lib/Analysis/ConstantFolding.cpp

   1 //===-- ConstantFolding.cpp - Analyze constant folding possibilities ------===//
   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 family of functions determines the possibility of performing constant
  11 // folding.
  12 //
  13 //===----------------------------------------------------------------------===//
  14
  15 #include "llvm/Analysis/ConstantFolding.h"
  16 #include "llvm/Constants.h"
  17 #include "llvm/DerivedTypes.h"
  18 #include "llvm/Function.h"
  19 #include "llvm/GlobalVariable.h"
  20 #include "llvm/Instructions.h"
  21 #include "llvm/Intrinsics.h"
  22 #include "llvm/LLVMContext.h"
  23 #include "llvm/ADT/SmallVector.h"
  24 #include "llvm/ADT/StringMap.h"
  25 #include "llvm/Target/TargetData.h"
  26 #include "llvm/Support/ErrorHandling.h"
  27 #include "llvm/Support/GetElementPtrTypeIterator.h"
  28 #include "llvm/Support/MathExtras.h"
  29 #include <cerrno>
  30 #include <cmath>
  31 using namespace llvm;
  32
  33 //===----------------------------------------------------------------------===//
  34 // Constant Folding internal helper functions
  35 //===----------------------------------------------------------------------===//
  36
  37 /// IsConstantOffsetFromGlobal - If this constant is actually a constant offset
  38 /// from a global, return the global and the constant.  Because of
  39 /// constantexprs, this function is recursive.
  40 static bool IsConstantOffsetFromGlobal(Constant *C, GlobalValue *&GV,
  41                                        int64_t &Offset, const TargetData &TD) {
  42   // Trivial case, constant is the global.
  43   if ((GV = dyn_cast<GlobalValue>(C))) {
  44     Offset = 0;
  45     return true;
  46   }
  47
  48   // Otherwise, if this isn't a constant expr, bail out.
  49   ConstantExpr *CE = dyn_cast<ConstantExpr>(C);
  50   if (!CE) return false;
  51
  52   // Look through ptr->int and ptr->ptr casts.
  53   if (CE->getOpcode() == Instruction::PtrToInt ||
  54       CE->getOpcode() == Instruction::BitCast)
  55     return IsConstantOffsetFromGlobal(CE->getOperand(0), GV, Offset, TD);
  56
  57   // i32* getelementptr ([5 x i32]* @a, i32 0, i32 5)
  58   if (CE->getOpcode() == Instruction::GetElementPtr) {
  59     // Cannot compute this if the element type of the pointer is missing size
  60     // info.
  61     if (!cast<PointerType>(CE->getOperand(0)->getType())
  62                  ->getElementType()->isSized())
  63       return false;
  64
  65     // If the base isn't a global+constant, we aren't either.
  66     if (!IsConstantOffsetFromGlobal(CE->getOperand(0), GV, Offset, TD))
  67       return false;
  68
  69     // Otherwise, add any offset that our operands provide.
  70     gep_type_iterator GTI = gep_type_begin(CE);
  71     for (User::const_op_iterator i = CE->op_begin() + 1, e = CE->op_end();
  72          i != e; ++i, ++GTI) {
  73       ConstantInt *CI = dyn_cast<ConstantInt>(*i);
  74       if (!CI) return false;  // Index isn't a simple constant?
  75       if (CI->getZExtValue() == 0) continue;  // Not adding anything.
  76
  77       if (const StructType *ST = dyn_cast<StructType>(*GTI)) {
  78         // N = N + Offset
  79         Offset += TD.getStructLayout(ST)->getElementOffset(CI->getZExtValue());
  80       } else {
  81         const SequentialType *SQT = cast<SequentialType>(*GTI);
  82         Offset += TD.getTypeAllocSize(SQT->getElementType())*CI->getSExtValue();
  83       }
  84     }
  85     return true;
  86   }
  87
  88   return false;
  89 }
  90
  91
  92 /// SymbolicallyEvaluateBinop - One of Op0/Op1 is a constant expression.
  93 /// Attempt to symbolically evaluate the result of a binary operator merging
  94 /// these together.  If target data info is available, it is provided as TD,
  95 /// otherwise TD is null.
  96 static Constant *SymbolicallyEvaluateBinop(unsigned Opc, Constant *Op0,
  97                                            Constant *Op1, const TargetData *TD,
  98                                            LLVMContext &Context){
  99   // SROA
 100
 101   // Fold (and 0xffffffff00000000, (shl x, 32)) -> shl.
 102   // Fold (lshr (or X, Y), 32) -> (lshr [X/Y], 32) if one doesn't contribute
 103   // bits.
 104
 105
 106   // If the constant expr is something like &A[123] - &A[4].f, fold this into a
 107   // constant.  This happens frequently when iterating over a global array.
 108   if (Opc == Instruction::Sub && TD) {
 109     GlobalValue *GV1, *GV2;
 110     int64_t Offs1, Offs2;
 111
 112     if (IsConstantOffsetFromGlobal(Op0, GV1, Offs1, *TD))
 113       if (IsConstantOffsetFromGlobal(Op1, GV2, Offs2, *TD) &&
 114           GV1 == GV2) {
 115         // (&GV+C1) - (&GV+C2) -> C1-C2, pointer arithmetic cannot overflow.
 116         return ConstantInt::get(Op0->getType(), Offs1-Offs2);
 117       }
 118   }
 119
 120   return 0;
 121 }
 122
 123 /// SymbolicallyEvaluateGEP - If we can symbolically evaluate the specified GEP
 124 /// constant expression, do so.
 125 static Constant *SymbolicallyEvaluateGEP(Constant* const* Ops, unsigned NumOps,
 126                                          const Type *ResultTy,
 127                                          LLVMContext &Context,
 128                                          const TargetData *TD) {
 129   Constant *Ptr = Ops[0];
 130   if (!TD || !cast<PointerType>(Ptr->getType())->getElementType()->isSized())
 131     return 0;
 132
 133   uint64_t BasePtr = 0;
 134   if (!Ptr->isNullValue()) {
 135     // If this is a inttoptr from a constant int, we can fold this as the base,
 136     // otherwise we can't.
 137     if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
 138       if (CE->getOpcode() == Instruction::IntToPtr)
 139         if (ConstantInt *Base = dyn_cast<ConstantInt>(CE->getOperand(0)))
 140           BasePtr = Base->getZExtValue();
 141
 142     if (BasePtr == 0)
 143       return 0;
 144   }
 145
 146   // If this is a constant expr gep that is effectively computing an
 147   // "offsetof", fold it into 'cast int Size to T*' instead of 'gep 0, 0, 12'
 148   for (unsigned i = 1; i != NumOps; ++i)
 149     if (!isa<ConstantInt>(Ops[i]))
 150       return false;
 151
 152   uint64_t Offset = TD->getIndexedOffset(Ptr->getType(),
 153                                          (Value**)Ops+1, NumOps-1);
 154   Constant *C = ConstantInt::get(TD->getIntPtrType(), Offset+BasePtr);
 155   return ConstantExpr::getIntToPtr(C, ResultTy);
 156 }
 157
 158 /// FoldBitCast - Constant fold bitcast, symbolically evaluating it with
 159 /// targetdata.  Return 0 if unfoldable.
 160 static Constant *FoldBitCast(Constant *C, const Type *DestTy,
 161                              const TargetData &TD, LLVMContext &Context) {
 162   // If this is a bitcast from constant vector -> vector, fold it.
 163   if (ConstantVector *CV = dyn_cast<ConstantVector>(C)) {
 164     if (const VectorType *DestVTy = dyn_cast<VectorType>(DestTy)) {
 165       // If the element types match, VMCore can fold it.
 166       unsigned NumDstElt = DestVTy->getNumElements();
 167       unsigned NumSrcElt = CV->getNumOperands();
 168       if (NumDstElt == NumSrcElt)
 169         return 0;
 170
 171       const Type *SrcEltTy = CV->getType()->getElementType();
 172       const Type *DstEltTy = DestVTy->getElementType();
 173
 174       // Otherwise, we're changing the number of elements in a vector, which
 175       // requires endianness information to do the right thing.  For example,
 176       //    bitcast (<2 x i64> <i64 0, i64 1> to <4 x i32>)
 177       // folds to (little endian):
 178       //    <4 x i32> <i32 0, i32 0, i32 1, i32 0>
 179       // and to (big endian):
 180       //    <4 x i32> <i32 0, i32 0, i32 0, i32 1>
 181
 182       // First thing is first.  We only want to think about integer here, so if
 183       // we have something in FP form, recast it as integer.
 184       if (DstEltTy->isFloatingPoint()) {
 185         // Fold to an vector of integers with same size as our FP type.
 186         unsigned FPWidth = DstEltTy->getPrimitiveSizeInBits();
 187         const Type *DestIVTy = VectorType::get(
 188                                    IntegerType::get(FPWidth), NumDstElt);
 189         // Recursively handle this integer conversion, if possible.
 190         C = FoldBitCast(C, DestIVTy, TD, Context);
 191         if (!C) return 0;
 192
 193         // Finally, VMCore can handle this now that #elts line up.
 194         return ConstantExpr::getBitCast(C, DestTy);
 195       }
 196
 197       // Okay, we know the destination is integer, if the input is FP, convert
 198       // it to integer first.
 199       if (SrcEltTy->isFloatingPoint()) {
 200         unsigned FPWidth = SrcEltTy->getPrimitiveSizeInBits();
 201         const Type *SrcIVTy = VectorType::get(
 202                                    IntegerType::get(FPWidth), NumSrcElt);
 203         // Ask VMCore to do the conversion now that #elts line up.
 204         C = ConstantExpr::getBitCast(C, SrcIVTy);
 205         CV = dyn_cast<ConstantVector>(C);
 206         if (!CV) return 0;  // If VMCore wasn't able to fold it, bail out.
 207       }
 208
 209       // Now we know that the input and output vectors are both integer vectors
 210       // of the same size, and that their #elements is not the same.  Do the
 211       // conversion here, which depends on whether the input or output has
 212       // more elements.
 213       bool isLittleEndian = TD.isLittleEndian();
 214
 215       SmallVector<Constant*, 32> Result;
 216       if (NumDstElt < NumSrcElt) {
 217         // Handle: bitcast (<4 x i32> <i32 0, i32 1, i32 2, i32 3> to <2 x i64>)
 218         Constant *Zero = Constant::getNullValue(DstEltTy);
 219         unsigned Ratio = NumSrcElt/NumDstElt;
 220         unsigned SrcBitSize = SrcEltTy->getPrimitiveSizeInBits();
 221         unsigned SrcElt = 0;
 222         for (unsigned i = 0; i != NumDstElt; ++i) {
 223           // Build each element of the result.
 224           Constant *Elt = Zero;
 225           unsigned ShiftAmt = isLittleEndian ? 0 : SrcBitSize*(Ratio-1);
 226           for (unsigned j = 0; j != Ratio; ++j) {
 227             Constant *Src = dyn_cast<ConstantInt>(CV->getOperand(SrcElt++));
 228             if (!Src) return 0;  // Reject constantexpr elements.
 229
 230             // Zero extend the element to the right size.
 231             Src = ConstantExpr::getZExt(Src, Elt->getType());
 232
 233             // Shift it to the right place, depending on endianness.
 234             Src = ConstantExpr::getShl(Src,
 235                              ConstantInt::get(Src->getType(), ShiftAmt));
 236             ShiftAmt += isLittleEndian ? SrcBitSize : -SrcBitSize;
 237
 238             // Mix it in.
 239             Elt = ConstantExpr::getOr(Elt, Src);
 240           }
 241           Result.push_back(Elt);
 242         }
 243       } else {
 244         // Handle: bitcast (<2 x i64> <i64 0, i64 1> to <4 x i32>)
 245         unsigned Ratio = NumDstElt/NumSrcElt;
 246         unsigned DstBitSize = DstEltTy->getPrimitiveSizeInBits();
 247
 248         // Loop over each source value, expanding into multiple results.
 249         for (unsigned i = 0; i != NumSrcElt; ++i) {
 250           Constant *Src = dyn_cast<ConstantInt>(CV->getOperand(i));
 251           if (!Src) return 0;  // Reject constantexpr elements.
 252
 253           unsigned ShiftAmt = isLittleEndian ? 0 : DstBitSize*(Ratio-1);
 254           for (unsigned j = 0; j != Ratio; ++j) {
 255             // Shift the piece of the value into the right place, depending on
 256             // endianness.
 257             Constant *Elt = ConstantExpr::getLShr(Src,
 258                             ConstantInt::get(Src->getType(), ShiftAmt));
 259             ShiftAmt += isLittleEndian ? DstBitSize : -DstBitSize;
 260
 261             // Truncate and remember this piece.
 262             Result.push_back(ConstantExpr::getTrunc(Elt, DstEltTy));
 263           }
 264         }
 265       }
 266
 267       return ConstantVector::get(Result.data(), Result.size());
 268     }
 269   }
 270
 271   return 0;
 272 }
 273
 274
 275 //===----------------------------------------------------------------------===//
 276 // Constant Folding public APIs
 277 //===----------------------------------------------------------------------===//
 278
 279
 280 /// ConstantFoldInstruction - Attempt to constant fold the specified
 281 /// instruction.  If successful, the constant result is returned, if not, null
 282 /// is returned.  Note that this function can only fail when attempting to fold
 283 /// instructions like loads and stores, which have no constant expression form.
 284 ///
 285 Constant *llvm::ConstantFoldInstruction(Instruction *I, LLVMContext &Context,
 286                                         const TargetData *TD) {
 287   if (PHINode *PN = dyn_cast<PHINode>(I)) {
 288     if (PN->getNumIncomingValues() == 0)
 289       return UndefValue::get(PN->getType());
 290
 291     Constant *Result = dyn_cast<Constant>(PN->getIncomingValue(0));
 292     if (Result == 0) return 0;
 293
 294     // Handle PHI nodes specially here...
 295     for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i)
 296       if (PN->getIncomingValue(i) != Result && PN->getIncomingValue(i) != PN)
 297         return 0;   // Not all the same incoming constants...
 298
 299     // If we reach here, all incoming values are the same constant.
 300     return Result;
 301   }
 302
 303   // Scan the operand list, checking to see if they are all constants, if so,
 304   // hand off to ConstantFoldInstOperands.
 305   SmallVector<Constant*, 8> Ops;
 306   for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
 307     if (Constant *Op = dyn_cast<Constant>(*i))
 308       Ops.push_back(Op);
 309     else
 310       return 0;  // All operands not constant!
 311
 312   if (const CmpInst *CI = dyn_cast<CmpInst>(I))
 313     return ConstantFoldCompareInstOperands(CI->getPredicate(),
 314                                            Ops.data(), Ops.size(),
 315                                            Context, TD);
 316   else
 317     return ConstantFoldInstOperands(I->getOpcode(), I->getType(),
 318                                     Ops.data(), Ops.size(), Context, TD);
 319 }
 320
 321 /// ConstantFoldConstantExpression - Attempt to fold the constant expression
 322 /// using the specified TargetData.  If successful, the constant result is
 323 /// result is returned, if not, null is returned.
 324 Constant *llvm::ConstantFoldConstantExpression(ConstantExpr *CE,
 325                                                LLVMContext &Context,
 326                                                const TargetData *TD) {
 327   SmallVector<Constant*, 8> Ops;
 328   for (User::op_iterator i = CE->op_begin(), e = CE->op_end(); i != e; ++i)
 329     Ops.push_back(cast<Constant>(*i));
 330
 331   if (CE->isCompare())
 332     return ConstantFoldCompareInstOperands(CE->getPredicate(),
 333                                            Ops.data(), Ops.size(),
 334                                            Context, TD);
 335   else
 336     return ConstantFoldInstOperands(CE->getOpcode(), CE->getType(),
 337                                     Ops.data(), Ops.size(), Context, TD);
 338 }
 339
 340 /// ConstantFoldInstOperands - Attempt to constant fold an instruction with the
 341 /// specified opcode and operands.  If successful, the constant result is
 342 /// returned, if not, null is returned.  Note that this function can fail when
 343 /// attempting to fold instructions like loads and stores, which have no
 344 /// constant expression form.
 345 ///
 346 Constant *llvm::ConstantFoldInstOperands(unsigned Opcode, const Type *DestTy,
 347                                          Constant* const* Ops, unsigned NumOps,
 348                                          LLVMContext &Context,
 349                                          const TargetData *TD) {
 350   // Handle easy binops first.
 351   if (Instruction::isBinaryOp(Opcode)) {
 352     if (isa<ConstantExpr>(Ops[0]) || isa<ConstantExpr>(Ops[1]))
 353       if (Constant *C = SymbolicallyEvaluateBinop(Opcode, Ops[0], Ops[1], TD,
 354                                                   Context))
 355         return C;
 356
 357     return ConstantExpr::get(Opcode, Ops[0], Ops[1]);
 358   }
 359
 360   switch (Opcode) {
 361   default: return 0;
 362   case Instruction::Call:
 363     if (Function *F = dyn_cast<Function>(Ops[0]))
 364       if (canConstantFoldCallTo(F))
 365         return ConstantFoldCall(F, Ops+1, NumOps-1);
 366     return 0;
 367   case Instruction::ICmp:
 368   case Instruction::FCmp:
 369     llvm_unreachable("This function is invalid for compares: no predicate specified");
 370   case Instruction::PtrToInt:
 371     // If the input is a inttoptr, eliminate the pair.  This requires knowing
 372     // the width of a pointer, so it can't be done in ConstantExpr::getCast.
 373     if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ops[0])) {
 374       if (TD && CE->getOpcode() == Instruction::IntToPtr) {
 375         Constant *Input = CE->getOperand(0);
 376         unsigned InWidth = Input->getType()->getScalarSizeInBits();
 377         if (TD->getPointerSizeInBits() < InWidth) {
 378           Constant *Mask =
 379             ConstantInt::get(Context, APInt::getLowBitsSet(InWidth,
 380                                                   TD->getPointerSizeInBits()));
 381           Input = ConstantExpr::getAnd(Input, Mask);
 382         }
 383         // Do a zext or trunc to get to the dest size.
 384         return ConstantExpr::getIntegerCast(Input, DestTy, false);
 385       }
 386     }
 387     return ConstantExpr::getCast(Opcode, Ops[0], DestTy);
 388   case Instruction::IntToPtr:
 389     // If the input is a ptrtoint, turn the pair into a ptr to ptr bitcast if
 390     // the int size is >= the ptr size.  This requires knowing the width of a
 391     // pointer, so it can't be done in ConstantExpr::getCast.
 392     if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ops[0])) {
 393       if (TD &&
 394           TD->getPointerSizeInBits() <=
 395           CE->getType()->getScalarSizeInBits()) {
 396         if (CE->getOpcode() == Instruction::PtrToInt) {
 397           Constant *Input = CE->getOperand(0);
 398           Constant *C = FoldBitCast(Input, DestTy, *TD, Context);
 399           return C ? C : ConstantExpr::getBitCast(Input, DestTy);
 400         }
 401         // If there's a constant offset added to the integer value before
 402         // it is casted back to a pointer, see if the expression can be
 403         // converted into a GEP.
 404         if (CE->getOpcode() == Instruction::Add)
 405           if (ConstantInt *L = dyn_cast<ConstantInt>(CE->getOperand(0)))
 406             if (ConstantExpr *R = dyn_cast<ConstantExpr>(CE->getOperand(1)))
 407               if (R->getOpcode() == Instruction::PtrToInt)
 408                 if (GlobalVariable *GV =
 409                       dyn_cast<GlobalVariable>(R->getOperand(0))) {
 410                   const PointerType *GVTy = cast<PointerType>(GV->getType());
 411                   if (const ArrayType *AT =
 412                         dyn_cast<ArrayType>(GVTy->getElementType())) {
 413                     const Type *ElTy = AT->getElementType();
 414                     uint64_t AllocSize = TD->getTypeAllocSize(ElTy);
 415                     APInt PSA(L->getValue().getBitWidth(), AllocSize);
 416                     if (ElTy == cast<PointerType>(DestTy)->getElementType() &&
 417                         L->getValue().urem(PSA) == 0) {
 418                       APInt ElemIdx = L->getValue().udiv(PSA);
 419                       if (ElemIdx.ult(APInt(ElemIdx.getBitWidth(),
 420                                             AT->getNumElements()))) {
 421                         Constant *Index[] = {
 422                           Constant::getNullValue(CE->getType()),
 423                           ConstantInt::get(Context, ElemIdx)
 424                         };
 425                         return
 426                         ConstantExpr::getGetElementPtr(GV, &Index[0], 2);
 427                       }
 428                     }
 429                   }
 430                 }
 431       }
 432     }
 433     return ConstantExpr::getCast(Opcode, Ops[0], DestTy);
 434   case Instruction::Trunc:
 435   case Instruction::ZExt:
 436   case Instruction::SExt:
 437   case Instruction::FPTrunc:
 438   case Instruction::FPExt:
 439   case Instruction::UIToFP:
 440   case Instruction::SIToFP:
 441   case Instruction::FPToUI:
 442   case Instruction::FPToSI:
 443       return ConstantExpr::getCast(Opcode, Ops[0], DestTy);
 444   case Instruction::BitCast:
 445     if (TD)
 446       if (Constant *C = FoldBitCast(Ops[0], DestTy, *TD, Context))
 447         return C;
 448     return ConstantExpr::getBitCast(Ops[0], DestTy);
 449   case Instruction::Select:
 450     return ConstantExpr::getSelect(Ops[0], Ops[1], Ops[2]);
 451   case Instruction::ExtractElement:
 452     return ConstantExpr::getExtractElement(Ops[0], Ops[1]);
 453   case Instruction::InsertElement:
 454     return ConstantExpr::getInsertElement(Ops[0], Ops[1], Ops[2]);
 455   case Instruction::ShuffleVector:
 456     return ConstantExpr::getShuffleVector(Ops[0], Ops[1], Ops[2]);
 457   case Instruction::GetElementPtr:
 458     if (Constant *C = SymbolicallyEvaluateGEP(Ops, NumOps, DestTy, Context, TD))
 459       return C;
 460
 461     return ConstantExpr::getGetElementPtr(Ops[0], Ops+1, NumOps-1);
 462   }
 463 }
 464
 465 /// ConstantFoldCompareInstOperands - Attempt to constant fold a compare
 466 /// instruction (icmp/fcmp) with the specified operands.  If it fails, it
 467 /// returns a constant expression of the specified operands.
 468 ///
 469 Constant *llvm::ConstantFoldCompareInstOperands(unsigned Predicate,
 470                                                 Constant*const * Ops,
 471                                                 unsigned NumOps,
 472                                                 LLVMContext &Context,
 473                                                 const TargetData *TD) {
 474   // fold: icmp (inttoptr x), null         -> icmp x, 0
 475   // fold: icmp (ptrtoint x), 0            -> icmp x, null
 476   // fold: icmp (inttoptr x), (inttoptr y) -> icmp trunc/zext x, trunc/zext y
 477   // fold: icmp (ptrtoint x), (ptrtoint y) -> icmp x, y
 478   //
 479   // ConstantExpr::getCompare cannot do this, because it doesn't have TD
 480   // around to know if bit truncation is happening.
 481   if (ConstantExpr *CE0 = dyn_cast<ConstantExpr>(Ops[0])) {
 482     if (TD && Ops[1]->isNullValue()) {
 483       const Type *IntPtrTy = TD->getIntPtrType();
 484       if (CE0->getOpcode() == Instruction::IntToPtr) {
 485         // Convert the integer value to the right size to ensure we get the
 486         // proper extension or truncation.
 487         Constant *C = ConstantExpr::getIntegerCast(CE0->getOperand(0),
 488                                                    IntPtrTy, false);
 489         Constant *NewOps[] = { C, Constant::getNullValue(C->getType()) };
 490         return ConstantFoldCompareInstOperands(Predicate, NewOps, 2,
 491                                                Context, TD);
 492       }
 493
 494       // Only do this transformation if the int is intptrty in size, otherwise
 495       // there is a truncation or extension that we aren't modeling.
 496       if (CE0->getOpcode() == Instruction::PtrToInt &&
 497           CE0->getType() == IntPtrTy) {
 498         Constant *C = CE0->getOperand(0);
 499         Constant *NewOps[] = { C, Constant::getNullValue(C->getType()) };
 500         // FIXME!
 501         return ConstantFoldCompareInstOperands(Predicate, NewOps, 2,
 502                                                Context, TD);
 503       }
 504     }
 505
 506     if (ConstantExpr *CE1 = dyn_cast<ConstantExpr>(Ops[1])) {
 507       if (TD && CE0->getOpcode() == CE1->getOpcode()) {
 508         const Type *IntPtrTy = TD->getIntPtrType();
 509
 510         if (CE0->getOpcode() == Instruction::IntToPtr) {
 511           // Convert the integer value to the right size to ensure we get the
 512           // proper extension or truncation.
 513           Constant *C0 = ConstantExpr::getIntegerCast(CE0->getOperand(0),
 514                                                       IntPtrTy, false);
 515           Constant *C1 = ConstantExpr::getIntegerCast(CE1->getOperand(0),
 516                                                       IntPtrTy, false);
 517           Constant *NewOps[] = { C0, C1 };
 518           return ConstantFoldCompareInstOperands(Predicate, NewOps, 2,
 519                                                  Context, TD);
 520         }
 521
 522         // Only do this transformation if the int is intptrty in size, otherwise
 523         // there is a truncation or extension that we aren't modeling.
 524         if ((CE0->getOpcode() == Instruction::PtrToInt &&
 525              CE0->getType() == IntPtrTy &&
 526              CE0->getOperand(0)->getType() == CE1->getOperand(0)->getType())) {
 527           Constant *NewOps[] = {
 528             CE0->getOperand(0), CE1->getOperand(0)
 529           };
 530           return ConstantFoldCompareInstOperands(Predicate, NewOps, 2,
 531                                                  Context, TD);
 532         }
 533       }
 534     }
 535   }
 536   return ConstantExpr::getCompare(Predicate, Ops[0], Ops[1]);
 537 }
 538
 539
 540 /// ConstantFoldLoadThroughGEPConstantExpr - Given a constant and a
 541 /// getelementptr constantexpr, return the constant value being addressed by the
 542 /// constant expression, or null if something is funny and we can't decide.
 543 Constant *llvm::ConstantFoldLoadThroughGEPConstantExpr(Constant *C,
 544                                                        ConstantExpr *CE,
 545                                                        LLVMContext &Context) {
 546   if (CE->getOperand(1) != Constant::getNullValue(CE->getOperand(1)->getType()))
 547     return 0;  // Do not allow stepping over the value!
 548
 549   // Loop over all of the operands, tracking down which value we are
 550   // addressing...
 551   gep_type_iterator I = gep_type_begin(CE), E = gep_type_end(CE);
 552   for (++I; I != E; ++I)
 553     if (const StructType *STy = dyn_cast<StructType>(*I)) {
 554       ConstantInt *CU = cast<ConstantInt>(I.getOperand());
 555       assert(CU->getZExtValue() < STy->getNumElements() &&
 556              "Struct index out of range!");
 557       unsigned El = (unsigned)CU->getZExtValue();
 558       if (ConstantStruct *CS = dyn_cast<ConstantStruct>(C)) {
 559         C = CS->getOperand(El);
 560       } else if (isa<ConstantAggregateZero>(C)) {
 561         C = Constant::getNullValue(STy->getElementType(El));
 562       } else if (isa<UndefValue>(C)) {
 563         C = UndefValue::get(STy->getElementType(El));
 564       } else {
 565         return 0;
 566       }
 567     } else if (ConstantInt *CI = dyn_cast<ConstantInt>(I.getOperand())) {
 568       if (const ArrayType *ATy = dyn_cast<ArrayType>(*I)) {
 569         if (CI->getZExtValue() >= ATy->getNumElements())
 570          return 0;
 571         if (ConstantArray *CA = dyn_cast<ConstantArray>(C))
 572           C = CA->getOperand(CI->getZExtValue());
 573         else if (isa<ConstantAggregateZero>(C))
 574           C = Constant::getNullValue(ATy->getElementType());
 575         else if (isa<UndefValue>(C))
 576           C = UndefValue::get(ATy->getElementType());
 577         else
 578           return 0;
 579       } else if (const VectorType *PTy = dyn_cast<VectorType>(*I)) {
 580         if (CI->getZExtValue() >= PTy->getNumElements())
 581           return 0;
 582         if (ConstantVector *CP = dyn_cast<ConstantVector>(C))
 583           C = CP->getOperand(CI->getZExtValue());
 584         else if (isa<ConstantAggregateZero>(C))
 585           C = Constant::getNullValue(PTy->getElementType());
 586         else if (isa<UndefValue>(C))
 587           C = UndefValue::get(PTy->getElementType());
 588         else
 589           return 0;
 590       } else {
 591         return 0;
 592       }
 593     } else {
 594       return 0;
 595     }
 596   return C;
 597 }
 598
 599
 600 //===----------------------------------------------------------------------===//
 601 //  Constant Folding for Calls
 602 //
 603
 604 /// canConstantFoldCallTo - Return true if its even possible to fold a call to
 605 /// the specified function.
 606 bool
 607 llvm::canConstantFoldCallTo(const Function *F) {
 608   switch (F->getIntrinsicID()) {
 609   case Intrinsic::sqrt:
 610   case Intrinsic::powi:
 611   case Intrinsic::bswap:
 612   case Intrinsic::ctpop:
 613   case Intrinsic::ctlz:
 614   case Intrinsic::cttz:
 615     return true;
 616   default: break;
 617   }
 618
 619   if (!F->hasName()) return false;
 620   StringRef Name = F->getName();
 621
 622   // In these cases, the check of the length is required.  We don't want to
 623   // return true for a name like "cos\0blah" which strcmp would return equal to
 624   // "cos", but has length 8.
 625   switch (Name[0]) {
 626   default: return false;
 627   case 'a':
 628     return Name == "acos" || Name == "asin" ||
 629       Name == "atan" || Name == "atan2";
 630   case 'c':
 631     return Name == "cos" || Name == "ceil" || Name == "cosf" || Name == "cosh";
 632   case 'e':
 633     return Name == "exp";
 634   case 'f':
 635     return Name == "fabs" || Name == "fmod" || Name == "floor";
 636   case 'l':
 637     return Name == "log" || Name == "log10";
 638   case 'p':
 639     return Name == "pow";
 640   case 's':
 641     return Name == "sin" || Name == "sinh" || Name == "sqrt" ||
 642       Name == "sinf" || Name == "sqrtf";
 643   case 't':
 644     return Name == "tan" || Name == "tanh";
 645   }
 646 }
 647
 648 static Constant *ConstantFoldFP(double (*NativeFP)(double), double V,
 649                                 const Type *Ty, LLVMContext &Context) {
 650   errno = 0;
 651   V = NativeFP(V);
 652   if (errno != 0) {
 653     errno = 0;
 654     return 0;
 655   }
 656
 657   if (Ty == Type::FloatTy)
 658     return ConstantFP::get(Context, APFloat((float)V));
 659   if (Ty == Type::DoubleTy)
 660     return ConstantFP::get(Context, APFloat(V));
 661   llvm_unreachable("Can only constant fold float/double");
 662   return 0; // dummy return to suppress warning
 663 }
 664
 665 static Constant *ConstantFoldBinaryFP(double (*NativeFP)(double, double),
 666                                       double V, double W,
 667                                       const Type *Ty,
 668                                       LLVMContext &Context) {
 669   errno = 0;
 670   V = NativeFP(V, W);
 671   if (errno != 0) {
 672     errno = 0;
 673     return 0;
 674   }
 675
 676   if (Ty == Type::FloatTy)
 677     return ConstantFP::get(Context, APFloat((float)V));
 678   if (Ty == Type::DoubleTy)
 679     return ConstantFP::get(Context, APFloat(V));
 680   llvm_unreachable("Can only constant fold float/double");
 681   return 0; // dummy return to suppress warning
 682 }
 683
 684 /// ConstantFoldCall - Attempt to constant fold a call to the specified function
 685 /// with the specified arguments, returning null if unsuccessful.
 686
 687 Constant *
 688 llvm::ConstantFoldCall(Function *F,
 689                        Constant* const* Operands, unsigned NumOperands) {
 690   if (!F->hasName()) return 0;
 691   LLVMContext &Context = F->getContext();
 692   StringRef Name = F->getName();
 693
 694   const Type *Ty = F->getReturnType();
 695   if (NumOperands == 1) {
 696     if (ConstantFP *Op = dyn_cast<ConstantFP>(Operands[0])) {
 697       if (Ty!=Type::FloatTy && Ty!=Type::DoubleTy)
 698         return 0;
 699       /// Currently APFloat versions of these functions do not exist, so we use
 700       /// the host native double versions.  Float versions are not called
 701       /// directly but for all these it is true (float)(f((double)arg)) ==
 702       /// f(arg).  Long double not supported yet.
 703       double V = Ty==Type::FloatTy ? (double)Op->getValueAPF().convertToFloat():
 704                                      Op->getValueAPF().convertToDouble();
 705       switch (Name[0]) {
 706       case 'a':
 707         if (Name == "acos")
 708           return ConstantFoldFP(acos, V, Ty, Context);
 709         else if (Name == "asin")
 710           return ConstantFoldFP(asin, V, Ty, Context);
 711         else if (Name == "atan")
 712           return ConstantFoldFP(atan, V, Ty, Context);
 713         break;
 714       case 'c':
 715         if (Name == "ceil")
 716           return ConstantFoldFP(ceil, V, Ty, Context);
 717         else if (Name == "cos")
 718           return ConstantFoldFP(cos, V, Ty, Context);
 719         else if (Name == "cosh")
 720           return ConstantFoldFP(cosh, V, Ty, Context);
 721         else if (Name == "cosf")
 722           return ConstantFoldFP(cos, V, Ty, Context);
 723         break;
 724       case 'e':
 725         if (Name == "exp")
 726           return ConstantFoldFP(exp, V, Ty, Context);
 727         break;
 728       case 'f':
 729         if (Name == "fabs")
 730           return ConstantFoldFP(fabs, V, Ty, Context);
 731         else if (Name == "floor")
 732           return ConstantFoldFP(floor, V, Ty, Context);
 733         break;
 734       case 'l':
 735         if (Name == "log" && V > 0)
 736           return ConstantFoldFP(log, V, Ty, Context);
 737         else if (Name == "log10" && V > 0)
 738           return ConstantFoldFP(log10, V, Ty, Context);
 739         else if (Name == "llvm.sqrt.f32" ||
 740                  Name == "llvm.sqrt.f64") {
 741           if (V >= -0.0)
 742             return ConstantFoldFP(sqrt, V, Ty, Context);
 743           else // Undefined
 744             return Constant::getNullValue(Ty);
 745         }
 746         break;
 747       case 's':
 748         if (Name == "sin")
 749           return ConstantFoldFP(sin, V, Ty, Context);
 750         else if (Name == "sinh")
 751           return ConstantFoldFP(sinh, V, Ty, Context);
 752         else if (Name == "sqrt" && V >= 0)
 753           return ConstantFoldFP(sqrt, V, Ty, Context);
 754         else if (Name == "sqrtf" && V >= 0)
 755           return ConstantFoldFP(sqrt, V, Ty, Context);
 756         else if (Name == "sinf")
 757           return ConstantFoldFP(sin, V, Ty, Context);
 758         break;
 759       case 't':
 760         if (Name == "tan")
 761           return ConstantFoldFP(tan, V, Ty, Context);
 762         else if (Name == "tanh")
 763           return ConstantFoldFP(tanh, V, Ty, Context);
 764         break;
 765       default:
 766         break;
 767       }
 768     } else if (ConstantInt *Op = dyn_cast<ConstantInt>(Operands[0])) {
 769       if (Name.startswith("llvm.bswap"))
 770         return ConstantInt::get(Context, Op->getValue().byteSwap());
 771       else if (Name.startswith("llvm.ctpop"))
 772         return ConstantInt::get(Ty, Op->getValue().countPopulation());
 773       else if (Name.startswith("llvm.cttz"))
 774         return ConstantInt::get(Ty, Op->getValue().countTrailingZeros());
 775       else if (Name.startswith("llvm.ctlz"))
 776         return ConstantInt::get(Ty, Op->getValue().countLeadingZeros());
 777     }
 778   } else if (NumOperands == 2) {
 779     if (ConstantFP *Op1 = dyn_cast<ConstantFP>(Operands[0])) {
 780       if (Ty!=Type::FloatTy && Ty!=Type::DoubleTy)
 781         return 0;
 782       double Op1V = Ty==Type::FloatTy ?
 783                       (double)Op1->getValueAPF().convertToFloat():
 784                       Op1->getValueAPF().convertToDouble();
 785       if (ConstantFP *Op2 = dyn_cast<ConstantFP>(Operands[1])) {
 786         double Op2V = Ty==Type::FloatTy ?
 787                       (double)Op2->getValueAPF().convertToFloat():
 788                       Op2->getValueAPF().convertToDouble();
 789
 790         if (Name == "pow") {
 791           return ConstantFoldBinaryFP(pow, Op1V, Op2V, Ty, Context);
 792         } else if (Name == "fmod") {
 793           return ConstantFoldBinaryFP(fmod, Op1V, Op2V, Ty, Context);
 794         } else if (Name == "atan2") {
 795           return ConstantFoldBinaryFP(atan2, Op1V, Op2V, Ty, Context);
 796         }
 797       } else if (ConstantInt *Op2C = dyn_cast<ConstantInt>(Operands[1])) {
 798         if (Name == "llvm.powi.f32") {
 799           return ConstantFP::get(Context, APFloat((float)std::pow((float)Op1V,
 800                                                  (int)Op2C->getZExtValue())));
 801         } else if (Name == "llvm.powi.f64") {
 802           return ConstantFP::get(Context, APFloat((double)std::pow((double)Op1V,
 803                                                  (int)Op2C->getZExtValue())));
 804         }
 805       }
 806     }
 807   }
 808   return 0;
 809 }
 810