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/Target/TargetData.h"
23 #include "llvm/Support/GetElementPtrTypeIterator.h"
24 #include "llvm/Support/MathExtras.h"
29 //===----------------------------------------------------------------------===//
30 // Constant Folding internal helper functions
31 //===----------------------------------------------------------------------===//
33 /// IsConstantOffsetFromGlobal - If this constant is actually a constant offset
34 /// from a global, return the global and the constant. Because of
35 /// constantexprs, this function is recursive.
36 static bool IsConstantOffsetFromGlobal(Constant *C, GlobalValue *&GV,
37 int64_t &Offset, const TargetData &TD) {
38 // Trivial case, constant is the global.
39 if ((GV = dyn_cast<GlobalValue>(C))) {
44 // Otherwise, if this isn't a constant expr, bail out.
45 ConstantExpr *CE = dyn_cast<ConstantExpr>(C);
46 if (!CE) return false;
48 // Look through ptr->int and ptr->ptr casts.
49 if (CE->getOpcode() == Instruction::PtrToInt ||
50 CE->getOpcode() == Instruction::BitCast)
51 return IsConstantOffsetFromGlobal(CE->getOperand(0), GV, Offset, TD);
53 // i32* getelementptr ([5 x i32]* @a, i32 0, i32 5)
54 if (CE->getOpcode() == Instruction::GetElementPtr) {
55 // Cannot compute this if the element type of the pointer is missing size
57 if (!cast<PointerType>(CE->getOperand(0)->getType())->getElementType()->isSized())
60 // If the base isn't a global+constant, we aren't either.
61 if (!IsConstantOffsetFromGlobal(CE->getOperand(0), GV, Offset, TD))
64 // Otherwise, add any offset that our operands provide.
65 gep_type_iterator GTI = gep_type_begin(CE);
66 for (unsigned i = 1, e = CE->getNumOperands(); i != e; ++i, ++GTI) {
67 ConstantInt *CI = dyn_cast<ConstantInt>(CE->getOperand(i));
68 if (!CI) return false; // Index isn't a simple constant?
69 if (CI->getZExtValue() == 0) continue; // Not adding anything.
71 if (const StructType *ST = dyn_cast<StructType>(*GTI)) {
73 Offset += TD.getStructLayout(ST)->getElementOffset(CI->getZExtValue());
75 const SequentialType *ST = cast<SequentialType>(*GTI);
76 Offset += TD.getTypeSize(ST->getElementType())*CI->getSExtValue();
86 /// SymbolicallyEvaluateBinop - One of Op0/Op1 is a constant expression.
87 /// Attempt to symbolically evaluate the result of a binary operator merging
88 /// these together. If target data info is available, it is provided as TD,
89 /// otherwise TD is null.
90 static Constant *SymbolicallyEvaluateBinop(unsigned Opc, Constant *Op0,
91 Constant *Op1, const TargetData *TD){
94 // Fold (and 0xffffffff00000000, (shl x, 32)) -> shl.
95 // Fold (lshr (or X, Y), 32) -> (lshr [X/Y], 32) if one doesn't contribute
99 // If the constant expr is something like &A[123] - &A[4].f, fold this into a
100 // constant. This happens frequently when iterating over a global array.
101 if (Opc == Instruction::Sub && TD) {
102 GlobalValue *GV1, *GV2;
103 int64_t Offs1, Offs2;
105 if (IsConstantOffsetFromGlobal(Op0, GV1, Offs1, *TD))
106 if (IsConstantOffsetFromGlobal(Op1, GV2, Offs2, *TD) &&
108 // (&GV+C1) - (&GV+C2) -> C1-C2, pointer arithmetic cannot overflow.
109 return ConstantInt::get(Op0->getType(), Offs1-Offs2);
113 // TODO: Fold icmp setne/seteq as well.
117 /// SymbolicallyEvaluateGEP - If we can symbolically evaluate the specified GEP
118 /// constant expression, do so.
119 static Constant *SymbolicallyEvaluateGEP(Constant** Ops, unsigned NumOps,
120 const Type *ResultTy,
121 const TargetData *TD) {
122 Constant *Ptr = Ops[0];
123 if (!cast<PointerType>(Ptr->getType())->getElementType()->isSized())
126 if (TD && Ptr->isNullValue()) {
127 // If this is a constant expr gep that is effectively computing an
128 // "offsetof", fold it into 'cast int Size to T*' instead of 'gep 0, 0, 12'
129 bool isFoldableGEP = true;
130 for (unsigned i = 1; i != NumOps; ++i)
131 if (!isa<ConstantInt>(Ops[i])) {
132 isFoldableGEP = false;
136 uint64_t Offset = TD->getIndexedOffset(Ptr->getType(),
137 (Value**)Ops+1, NumOps-1);
138 Constant *C = ConstantInt::get(TD->getIntPtrType(), Offset);
139 return ConstantExpr::getIntToPtr(C, ResultTy);
147 //===----------------------------------------------------------------------===//
148 // Constant Folding public APIs
149 //===----------------------------------------------------------------------===//
152 /// ConstantFoldInstruction - Attempt to constant fold the specified
153 /// instruction. If successful, the constant result is returned, if not, null
154 /// is returned. Note that this function can only fail when attempting to fold
155 /// instructions like loads and stores, which have no constant expression form.
157 Constant *llvm::ConstantFoldInstruction(Instruction *I, const TargetData *TD) {
158 if (PHINode *PN = dyn_cast<PHINode>(I)) {
159 if (PN->getNumIncomingValues() == 0)
160 return Constant::getNullValue(PN->getType());
162 Constant *Result = dyn_cast<Constant>(PN->getIncomingValue(0));
163 if (Result == 0) return 0;
165 // Handle PHI nodes specially here...
166 for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i)
167 if (PN->getIncomingValue(i) != Result && PN->getIncomingValue(i) != PN)
168 return 0; // Not all the same incoming constants...
170 // If we reach here, all incoming values are the same constant.
174 // Scan the operand list, checking to see if they are all constants, if so,
175 // hand off to ConstantFoldInstOperands.
176 SmallVector<Constant*, 8> Ops;
177 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
178 if (Constant *Op = dyn_cast<Constant>(I->getOperand(i)))
181 return 0; // All operands not constant!
183 return ConstantFoldInstOperands(I, &Ops[0], Ops.size(), TD);
186 /// ConstantFoldInstOperands - Attempt to constant fold an instruction with the
187 /// specified opcode and operands. If successful, the constant result is
188 /// returned, if not, null is returned. Note that this function can fail when
189 /// attempting to fold instructions like loads and stores, which have no
190 /// constant expression form.
192 Constant *llvm::ConstantFoldInstOperands(const Instruction* I,
193 Constant** Ops, unsigned NumOps,
194 const TargetData *TD) {
195 unsigned Opc = I->getOpcode();
196 const Type *DestTy = I->getType();
198 // Handle easy binops first.
199 if (isa<BinaryOperator>(I)) {
200 if (isa<ConstantExpr>(Ops[0]) || isa<ConstantExpr>(Ops[1]))
201 if (Constant *C = SymbolicallyEvaluateBinop(I->getOpcode(), Ops[0],
205 return ConstantExpr::get(Opc, Ops[0], Ops[1]);
210 case Instruction::Call:
211 if (Function *F = dyn_cast<Function>(Ops[0]))
212 if (canConstantFoldCallTo(F))
213 return ConstantFoldCall(F, Ops+1, NumOps-1);
215 case Instruction::ICmp:
216 case Instruction::FCmp:
217 return ConstantExpr::getCompare(cast<CmpInst>(I)->getPredicate(), Ops[0],
219 case Instruction::Trunc:
220 case Instruction::ZExt:
221 case Instruction::SExt:
222 case Instruction::FPTrunc:
223 case Instruction::FPExt:
224 case Instruction::UIToFP:
225 case Instruction::SIToFP:
226 case Instruction::FPToUI:
227 case Instruction::FPToSI:
228 case Instruction::PtrToInt:
229 case Instruction::IntToPtr:
230 case Instruction::BitCast:
231 return ConstantExpr::getCast(Opc, Ops[0], DestTy);
232 case Instruction::Select:
233 return ConstantExpr::getSelect(Ops[0], Ops[1], Ops[2]);
234 case Instruction::ExtractElement:
235 return ConstantExpr::getExtractElement(Ops[0], Ops[1]);
236 case Instruction::InsertElement:
237 return ConstantExpr::getInsertElement(Ops[0], Ops[1], Ops[2]);
238 case Instruction::ShuffleVector:
239 return ConstantExpr::getShuffleVector(Ops[0], Ops[1], Ops[2]);
240 case Instruction::GetElementPtr:
241 if (Constant *C = SymbolicallyEvaluateGEP(Ops, NumOps, I->getType(), TD))
244 return ConstantExpr::getGetElementPtr(Ops[0], Ops+1, NumOps-1);
248 /// ConstantFoldLoadThroughGEPConstantExpr - Given a constant and a
249 /// getelementptr constantexpr, return the constant value being addressed by the
250 /// constant expression, or null if something is funny and we can't decide.
251 Constant *llvm::ConstantFoldLoadThroughGEPConstantExpr(Constant *C,
253 if (CE->getOperand(1) != Constant::getNullValue(CE->getOperand(1)->getType()))
254 return 0; // Do not allow stepping over the value!
256 // Loop over all of the operands, tracking down which value we are
258 gep_type_iterator I = gep_type_begin(CE), E = gep_type_end(CE);
259 for (++I; I != E; ++I)
260 if (const StructType *STy = dyn_cast<StructType>(*I)) {
261 ConstantInt *CU = cast<ConstantInt>(I.getOperand());
262 assert(CU->getZExtValue() < STy->getNumElements() &&
263 "Struct index out of range!");
264 unsigned El = (unsigned)CU->getZExtValue();
265 if (ConstantStruct *CS = dyn_cast<ConstantStruct>(C)) {
266 C = CS->getOperand(El);
267 } else if (isa<ConstantAggregateZero>(C)) {
268 C = Constant::getNullValue(STy->getElementType(El));
269 } else if (isa<UndefValue>(C)) {
270 C = UndefValue::get(STy->getElementType(El));
274 } else if (ConstantInt *CI = dyn_cast<ConstantInt>(I.getOperand())) {
275 if (const ArrayType *ATy = dyn_cast<ArrayType>(*I)) {
276 if (CI->getZExtValue() >= ATy->getNumElements())
278 if (ConstantArray *CA = dyn_cast<ConstantArray>(C))
279 C = CA->getOperand(CI->getZExtValue());
280 else if (isa<ConstantAggregateZero>(C))
281 C = Constant::getNullValue(ATy->getElementType());
282 else if (isa<UndefValue>(C))
283 C = UndefValue::get(ATy->getElementType());
286 } else if (const VectorType *PTy = dyn_cast<VectorType>(*I)) {
287 if (CI->getZExtValue() >= PTy->getNumElements())
289 if (ConstantVector *CP = dyn_cast<ConstantVector>(C))
290 C = CP->getOperand(CI->getZExtValue());
291 else if (isa<ConstantAggregateZero>(C))
292 C = Constant::getNullValue(PTy->getElementType());
293 else if (isa<UndefValue>(C))
294 C = UndefValue::get(PTy->getElementType());
307 //===----------------------------------------------------------------------===//
308 // Constant Folding for Calls
311 /// canConstantFoldCallTo - Return true if its even possible to fold a call to
312 /// the specified function.
314 llvm::canConstantFoldCallTo(Function *F) {
315 const std::string &Name = F->getName();
317 switch (F->getIntrinsicID()) {
318 case Intrinsic::sqrt_f32:
319 case Intrinsic::sqrt_f64:
320 case Intrinsic::bswap_i16:
321 case Intrinsic::bswap_i32:
322 case Intrinsic::bswap_i64:
323 case Intrinsic::powi_f32:
324 case Intrinsic::powi_f64:
325 // FIXME: these should be constant folded as well
326 //case Intrinsic::ctpop_i8:
327 //case Intrinsic::ctpop_i16:
328 //case Intrinsic::ctpop_i32:
329 //case Intrinsic::ctpop_i64:
330 //case Intrinsic::ctlz_i8:
331 //case Intrinsic::ctlz_i16:
332 //case Intrinsic::ctlz_i32:
333 //case Intrinsic::ctlz_i64:
334 //case Intrinsic::cttz_i8:
335 //case Intrinsic::cttz_i16:
336 //case Intrinsic::cttz_i32:
337 //case Intrinsic::cttz_i64:
345 return Name == "acos" || Name == "asin" || Name == "atan" ||
348 return Name == "ceil" || Name == "cos" || Name == "cosf" ||
351 return Name == "exp";
353 return Name == "fabs" || Name == "fmod" || Name == "floor";
355 return Name == "log" || Name == "log10";
357 return Name == "pow";
359 return Name == "sin" || Name == "sinh" ||
360 Name == "sqrt" || Name == "sqrtf";
362 return Name == "tan" || Name == "tanh";
368 static Constant *ConstantFoldFP(double (*NativeFP)(double), double V,
373 return ConstantFP::get(Ty, V);
378 /// ConstantFoldCall - Attempt to constant fold a call to the specified function
379 /// with the specified arguments, returning null if unsuccessful.
381 llvm::ConstantFoldCall(Function *F, Constant** Operands, unsigned NumOperands) {
382 const std::string &Name = F->getName();
383 const Type *Ty = F->getReturnType();
385 if (NumOperands == 1) {
386 if (ConstantFP *Op = dyn_cast<ConstantFP>(Operands[0])) {
387 double V = Op->getValue();
392 return ConstantFoldFP(acos, V, Ty);
393 else if (Name == "asin")
394 return ConstantFoldFP(asin, V, Ty);
395 else if (Name == "atan")
396 return ConstantFP::get(Ty, atan(V));
400 return ConstantFoldFP(ceil, V, Ty);
401 else if (Name == "cos")
402 return ConstantFP::get(Ty, cos(V));
403 else if (Name == "cosh")
404 return ConstantFP::get(Ty, cosh(V));
408 return ConstantFP::get(Ty, exp(V));
412 return ConstantFP::get(Ty, fabs(V));
413 else if (Name == "floor")
414 return ConstantFoldFP(floor, V, Ty);
417 if (Name == "log" && V > 0)
418 return ConstantFP::get(Ty, log(V));
419 else if (Name == "log10" && V > 0)
420 return ConstantFoldFP(log10, V, Ty);
421 else if (Name == "llvm.sqrt.f32" || Name == "llvm.sqrt.f64") {
423 return ConstantFP::get(Ty, sqrt(V));
425 return ConstantFP::get(Ty, 0.0);
430 return ConstantFP::get(Ty, sin(V));
431 else if (Name == "sinh")
432 return ConstantFP::get(Ty, sinh(V));
433 else if (Name == "sqrt" && V >= 0)
434 return ConstantFP::get(Ty, sqrt(V));
435 else if (Name == "sqrtf" && V >= 0)
436 return ConstantFP::get(Ty, sqrt((float)V));
440 return ConstantFP::get(Ty, tan(V));
441 else if (Name == "tanh")
442 return ConstantFP::get(Ty, tanh(V));
447 } else if (ConstantInt *Op = dyn_cast<ConstantInt>(Operands[0])) {
448 uint64_t V = Op->getZExtValue();
449 if (Name == "llvm.bswap.i16")
450 return ConstantInt::get(Ty, ByteSwap_16(V));
451 else if (Name == "llvm.bswap.i32")
452 return ConstantInt::get(Ty, ByteSwap_32(V));
453 else if (Name == "llvm.bswap.i64")
454 return ConstantInt::get(Ty, ByteSwap_64(V));
456 } else if (NumOperands == 2) {
457 if (ConstantFP *Op1 = dyn_cast<ConstantFP>(Operands[0])) {
458 double Op1V = Op1->getValue();
459 if (ConstantFP *Op2 = dyn_cast<ConstantFP>(Operands[1])) {
460 double Op2V = Op2->getValue();
464 double V = pow(Op1V, Op2V);
466 return ConstantFP::get(Ty, V);
467 } else if (Name == "fmod") {
469 double V = fmod(Op1V, Op2V);
471 return ConstantFP::get(Ty, V);
472 } else if (Name == "atan2") {
473 return ConstantFP::get(Ty, atan2(Op1V,Op2V));
475 } else if (ConstantInt *Op2C = dyn_cast<ConstantInt>(Operands[1])) {
476 if (Name == "llvm.powi.f32") {
477 return ConstantFP::get(Ty, std::pow((float)Op1V,
478 (int)Op2C->getZExtValue()));
479 } else if (Name == "llvm.powi.f64") {
480 return ConstantFP::get(Ty, std::pow((double)Op1V,
481 (int)Op2C->getZExtValue()));