1 //===-- ConstantFolding.cpp - Analyze constant folding possibilities ------===//
3 // The LLVM Compiler Infrastructure
5 // This file was developed by the LLVM research group and is distributed under
6 // the University of Illinois Open Source License. See LICENSE.TXT for details.
8 //===----------------------------------------------------------------------===//
10 // This family of functions determines the possibility of performing constant
13 //===----------------------------------------------------------------------===//
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"
30 //===----------------------------------------------------------------------===//
31 // Constant Folding internal helper functions
32 //===----------------------------------------------------------------------===//
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.
37 static 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))) {
45 // Otherwise, if this isn't a constant expr, bail out.
46 ConstantExpr *CE = dyn_cast<ConstantExpr>(C);
47 if (!CE) return false;
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);
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
58 if (!cast<PointerType>(CE->getOperand(0)->getType())->getElementType()->isSized())
61 // If the base isn't a global+constant, we aren't either.
62 if (!IsConstantOffsetFromGlobal(CE->getOperand(0), GV, Offset, TD))
65 // Otherwise, add any offset that our operands provide.
66 gep_type_iterator GTI = gep_type_begin(CE);
67 for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i, ++GTI) {
68 ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(i));
69 if (!CI) return false; // Index isn't a simple constant?
70 if (CI->getZExtValue() == 0) continue; // Not adding anything.
72 if (const StructType *ST = dyn_cast<StructType>(*GTI)) {
74 Offset += TD.getStructLayout(ST)->getElementOffset(CI->getZExtValue());
76 const SequentialType *SQT = cast<SequentialType>(*GTI);
77 Offset += TD.getTypeSize(SQT->getElementType())*CI->getSExtValue();
87 /// SymbolicallyEvaluateBinop - One of Op0/Op1 is a constant expression.
88 /// Attempt to symbolically evaluate the result of a binary operator merging
89 /// these together. If target data info is available, it is provided as TD,
90 /// otherwise TD is null.
91 static Constant *SymbolicallyEvaluateBinop(unsigned Opc, Constant *Op0,
92 Constant *Op1, const TargetData *TD){
95 // Fold (and 0xffffffff00000000, (shl x, 32)) -> shl.
96 // Fold (lshr (or X, Y), 32) -> (lshr [X/Y], 32) if one doesn't contribute
100 // If the constant expr is something like &A[123] - &A[4].f, fold this into a
101 // constant. This happens frequently when iterating over a global array.
102 if (Opc == Instruction::Sub && TD) {
103 GlobalValue *GV1, *GV2;
104 int64_t Offs1, Offs2;
106 if (IsConstantOffsetFromGlobal(Op0, GV1, Offs1, *TD))
107 if (IsConstantOffsetFromGlobal(Op1, GV2, Offs2, *TD) &&
109 // (&GV+C1) - (&GV+C2) -> C1-C2, pointer arithmetic cannot overflow.
110 return ConstantInt::get(Op0->getType(), Offs1-Offs2);
114 // TODO: Fold icmp setne/seteq as well.
118 /// SymbolicallyEvaluateGEP - If we can symbolically evaluate the specified GEP
119 /// constant expression, do so.
120 static Constant *SymbolicallyEvaluateGEP(Constant** Ops, unsigned NumOps,
121 const Type *ResultTy,
122 const TargetData *TD) {
123 Constant *Ptr = Ops[0];
124 if (!cast<PointerType>(Ptr->getType())->getElementType()->isSized())
127 if (TD && Ptr->isNullValue()) {
128 // If this is a constant expr gep that is effectively computing an
129 // "offsetof", fold it into 'cast int Size to T*' instead of 'gep 0, 0, 12'
130 bool isFoldableGEP = true;
131 for (unsigned i = 1; i != NumOps; ++i)
132 if (!isa<ConstantInt>(Ops[i])) {
133 isFoldableGEP = false;
137 uint64_t Offset = TD->getIndexedOffset(Ptr->getType(),
138 (Value**)Ops+1, NumOps-1);
139 Constant *C = ConstantInt::get(TD->getIntPtrType(), Offset);
140 return ConstantExpr::getIntToPtr(C, ResultTy);
148 //===----------------------------------------------------------------------===//
149 // Constant Folding public APIs
150 //===----------------------------------------------------------------------===//
153 /// ConstantFoldInstruction - Attempt to constant fold the specified
154 /// instruction. If successful, the constant result is returned, if not, null
155 /// is returned. Note that this function can only fail when attempting to fold
156 /// instructions like loads and stores, which have no constant expression form.
158 Constant *llvm::ConstantFoldInstruction(Instruction *I, const TargetData *TD) {
159 if (PHINode *PN = dyn_cast<PHINode>(I)) {
160 if (PN->getNumIncomingValues() == 0)
161 return Constant::getNullValue(PN->getType());
163 Constant *Result = dyn_cast<Constant>(PN->getIncomingValue(0));
164 if (Result == 0) return 0;
166 // Handle PHI nodes specially here...
167 for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i)
168 if (PN->getIncomingValue(i) != Result && PN->getIncomingValue(i) != PN)
169 return 0; // Not all the same incoming constants...
171 // If we reach here, all incoming values are the same constant.
175 // Scan the operand list, checking to see if they are all constants, if so,
176 // hand off to ConstantFoldInstOperands.
177 SmallVector<Constant*, 8> Ops;
178 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
179 if (Constant *Op = dyn_cast<Constant>(I->getOperand(i)))
182 return 0; // All operands not constant!
184 return ConstantFoldInstOperands(I, &Ops[0], Ops.size(), TD);
187 /// ConstantFoldInstOperands - Attempt to constant fold an instruction with the
188 /// specified opcode and operands. If successful, the constant result is
189 /// returned, if not, null is returned. Note that this function can fail when
190 /// attempting to fold instructions like loads and stores, which have no
191 /// constant expression form.
193 Constant *llvm::ConstantFoldInstOperands(const Instruction* I,
194 Constant** Ops, unsigned NumOps,
195 const TargetData *TD) {
196 unsigned Opc = I->getOpcode();
197 const Type *DestTy = I->getType();
199 // Handle easy binops first.
200 if (isa<BinaryOperator>(I)) {
201 if (isa<ConstantExpr>(Ops[0]) || isa<ConstantExpr>(Ops[1]))
202 if (Constant *C = SymbolicallyEvaluateBinop(I->getOpcode(), Ops[0],
206 return ConstantExpr::get(Opc, Ops[0], Ops[1]);
211 case Instruction::Call:
212 if (Function *F = dyn_cast<Function>(Ops[0]))
213 if (canConstantFoldCallTo(F))
214 return ConstantFoldCall(F, Ops+1, NumOps-1);
216 case Instruction::ICmp:
217 case Instruction::FCmp:
218 return ConstantExpr::getCompare(cast<CmpInst>(I)->getPredicate(), Ops[0],
220 case Instruction::PtrToInt:
221 // If the input is a inttoptr, eliminate the pair. This requires knowing
222 // the width of a pointer, so it can't be done in ConstantExpr::getCast.
223 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ops[0])) {
224 if (TD && CE->getOpcode() == Instruction::IntToPtr) {
225 Constant *Input = CE->getOperand(0);
226 unsigned InWidth = Input->getType()->getPrimitiveSizeInBits();
228 ConstantInt::get(APInt::getLowBitsSet(InWidth,
229 TD->getPointerSizeInBits()));
230 Input = ConstantExpr::getAnd(Input, Mask);
231 // Do a zext or trunc to get to the dest size.
232 return ConstantExpr::getIntegerCast(Input, I->getType(), false);
236 case Instruction::IntToPtr:
237 case Instruction::Trunc:
238 case Instruction::ZExt:
239 case Instruction::SExt:
240 case Instruction::FPTrunc:
241 case Instruction::FPExt:
242 case Instruction::UIToFP:
243 case Instruction::SIToFP:
244 case Instruction::FPToUI:
245 case Instruction::FPToSI:
246 case Instruction::BitCast:
247 return ConstantExpr::getCast(Opc, Ops[0], DestTy);
248 case Instruction::Select:
249 return ConstantExpr::getSelect(Ops[0], Ops[1], Ops[2]);
250 case Instruction::ExtractElement:
251 return ConstantExpr::getExtractElement(Ops[0], Ops[1]);
252 case Instruction::InsertElement:
253 return ConstantExpr::getInsertElement(Ops[0], Ops[1], Ops[2]);
254 case Instruction::ShuffleVector:
255 return ConstantExpr::getShuffleVector(Ops[0], Ops[1], Ops[2]);
256 case Instruction::GetElementPtr:
257 if (Constant *C = SymbolicallyEvaluateGEP(Ops, NumOps, I->getType(), TD))
260 return ConstantExpr::getGetElementPtr(Ops[0], Ops+1, NumOps-1);
264 /// ConstantFoldLoadThroughGEPConstantExpr - Given a constant and a
265 /// getelementptr constantexpr, return the constant value being addressed by the
266 /// constant expression, or null if something is funny and we can't decide.
267 Constant *llvm::ConstantFoldLoadThroughGEPConstantExpr(Constant *C,
269 if (CE->getOperand(1) != Constant::getNullValue(CE->getOperand(1)->getType()))
270 return 0; // Do not allow stepping over the value!
272 // Loop over all of the operands, tracking down which value we are
274 gep_type_iterator I = gep_type_begin(CE), E = gep_type_end(CE);
275 for (++I; I != E; ++I)
276 if (const StructType *STy = dyn_cast<StructType>(*I)) {
277 ConstantInt *CU = cast<ConstantInt>(I.getOperand());
278 assert(CU->getZExtValue() < STy->getNumElements() &&
279 "Struct index out of range!");
280 unsigned El = (unsigned)CU->getZExtValue();
281 if (ConstantStruct *CS = dyn_cast<ConstantStruct>(C)) {
282 C = CS->getOperand(El);
283 } else if (isa<ConstantAggregateZero>(C)) {
284 C = Constant::getNullValue(STy->getElementType(El));
285 } else if (isa<UndefValue>(C)) {
286 C = UndefValue::get(STy->getElementType(El));
290 } else if (ConstantInt *CI = dyn_cast<ConstantInt>(I.getOperand())) {
291 if (const ArrayType *ATy = dyn_cast<ArrayType>(*I)) {
292 if (CI->getZExtValue() >= ATy->getNumElements())
294 if (ConstantArray *CA = dyn_cast<ConstantArray>(C))
295 C = CA->getOperand(CI->getZExtValue());
296 else if (isa<ConstantAggregateZero>(C))
297 C = Constant::getNullValue(ATy->getElementType());
298 else if (isa<UndefValue>(C))
299 C = UndefValue::get(ATy->getElementType());
302 } else if (const VectorType *PTy = dyn_cast<VectorType>(*I)) {
303 if (CI->getZExtValue() >= PTy->getNumElements())
305 if (ConstantVector *CP = dyn_cast<ConstantVector>(C))
306 C = CP->getOperand(CI->getZExtValue());
307 else if (isa<ConstantAggregateZero>(C))
308 C = Constant::getNullValue(PTy->getElementType());
309 else if (isa<UndefValue>(C))
310 C = UndefValue::get(PTy->getElementType());
323 //===----------------------------------------------------------------------===//
324 // Constant Folding for Calls
327 /// canConstantFoldCallTo - Return true if its even possible to fold a call to
328 /// the specified function.
330 llvm::canConstantFoldCallTo(Function *F) {
331 switch (F->getIntrinsicID()) {
332 case Intrinsic::sqrt_f32:
333 case Intrinsic::sqrt_f64:
334 case Intrinsic::powi_f32:
335 case Intrinsic::powi_f64:
336 case Intrinsic::bswap:
337 case Intrinsic::ctpop:
338 case Intrinsic::ctlz:
339 case Intrinsic::cttz:
344 const ValueName *NameVal = F->getValueName();
345 if (NameVal == 0) return false;
346 const char *Str = NameVal->getKeyData();
347 unsigned Len = NameVal->getKeyLength();
349 // In these cases, the check of the length is required. We don't want to
350 // return true for a name like "cos\0blah" which strcmp would return equal to
351 // "cos", but has length 8.
353 default: return false;
356 return !strcmp(Str, "acos") || !strcmp(Str, "asin") ||
357 !strcmp(Str, "atan");
359 return !strcmp(Str, "atan2");
363 return !strcmp(Str, "cos");
365 return !strcmp(Str, "ceil") || !strcmp(Str, "cosf") ||
366 !strcmp(Str, "cosh");
370 return !strcmp(Str, "exp");
374 return !strcmp(Str, "fabs") || !strcmp(Str, "fmod");
376 return !strcmp(Str, "floor");
380 if (Len == 3 && !strcmp(Str, "log"))
382 if (Len == 5 && !strcmp(Str, "log10"))
386 if (Len == 3 && !strcmp(Str, "pow"))
391 return !strcmp(Str, "sin");
393 return !strcmp(Str, "sinh") || !strcmp(Str, "sqrt");
395 return !strcmp(Str, "sqrtf");
398 if (Len == 3 && !strcmp(Str, "tan"))
400 else if (Len == 4 && !strcmp(Str, "tanh"))
406 static Constant *ConstantFoldFP(double (*NativeFP)(double), double V,
411 return ConstantFP::get(Ty, V);
416 static Constant *ConstantFoldBinaryFP(double (*NativeFP)(double, double),
422 return ConstantFP::get(Ty, V);
427 /// ConstantFoldCall - Attempt to constant fold a call to the specified function
428 /// with the specified arguments, returning null if unsuccessful.
430 llvm::ConstantFoldCall(Function *F, Constant** Operands, unsigned NumOperands) {
431 const ValueName *NameVal = F->getValueName();
432 if (NameVal == 0) return 0;
433 const char *Str = NameVal->getKeyData();
434 unsigned Len = NameVal->getKeyLength();
436 const Type *Ty = F->getReturnType();
437 if (NumOperands == 1) {
438 if (ConstantFP *Op = dyn_cast<ConstantFP>(Operands[0])) {
439 double V = Op->getValue();
442 if (Len == 4 && !strcmp(Str, "acos"))
443 return ConstantFoldFP(acos, V, Ty);
444 else if (Len == 4 && !strcmp(Str, "asin"))
445 return ConstantFoldFP(asin, V, Ty);
446 else if (Len == 4 && !strcmp(Str, "atan"))
447 return ConstantFoldFP(atan, V, Ty);
450 if (Len == 4 && !strcmp(Str, "ceil"))
451 return ConstantFoldFP(ceil, V, Ty);
452 else if (Len == 3 && !strcmp(Str, "cos"))
453 return ConstantFoldFP(cos, V, Ty);
454 else if (Len == 4 && !strcmp(Str, "cosh"))
455 return ConstantFoldFP(cosh, V, Ty);
458 if (Len == 3 && !strcmp(Str, "exp"))
459 return ConstantFoldFP(exp, V, Ty);
462 if (Len == 4 && !strcmp(Str, "fabs"))
463 return ConstantFP::get(Ty, fabs(V));
464 else if (Len == 5 && !strcmp(Str, "floor"))
465 return ConstantFoldFP(floor, V, Ty);
468 if (Len == 3 && !strcmp(Str, "log") && V > 0)
469 return ConstantFoldFP(log, V, Ty);
470 else if (Len == 5 && !strcmp(Str, "log10") && V > 0)
471 return ConstantFoldFP(log10, V, Ty);
472 else if (!strcmp(Str, "llvm.sqrt.f32") ||
473 !strcmp(Str, "llvm.sqrt.f64")) {
475 return ConstantFP::get(Ty, sqrt(V));
477 return ConstantFP::get(Ty, 0.0);
481 if (Len == 3 && !strcmp(Str, "sin"))
482 return ConstantFoldFP(sin, V, Ty);
483 else if (Len == 4 && !strcmp(Str, "sinh"))
484 return ConstantFoldFP(sinh, V, Ty);
485 else if (Len == 4 && !strcmp(Str, "sqrt") && V >= 0)
486 return ConstantFoldFP(sqrt, V, Ty);
487 else if (Len == 5 && !strcmp(Str, "sqrtf") && V >= 0)
488 return ConstantFoldFP(sqrt, V, Ty);
491 if (Len == 3 && !strcmp(Str, "tan"))
492 return ConstantFoldFP(tan, V, Ty);
493 else if (Len == 4 && !strcmp(Str, "tanh"))
494 return ConstantFoldFP(tanh, V, Ty);
499 } else if (ConstantInt *Op = dyn_cast<ConstantInt>(Operands[0])) {
500 if (Len > 11 && !memcmp(Str, "llvm.bswap", 10)) {
501 return ConstantInt::get(Op->getValue().byteSwap());
502 } else if (Len > 11 && !memcmp(Str, "llvm.ctpop", 10)) {
503 uint64_t ctpop = Op->getValue().countPopulation();
504 return ConstantInt::get(Ty, ctpop);
505 } else if (Len > 10 && !memcmp(Str, "llvm.cttz", 9)) {
506 uint64_t cttz = Op->getValue().countTrailingZeros();
507 return ConstantInt::get(Ty, cttz);
508 } else if (Len > 10 && !memcmp(Str, "llvm.ctlz", 9)) {
509 uint64_t ctlz = Op->getValue().countLeadingZeros();
510 return ConstantInt::get(Ty, ctlz);
513 } else if (NumOperands == 2) {
514 if (ConstantFP *Op1 = dyn_cast<ConstantFP>(Operands[0])) {
515 double Op1V = Op1->getValue();
516 if (ConstantFP *Op2 = dyn_cast<ConstantFP>(Operands[1])) {
517 double Op2V = Op2->getValue();
519 if (Len == 3 && !strcmp(Str, "pow")) {
520 return ConstantFoldBinaryFP(pow, Op1V, Op2V, Ty);
521 } else if (Len == 4 && !strcmp(Str, "fmod")) {
522 return ConstantFoldBinaryFP(fmod, Op1V, Op2V, Ty);
523 } else if (Len == 5 && !strcmp(Str, "atan2")) {
524 return ConstantFoldBinaryFP(atan2, Op1V, Op2V, Ty);
526 } else if (ConstantInt *Op2C = dyn_cast<ConstantInt>(Operands[1])) {
527 if (!strcmp(Str, "llvm.powi.f32")) {
528 return ConstantFP::get(Ty, std::pow((float)Op1V,
529 (int)Op2C->getZExtValue()));
530 } else if (!strcmp(Str, "llvm.powi.f64")) {
531 return ConstantFP::get(Ty, std::pow((double)Op1V,
532 (int)Op2C->getZExtValue()));