lib/Transforms/LevelRaise.cpp

   1 //===- LevelRaise.cpp - Code to change LLVM to higher level ---------------===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file was developed by the LLVM research group and is distributed under
   6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // This file implements the 'raising' part of the LevelChange API.  This is
  11 // useful because, in general, it makes the LLVM code terser and easier to
  12 // analyze.
  13 //
  14 //===----------------------------------------------------------------------===//
  15
  16 #include "llvm/Transforms/Scalar.h"
  17 #include "llvm/Transforms/Utils/Local.h"
  18 #include "TransformInternals.h"
  19 #include "llvm/Instructions.h"
  20 #include "llvm/Pass.h"
  21 #include "llvm/Transforms/Utils/BasicBlockUtils.h"
  22 #include "llvm/Support/CommandLine.h"
  23 #include "llvm/Support/Debug.h"
  24 #include "llvm/ADT/Statistic.h"
  25 #include "llvm/ADT/STLExtras.h"
  26 #include <algorithm>
  27 #include <iostream>
  28 using namespace llvm;
  29
  30 // StartInst - This enables the -raise-start-inst=foo option to cause the level
  31 // raising pass to start at instruction "foo", which is immensely useful for
  32 // debugging!
  33 //
  34 static cl::opt<std::string>
  35 StartInst("raise-start-inst", cl::Hidden, cl::value_desc("inst name"),
  36        cl::desc("Start raise pass at the instruction with the specified name"));
  37
  38 static Statistic<>
  39 NumLoadStorePeepholes("raise", "Number of load/store peepholes");
  40
  41 static Statistic<>
  42 NumGEPInstFormed("raise", "Number of other getelementptr's formed");
  43
  44 static Statistic<>
  45 NumExprTreesConv("raise", "Number of expression trees converted");
  46
  47 static Statistic<>
  48 NumCastOfCast("raise", "Number of cast-of-self removed");
  49
  50 static Statistic<>
  51 NumDCEorCP("raise", "Number of insts DCEd or constprop'd");
  52
  53 static Statistic<>
  54 NumVarargCallChanges("raise", "Number of vararg call peepholes");
  55
  56 #define PRINT_PEEPHOLE(ID, NUM, I)            \
  57   DEBUG(std::cerr << "Inst P/H " << ID << "[" << NUM << "] " << I)
  58
  59 #define PRINT_PEEPHOLE1(ID, I1) do { PRINT_PEEPHOLE(ID, 0, I1); } while (0)
  60 #define PRINT_PEEPHOLE2(ID, I1, I2) \
  61   do { PRINT_PEEPHOLE(ID, 0, I1); PRINT_PEEPHOLE(ID, 1, I2); } while (0)
  62 #define PRINT_PEEPHOLE3(ID, I1, I2, I3) \
  63   do { PRINT_PEEPHOLE(ID, 0, I1); PRINT_PEEPHOLE(ID, 1, I2); \
  64        PRINT_PEEPHOLE(ID, 2, I3); } while (0)
  65 #define PRINT_PEEPHOLE4(ID, I1, I2, I3, I4) \
  66   do { PRINT_PEEPHOLE(ID, 0, I1); PRINT_PEEPHOLE(ID, 1, I2); \
  67        PRINT_PEEPHOLE(ID, 2, I3); PRINT_PEEPHOLE(ID, 3, I4); } while (0)
  68
  69 namespace {
  70   struct RPR : public FunctionPass {
  71     virtual bool runOnFunction(Function &F);
  72
  73     virtual void getAnalysisUsage(AnalysisUsage &AU) const {
  74       AU.setPreservesCFG();
  75       AU.addRequired<TargetData>();
  76     }
  77
  78   private:
  79     bool DoRaisePass(Function &F);
  80     bool PeepholeOptimize(BasicBlock *BB, BasicBlock::iterator &BI);
  81   };
  82
  83   RegisterOpt<RPR> X("raise", "Raise Pointer References");
  84 }
  85
  86
  87 FunctionPass *llvm::createRaisePointerReferencesPass() {
  88   return new RPR();
  89 }
  90
  91
  92 // isReinterpretingCast - Return true if the cast instruction specified will
  93 // cause the operand to be "reinterpreted".  A value is reinterpreted if the
  94 // cast instruction would cause the underlying bits to change.
  95 //
  96 static inline bool isReinterpretingCast(const CastInst *CI) {
  97   return!CI->getOperand(0)->getType()->isLosslesslyConvertibleTo(CI->getType());
  98 }
  99
 100 bool RPR::PeepholeOptimize(BasicBlock *BB, BasicBlock::iterator &BI) {
 101   Instruction *I = BI;
 102   const TargetData &TD = getAnalysis<TargetData>();
 103
 104   if (CastInst *CI = dyn_cast<CastInst>(I)) {
 105     Value       *Src    = CI->getOperand(0);
 106     const Type  *DestTy = CI->getType();
 107
 108     // Peephole optimize the following instruction:
 109     // %V2 = cast <ty> %V to <ty>
 110     //
 111     // Into: <nothing>
 112     //
 113     if (DestTy == Src->getType()) {   // Check for a cast to same type as src!!
 114       PRINT_PEEPHOLE1("cast-of-self-ty", *CI);
 115       CI->replaceAllUsesWith(Src);
 116       if (!Src->hasName() && CI->hasName()) {
 117         std::string Name = CI->getName();
 118         CI->setName("");
 119         Src->setName(Name);
 120       }
 121
 122       // DCE the instruction now, to avoid having the iterative version of DCE
 123       // have to worry about it.
 124       //
 125       BI = BB->getInstList().erase(BI);
 126
 127       ++NumCastOfCast;
 128       return true;
 129     }
 130
 131     // Check to see if it's a cast of an instruction that does not depend on the
 132     // specific type of the operands to do it's job.
 133     if (!isReinterpretingCast(CI)) {
 134       ValueTypeCache ConvertedTypes;
 135
 136       // Check to see if we can convert the source of the cast to match the
 137       // destination type of the cast...
 138       //
 139       ConvertedTypes[CI] = CI->getType();  // Make sure the cast doesn't change
 140       if (ExpressionConvertibleToType(Src, DestTy, ConvertedTypes, TD)) {
 141         PRINT_PEEPHOLE3("CAST-SRC-EXPR-CONV:in ", *Src, *CI, *BB->getParent());
 142
 143         DEBUG(std::cerr << "\nCONVERTING SRC EXPR TYPE:\n");
 144         { // ValueMap must be destroyed before function verified!
 145           ValueMapCache ValueMap;
 146           Value *E = ConvertExpressionToType(Src, DestTy, ValueMap, TD);
 147
 148           if (Constant *CPV = dyn_cast<Constant>(E))
 149             CI->replaceAllUsesWith(CPV);
 150
 151           PRINT_PEEPHOLE1("CAST-SRC-EXPR-CONV:out", *E);
 152           DEBUG(std::cerr << "DONE CONVERTING SRC EXPR TYPE: \n"
 153                           << *BB->getParent());
 154         }
 155
 156         BI = BB->begin();  // Rescan basic block.  BI might be invalidated.
 157         ++NumExprTreesConv;
 158         return true;
 159       }
 160
 161       // Check to see if we can convert the users of the cast value to match the
 162       // source type of the cast...
 163       //
 164       ConvertedTypes.clear();
 165       // Make sure the source doesn't change type
 166       ConvertedTypes[Src] = Src->getType();
 167       if (ValueConvertibleToType(CI, Src->getType(), ConvertedTypes, TD)) {
 168         //PRINT_PEEPHOLE3("CAST-DEST-EXPR-CONV:in ", *Src, *CI,
 169         //                *BB->getParent());
 170
 171         DEBUG(std::cerr << "\nCONVERTING EXPR TYPE:\n");
 172         { // ValueMap must be destroyed before function verified!
 173           ValueMapCache ValueMap;
 174           ConvertValueToNewType(CI, Src, ValueMap, TD);  // This will delete CI!
 175         }
 176
 177         PRINT_PEEPHOLE1("CAST-DEST-EXPR-CONV:out", *Src);
 178         DEBUG(std::cerr << "DONE CONVERTING EXPR TYPE: \n\n" <<
 179               *BB->getParent());
 180
 181         BI = BB->begin();  // Rescan basic block.  BI might be invalidated.
 182         ++NumExprTreesConv;
 183         return true;
 184       }
 185     }
 186
 187     // Check to see if we are casting from a structure pointer to a pointer to
 188     // the first element of the structure... to avoid munching other peepholes,
 189     // we only let this happen if there are no add uses of the cast.
 190     //
 191     // Peephole optimize the following instructions:
 192     // %t1 = cast {<...>} * %StructPtr to <ty> *
 193     //
 194     // Into: %t2 = getelementptr {<...>} * %StructPtr, <0, 0, 0, ...>
 195     //       %t1 = cast <eltype> * %t1 to <ty> *
 196     //
 197     if (const CompositeType *CTy = getPointedToComposite(Src->getType()))
 198       if (const PointerType *DestPTy = dyn_cast<PointerType>(DestTy)) {
 199
 200         // Loop over uses of the cast, checking for add instructions.  If an add
 201         // exists, this is probably a part of a more complex GEP, so we don't
 202         // want to mess around with the cast.
 203         //
 204         bool HasAddUse = false;
 205         for (Value::use_iterator I = CI->use_begin(), E = CI->use_end();
 206              I != E; ++I)
 207           if (isa<Instruction>(*I) &&
 208               cast<Instruction>(*I)->getOpcode() == Instruction::Add) {
 209             HasAddUse = true; break;
 210           }
 211
 212         // If it doesn't have an add use, check to see if the dest type is
 213         // losslessly convertible to one of the types in the start of the struct
 214         // type.
 215         //
 216         if (!HasAddUse) {
 217           const Type *DestPointedTy = DestPTy->getElementType();
 218           unsigned Depth = 1;
 219           const CompositeType *CurCTy = CTy;
 220           const Type *ElTy = 0;
 221
 222           // Build the index vector, full of all zeros
 223           std::vector<Value*> Indices;
 224
 225           Indices.push_back(Constant::getNullValue(Type::UIntTy));
 226           while (CurCTy && !isa<PointerType>(CurCTy)) {
 227             if (const StructType *CurSTy = dyn_cast<StructType>(CurCTy)) {
 228               // Check for a zero element struct type... if we have one, bail.
 229               if (CurSTy->getNumElements() == 0) break;
 230
 231               // Grab the first element of the struct type, which must lie at
 232               // offset zero in the struct.
 233               //
 234               ElTy = CurSTy->getElementType(0);
 235             } else {
 236               ElTy = cast<SequentialType>(CurCTy)->getElementType();
 237             }
 238
 239             // Insert a zero to index through this type...
 240             Indices.push_back(Constant::getNullValue(Type::UIntTy));
 241
 242             // Did we find what we're looking for?
 243             if (ElTy->isLosslesslyConvertibleTo(DestPointedTy)) break;
 244
 245             // Nope, go a level deeper.
 246             ++Depth;
 247             CurCTy = dyn_cast<CompositeType>(ElTy);
 248             ElTy = 0;
 249           }
 250
 251           // Did we find what we were looking for? If so, do the transformation
 252           if (ElTy) {
 253             PRINT_PEEPHOLE1("cast-for-first:in", *CI);
 254
 255             std::string Name = CI->getName(); CI->setName("");
 256
 257             // Insert the new T cast instruction... stealing old T's name
 258             GetElementPtrInst *GEP = new GetElementPtrInst(Src, Indices,
 259                                                            Name, BI);
 260
 261             // Make the old cast instruction reference the new GEP instead of
 262             // the old src value.
 263             //
 264             CI->setOperand(0, GEP);
 265
 266             PRINT_PEEPHOLE2("cast-for-first:out", *GEP, *CI);
 267             ++NumGEPInstFormed;
 268             return true;
 269           }
 270         }
 271       }
 272
 273   } else if (StoreInst *SI = dyn_cast<StoreInst>(I)) {
 274     Value *Val     = SI->getOperand(0);
 275     Value *Pointer = SI->getPointerOperand();
 276
 277     // Peephole optimize the following instructions:
 278     // %t = cast <T1>* %P to <T2> * ;; If T1 is losslessly convertible to T2
 279     // store <T2> %V, <T2>* %t
 280     //
 281     // Into:
 282     // %t = cast <T2> %V to <T1>
 283     // store <T1> %t2, <T1>* %P
 284     //
 285     // Note: This is not taken care of by expr conversion because there might
 286     // not be a cast available for the store to convert the incoming value of.
 287     // This code is basically here to make sure that pointers don't have casts
 288     // if possible.
 289     //
 290     if (CastInst *CI = dyn_cast<CastInst>(Pointer))
 291       if (Value *CastSrc = CI->getOperand(0)) // CSPT = CastSrcPointerType
 292         if (const PointerType *CSPT = dyn_cast<PointerType>(CastSrc->getType()))
 293           // convertible types?
 294           if (Val->getType()->isLosslesslyConvertibleTo(CSPT->getElementType())) {
 295             PRINT_PEEPHOLE3("st-src-cast:in ", *Pointer, *Val, *SI);
 296
 297             // Insert the new T cast instruction... stealing old T's name
 298             std::string Name(CI->getName()); CI->setName("");
 299             CastInst *NCI = new CastInst(Val, CSPT->getElementType(),
 300                                          Name, BI);
 301
 302             // Replace the old store with a new one!
 303             ReplaceInstWithInst(BB->getInstList(), BI,
 304                                 SI = new StoreInst(NCI, CastSrc));
 305             PRINT_PEEPHOLE3("st-src-cast:out", *NCI, *CastSrc, *SI);
 306             ++NumLoadStorePeepholes;
 307             return true;
 308           }
 309
 310   } else if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
 311     Value *Pointer = LI->getOperand(0);
 312     const Type *PtrElType =
 313       cast<PointerType>(Pointer->getType())->getElementType();
 314
 315     // Peephole optimize the following instructions:
 316     // %Val = cast <T1>* to <T2>*    ;; If T1 is losslessly convertible to T2
 317     // %t = load <T2>* %P
 318     //
 319     // Into:
 320     // %t = load <T1>* %P
 321     // %Val = cast <T1> to <T2>
 322     //
 323     // Note: This is not taken care of by expr conversion because there might
 324     // not be a cast available for the store to convert the incoming value of.
 325     // This code is basically here to make sure that pointers don't have casts
 326     // if possible.
 327     //
 328     if (CastInst *CI = dyn_cast<CastInst>(Pointer))
 329       if (Value *CastSrc = CI->getOperand(0)) // CSPT = CastSrcPointerType
 330         if (const PointerType *CSPT = dyn_cast<PointerType>(CastSrc->getType()))
 331           // convertible types?
 332           if (PtrElType->isLosslesslyConvertibleTo(CSPT->getElementType())) {
 333             PRINT_PEEPHOLE2("load-src-cast:in ", *Pointer, *LI);
 334
 335             // Create the new load instruction... loading the pre-casted value
 336             LoadInst *NewLI = new LoadInst(CastSrc, LI->getName(), BI);
 337
 338             // Insert the new T cast instruction... stealing old T's name
 339             CastInst *NCI = new CastInst(NewLI, LI->getType(), CI->getName());
 340
 341             // Replace the old store with a new one!
 342             ReplaceInstWithInst(BB->getInstList(), BI, NCI);
 343             PRINT_PEEPHOLE3("load-src-cast:out", *NCI, *CastSrc, *NewLI);
 344             ++NumLoadStorePeepholes;
 345             return true;
 346           }
 347
 348   } else if (CallInst *CI = dyn_cast<CallInst>(I)) {
 349     // If we have a call with all varargs arguments, convert the call to use the
 350     // actual argument types present...
 351     //
 352     const PointerType *PTy = cast<PointerType>(CI->getCalledValue()->getType());
 353     const FunctionType *FTy = cast<FunctionType>(PTy->getElementType());
 354
 355     // Is the call to a vararg variable with no real parameters?
 356     if (FTy->isVarArg() && FTy->getNumParams() == 0 &&
 357         !CI->getCalledFunction()) {
 358       // If so, insert a new cast instruction, casting it to a function type
 359       // that matches the current arguments...
 360       //
 361       std::vector<const Type *> Params;  // Parameter types...
 362       for (unsigned i = 1, e = CI->getNumOperands(); i != e; ++i)
 363         Params.push_back(CI->getOperand(i)->getType());
 364
 365       FunctionType *NewFT = FunctionType::get(FTy->getReturnType(),
 366                                               Params, false);
 367       PointerType *NewPFunTy = PointerType::get(NewFT);
 368
 369       // Create a new cast, inserting it right before the function call...
 370       Value *NewCast;
 371       Constant *ConstantCallSrc = 0;
 372       if (Constant *CS = dyn_cast<Constant>(CI->getCalledValue()))
 373         ConstantCallSrc = CS;
 374
 375       if (ConstantCallSrc)
 376         NewCast = ConstantExpr::getCast(ConstantCallSrc, NewPFunTy);
 377       else
 378         NewCast = new CastInst(CI->getCalledValue(), NewPFunTy,
 379                                CI->getCalledValue()->getName()+"_c",CI);
 380
 381       // Create a new call instruction...
 382       CallInst *NewCall = new CallInst(NewCast,
 383                            std::vector<Value*>(CI->op_begin()+1, CI->op_end()));
 384       if (CI->isTailCall()) NewCall->setTailCall();
 385       NewCall->setCallingConv(CI->getCallingConv());
 386       ++BI;
 387       ReplaceInstWithInst(CI, NewCall);
 388
 389       ++NumVarargCallChanges;
 390       return true;
 391     }
 392
 393   }
 394
 395   return false;
 396 }
 397
 398
 399
 400
 401 bool RPR::DoRaisePass(Function &F) {
 402   bool Changed = false;
 403   for (Function::iterator BB = F.begin(), BBE = F.end(); BB != BBE; ++BB)
 404     for (BasicBlock::iterator BI = BB->begin(); BI != BB->end();) {
 405       DEBUG(std::cerr << "LevelRaising: " << *BI);
 406       if (dceInstruction(BI) || doConstantPropagation(BI)) {
 407         Changed = true;
 408         ++NumDCEorCP;
 409         DEBUG(std::cerr << "***\t\t^^-- Dead code eliminated!\n");
 410       } else if (PeepholeOptimize(BB, BI)) {
 411         Changed = true;
 412       } else {
 413         ++BI;
 414       }
 415     }
 416
 417   return Changed;
 418 }
 419
 420
 421 // runOnFunction - Raise a function representation to a higher level.
 422 bool RPR::runOnFunction(Function &F) {
 423   DEBUG(std::cerr << "\n\n\nStarting to work on Function '" << F.getName()
 424                   << "'\n");
 425
 426   // Insert casts for all incoming pointer pointer values that are treated as
 427   // arrays...
 428   //
 429   bool Changed = false, LocalChange;
 430
 431   // If the StartInst option was specified, then Peephole optimize that
 432   // instruction first if it occurs in this function.
 433   //
 434   if (!StartInst.empty()) {
 435     for (Function::iterator BB = F.begin(), BBE = F.end(); BB != BBE; ++BB)
 436       for (BasicBlock::iterator BI = BB->begin(); BI != BB->end(); ++BI)
 437         if (BI->getName() == StartInst) {
 438           bool SavedDebug = DebugFlag;  // Save the DEBUG() controlling flag.
 439           DebugFlag = true;             // Turn on DEBUG's
 440           Changed |= PeepholeOptimize(BB, BI);
 441           DebugFlag = SavedDebug;       // Restore DebugFlag to previous state
 442         }
 443   }
 444
 445   do {
 446     DEBUG(std::cerr << "Looping: \n" << F);
 447
 448     // Iterate over the function, refining it, until it converges on a stable
 449     // state
 450     LocalChange = false;
 451     while (DoRaisePass(F)) LocalChange = true;
 452     Changed |= LocalChange;
 453
 454   } while (LocalChange);
 455
 456   return Changed;
 457 }
 458