ++PI)
+    for (SymbolTable::value_const_iterator VI = PI->second.begin(),
+	   VE = PI->second.end(); VI != VE; ++VI)
+      if (isa<Constant>(VI->second) || isa<GlobalValue>(VI->second))
+	getOrCreateCompactionTableSlot(VI->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, do not compactify the type plane if
+  // it will not save us anything.  Because we have not yet incorporated the
+  // function body itself yet, we don't know whether or not it's a good idea to
+  // compactify other planes.  We will defer this decision until later.
+  TypePlane &GlobalTypes = Table[Type::TypeTyID];
+  
+  // All of the values types will be scrunched to the start of the types plane
+  // of the global table.  Figure out just how many there are.
+  assert(!GlobalTypes.empty() && "No global types???");
+  unsigned NumFCTypes = GlobalTypes.size()-1;
+  while (!cast<Type>(GlobalTypes[NumFCTypes])->isFirstClassType())
+    --NumFCTypes;
+
+  // If there are fewer that 64 types, no instructions will be exploded due to
+  // the size of the type operands.  Thus there is no need to compactify types.
+  // Also, if the compaction table contains most of the entries in the global
+  // table, there really is no reason to compactify either.
+  if (NumFCTypes < 64) {
+    // Decompactifying types is tricky, because we have to move type planes all
+    // over the place.  At least we don't need to worry about updating the
+    // CompactionNodeMap for non-types though.
+    std::vector<TypePlane> TmpCompactionTable;
+    std::swap(CompactionTable, TmpCompactionTable);
+    TypePlane Types;
+    std::swap(Types, TmpCompactionTable[Type::TypeTyID]);
+    
+    // Move each plane back over to the uncompactified plane
+    while (!Types.empty()) {
+      const Type *Ty = cast<Type>(Types.back());
+      Types.pop_back();
+      CompactionNodeMap.erase(Ty);  // Decompactify type!
+
+      if (Ty != Type::TypeTy) {
+        // Find the global slot number for this type.
+        int TySlot = getSlot(Ty);
+        assert(TySlot != -1 && "Type doesn't exist in global table?");
+        
+        // Now we know where to put the compaction table plane.
+        if (CompactionTable.size() <= unsigned(TySlot))
+          CompactionTable.resize(TySlot+1);
+        // Move the plane back into the compaction table.
+        std::swap(CompactionTable[TySlot], TmpCompactionTable[Types.size()]);
+
+        // And remove the empty plane we just moved in.
+        TmpCompactionTable.pop_back();
+      }
+    }
+  }
+}
+
+
+/// pruneCompactionTable - Once the entire function being processed has been
+/// incorporated into the current compaction table, look over the compaction
+/// table and check to see if there are any values whose compaction will not
+/// save us any space in the bytecode file.  If compactifying these values
+/// serves no purpose, then we might as well not even emit the compactification
+/// information to the bytecode file, saving a bit more space.
+///
+/// Note that the type plane has already been compactified if possible.
+///
+void SlotCalculator::pruneCompactionTable() {
+  TypePlane &TyPlane = CompactionTable[Type::TypeTyID];
+  for (unsigned ctp = 0, e = CompactionTable.size(); ctp != e; ++ctp)
+    if (ctp != Type::TypeTyID && !CompactionTable[ctp].empty()) {
+      TypePlane &CPlane = CompactionTable[ctp];
+      unsigned GlobalSlot = ctp;
+      if (!TyPlane.empty())
+        GlobalSlot = getGlobalSlot(TyPlane[ctp]);
+
+      if (GlobalSlot >= Table.size())
+        Table.resize(GlobalSlot+1);
+      TypePlane &GPlane = Table[GlobalSlot];
+      
+      unsigned ModLevel = getModuleLevel(ctp);
+      unsigned NumFunctionObjs = CPlane.size()-ModLevel;
+
+      // If the maximum index required if all entries in this plane were merged
+      // into the global plane is less than 64, go ahead and eliminate the
+      // plane.
+      bool PrunePlane = GPlane.size() + NumFunctionObjs < 64;
+
+      // If there are no function-local values defined, and the maximum
+      // referenced global entry is less than 64, we don't need to compactify.
+      if (!PrunePlane && NumFunctionObjs == 0) {
+        unsigned MaxIdx = 0;
+        for (unsigned i = 0; i != ModLevel; ++i) {
+          unsigned Idx = NodeMap[CPlane[i]];
+          if (Idx > MaxIdx) MaxIdx = Idx;
+        }
+        PrunePlane = MaxIdx < 64;
+      }
+
+      // Ok, finally, if we decided to prune this plane out of the compaction
+      // table, do so now.
+      if (PrunePlane) {
+        TypePlane OldPlane;
+        std::swap(OldPlane, CPlane);
+
+        // Loop over the function local objects, relocating them to the global
+        // table plane.
+        for (unsigned i = ModLevel, e = OldPlane.size(); i != e; ++i) {
+          const Value *V = OldPlane[i];
+          CompactionNodeMap.erase(V);
+          assert(NodeMap.count(V) == 0 && "Value already in table??");
+          getOrCreateSlot(V);
+        }
+
+        // For compactified global values, just remove them from the compaction
+        // node map.
+        for (unsigned i = 0; i != ModLevel; ++i)
+          CompactionNodeMap.erase(OldPlane[i]);
+
+        // Update the new modulelevel for this plane.
+        assert(ctp < ModuleLevel.size() && "Cannot set modulelevel!");
+        ModuleLevel[ctp] = GPlane.size()-NumFunctionObjs;
+        assert((int)ModuleLevel[ctp] >= 0 && "Bad computation!");
+      }
+    }
+}
+
+
+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;
+    // Otherwise, if it's not in the compaction table, it must be in a
+    // non-compactified plane.
+  }
+
+  std::map<const Value*, unsigned>::const_iterator I = NodeMap.find(V);
+  if (I != NodeMap.end())
+    return (int)I->second;
+
+  // Do not number ConstantPointerRef's at all.  They are an abomination.
+  if (const ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(V))
+    return getSlot(CPR->getValue());
+
+  return -1;
+}
+
+
+int SlotCalculator::getOrCreateSlot(const Value *V) {
+  if (V->getType() == Type::VoidTy) return -1;
+
+  int SlotNo = getSlot(V);        // Check to see if it's already in!
+  if (SlotNo != -1) return SlotNo;
+
+  // Do not number ConstantPointerRef's at all.  They are an abomination.
+  if (const ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(V))
+    return getOrCreateSlot(CPR->getValue());
+
+  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!");
+
+      // 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.
+      if (!isa<ConstantArray>(C) || !cast<ConstantArray>(C)->isString()) {
+        // This makes sure that if a constant has uses (for example an array of
+        // const ints), that they are inserted also.
+        //
+        for (User::const_op_iterator I = C->op_begin(), E = C->op_end();
+             I != E; ++I)
+          getOrCreateSlot(*I);
+      } else {
+        assert(ModuleLevel.empty() &&
+               "How can a constant string be directly accessed in a function?");
+        // Otherwise, if we are emitting a bytecode file and this IS a string,
+        // remember it.
+        if (!C->isNullValue())
+          ConstantStrings.push_back(cast<ConstantArray>(C));
+      }
+    }
+
+  return insertValue(V);
+}
+
+
+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!");
+
+    int Plane = getSlot(D->getType());
+    assert(Plane != -1 && CompactionTable.size() > (unsigned)Plane &&
+           "Didn't find value type!");
+    if (!CompactionTable[Plane].empty())
+      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.
+  //
+  if (!dontIgnore)                               // Don't ignore nonignorables!
+    if (D->getType() == Type::VoidTy ) {         // Ignore void type nodes
+      SC_DEBUG("ignored value " << *D << "\n");
+      return -1;                  // We do need types unconditionally though
+    }
+
+  // If it's a type, make sure that all subtypes of the type are included...
+  if (const Type *TheTy = dyn_cast<Type>(D)) {
+
+    // Insert the current type before any subtypes.  This is important because
+    // recursive types elements are inserted in a bottom up order.  Changing
+    // this here can break things.  For example:
+    //
+    //    global { \2 * } { { \2 }* null }
+    //
+    int ResultSlot = doInsertValue(TheTy);
+    SC_DEBUG("  Inserted type: " << TheTy->getDescription() << " slot=" <<
+             ResultSlot << "\n");
+
+    // Loop over any contained types in the definition... in post
+    // order.
+    //
+    for (po_iterator<const Type*> I = po_begin(TheTy), E = po_end(TheTy);
+         I != E; ++I) {
+      if (*I != TheTy) {
+        const Type *SubTy = *I;
+	// If we haven't seen this sub type before, add it to our type table!
+        if (getSlot(SubTy) == -1) {
+          SC_DEBUG("  Inserting subtype: " << SubTy->getDescription() << "\n");
+          int Slot = doInsertValue(SubTy);
+          SC_DEBUG("  Inserted subtype: " << SubTy->getDescription() << 
+                   " slot=" << Slot << "\n");
+        }
+      }
+    }
+    return ResultSlot;
+  }
+
+  // Okay, everything is happy, actually insert the silly value now...
+  return doInsertValue(D);
+}
+
+// doInsertValue - This is a small helper function to be called only
+// be insertValue.
+//
+int SlotCalculator::doInsertValue(const Value *D) {
+  const Type *Typ = D->getType();
+  unsigned Ty;
+
+  // Used for debugging DefSlot=-1 assertion...
+  //if (Typ == Type::TypeTy)
+  //  cerr << "Inserting type '" << cast<Type>(D)->getDescription() << "'!\n";
+
+  if (Typ->isDerivedType()) {
+    int ValSlot;
+    if (CompactionTable.empty())
+      ValSlot = getSlot(Typ);
+    else
+      ValSlot = getGlobalSlot(Typ);
+    if (ValSlot == -1) {                // Have we already entered this type?
+      // Nope, this is the first we have seen the type, process it.
+      ValSlot = insertValue(Typ, true);
+      assert(ValSlot != -1 && "ProcessType returned -1 for a type?");
+    }
+    Ty = (unsigned)ValSlot;
+  } else {
+    Ty = Typ->getPrimitiveID();
+  }
+  
+  if (Table.size() <= Ty)    // Make sure we have the type plane allocated...
+    Table.resize(Ty+1, TypePlane());
+
+  // If this is the first value to get inserted into the type plane, make sure
+  // to insert the implicit null value...
+  if (Table[Ty].empty() &&  hasNullValue(Ty)) {
+    Value *ZeroInitializer = Constant::getNullValue(Typ);
+
+    // If we are pushing zeroinit, it will be handled below.
+    if (D != ZeroInitializer) {
+      Table[Ty].push_back(ZeroInitializer);
+      NodeMap[ZeroInitializer] = 0;
+    }
+  }
+
+  // Insert node into table and NodeMap...
+  unsigned DestSlot = NodeMap[D] = Table[Ty].size();
+  Table[Ty].push_back(D);
+
+  SC_DEBUG("  Inserting value [" << Ty << "] = " << D << " slot=" << 
+	   DestSlot << " [");
+  // G = Global, C = Constant, T = Type, F = Function, o = other
+  SC_DEBUG((isa<GlobalVariable>(D) ? "G" : (isa<Constant>(D) ? "C" : 
+           (isa<Type>(D) ? "T" : (isa<Function>(D) ? "F" : "o")))));
+  SC_DEBUG("]\n");
+  return (int)DestSlot;
+}