LLVM API Documentation

BBLiveVar.cpp

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00001 //===-- BBLiveVar.cpp - Live Variable Analysis for a BasicBlock -----------===//
00002 //
00003 //                     The LLVM Compiler Infrastructure
00004 //
00005 // This file was developed by the LLVM research group and is distributed under
00006 // the University of Illinois Open Source License. See LICENSE.TXT for details.
00007 //
00008 //===----------------------------------------------------------------------===//
00009 //
00010 // This is a wrapper class for BasicBlock which is used by live var analysis.
00011 //
00012 //===----------------------------------------------------------------------===//
00013 
00014 #include "BBLiveVar.h"
00015 #include "FunctionLiveVarInfo.h"
00016 #include "llvm/CodeGen/MachineInstr.h"
00017 #include "llvm/CodeGen/MachineBasicBlock.h"
00018 #include "llvm/Support/CFG.h"
00019 #include "llvm/ADT/SetOperations.h"
00020 #include "../SparcV9Internals.h"
00021 #include <iostream>
00022 
00023 namespace llvm {
00024 
00025 BBLiveVar::BBLiveVar(const BasicBlock &bb,
00026                      const MachineBasicBlock &mbb,
00027                      unsigned id)
00028   : BB(bb), MBB(mbb), POID(id) {
00029   InSetChanged = OutSetChanged = false;
00030 
00031   calcDefUseSets();
00032 }
00033 
00034 //-----------------------------------------------------------------------------
00035 // calculates def and use sets for each BB
00036 // There are two passes over operands of a machine instruction. This is
00037 // because, we can have instructions like V = V + 1, since we no longer
00038 // assume single definition.
00039 //-----------------------------------------------------------------------------
00040 
00041 void BBLiveVar::calcDefUseSets() {
00042   // iterate over all the machine instructions in BB
00043   for (MachineBasicBlock::const_reverse_iterator MII = MBB.rbegin(),
00044          MIE = MBB.rend(); MII != MIE; ++MII) {
00045     const MachineInstr *MI = &*MII;
00046 
00047     if (DEBUG_LV >= LV_DEBUG_Verbose) {
00048       std::cerr << " *Iterating over machine instr ";
00049       MI->dump();
00050       std::cerr << "\n";
00051     }
00052 
00053     // iterate over  MI operands to find defs
00054     for (MachineInstr::const_val_op_iterator OpI = MI->begin(), OpE = MI->end();
00055          OpI != OpE; ++OpI)
00056       if (OpI.isDef()) // add to Defs if this operand is a def
00057         addDef(*OpI);
00058 
00059     // do for implicit operands as well
00060     for (unsigned i = 0; i < MI->getNumImplicitRefs(); ++i)
00061       if (MI->getImplicitOp(i).isDef())
00062         addDef(MI->getImplicitRef(i));
00063 
00064     // iterate over MI operands to find uses
00065     for (MachineInstr::const_val_op_iterator OpI = MI->begin(), OpE = MI->end();
00066          OpI != OpE; ++OpI) {
00067       const Value *Op = *OpI;
00068 
00069       if (isa<BasicBlock>(Op))
00070         continue;             // don't process labels
00071 
00072       if (OpI.isUse()) { // add to Uses only if this operand is a use
00073         //
00074         // *** WARNING: The following code for handling dummy PHI machine
00075         //     instructions is untested.  The previous code was broken and I
00076         //     fixed it, but it turned out to be unused as long as Phi
00077         //     elimination is performed during instruction selection.
00078         //
00079         // Put Phi operands in UseSet for the incoming edge, not node.
00080         // They must not "hide" later defs, and must be handled specially
00081         // during set propagation over the CFG.
00082         if (MI->getOpcode() == V9::PHI) {         // for a phi node
00083           const Value *ArgVal = Op;
00084           const BasicBlock *PredBB = cast<BasicBlock>(*++OpI); // next ptr is BB
00085 
00086           PredToEdgeInSetMap[PredBB].insert(ArgVal);
00087 
00088           if (DEBUG_LV >= LV_DEBUG_Verbose)
00089             std::cerr << "   - phi operand " << RAV(ArgVal) << " came from BB "
00090                       << RAV(PredBB) << "\n";
00091         } // if( IsPhi )
00092         else {
00093           // It is not a Phi use: add to regular use set and remove later defs.
00094           addUse(Op);
00095         }
00096       } // if a use
00097     } // for all operands
00098 
00099     // do for implicit operands as well
00100     for (unsigned i = 0; i < MI->getNumImplicitRefs(); ++i) {
00101       assert(MI->getOpcode() != V9::PHI && "Phi cannot have implicit operands");
00102       const Value *Op = MI->getImplicitRef(i);
00103 
00104       if (Op->getType() == Type::LabelTy)             // don't process labels
00105         continue;
00106 
00107       if (MI->getImplicitOp(i).isUse())
00108         addUse(Op);
00109     }
00110   } // for all machine instructions
00111 }
00112 
00113 
00114 
00115 //-----------------------------------------------------------------------------
00116 // To add an operand which is a def
00117 //-----------------------------------------------------------------------------
00118 void BBLiveVar::addDef(const Value *Op) {
00119   DefSet.insert(Op);     // operand is a def - so add to def set
00120   InSet.erase(Op);       // this definition kills any later uses
00121   InSetChanged = true;
00122 
00123   if (DEBUG_LV >= LV_DEBUG_Verbose) std::cerr << "  +Def: " << RAV(Op) << "\n";
00124 }
00125 
00126 
00127 //-----------------------------------------------------------------------------
00128 // To add an operand which is a use
00129 //-----------------------------------------------------------------------------
00130 void  BBLiveVar::addUse(const Value *Op) {
00131   InSet.insert(Op);   // An operand is a use - so add to use set
00132   DefSet.erase(Op);   // remove if there is a def below this use
00133   InSetChanged = true;
00134 
00135   if (DEBUG_LV >= LV_DEBUG_Verbose) std::cerr << "   Use: " << RAV(Op) << "\n";
00136 }
00137 
00138 
00139 //-----------------------------------------------------------------------------
00140 // Applies the transfer function to a basic block to produce the InSet using
00141 // the OutSet.
00142 //-----------------------------------------------------------------------------
00143 
00144 bool BBLiveVar::applyTransferFunc() {
00145   // IMPORTANT: caller should check whether the OutSet changed
00146   //           (else no point in calling)
00147 
00148   ValueSet OutMinusDef = set_difference(OutSet, DefSet);
00149   InSetChanged = set_union(InSet, OutMinusDef);
00150 
00151   OutSetChanged = false;      // no change to OutSet since transf func applied
00152   return InSetChanged;
00153 }
00154 
00155 
00156 //-----------------------------------------------------------------------------
00157 // calculates Out set using In sets of the successors
00158 //-----------------------------------------------------------------------------
00159 
00160 bool BBLiveVar::setPropagate(ValueSet *OutSet, const ValueSet *InSet,
00161                              const BasicBlock *PredBB) {
00162   bool Changed = false;
00163 
00164   // merge all members of InSet into OutSet of the predecessor
00165   for (ValueSet::const_iterator InIt = InSet->begin(), InE = InSet->end();
00166        InIt != InE; ++InIt)
00167     if ((OutSet->insert(*InIt)).second)
00168       Changed = true;
00169 
00170   //
00171   //**** WARNING: The following code for handling dummy PHI machine
00172   //     instructions is untested.  See explanation above.
00173   //
00174   // then merge all members of the EdgeInSet for the predecessor into the OutSet
00175   const ValueSet& EdgeInSet = PredToEdgeInSetMap[PredBB];
00176   for (ValueSet::const_iterator InIt = EdgeInSet.begin(), InE = EdgeInSet.end();
00177        InIt != InE; ++InIt)
00178     if ((OutSet->insert(*InIt)).second)
00179       Changed = true;
00180   //
00181   //****
00182 
00183   return Changed;
00184 }
00185 
00186 
00187 //-----------------------------------------------------------------------------
00188 // propagates in set to OutSets of PREDECESSORs
00189 //-----------------------------------------------------------------------------
00190 
00191 bool BBLiveVar::applyFlowFunc(hash_map<const BasicBlock*,
00192                                        BBLiveVar*> &BBLiveVarInfo) {
00193   // IMPORTANT: caller should check whether inset changed
00194   //            (else no point in calling)
00195 
00196   // If this BB changed any OutSets of preds whose POID is lower, than we need
00197   // another iteration...
00198   //
00199   bool needAnotherIt = false;
00200 
00201   for (pred_const_iterator PI = pred_begin(&BB), PE = pred_end(&BB);
00202        PI != PE ; ++PI) {
00203     BBLiveVar *PredLVBB = BBLiveVarInfo[*PI];
00204 
00205     // do set union
00206     if (setPropagate(&PredLVBB->OutSet, &InSet, *PI)) {
00207       PredLVBB->OutSetChanged = true;
00208 
00209       // if the predec POID is lower than mine
00210       if (PredLVBB->getPOId() <= POID)
00211         needAnotherIt = true;
00212     }
00213   }  // for
00214 
00215   return needAnotherIt;
00216 }
00217 
00218 
00219 
00220 // ----------------- Methods For Debugging (Printing) -----------------
00221 
00222 void BBLiveVar::printAllSets() const {
00223   std::cerr << "  Defs: "; printSet(DefSet);  std::cerr << "\n";
00224   std::cerr << "  In: ";  printSet(InSet);  std::cerr << "\n";
00225   std::cerr << "  Out: "; printSet(OutSet);  std::cerr << "\n";
00226 }
00227 
00228 void BBLiveVar::printInOutSets() const {
00229   std::cerr << "  In: ";   printSet(InSet);  std::cerr << "\n";
00230   std::cerr << "  Out: ";  printSet(OutSet);  std::cerr << "\n";
00231 }
00232 
00233 } // End llvm namespace