lib/Analysis/InstructionSimplify.cpp

   1 //===- InstructionSimplify.cpp - Fold instruction operands ----------------===//
   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 implements routines for folding instructions into simpler forms
  11 // that do not require creating new instructions.  For example, this does
  12 // constant folding, and can handle identities like (X&0)->0.
  13 //
  14 //===----------------------------------------------------------------------===//
  15
  16 #include "llvm/Analysis/InstructionSimplify.h"
  17 #include "llvm/Analysis/ConstantFolding.h"
  18 #include "llvm/Support/ValueHandle.h"
  19 #include "llvm/Instructions.h"
  20 #include "llvm/Support/PatternMatch.h"
  21 using namespace llvm;
  22 using namespace llvm::PatternMatch;
  23
  24 /// SimplifyAddInst - Given operands for an Add, see if we can
  25 /// fold the result.  If not, this returns null.
  26 Value *llvm::SimplifyAddInst(Value *Op0, Value *Op1, bool isNSW, bool isNUW,
  27                              const TargetData *TD) {
  28   if (Constant *CLHS = dyn_cast<Constant>(Op0)) {
  29     if (Constant *CRHS = dyn_cast<Constant>(Op1)) {
  30       Constant *Ops[] = { CLHS, CRHS };
  31       return ConstantFoldInstOperands(Instruction::Add, CLHS->getType(),
  32                                       Ops, 2, TD);
  33     }
  34
  35     // Canonicalize the constant to the RHS.
  36     std::swap(Op0, Op1);
  37   }
  38
  39   if (Constant *Op1C = dyn_cast<Constant>(Op1)) {
  40     // X + undef -> undef
  41     if (isa<UndefValue>(Op1C))
  42       return Op1C;
  43
  44     // X + 0 --> X
  45     if (Op1C->isNullValue())
  46       return Op0;
  47   }
  48
  49   // FIXME: Could pull several more out of instcombine.
  50   return 0;
  51 }
  52
  53 /// SimplifyAndInst - Given operands for an And, see if we can
  54 /// fold the result.  If not, this returns null.
  55 Value *llvm::SimplifyAndInst(Value *Op0, Value *Op1, const TargetData *TD) {
  56   if (Constant *CLHS = dyn_cast<Constant>(Op0)) {
  57     if (Constant *CRHS = dyn_cast<Constant>(Op1)) {
  58       Constant *Ops[] = { CLHS, CRHS };
  59       return ConstantFoldInstOperands(Instruction::And, CLHS->getType(),
  60                                       Ops, 2, TD);
  61     }
  62
  63     // Canonicalize the constant to the RHS.
  64     std::swap(Op0, Op1);
  65   }
  66
  67   // X & undef -> 0
  68   if (isa<UndefValue>(Op1))
  69     return Constant::getNullValue(Op0->getType());
  70
  71   // X & X = X
  72   if (Op0 == Op1)
  73     return Op0;
  74
  75   // X & <0,0> = <0,0>
  76   if (isa<ConstantAggregateZero>(Op1))
  77     return Op1;
  78
  79   // X & <-1,-1> = X
  80   if (ConstantVector *CP = dyn_cast<ConstantVector>(Op1))
  81     if (CP->isAllOnesValue())
  82       return Op0;
  83
  84   if (ConstantInt *Op1CI = dyn_cast<ConstantInt>(Op1)) {
  85     // X & 0 = 0
  86     if (Op1CI->isZero())
  87       return Op1CI;
  88     // X & -1 = X
  89     if (Op1CI->isAllOnesValue())
  90       return Op0;
  91   }
  92
  93   // A & ~A  =  ~A & A  =  0
  94   Value *A, *B;
  95   if ((match(Op0, m_Not(m_Value(A))) && A == Op1) ||
  96       (match(Op1, m_Not(m_Value(A))) && A == Op0))
  97     return Constant::getNullValue(Op0->getType());
  98
  99   // (A | ?) & A = A
 100   if (match(Op0, m_Or(m_Value(A), m_Value(B))) &&
 101       (A == Op1 || B == Op1))
 102     return Op1;
 103
 104   // A & (A | ?) = A
 105   if (match(Op1, m_Or(m_Value(A), m_Value(B))) &&
 106       (A == Op0 || B == Op0))
 107     return Op0;
 108
 109   // (A & B) & A -> A & B
 110   if (match(Op0, m_And(m_Value(A), m_Value(B))) &&
 111       (A == Op1 || B == Op1))
 112     return Op0;
 113
 114   // A & (A & B) -> A & B
 115   if (match(Op1, m_And(m_Value(A), m_Value(B))) &&
 116       (A == Op0 || B == Op0))
 117     return Op1;
 118
 119   return 0;
 120 }
 121
 122 /// SimplifyOrInst - Given operands for an Or, see if we can
 123 /// fold the result.  If not, this returns null.
 124 Value *llvm::SimplifyOrInst(Value *Op0, Value *Op1, const TargetData *TD) {
 125   if (Constant *CLHS = dyn_cast<Constant>(Op0)) {
 126     if (Constant *CRHS = dyn_cast<Constant>(Op1)) {
 127       Constant *Ops[] = { CLHS, CRHS };
 128       return ConstantFoldInstOperands(Instruction::Or, CLHS->getType(),
 129                                       Ops, 2, TD);
 130     }
 131
 132     // Canonicalize the constant to the RHS.
 133     std::swap(Op0, Op1);
 134   }
 135
 136   // X | undef -> -1
 137   if (isa<UndefValue>(Op1))
 138     return Constant::getAllOnesValue(Op0->getType());
 139
 140   // X | X = X
 141   if (Op0 == Op1)
 142     return Op0;
 143
 144   // X | <0,0> = X
 145   if (isa<ConstantAggregateZero>(Op1))
 146     return Op0;
 147
 148   // X | <-1,-1> = <-1,-1>
 149   if (ConstantVector *CP = dyn_cast<ConstantVector>(Op1))
 150     if (CP->isAllOnesValue())
 151       return Op1;
 152
 153   if (ConstantInt *Op1CI = dyn_cast<ConstantInt>(Op1)) {
 154     // X | 0 = X
 155     if (Op1CI->isZero())
 156       return Op0;
 157     // X | -1 = -1
 158     if (Op1CI->isAllOnesValue())
 159       return Op1CI;
 160   }
 161
 162   // A | ~A  =  ~A | A  =  -1
 163   Value *A, *B;
 164   if ((match(Op0, m_Not(m_Value(A))) && A == Op1) ||
 165       (match(Op1, m_Not(m_Value(A))) && A == Op0))
 166     return Constant::getAllOnesValue(Op0->getType());
 167
 168   // (A & ?) | A = A
 169   if (match(Op0, m_And(m_Value(A), m_Value(B))) &&
 170       (A == Op1 || B == Op1))
 171     return Op1;
 172
 173   // A | (A & ?) = A
 174   if (match(Op1, m_And(m_Value(A), m_Value(B))) &&
 175       (A == Op0 || B == Op0))
 176     return Op0;
 177
 178   // (A | B) | A -> A | B
 179   if (match(Op0, m_Or(m_Value(A), m_Value(B))) &&
 180       (A == Op1 || B == Op1))
 181     return Op0;
 182
 183   // A | (A | B) -> A | B
 184   if (match(Op1, m_Or(m_Value(A), m_Value(B))) &&
 185       (A == Op0 || B == Op0))
 186     return Op1;
 187
 188   return 0;
 189 }
 190
 191
 192 static const Type *GetCompareTy(Value *Op) {
 193   return CmpInst::makeCmpResultType(Op->getType());
 194 }
 195
 196
 197 /// SimplifyICmpInst - Given operands for an ICmpInst, see if we can
 198 /// fold the result.  If not, this returns null.
 199 Value *llvm::SimplifyICmpInst(unsigned Predicate, Value *LHS, Value *RHS,
 200                               const TargetData *TD) {
 201   CmpInst::Predicate Pred = (CmpInst::Predicate)Predicate;
 202   assert(CmpInst::isIntPredicate(Pred) && "Not an integer compare!");
 203
 204   if (Constant *CLHS = dyn_cast<Constant>(LHS)) {
 205     if (Constant *CRHS = dyn_cast<Constant>(RHS))
 206       return ConstantFoldCompareInstOperands(Pred, CLHS, CRHS, TD);
 207
 208     // If we have a constant, make sure it is on the RHS.
 209     std::swap(LHS, RHS);
 210     Pred = CmpInst::getSwappedPredicate(Pred);
 211   }
 212
 213   // ITy - This is the return type of the compare we're considering.
 214   const Type *ITy = GetCompareTy(LHS);
 215
 216   // icmp X, X -> true/false
 217   // X icmp undef -> true/false.  For example, icmp ugt %X, undef -> false
 218   // because X could be 0.
 219   if (LHS == RHS || isa<UndefValue>(RHS))
 220     return ConstantInt::get(ITy, CmpInst::isTrueWhenEqual(Pred));
 221
 222   // icmp <global/alloca*/null>, <global/alloca*/null> - Global/Stack value
 223   // addresses never equal each other!  We already know that Op0 != Op1.
 224   if ((isa<GlobalValue>(LHS) || isa<AllocaInst>(LHS) ||
 225        isa<ConstantPointerNull>(LHS)) &&
 226       (isa<GlobalValue>(RHS) || isa<AllocaInst>(RHS) ||
 227        isa<ConstantPointerNull>(RHS)))
 228     return ConstantInt::get(ITy, CmpInst::isFalseWhenEqual(Pred));
 229
 230   // See if we are doing a comparison with a constant.
 231   if (ConstantInt *CI = dyn_cast<ConstantInt>(RHS)) {
 232     // If we have an icmp le or icmp ge instruction, turn it into the
 233     // appropriate icmp lt or icmp gt instruction.  This allows us to rely on
 234     // them being folded in the code below.
 235     switch (Pred) {
 236     default: break;
 237     case ICmpInst::ICMP_ULE:
 238       if (CI->isMaxValue(false))                 // A <=u MAX -> TRUE
 239         return ConstantInt::getTrue(CI->getContext());
 240       break;
 241     case ICmpInst::ICMP_SLE:
 242       if (CI->isMaxValue(true))                  // A <=s MAX -> TRUE
 243         return ConstantInt::getTrue(CI->getContext());
 244       break;
 245     case ICmpInst::ICMP_UGE:
 246       if (CI->isMinValue(false))                 // A >=u MIN -> TRUE
 247         return ConstantInt::getTrue(CI->getContext());
 248       break;
 249     case ICmpInst::ICMP_SGE:
 250       if (CI->isMinValue(true))                  // A >=s MIN -> TRUE
 251         return ConstantInt::getTrue(CI->getContext());
 252       break;
 253     }
 254   }
 255
 256
 257   return 0;
 258 }
 259
 260 /// SimplifyFCmpInst - Given operands for an FCmpInst, see if we can
 261 /// fold the result.  If not, this returns null.
 262 Value *llvm::SimplifyFCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
 263                               const TargetData *TD) {
 264   CmpInst::Predicate Pred = (CmpInst::Predicate)Predicate;
 265   assert(CmpInst::isFPPredicate(Pred) && "Not an FP compare!");
 266
 267   if (Constant *CLHS = dyn_cast<Constant>(LHS)) {
 268     if (Constant *CRHS = dyn_cast<Constant>(RHS))
 269       return ConstantFoldCompareInstOperands(Pred, CLHS, CRHS, TD);
 270
 271     // If we have a constant, make sure it is on the RHS.
 272     std::swap(LHS, RHS);
 273     Pred = CmpInst::getSwappedPredicate(Pred);
 274   }
 275
 276   // Fold trivial predicates.
 277   if (Pred == FCmpInst::FCMP_FALSE)
 278     return ConstantInt::get(GetCompareTy(LHS), 0);
 279   if (Pred == FCmpInst::FCMP_TRUE)
 280     return ConstantInt::get(GetCompareTy(LHS), 1);
 281
 282   if (isa<UndefValue>(RHS))                  // fcmp pred X, undef -> undef
 283     return UndefValue::get(GetCompareTy(LHS));
 284
 285   // fcmp x,x -> true/false.  Not all compares are foldable.
 286   if (LHS == RHS) {
 287     if (CmpInst::isTrueWhenEqual(Pred))
 288       return ConstantInt::get(GetCompareTy(LHS), 1);
 289     if (CmpInst::isFalseWhenEqual(Pred))
 290       return ConstantInt::get(GetCompareTy(LHS), 0);
 291   }
 292
 293   // Handle fcmp with constant RHS
 294   if (Constant *RHSC = dyn_cast<Constant>(RHS)) {
 295     // If the constant is a nan, see if we can fold the comparison based on it.
 296     if (ConstantFP *CFP = dyn_cast<ConstantFP>(RHSC)) {
 297       if (CFP->getValueAPF().isNaN()) {
 298         if (FCmpInst::isOrdered(Pred))   // True "if ordered and foo"
 299           return ConstantInt::getFalse(CFP->getContext());
 300         assert(FCmpInst::isUnordered(Pred) &&
 301                "Comparison must be either ordered or unordered!");
 302         // True if unordered.
 303         return ConstantInt::getTrue(CFP->getContext());
 304       }
 305       // Check whether the constant is an infinity.
 306       if (CFP->getValueAPF().isInfinity()) {
 307         if (CFP->getValueAPF().isNegative()) {
 308           switch (Pred) {
 309           case FCmpInst::FCMP_OLT:
 310             // No value is ordered and less than negative infinity.
 311             return ConstantInt::getFalse(CFP->getContext());
 312           case FCmpInst::FCMP_UGE:
 313             // All values are unordered with or at least negative infinity.
 314             return ConstantInt::getTrue(CFP->getContext());
 315           default:
 316             break;
 317           }
 318         } else {
 319           switch (Pred) {
 320           case FCmpInst::FCMP_OGT:
 321             // No value is ordered and greater than infinity.
 322             return ConstantInt::getFalse(CFP->getContext());
 323           case FCmpInst::FCMP_ULE:
 324             // All values are unordered with and at most infinity.
 325             return ConstantInt::getTrue(CFP->getContext());
 326           default:
 327             break;
 328           }
 329         }
 330       }
 331     }
 332   }
 333
 334   return 0;
 335 }
 336
 337 /// SimplifySelectInst - Given operands for a SelectInst, see if we can fold
 338 /// the result.  If not, this returns null.
 339 Value *llvm::SimplifySelectInst(Value *CondVal, Value *TrueVal, Value *FalseVal,
 340                                 const TargetData *TD) {
 341   // select true, X, Y  -> X
 342   // select false, X, Y -> Y
 343   if (ConstantInt *CB = dyn_cast<ConstantInt>(CondVal))
 344     return CB->getZExtValue() ? TrueVal : FalseVal;
 345
 346   // select C, X, X -> X
 347   if (TrueVal == FalseVal)
 348     return TrueVal;
 349
 350   if (isa<UndefValue>(TrueVal))   // select C, undef, X -> X
 351     return FalseVal;
 352   if (isa<UndefValue>(FalseVal))   // select C, X, undef -> X
 353     return TrueVal;
 354   if (isa<UndefValue>(CondVal)) {  // select undef, X, Y -> X or Y
 355     if (isa<Constant>(TrueVal))
 356       return TrueVal;
 357     return FalseVal;
 358   }
 359
 360
 361
 362   return 0;
 363 }
 364
 365
 366 /// SimplifyGEPInst - Given operands for an GetElementPtrInst, see if we can
 367 /// fold the result.  If not, this returns null.
 368 Value *llvm::SimplifyGEPInst(Value *const *Ops, unsigned NumOps,
 369                              const TargetData *TD) {
 370   // getelementptr P -> P.
 371   if (NumOps == 1)
 372     return Ops[0];
 373
 374   // TODO.
 375   //if (isa<UndefValue>(Ops[0]))
 376   //  return UndefValue::get(GEP.getType());
 377
 378   // getelementptr P, 0 -> P.
 379   if (NumOps == 2)
 380     if (ConstantInt *C = dyn_cast<ConstantInt>(Ops[1]))
 381       if (C->isZero())
 382         return Ops[0];
 383
 384   // Check to see if this is constant foldable.
 385   for (unsigned i = 0; i != NumOps; ++i)
 386     if (!isa<Constant>(Ops[i]))
 387       return 0;
 388
 389   return ConstantExpr::getGetElementPtr(cast<Constant>(Ops[0]),
 390                                         (Constant *const*)Ops+1, NumOps-1);
 391 }
 392
 393
 394 //=== Helper functions for higher up the class hierarchy.
 395
 396 /// SimplifyBinOp - Given operands for a BinaryOperator, see if we can
 397 /// fold the result.  If not, this returns null.
 398 Value *llvm::SimplifyBinOp(unsigned Opcode, Value *LHS, Value *RHS,
 399                            const TargetData *TD) {
 400   switch (Opcode) {
 401   case Instruction::And: return SimplifyAndInst(LHS, RHS, TD);
 402   case Instruction::Or:  return SimplifyOrInst(LHS, RHS, TD);
 403   default:
 404     if (Constant *CLHS = dyn_cast<Constant>(LHS))
 405       if (Constant *CRHS = dyn_cast<Constant>(RHS)) {
 406         Constant *COps[] = {CLHS, CRHS};
 407         return ConstantFoldInstOperands(Opcode, LHS->getType(), COps, 2, TD);
 408       }
 409     return 0;
 410   }
 411 }
 412
 413 /// SimplifyCmpInst - Given operands for a CmpInst, see if we can
 414 /// fold the result.
 415 Value *llvm::SimplifyCmpInst(unsigned Predicate, Value *LHS, Value *RHS,
 416                              const TargetData *TD) {
 417   if (CmpInst::isIntPredicate((CmpInst::Predicate)Predicate))
 418     return SimplifyICmpInst(Predicate, LHS, RHS, TD);
 419   return SimplifyFCmpInst(Predicate, LHS, RHS, TD);
 420 }
 421
 422
 423 /// SimplifyInstruction - See if we can compute a simplified version of this
 424 /// instruction.  If not, this returns null.
 425 Value *llvm::SimplifyInstruction(Instruction *I, const TargetData *TD) {
 426   switch (I->getOpcode()) {
 427   default:
 428     return ConstantFoldInstruction(I, TD);
 429   case Instruction::Add:
 430     return SimplifyAddInst(I->getOperand(0), I->getOperand(1),
 431                            cast<BinaryOperator>(I)->hasNoSignedWrap(),
 432                            cast<BinaryOperator>(I)->hasNoUnsignedWrap(), TD);
 433   case Instruction::And:
 434     return SimplifyAndInst(I->getOperand(0), I->getOperand(1), TD);
 435   case Instruction::Or:
 436     return SimplifyOrInst(I->getOperand(0), I->getOperand(1), TD);
 437   case Instruction::ICmp:
 438     return SimplifyICmpInst(cast<ICmpInst>(I)->getPredicate(),
 439                             I->getOperand(0), I->getOperand(1), TD);
 440   case Instruction::FCmp:
 441     return SimplifyFCmpInst(cast<FCmpInst>(I)->getPredicate(),
 442                             I->getOperand(0), I->getOperand(1), TD);
 443   case Instruction::Select:
 444     return SimplifySelectInst(I->getOperand(0), I->getOperand(1),
 445                               I->getOperand(2), TD);
 446   case Instruction::GetElementPtr: {
 447     SmallVector<Value*, 8> Ops(I->op_begin(), I->op_end());
 448     return SimplifyGEPInst(&Ops[0], Ops.size(), TD);
 449   }
 450   }
 451 }
 452
 453 /// ReplaceAndSimplifyAllUses - Perform From->replaceAllUsesWith(To) and then
 454 /// delete the From instruction.  In addition to a basic RAUW, this does a
 455 /// recursive simplification of the newly formed instructions.  This catches
 456 /// things where one simplification exposes other opportunities.  This only
 457 /// simplifies and deletes scalar operations, it does not change the CFG.
 458 ///
 459 void llvm::ReplaceAndSimplifyAllUses(Instruction *From, Value *To,
 460                                      const TargetData *TD) {
 461   assert(From != To && "ReplaceAndSimplifyAllUses(X,X) is not valid!");
 462
 463   // FromHandle/ToHandle - This keeps a WeakVH on the from/to values so that
 464   // we can know if it gets deleted out from under us or replaced in a
 465   // recursive simplification.
 466   WeakVH FromHandle(From);
 467   WeakVH ToHandle(To);
 468
 469   while (!From->use_empty()) {
 470     // Update the instruction to use the new value.
 471     Use &TheUse = From->use_begin().getUse();
 472     Instruction *User = cast<Instruction>(TheUse.getUser());
 473     TheUse = To;
 474
 475     // Check to see if the instruction can be folded due to the operand
 476     // replacement.  For example changing (or X, Y) into (or X, -1) can replace
 477     // the 'or' with -1.
 478     Value *SimplifiedVal;
 479     {
 480       // Sanity check to make sure 'User' doesn't dangle across
 481       // SimplifyInstruction.
 482       AssertingVH<> UserHandle(User);
 483
 484       SimplifiedVal = SimplifyInstruction(User, TD);
 485       if (SimplifiedVal == 0) continue;
 486     }
 487
 488     // Recursively simplify this user to the new value.
 489     ReplaceAndSimplifyAllUses(User, SimplifiedVal, TD);
 490     From = dyn_cast_or_null<Instruction>((Value*)FromHandle);
 491     To = ToHandle;
 492
 493     assert(ToHandle && "To value deleted by recursive simplification?");
 494
 495     // If the recursive simplification ended up revisiting and deleting
 496     // 'From' then we're done.
 497     if (From == 0)
 498       return;
 499   }
 500
 501   // If 'From' has value handles referring to it, do a real RAUW to update them.
 502   From->replaceAllUsesWith(To);
 503
 504   From->eraseFromParent();
 505 }
 506