lib/CodeGen/Analysis.cpp

   1 //===-- Analysis.cpp - CodeGen LLVM IR Analysis Utilities --*- C++ ------*-===//
   2 //
   3 //                     The LLVM Compiler Infrastructure
   4 //
   5 // This file is distributed under the University of Illinois Open Source
   6 // License. See LICENSE.TXT for details.
   7 //
   8 //===----------------------------------------------------------------------===//
   9 //
  10 // This file defines several CodeGen-specific LLVM IR analysis utilties.
  11 //
  12 //===----------------------------------------------------------------------===//
  13
  14 #include "llvm/CodeGen/Analysis.h"
  15 #include "llvm/DerivedTypes.h"
  16 #include "llvm/Function.h"
  17 #include "llvm/Instructions.h"
  18 #include "llvm/IntrinsicInst.h"
  19 #include "llvm/LLVMContext.h"
  20 #include "llvm/Module.h"
  21 #include "llvm/CodeGen/MachineFunction.h"
  22 #include "llvm/CodeGen/SelectionDAG.h"
  23 #include "llvm/Target/TargetData.h"
  24 #include "llvm/Target/TargetLowering.h"
  25 #include "llvm/Target/TargetOptions.h"
  26 #include "llvm/Support/ErrorHandling.h"
  27 #include "llvm/Support/MathExtras.h"
  28 using namespace llvm;
  29
  30 /// ComputeLinearIndex - Given an LLVM IR aggregate type and a sequence
  31 /// of insertvalue or extractvalue indices that identify a member, return
  32 /// the linearized index of the start of the member.
  33 ///
  34 unsigned llvm::ComputeLinearIndex(const Type *Ty,
  35                                   const unsigned *Indices,
  36                                   const unsigned *IndicesEnd,
  37                                   unsigned CurIndex) {
  38   // Base case: We're done.
  39   if (Indices && Indices == IndicesEnd)
  40     return CurIndex;
  41
  42   // Given a struct type, recursively traverse the elements.
  43   if (const StructType *STy = dyn_cast<StructType>(Ty)) {
  44     for (StructType::element_iterator EB = STy->element_begin(),
  45                                       EI = EB,
  46                                       EE = STy->element_end();
  47         EI != EE; ++EI) {
  48       if (Indices && *Indices == unsigned(EI - EB))
  49         return ComputeLinearIndex(*EI, Indices+1, IndicesEnd, CurIndex);
  50       CurIndex = ComputeLinearIndex(*EI, 0, 0, CurIndex);
  51     }
  52     return CurIndex;
  53   }
  54   // Given an array type, recursively traverse the elements.
  55   else if (const ArrayType *ATy = dyn_cast<ArrayType>(Ty)) {
  56     const Type *EltTy = ATy->getElementType();
  57     for (unsigned i = 0, e = ATy->getNumElements(); i != e; ++i) {
  58       if (Indices && *Indices == i)
  59         return ComputeLinearIndex(EltTy, Indices+1, IndicesEnd, CurIndex);
  60       CurIndex = ComputeLinearIndex(EltTy, 0, 0, CurIndex);
  61     }
  62     return CurIndex;
  63   }
  64   // We haven't found the type we're looking for, so keep searching.
  65   return CurIndex + 1;
  66 }
  67
  68 /// ComputeValueVTs - Given an LLVM IR type, compute a sequence of
  69 /// EVTs that represent all the individual underlying
  70 /// non-aggregate types that comprise it.
  71 ///
  72 /// If Offsets is non-null, it points to a vector to be filled in
  73 /// with the in-memory offsets of each of the individual values.
  74 ///
  75 void llvm::ComputeValueVTs(const TargetLowering &TLI, const Type *Ty,
  76                            SmallVectorImpl<EVT> &ValueVTs,
  77                            SmallVectorImpl<uint64_t> *Offsets,
  78                            uint64_t StartingOffset) {
  79   // Given a struct type, recursively traverse the elements.
  80   if (const StructType *STy = dyn_cast<StructType>(Ty)) {
  81     const StructLayout *SL = TLI.getTargetData()->getStructLayout(STy);
  82     for (StructType::element_iterator EB = STy->element_begin(),
  83                                       EI = EB,
  84                                       EE = STy->element_end();
  85          EI != EE; ++EI)
  86       ComputeValueVTs(TLI, *EI, ValueVTs, Offsets,
  87                       StartingOffset + SL->getElementOffset(EI - EB));
  88     return;
  89   }
  90   // Given an array type, recursively traverse the elements.
  91   if (const ArrayType *ATy = dyn_cast<ArrayType>(Ty)) {
  92     const Type *EltTy = ATy->getElementType();
  93     uint64_t EltSize = TLI.getTargetData()->getTypeAllocSize(EltTy);
  94     for (unsigned i = 0, e = ATy->getNumElements(); i != e; ++i)
  95       ComputeValueVTs(TLI, EltTy, ValueVTs, Offsets,
  96                       StartingOffset + i * EltSize);
  97     return;
  98   }
  99   // Interpret void as zero return values.
 100   if (Ty->isVoidTy())
 101     return;
 102   // Base case: we can get an EVT for this LLVM IR type.
 103   ValueVTs.push_back(TLI.getValueType(Ty));
 104   if (Offsets)
 105     Offsets->push_back(StartingOffset);
 106 }
 107
 108 /// ExtractTypeInfo - Returns the type info, possibly bitcast, encoded in V.
 109 GlobalVariable *llvm::ExtractTypeInfo(Value *V) {
 110   V = V->stripPointerCasts();
 111   GlobalVariable *GV = dyn_cast<GlobalVariable>(V);
 112
 113   if (GV && GV->getName() == "llvm.eh.catch.all.value") {
 114     assert(GV->hasInitializer() &&
 115            "The EH catch-all value must have an initializer");
 116     Value *Init = GV->getInitializer();
 117     GV = dyn_cast<GlobalVariable>(Init);
 118     if (!GV) V = cast<ConstantPointerNull>(Init);
 119   }
 120
 121   assert((GV || isa<ConstantPointerNull>(V)) &&
 122          "TypeInfo must be a global variable or NULL");
 123   return GV;
 124 }
 125
 126 /// hasInlineAsmMemConstraint - Return true if the inline asm instruction being
 127 /// processed uses a memory 'm' constraint.
 128 bool
 129 llvm::hasInlineAsmMemConstraint(InlineAsm::ConstraintInfoVector &CInfos,
 130                                 const TargetLowering &TLI) {
 131   for (unsigned i = 0, e = CInfos.size(); i != e; ++i) {
 132     InlineAsm::ConstraintInfo &CI = CInfos[i];
 133     for (unsigned j = 0, ee = CI.Codes.size(); j != ee; ++j) {
 134       TargetLowering::ConstraintType CType = TLI.getConstraintType(CI.Codes[j]);
 135       if (CType == TargetLowering::C_Memory)
 136         return true;
 137     }
 138
 139     // Indirect operand accesses access memory.
 140     if (CI.isIndirect)
 141       return true;
 142   }
 143
 144   return false;
 145 }
 146
 147 /// getFCmpCondCode - Return the ISD condition code corresponding to
 148 /// the given LLVM IR floating-point condition code.  This includes
 149 /// consideration of global floating-point math flags.
 150 ///
 151 ISD::CondCode llvm::getFCmpCondCode(FCmpInst::Predicate Pred) {
 152   ISD::CondCode FPC, FOC;
 153   switch (Pred) {
 154   case FCmpInst::FCMP_FALSE: FOC = FPC = ISD::SETFALSE; break;
 155   case FCmpInst::FCMP_OEQ:   FOC = ISD::SETEQ; FPC = ISD::SETOEQ; break;
 156   case FCmpInst::FCMP_OGT:   FOC = ISD::SETGT; FPC = ISD::SETOGT; break;
 157   case FCmpInst::FCMP_OGE:   FOC = ISD::SETGE; FPC = ISD::SETOGE; break;
 158   case FCmpInst::FCMP_OLT:   FOC = ISD::SETLT; FPC = ISD::SETOLT; break;
 159   case FCmpInst::FCMP_OLE:   FOC = ISD::SETLE; FPC = ISD::SETOLE; break;
 160   case FCmpInst::FCMP_ONE:   FOC = ISD::SETNE; FPC = ISD::SETONE; break;
 161   case FCmpInst::FCMP_ORD:   FOC = FPC = ISD::SETO;   break;
 162   case FCmpInst::FCMP_UNO:   FOC = FPC = ISD::SETUO;  break;
 163   case FCmpInst::FCMP_UEQ:   FOC = ISD::SETEQ; FPC = ISD::SETUEQ; break;
 164   case FCmpInst::FCMP_UGT:   FOC = ISD::SETGT; FPC = ISD::SETUGT; break;
 165   case FCmpInst::FCMP_UGE:   FOC = ISD::SETGE; FPC = ISD::SETUGE; break;
 166   case FCmpInst::FCMP_ULT:   FOC = ISD::SETLT; FPC = ISD::SETULT; break;
 167   case FCmpInst::FCMP_ULE:   FOC = ISD::SETLE; FPC = ISD::SETULE; break;
 168   case FCmpInst::FCMP_UNE:   FOC = ISD::SETNE; FPC = ISD::SETUNE; break;
 169   case FCmpInst::FCMP_TRUE:  FOC = FPC = ISD::SETTRUE; break;
 170   default:
 171     llvm_unreachable("Invalid FCmp predicate opcode!");
 172     FOC = FPC = ISD::SETFALSE;
 173     break;
 174   }
 175   if (NoNaNsFPMath)
 176     return FOC;
 177   else
 178     return FPC;
 179 }
 180
 181 /// getICmpCondCode - Return the ISD condition code corresponding to
 182 /// the given LLVM IR integer condition code.
 183 ///
 184 ISD::CondCode llvm::getICmpCondCode(ICmpInst::Predicate Pred) {
 185   switch (Pred) {
 186   case ICmpInst::ICMP_EQ:  return ISD::SETEQ;
 187   case ICmpInst::ICMP_NE:  return ISD::SETNE;
 188   case ICmpInst::ICMP_SLE: return ISD::SETLE;
 189   case ICmpInst::ICMP_ULE: return ISD::SETULE;
 190   case ICmpInst::ICMP_SGE: return ISD::SETGE;
 191   case ICmpInst::ICMP_UGE: return ISD::SETUGE;
 192   case ICmpInst::ICMP_SLT: return ISD::SETLT;
 193   case ICmpInst::ICMP_ULT: return ISD::SETULT;
 194   case ICmpInst::ICMP_SGT: return ISD::SETGT;
 195   case ICmpInst::ICMP_UGT: return ISD::SETUGT;
 196   default:
 197     llvm_unreachable("Invalid ICmp predicate opcode!");
 198     return ISD::SETNE;
 199   }
 200 }
 201
 202 /// Test if the given instruction is in a position to be optimized
 203 /// with a tail-call. This roughly means that it's in a block with
 204 /// a return and there's nothing that needs to be scheduled
 205 /// between it and the return.
 206 ///
 207 /// This function only tests target-independent requirements.
 208 bool llvm::isInTailCallPosition(ImmutableCallSite CS, Attributes CalleeRetAttr,
 209                                 const TargetLowering &TLI) {
 210   const Instruction *I = CS.getInstruction();
 211   const BasicBlock *ExitBB = I->getParent();
 212   const TerminatorInst *Term = ExitBB->getTerminator();
 213   const ReturnInst *Ret = dyn_cast<ReturnInst>(Term);
 214
 215   // The block must end in a return statement or unreachable.
 216   //
 217   // FIXME: Decline tailcall if it's not guaranteed and if the block ends in
 218   // an unreachable, for now. The way tailcall optimization is currently
 219   // implemented means it will add an epilogue followed by a jump. That is
 220   // not profitable. Also, if the callee is a special function (e.g.
 221   // longjmp on x86), it can end up causing miscompilation that has not
 222   // been fully understood.
 223   if (!Ret &&
 224       (!GuaranteedTailCallOpt || !isa<UnreachableInst>(Term))) return false;
 225
 226   // If I will have a chain, make sure no other instruction that will have a
 227   // chain interposes between I and the return.
 228   if (I->mayHaveSideEffects() || I->mayReadFromMemory() ||
 229       !I->isSafeToSpeculativelyExecute())
 230     for (BasicBlock::const_iterator BBI = prior(prior(ExitBB->end())); ;
 231          --BBI) {
 232       if (&*BBI == I)
 233         break;
 234       // Debug info intrinsics do not get in the way of tail call optimization.
 235       if (isa<DbgInfoIntrinsic>(BBI))
 236         continue;
 237       if (BBI->mayHaveSideEffects() || BBI->mayReadFromMemory() ||
 238           !BBI->isSafeToSpeculativelyExecute())
 239         return false;
 240     }
 241
 242   // If the block ends with a void return or unreachable, it doesn't matter
 243   // what the call's return type is.
 244   if (!Ret || Ret->getNumOperands() == 0) return true;
 245
 246   // If the return value is undef, it doesn't matter what the call's
 247   // return type is.
 248   if (isa<UndefValue>(Ret->getOperand(0))) return true;
 249
 250   // Conservatively require the attributes of the call to match those of
 251   // the return. Ignore noalias because it doesn't affect the call sequence.
 252   const Function *F = ExitBB->getParent();
 253   unsigned CallerRetAttr = F->getAttributes().getRetAttributes();
 254   if ((CalleeRetAttr ^ CallerRetAttr) & ~Attribute::NoAlias)
 255     return false;
 256
 257   // It's not safe to eliminate the sign / zero extension of the return value.
 258   if ((CallerRetAttr & Attribute::ZExt) || (CallerRetAttr & Attribute::SExt))
 259     return false;
 260
 261   // Otherwise, make sure the unmodified return value of I is the return value.
 262   for (const Instruction *U = dyn_cast<Instruction>(Ret->getOperand(0)); ;
 263        U = dyn_cast<Instruction>(U->getOperand(0))) {
 264     if (!U)
 265       return false;
 266     if (!U->hasOneUse())
 267       return false;
 268     if (U == I)
 269       break;
 270     // Check for a truly no-op truncate.
 271     if (isa<TruncInst>(U) &&
 272         TLI.isTruncateFree(U->getOperand(0)->getType(), U->getType()))
 273       continue;
 274     // Check for a truly no-op bitcast.
 275     if (isa<BitCastInst>(U) &&
 276         (U->getOperand(0)->getType() == U->getType() ||
 277          (U->getOperand(0)->getType()->isPointerTy() &&
 278           U->getType()->isPointerTy())))
 279       continue;
 280     // Otherwise it's not a true no-op.
 281     return false;
 282   }
 283
 284   return true;
 285 }
 286
 287 bool llvm::isInTailCallPosition(SelectionDAG &DAG, SDNode *Node,
 288                                 const TargetLowering &TLI) {
 289   const Function *F = DAG.getMachineFunction().getFunction();
 290
 291   // Conservatively require the attributes of the call to match those of
 292   // the return. Ignore noalias because it doesn't affect the call sequence.
 293   unsigned CallerRetAttr = F->getAttributes().getRetAttributes();
 294   if (CallerRetAttr & ~Attribute::NoAlias)
 295     return false;
 296
 297   // It's not safe to eliminate the sign / zero extension of the return value.
 298   if ((CallerRetAttr & Attribute::ZExt) || (CallerRetAttr & Attribute::SExt))
 299     return false;
 300
 301   // Check if the only use is a function return node.
 302   return TLI.isUsedByReturnOnly(Node);
 303 }