path: root/lib/Bytecode/Writer/SlotCalculator.cpp

//===-- 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 as required.
//
// This is used primarily for when writing a file to disk, either in bytecode
// or source format.
//
//===----------------------------------------------------------------------===//

#include "llvm/SlotCalculator.h"
#include "llvm/Analysis/ConstantsScanner.h"
#include "llvm/Constants.h"
#include "llvm/DerivedTypes.h"
#include "llvm/iOther.h"
#include "llvm/Module.h"
#include "llvm/SymbolTable.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, bool buildBytecodeInfo) {
  BuildBytecodeInfo = buildBytecodeInfo;
  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, bool buildBytecodeInfo) {
  BuildBytecodeInfo = buildBytecodeInfo;
  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
}


// 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.
  //
  if (BuildBytecodeInfo) {
    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 (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 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.
  if (BuildBytecodeInfo) {
    SC_DEBUG("Inserting function constants:\n");
    for (Module::const_iterator F = TheModule->begin(), E = TheModule->end();
         F != E; ++F)
      for_each(constant_begin(F), constant_end(F),
               bind_obj(this, &SlotCalculator::getOrCreateSlot));
  }
#endif

  // Insert constants that are named at module level into the slot pool so that
  // the module symbol table can refer to them...
  //
  if (BuildBytecodeInfo) {
    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 (BuildBytecodeInfo && 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) {
  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)
      getOrCreateSlot(TI->second);
}

void SlotCalculator::processSymbolTableConstants(const SymbolTable *ST) {
  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))
	getOrCreateSlot(TI->second);
}


void SlotCalculator::incorporateFunction(const Function *F)