ConstantFolding.cpp revision 6f532a988e5c02fcb271fb65e9e7b83f0147d3f2
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/Instructions.h" 20#include "llvm/Intrinsics.h" 21#include "llvm/ADT/SmallVector.h" 22#include "llvm/ADT/StringMap.h" 23#include "llvm/Target/TargetData.h" 24#include "llvm/Support/GetElementPtrTypeIterator.h" 25#include "llvm/Support/MathExtras.h" 26#include <cerrno> 27#include <cmath> 28using namespace llvm; 29 30//===----------------------------------------------------------------------===// 31// Constant Folding internal helper functions 32//===----------------------------------------------------------------------===// 33 34/// IsConstantOffsetFromGlobal - If this constant is actually a constant offset 35/// from a global, return the global and the constant. Because of 36/// constantexprs, this function is recursive. 37static bool IsConstantOffsetFromGlobal(Constant *C, GlobalValue *&GV, 38 int64_t &Offset, const TargetData &TD) { 39 // Trivial case, constant is the global. 40 if ((GV = dyn_cast<GlobalValue>(C))) { 41 Offset = 0; 42 return true; 43 } 44 45 // Otherwise, if this isn't a constant expr, bail out. 46 ConstantExpr *CE = dyn_cast<ConstantExpr>(C); 47 if (!CE) return false; 48 49 // Look through ptr->int and ptr->ptr casts. 50 if (CE->getOpcode() == Instruction::PtrToInt || 51 CE->getOpcode() == Instruction::BitCast) 52 return IsConstantOffsetFromGlobal(CE->getOperand(0), GV, Offset, TD); 53 54 // i32* getelementptr ([5 x i32]* @a, i32 0, i32 5) 55 if (CE->getOpcode() == Instruction::GetElementPtr) { 56 // Cannot compute this if the element type of the pointer is missing size 57 // info. 58 if (!cast<PointerType>(CE->getOperand(0)->getType()) 59 ->getElementType()->isSized()) 60 return false; 61 62 // If the base isn't a global+constant, we aren't either. 63 if (!IsConstantOffsetFromGlobal(CE->getOperand(0), GV, Offset, TD)) 64 return false; 65 66 // Otherwise, add any offset that our operands provide. 67 gep_type_iterator GTI = gep_type_begin(CE); 68 for (User::const_op_iterator i = CE->op_begin() + 1, e = CE->op_end(); 69 i != e; ++i, ++GTI) { 70 ConstantInt *CI = dyn_cast<ConstantInt>(*i); 71 if (!CI) return false; // Index isn't a simple constant? 72 if (CI->getZExtValue() == 0) continue; // Not adding anything. 73 74 if (const StructType *ST = dyn_cast<StructType>(*GTI)) { 75 // N = N + Offset 76 Offset += TD.getStructLayout(ST)->getElementOffset(CI->getZExtValue()); 77 } else { 78 const SequentialType *SQT = cast<SequentialType>(*GTI); 79 Offset += TD.getTypePaddedSize(SQT->getElementType())*CI->getSExtValue(); 80 } 81 } 82 return true; 83 } 84 85 return false; 86} 87 88 89/// SymbolicallyEvaluateBinop - One of Op0/Op1 is a constant expression. 90/// Attempt to symbolically evaluate the result of a binary operator merging 91/// these together. If target data info is available, it is provided as TD, 92/// otherwise TD is null. 93static Constant *SymbolicallyEvaluateBinop(unsigned Opc, Constant *Op0, 94 Constant *Op1, const TargetData *TD){ 95 // SROA 96 97 // Fold (and 0xffffffff00000000, (shl x, 32)) -> shl. 98 // Fold (lshr (or X, Y), 32) -> (lshr [X/Y], 32) if one doesn't contribute 99 // bits. 100 101 102 // If the constant expr is something like &A[123] - &A[4].f, fold this into a 103 // constant. This happens frequently when iterating over a global array. 104 if (Opc == Instruction::Sub && TD) { 105 GlobalValue *GV1, *GV2; 106 int64_t Offs1, Offs2; 107 108 if (IsConstantOffsetFromGlobal(Op0, GV1, Offs1, *TD)) 109 if (IsConstantOffsetFromGlobal(Op1, GV2, Offs2, *TD) && 110 GV1 == GV2) { 111 // (&GV+C1) - (&GV+C2) -> C1-C2, pointer arithmetic cannot overflow. 112 return ConstantInt::get(Op0->getType(), Offs1-Offs2); 113 } 114 } 115 116 return 0; 117} 118 119/// SymbolicallyEvaluateGEP - If we can symbolically evaluate the specified GEP 120/// constant expression, do so. 121static Constant *SymbolicallyEvaluateGEP(Constant* const* Ops, unsigned NumOps, 122 const Type *ResultTy, 123 const TargetData *TD) { 124 Constant *Ptr = Ops[0]; 125 if (!TD || !cast<PointerType>(Ptr->getType())->getElementType()->isSized()) 126 return 0; 127 128 uint64_t BasePtr = 0; 129 if (!Ptr->isNullValue()) { 130 // If this is a inttoptr from a constant int, we can fold this as the base, 131 // otherwise we can't. 132 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr)) 133 if (CE->getOpcode() == Instruction::IntToPtr) 134 if (ConstantInt *Base = dyn_cast<ConstantInt>(CE->getOperand(0))) 135 BasePtr = Base->getZExtValue(); 136 137 if (BasePtr == 0) 138 return 0; 139 } 140 141 // If this is a constant expr gep that is effectively computing an 142 // "offsetof", fold it into 'cast int Size to T*' instead of 'gep 0, 0, 12' 143 for (unsigned i = 1; i != NumOps; ++i) 144 if (!isa<ConstantInt>(Ops[i])) 145 return false; 146 147 uint64_t Offset = TD->getIndexedOffset(Ptr->getType(), 148 (Value**)Ops+1, NumOps-1); 149 Constant *C = ConstantInt::get(TD->getIntPtrType(), Offset+BasePtr); 150 return ConstantExpr::getIntToPtr(C, ResultTy); 151} 152 153/// FoldBitCast - Constant fold bitcast, symbolically evaluating it with 154/// targetdata. Return 0 if unfoldable. 155static Constant *FoldBitCast(Constant *C, const Type *DestTy, 156 const TargetData &TD) { 157 // If this is a bitcast from constant vector -> vector, fold it. 158 if (ConstantVector *CV = dyn_cast<ConstantVector>(C)) { 159 if (const VectorType *DestVTy = dyn_cast<VectorType>(DestTy)) { 160 // If the element types match, VMCore can fold it. 161 unsigned NumDstElt = DestVTy->getNumElements(); 162 unsigned NumSrcElt = CV->getNumOperands(); 163 if (NumDstElt == NumSrcElt) 164 return 0; 165 166 const Type *SrcEltTy = CV->getType()->getElementType(); 167 const Type *DstEltTy = DestVTy->getElementType(); 168 169 // Otherwise, we're changing the number of elements in a vector, which 170 // requires endianness information to do the right thing. For example, 171 // bitcast (<2 x i64> <i64 0, i64 1> to <4 x i32>) 172 // folds to (little endian): 173 // <4 x i32> <i32 0, i32 0, i32 1, i32 0> 174 // and to (big endian): 175 // <4 x i32> <i32 0, i32 0, i32 0, i32 1> 176 177 // First thing is first. We only want to think about integer here, so if 178 // we have something in FP form, recast it as integer. 179 if (DstEltTy->isFloatingPoint()) { 180 // Fold to an vector of integers with same size as our FP type. 181 unsigned FPWidth = DstEltTy->getPrimitiveSizeInBits(); 182 const Type *DestIVTy = VectorType::get(IntegerType::get(FPWidth), 183 NumDstElt); 184 // Recursively handle this integer conversion, if possible. 185 C = FoldBitCast(C, DestIVTy, TD); 186 if (!C) return 0; 187 188 // Finally, VMCore can handle this now that #elts line up. 189 return ConstantExpr::getBitCast(C, DestTy); 190 } 191 192 // Okay, we know the destination is integer, if the input is FP, convert 193 // it to integer first. 194 if (SrcEltTy->isFloatingPoint()) { 195 unsigned FPWidth = SrcEltTy->getPrimitiveSizeInBits(); 196 const Type *SrcIVTy = VectorType::get(IntegerType::get(FPWidth), 197 NumSrcElt); 198 // Ask VMCore to do the conversion now that #elts line up. 199 C = ConstantExpr::getBitCast(C, SrcIVTy); 200 CV = dyn_cast<ConstantVector>(C); 201 if (!CV) return 0; // If VMCore wasn't able to fold it, bail out. 202 } 203 204 // Now we know that the input and output vectors are both integer vectors 205 // of the same size, and that their #elements is not the same. Do the 206 // conversion here, which depends on whether the input or output has 207 // more elements. 208 bool isLittleEndian = TD.isLittleEndian(); 209 210 SmallVector<Constant*, 32> Result; 211 if (NumDstElt < NumSrcElt) { 212 // Handle: bitcast (<4 x i32> <i32 0, i32 1, i32 2, i32 3> to <2 x i64>) 213 Constant *Zero = Constant::getNullValue(DstEltTy); 214 unsigned Ratio = NumSrcElt/NumDstElt; 215 unsigned SrcBitSize = SrcEltTy->getPrimitiveSizeInBits(); 216 unsigned SrcElt = 0; 217 for (unsigned i = 0; i != NumDstElt; ++i) { 218 // Build each element of the result. 219 Constant *Elt = Zero; 220 unsigned ShiftAmt = isLittleEndian ? 0 : SrcBitSize*(Ratio-1); 221 for (unsigned j = 0; j != Ratio; ++j) { 222 Constant *Src = dyn_cast<ConstantInt>(CV->getOperand(SrcElt++)); 223 if (!Src) return 0; // Reject constantexpr elements. 224 225 // Zero extend the element to the right size. 226 Src = ConstantExpr::getZExt(Src, Elt->getType()); 227 228 // Shift it to the right place, depending on endianness. 229 Src = ConstantExpr::getShl(Src, 230 ConstantInt::get(Src->getType(), ShiftAmt)); 231 ShiftAmt += isLittleEndian ? SrcBitSize : -SrcBitSize; 232 233 // Mix it in. 234 Elt = ConstantExpr::getOr(Elt, Src); 235 } 236 Result.push_back(Elt); 237 } 238 } else { 239 // Handle: bitcast (<2 x i64> <i64 0, i64 1> to <4 x i32>) 240 unsigned Ratio = NumDstElt/NumSrcElt; 241 unsigned DstBitSize = DstEltTy->getPrimitiveSizeInBits(); 242 243 // Loop over each source value, expanding into multiple results. 244 for (unsigned i = 0; i != NumSrcElt; ++i) { 245 Constant *Src = dyn_cast<ConstantInt>(CV->getOperand(i)); 246 if (!Src) return 0; // Reject constantexpr elements. 247 248 unsigned ShiftAmt = isLittleEndian ? 0 : DstBitSize*(Ratio-1); 249 for (unsigned j = 0; j != Ratio; ++j) { 250 // Shift the piece of the value into the right place, depending on 251 // endianness. 252 Constant *Elt = ConstantExpr::getLShr(Src, 253 ConstantInt::get(Src->getType(), ShiftAmt)); 254 ShiftAmt += isLittleEndian ? DstBitSize : -DstBitSize; 255 256 // Truncate and remember this piece. 257 Result.push_back(ConstantExpr::getTrunc(Elt, DstEltTy)); 258 } 259 } 260 } 261 262 return ConstantVector::get(&Result[0], Result.size()); 263 } 264 } 265 266 return 0; 267} 268 269 270//===----------------------------------------------------------------------===// 271// Constant Folding public APIs 272//===----------------------------------------------------------------------===// 273 274 275/// ConstantFoldInstruction - Attempt to constant fold the specified 276/// instruction. If successful, the constant result is returned, if not, null 277/// is returned. Note that this function can only fail when attempting to fold 278/// instructions like loads and stores, which have no constant expression form. 279/// 280Constant *llvm::ConstantFoldInstruction(Instruction *I, const TargetData *TD) { 281 if (PHINode *PN = dyn_cast<PHINode>(I)) { 282 if (PN->getNumIncomingValues() == 0) 283 return UndefValue::get(PN->getType()); 284 285 Constant *Result = dyn_cast<Constant>(PN->getIncomingValue(0)); 286 if (Result == 0) return 0; 287 288 // Handle PHI nodes specially here... 289 for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i) 290 if (PN->getIncomingValue(i) != Result && PN->getIncomingValue(i) != PN) 291 return 0; // Not all the same incoming constants... 292 293 // If we reach here, all incoming values are the same constant. 294 return Result; 295 } 296 297 // Scan the operand list, checking to see if they are all constants, if so, 298 // hand off to ConstantFoldInstOperands. 299 SmallVector<Constant*, 8> Ops; 300 for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i) 301 if (Constant *Op = dyn_cast<Constant>(*i)) 302 Ops.push_back(Op); 303 else 304 return 0; // All operands not constant! 305 306 if (const CmpInst *CI = dyn_cast<CmpInst>(I)) 307 return ConstantFoldCompareInstOperands(CI->getPredicate(), 308 &Ops[0], Ops.size(), TD); 309 else 310 return ConstantFoldInstOperands(I->getOpcode(), I->getType(), 311 &Ops[0], Ops.size(), TD); 312} 313 314/// ConstantFoldConstantExpression - Attempt to fold the constant expression 315/// using the specified TargetData. If successful, the constant result is 316/// result is returned, if not, null is returned. 317Constant *llvm::ConstantFoldConstantExpression(ConstantExpr *CE, 318 const TargetData *TD) { 319 assert(TD && "ConstantFoldConstantExpression requires a valid TargetData."); 320 321 SmallVector<Constant*, 8> Ops; 322 for (User::op_iterator i = CE->op_begin(), e = CE->op_end(); i != e; ++i) 323 Ops.push_back(cast<Constant>(*i)); 324 325 if (CE->isCompare()) 326 return ConstantFoldCompareInstOperands(CE->getPredicate(), 327 &Ops[0], Ops.size(), TD); 328 else 329 return ConstantFoldInstOperands(CE->getOpcode(), CE->getType(), 330 &Ops[0], Ops.size(), TD); 331} 332 333/// ConstantFoldInstOperands - Attempt to constant fold an instruction with the 334/// specified opcode and operands. If successful, the constant result is 335/// returned, if not, null is returned. Note that this function can fail when 336/// attempting to fold instructions like loads and stores, which have no 337/// constant expression form. 338/// 339Constant *llvm::ConstantFoldInstOperands(unsigned Opcode, const Type *DestTy, 340 Constant* const* Ops, unsigned NumOps, 341 const TargetData *TD) { 342 // Handle easy binops first. 343 if (Instruction::isBinaryOp(Opcode)) { 344 if (isa<ConstantExpr>(Ops[0]) || isa<ConstantExpr>(Ops[1])) 345 if (Constant *C = SymbolicallyEvaluateBinop(Opcode, Ops[0], Ops[1], TD)) 346 return C; 347 348 return ConstantExpr::get(Opcode, Ops[0], Ops[1]); 349 } 350 351 switch (Opcode) { 352 default: return 0; 353 case Instruction::Call: 354 if (Function *F = dyn_cast<Function>(Ops[0])) 355 if (canConstantFoldCallTo(F)) 356 return ConstantFoldCall(F, Ops+1, NumOps-1); 357 return 0; 358 case Instruction::ICmp: 359 case Instruction::FCmp: 360 case Instruction::VICmp: 361 case Instruction::VFCmp: 362 assert(0 &&"This function is invalid for compares: no predicate specified"); 363 case Instruction::PtrToInt: 364 // If the input is a inttoptr, eliminate the pair. This requires knowing 365 // the width of a pointer, so it can't be done in ConstantExpr::getCast. 366 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ops[0])) { 367 if (TD && CE->getOpcode() == Instruction::IntToPtr) { 368 Constant *Input = CE->getOperand(0); 369 unsigned InWidth = Input->getType()->getPrimitiveSizeInBits(); 370 if (TD->getPointerSizeInBits() < InWidth) { 371 Constant *Mask = 372 ConstantInt::get(APInt::getLowBitsSet(InWidth, 373 TD->getPointerSizeInBits())); 374 Input = ConstantExpr::getAnd(Input, Mask); 375 } 376 // Do a zext or trunc to get to the dest size. 377 return ConstantExpr::getIntegerCast(Input, DestTy, false); 378 } 379 } 380 return ConstantExpr::getCast(Opcode, Ops[0], DestTy); 381 case Instruction::IntToPtr: 382 // If the input is a ptrtoint, turn the pair into a ptr to ptr bitcast if 383 // the int size is >= the ptr size. This requires knowing the width of a 384 // pointer, so it can't be done in ConstantExpr::getCast. 385 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ops[0])) { 386 if (TD && CE->getOpcode() == Instruction::PtrToInt && 387 TD->getPointerSizeInBits() <= 388 CE->getType()->getPrimitiveSizeInBits()) { 389 Constant *Input = CE->getOperand(0); 390 Constant *C = FoldBitCast(Input, DestTy, *TD); 391 return C ? C : ConstantExpr::getBitCast(Input, DestTy); 392 } 393 } 394 return ConstantExpr::getCast(Opcode, Ops[0], DestTy); 395 case Instruction::Trunc: 396 case Instruction::ZExt: 397 case Instruction::SExt: 398 case Instruction::FPTrunc: 399 case Instruction::FPExt: 400 case Instruction::UIToFP: 401 case Instruction::SIToFP: 402 case Instruction::FPToUI: 403 case Instruction::FPToSI: 404 return ConstantExpr::getCast(Opcode, Ops[0], DestTy); 405 case Instruction::BitCast: 406 if (TD) 407 if (Constant *C = FoldBitCast(Ops[0], DestTy, *TD)) 408 return C; 409 return ConstantExpr::getBitCast(Ops[0], DestTy); 410 case Instruction::Select: 411 return ConstantExpr::getSelect(Ops[0], Ops[1], Ops[2]); 412 case Instruction::ExtractElement: 413 return ConstantExpr::getExtractElement(Ops[0], Ops[1]); 414 case Instruction::InsertElement: 415 return ConstantExpr::getInsertElement(Ops[0], Ops[1], Ops[2]); 416 case Instruction::ShuffleVector: 417 return ConstantExpr::getShuffleVector(Ops[0], Ops[1], Ops[2]); 418 case Instruction::GetElementPtr: 419 if (Constant *C = SymbolicallyEvaluateGEP(Ops, NumOps, DestTy, TD)) 420 return C; 421 422 return ConstantExpr::getGetElementPtr(Ops[0], Ops+1, NumOps-1); 423 } 424} 425 426/// ConstantFoldCompareInstOperands - Attempt to constant fold a compare 427/// instruction (icmp/fcmp) with the specified operands. If it fails, it 428/// returns a constant expression of the specified operands. 429/// 430Constant *llvm::ConstantFoldCompareInstOperands(unsigned Predicate, 431 Constant*const * Ops, 432 unsigned NumOps, 433 const TargetData *TD) { 434 // fold: icmp (inttoptr x), null -> icmp x, 0 435 // fold: icmp (ptrtoint x), 0 -> icmp x, null 436 // fold: icmp (inttoptr x), (inttoptr y) -> icmp trunc/zext x, trunc/zext y 437 // fold: icmp (ptrtoint x), (ptrtoint y) -> icmp x, y 438 // 439 // ConstantExpr::getCompare cannot do this, because it doesn't have TD 440 // around to know if bit truncation is happening. 441 if (ConstantExpr *CE0 = dyn_cast<ConstantExpr>(Ops[0])) { 442 if (TD && Ops[1]->isNullValue()) { 443 const Type *IntPtrTy = TD->getIntPtrType(); 444 if (CE0->getOpcode() == Instruction::IntToPtr) { 445 // Convert the integer value to the right size to ensure we get the 446 // proper extension or truncation. 447 Constant *C = ConstantExpr::getIntegerCast(CE0->getOperand(0), 448 IntPtrTy, false); 449 Constant *NewOps[] = { C, Constant::getNullValue(C->getType()) }; 450 return ConstantFoldCompareInstOperands(Predicate, NewOps, 2, TD); 451 } 452 453 // Only do this transformation if the int is intptrty in size, otherwise 454 // there is a truncation or extension that we aren't modeling. 455 if (CE0->getOpcode() == Instruction::PtrToInt && 456 CE0->getType() == IntPtrTy) { 457 Constant *C = CE0->getOperand(0); 458 Constant *NewOps[] = { C, Constant::getNullValue(C->getType()) }; 459 // FIXME! 460 return ConstantFoldCompareInstOperands(Predicate, NewOps, 2, TD); 461 } 462 } 463 464 if (ConstantExpr *CE1 = dyn_cast<ConstantExpr>(Ops[1])) { 465 if (TD && CE0->getOpcode() == CE1->getOpcode()) { 466 const Type *IntPtrTy = TD->getIntPtrType(); 467 468 if (CE0->getOpcode() == Instruction::IntToPtr) { 469 // Convert the integer value to the right size to ensure we get the 470 // proper extension or truncation. 471 Constant *C0 = ConstantExpr::getIntegerCast(CE0->getOperand(0), 472 IntPtrTy, false); 473 Constant *C1 = ConstantExpr::getIntegerCast(CE1->getOperand(0), 474 IntPtrTy, false); 475 Constant *NewOps[] = { C0, C1 }; 476 return ConstantFoldCompareInstOperands(Predicate, NewOps, 2, TD); 477 } 478 479 // Only do this transformation if the int is intptrty in size, otherwise 480 // there is a truncation or extension that we aren't modeling. 481 if ((CE0->getOpcode() == Instruction::PtrToInt && 482 CE0->getType() == IntPtrTy && 483 CE0->getOperand(0)->getType() == CE1->getOperand(0)->getType())) { 484 Constant *NewOps[] = { 485 CE0->getOperand(0), CE1->getOperand(0) 486 }; 487 return ConstantFoldCompareInstOperands(Predicate, NewOps, 2, TD); 488 } 489 } 490 } 491 } 492 return ConstantExpr::getCompare(Predicate, Ops[0], Ops[1]); 493} 494 495 496/// ConstantFoldLoadThroughGEPConstantExpr - Given a constant and a 497/// getelementptr constantexpr, return the constant value being addressed by the 498/// constant expression, or null if something is funny and we can't decide. 499Constant *llvm::ConstantFoldLoadThroughGEPConstantExpr(Constant *C, 500 ConstantExpr *CE) { 501 if (CE->getOperand(1) != Constant::getNullValue(CE->getOperand(1)->getType())) 502 return 0; // Do not allow stepping over the value! 503 504 // Loop over all of the operands, tracking down which value we are 505 // addressing... 506 gep_type_iterator I = gep_type_begin(CE), E = gep_type_end(CE); 507 for (++I; I != E; ++I) 508 if (const StructType *STy = dyn_cast<StructType>(*I)) { 509 ConstantInt *CU = cast<ConstantInt>(I.getOperand()); 510 assert(CU->getZExtValue() < STy->getNumElements() && 511 "Struct index out of range!"); 512 unsigned El = (unsigned)CU->getZExtValue(); 513 if (ConstantStruct *CS = dyn_cast<ConstantStruct>(C)) { 514 C = CS->getOperand(El); 515 } else if (isa<ConstantAggregateZero>(C)) { 516 C = Constant::getNullValue(STy->getElementType(El)); 517 } else if (isa<UndefValue>(C)) { 518 C = UndefValue::get(STy->getElementType(El)); 519 } else { 520 return 0; 521 } 522 } else if (ConstantInt *CI = dyn_cast<ConstantInt>(I.getOperand())) { 523 if (const ArrayType *ATy = dyn_cast<ArrayType>(*I)) { 524 if (CI->getZExtValue() >= ATy->getNumElements()) 525 return 0; 526 if (ConstantArray *CA = dyn_cast<ConstantArray>(C)) 527 C = CA->getOperand(CI->getZExtValue()); 528 else if (isa<ConstantAggregateZero>(C)) 529 C = Constant::getNullValue(ATy->getElementType()); 530 else if (isa<UndefValue>(C)) 531 C = UndefValue::get(ATy->getElementType()); 532 else 533 return 0; 534 } else if (const VectorType *PTy = dyn_cast<VectorType>(*I)) { 535 if (CI->getZExtValue() >= PTy->getNumElements()) 536 return 0; 537 if (ConstantVector *CP = dyn_cast<ConstantVector>(C)) 538 C = CP->getOperand(CI->getZExtValue()); 539 else if (isa<ConstantAggregateZero>(C)) 540 C = Constant::getNullValue(PTy->getElementType()); 541 else if (isa<UndefValue>(C)) 542 C = UndefValue::get(PTy->getElementType()); 543 else 544 return 0; 545 } else { 546 return 0; 547 } 548 } else { 549 return 0; 550 } 551 return C; 552} 553 554 555//===----------------------------------------------------------------------===// 556// Constant Folding for Calls 557// 558 559/// canConstantFoldCallTo - Return true if its even possible to fold a call to 560/// the specified function. 561bool 562llvm::canConstantFoldCallTo(const Function *F) { 563 switch (F->getIntrinsicID()) { 564 case Intrinsic::sqrt: 565 case Intrinsic::powi: 566 case Intrinsic::bswap: 567 case Intrinsic::ctpop: 568 case Intrinsic::ctlz: 569 case Intrinsic::cttz: 570 return true; 571 default: break; 572 } 573 574 if (!F->hasName()) return false; 575 const char *Str = F->getNameStart(); 576 unsigned Len = F->getNameLen(); 577 578 // In these cases, the check of the length is required. We don't want to 579 // return true for a name like "cos\0blah" which strcmp would return equal to 580 // "cos", but has length 8. 581 switch (Str[0]) { 582 default: return false; 583 case 'a': 584 if (Len == 4) 585 return !strcmp(Str, "acos") || !strcmp(Str, "asin") || 586 !strcmp(Str, "atan"); 587 else if (Len == 5) 588 return !strcmp(Str, "atan2"); 589 return false; 590 case 'c': 591 if (Len == 3) 592 return !strcmp(Str, "cos"); 593 else if (Len == 4) 594 return !strcmp(Str, "ceil") || !strcmp(Str, "cosf") || 595 !strcmp(Str, "cosh"); 596 return false; 597 case 'e': 598 if (Len == 3) 599 return !strcmp(Str, "exp"); 600 return false; 601 case 'f': 602 if (Len == 4) 603 return !strcmp(Str, "fabs") || !strcmp(Str, "fmod"); 604 else if (Len == 5) 605 return !strcmp(Str, "floor"); 606 return false; 607 break; 608 case 'l': 609 if (Len == 3 && !strcmp(Str, "log")) 610 return true; 611 if (Len == 5 && !strcmp(Str, "log10")) 612 return true; 613 return false; 614 case 'p': 615 if (Len == 3 && !strcmp(Str, "pow")) 616 return true; 617 return false; 618 case 's': 619 if (Len == 3) 620 return !strcmp(Str, "sin"); 621 if (Len == 4) 622 return !strcmp(Str, "sinh") || !strcmp(Str, "sqrt") || 623 !strcmp(Str, "sinf"); 624 if (Len == 5) 625 return !strcmp(Str, "sqrtf"); 626 return false; 627 case 't': 628 if (Len == 3 && !strcmp(Str, "tan")) 629 return true; 630 else if (Len == 4 && !strcmp(Str, "tanh")) 631 return true; 632 return false; 633 } 634} 635 636static Constant *ConstantFoldFP(double (*NativeFP)(double), double V, 637 const Type *Ty) { 638 errno = 0; 639 V = NativeFP(V); 640 if (errno != 0) { 641 errno = 0; 642 return 0; 643 } 644 645 if (Ty == Type::FloatTy) 646 return ConstantFP::get(APFloat((float)V)); 647 if (Ty == Type::DoubleTy) 648 return ConstantFP::get(APFloat(V)); 649 assert(0 && "Can only constant fold float/double"); 650 return 0; // dummy return to suppress warning 651} 652 653static Constant *ConstantFoldBinaryFP(double (*NativeFP)(double, double), 654 double V, double W, 655 const Type *Ty) { 656 errno = 0; 657 V = NativeFP(V, W); 658 if (errno != 0) { 659 errno = 0; 660 return 0; 661 } 662 663 if (Ty == Type::FloatTy) 664 return ConstantFP::get(APFloat((float)V)); 665 if (Ty == Type::DoubleTy) 666 return ConstantFP::get(APFloat(V)); 667 assert(0 && "Can only constant fold float/double"); 668 return 0; // dummy return to suppress warning 669} 670 671/// ConstantFoldCall - Attempt to constant fold a call to the specified function 672/// with the specified arguments, returning null if unsuccessful. 673 674Constant * 675llvm::ConstantFoldCall(Function *F, 676 Constant* const* Operands, unsigned NumOperands) { 677 if (!F->hasName()) return 0; 678 const char *Str = F->getNameStart(); 679 unsigned Len = F->getNameLen(); 680 681 const Type *Ty = F->getReturnType(); 682 if (NumOperands == 1) { 683 if (ConstantFP *Op = dyn_cast<ConstantFP>(Operands[0])) { 684 if (Ty!=Type::FloatTy && Ty!=Type::DoubleTy) 685 return 0; 686 /// Currently APFloat versions of these functions do not exist, so we use 687 /// the host native double versions. Float versions are not called 688 /// directly but for all these it is true (float)(f((double)arg)) == 689 /// f(arg). Long double not supported yet. 690 double V = Ty==Type::FloatTy ? (double)Op->getValueAPF().convertToFloat(): 691 Op->getValueAPF().convertToDouble(); 692 switch (Str[0]) { 693 case 'a': 694 if (Len == 4 && !strcmp(Str, "acos")) 695 return ConstantFoldFP(acos, V, Ty); 696 else if (Len == 4 && !strcmp(Str, "asin")) 697 return ConstantFoldFP(asin, V, Ty); 698 else if (Len == 4 && !strcmp(Str, "atan")) 699 return ConstantFoldFP(atan, V, Ty); 700 break; 701 case 'c': 702 if (Len == 4 && !strcmp(Str, "ceil")) 703 return ConstantFoldFP(ceil, V, Ty); 704 else if (Len == 3 && !strcmp(Str, "cos")) 705 return ConstantFoldFP(cos, V, Ty); 706 else if (Len == 4 && !strcmp(Str, "cosh")) 707 return ConstantFoldFP(cosh, V, Ty); 708 else if (Len == 4 && !strcmp(Str, "cosf")) 709 return ConstantFoldFP(cos, V, Ty); 710 break; 711 case 'e': 712 if (Len == 3 && !strcmp(Str, "exp")) 713 return ConstantFoldFP(exp, V, Ty); 714 break; 715 case 'f': 716 if (Len == 4 && !strcmp(Str, "fabs")) 717 return ConstantFoldFP(fabs, V, Ty); 718 else if (Len == 5 && !strcmp(Str, "floor")) 719 return ConstantFoldFP(floor, V, Ty); 720 break; 721 case 'l': 722 if (Len == 3 && !strcmp(Str, "log") && V > 0) 723 return ConstantFoldFP(log, V, Ty); 724 else if (Len == 5 && !strcmp(Str, "log10") && V > 0) 725 return ConstantFoldFP(log10, V, Ty); 726 else if (!strcmp(Str, "llvm.sqrt.f32") || 727 !strcmp(Str, "llvm.sqrt.f64")) { 728 if (V >= -0.0) 729 return ConstantFoldFP(sqrt, V, Ty); 730 else // Undefined 731 return Constant::getNullValue(Ty); 732 } 733 break; 734 case 's': 735 if (Len == 3 && !strcmp(Str, "sin")) 736 return ConstantFoldFP(sin, V, Ty); 737 else if (Len == 4 && !strcmp(Str, "sinh")) 738 return ConstantFoldFP(sinh, V, Ty); 739 else if (Len == 4 && !strcmp(Str, "sqrt") && V >= 0) 740 return ConstantFoldFP(sqrt, V, Ty); 741 else if (Len == 5 && !strcmp(Str, "sqrtf") && V >= 0) 742 return ConstantFoldFP(sqrt, V, Ty); 743 else if (Len == 4 && !strcmp(Str, "sinf")) 744 return ConstantFoldFP(sin, V, Ty); 745 break; 746 case 't': 747 if (Len == 3 && !strcmp(Str, "tan")) 748 return ConstantFoldFP(tan, V, Ty); 749 else if (Len == 4 && !strcmp(Str, "tanh")) 750 return ConstantFoldFP(tanh, V, Ty); 751 break; 752 default: 753 break; 754 } 755 } else if (ConstantInt *Op = dyn_cast<ConstantInt>(Operands[0])) { 756 if (Len > 11 && !memcmp(Str, "llvm.bswap", 10)) 757 return ConstantInt::get(Op->getValue().byteSwap()); 758 else if (Len > 11 && !memcmp(Str, "llvm.ctpop", 10)) 759 return ConstantInt::get(Ty, Op->getValue().countPopulation()); 760 else if (Len > 10 && !memcmp(Str, "llvm.cttz", 9)) 761 return ConstantInt::get(Ty, Op->getValue().countTrailingZeros()); 762 else if (Len > 10 && !memcmp(Str, "llvm.ctlz", 9)) 763 return ConstantInt::get(Ty, Op->getValue().countLeadingZeros()); 764 } 765 } else if (NumOperands == 2) { 766 if (ConstantFP *Op1 = dyn_cast<ConstantFP>(Operands[0])) { 767 if (Ty!=Type::FloatTy && Ty!=Type::DoubleTy) 768 return 0; 769 double Op1V = Ty==Type::FloatTy ? 770 (double)Op1->getValueAPF().convertToFloat(): 771 Op1->getValueAPF().convertToDouble(); 772 if (ConstantFP *Op2 = dyn_cast<ConstantFP>(Operands[1])) { 773 double Op2V = Ty==Type::FloatTy ? 774 (double)Op2->getValueAPF().convertToFloat(): 775 Op2->getValueAPF().convertToDouble(); 776 777 if (Len == 3 && !strcmp(Str, "pow")) { 778 return ConstantFoldBinaryFP(pow, Op1V, Op2V, Ty); 779 } else if (Len == 4 && !strcmp(Str, "fmod")) { 780 return ConstantFoldBinaryFP(fmod, Op1V, Op2V, Ty); 781 } else if (Len == 5 && !strcmp(Str, "atan2")) { 782 return ConstantFoldBinaryFP(atan2, Op1V, Op2V, Ty); 783 } 784 } else if (ConstantInt *Op2C = dyn_cast<ConstantInt>(Operands[1])) { 785 if (!strcmp(Str, "llvm.powi.f32")) { 786 return ConstantFP::get(APFloat((float)std::pow((float)Op1V, 787 (int)Op2C->getZExtValue()))); 788 } else if (!strcmp(Str, "llvm.powi.f64")) { 789 return ConstantFP::get(APFloat((double)std::pow((double)Op1V, 790 (int)Op2C->getZExtValue()))); 791 } 792 } 793 } 794 } 795 return 0; 796} 797 798