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)->MemberOffsets[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 std::vector<Value*> NewOps(Ops+1, Ops+NumOps);
137 uint64_t Offset = TD->getIndexedOffset(Ptr->getType(), NewOps);
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);
215 case Instruction::ICmp:
216 case Instruction::FCmp:
217 return ConstantExpr::getCompare(cast<CmpInst>(I)->getPredicate(), Ops[0],
219 case Instruction::Shl:
220 case Instruction::LShr:
221 case Instruction::AShr:
222 return ConstantExpr::get(Opc, Ops[0], Ops[1]);
223 case Instruction::Trunc:
224 case Instruction::ZExt:
225 case Instruction::SExt:
226 case Instruction::FPTrunc:
227 case Instruction::FPExt:
228 case Instruction::UIToFP:
229 case Instruction::SIToFP:
230 case Instruction::FPToUI:
231 case Instruction::FPToSI:
232 case Instruction::PtrToInt:
233 case Instruction::IntToPtr:
234 case Instruction::BitCast:
235 return ConstantExpr::getCast(Opc, Ops[0], DestTy);
236 case Instruction::Select:
237 return ConstantExpr::getSelect(Ops[0], Ops[1], Ops[2]);
238 case Instruction::ExtractElement:
239 return ConstantExpr::getExtractElement(Ops[0], Ops[1]);
240 case Instruction::InsertElement:
241 return ConstantExpr::getInsertElement(Ops[0], Ops[1], Ops[2]);
242 case Instruction::ShuffleVector:
243 return ConstantExpr::getShuffleVector(Ops[0], Ops[1], Ops[2]);
244 case Instruction::GetElementPtr:
245 if (Constant *C = SymbolicallyEvaluateGEP(Ops, NumOps, I->getType(), TD))
248 return ConstantExpr::getGetElementPtr(Ops[0],
249 std::vector<Constant*>(Ops+1,
254 /// ConstantFoldLoadThroughGEPConstantExpr - Given a constant and a
255 /// getelementptr constantexpr, return the constant value being addressed by the
256 /// constant expression, or null if something is funny and we can't decide.
257 Constant *llvm::ConstantFoldLoadThroughGEPConstantExpr(Constant *C,
259 if (CE->getOperand(1) != Constant::getNullValue(CE->getOperand(1)->getType()))
260 return 0; // Do not allow stepping over the value!
262 // Loop over all of the operands, tracking down which value we are
264 gep_type_iterator I = gep_type_begin(CE), E = gep_type_end(CE);
265 for (++I; I != E; ++I)
266 if (const StructType *STy = dyn_cast<StructType>(*I)) {
267 ConstantInt *CU = cast<ConstantInt>(I.getOperand());
268 assert(CU->getZExtValue() < STy->getNumElements() &&
269 "Struct index out of range!");
270 unsigned El = (unsigned)CU->getZExtValue();
271 if (ConstantStruct *CS = dyn_cast<ConstantStruct>(C)) {
272 C = CS->getOperand(El);
273 } else if (isa<ConstantAggregateZero>(C)) {
274 C = Constant::getNullValue(STy->getElementType(El));
275 } else if (isa<UndefValue>(C)) {
276 C = UndefValue::get(STy->getElementType(El));
280 } else if (ConstantInt *CI = dyn_cast<ConstantInt>(I.getOperand())) {
281 if (const ArrayType *ATy = dyn_cast<ArrayType>(*I)) {
282 if (CI->getZExtValue() >= ATy->getNumElements())
284 if (ConstantArray *CA = dyn_cast<ConstantArray>(C))
285 C = CA->getOperand(CI->getZExtValue());
286 else if (isa<ConstantAggregateZero>(C))
287 C = Constant::getNullValue(ATy->getElementType());
288 else if (isa<UndefValue>(C))
289 C = UndefValue::get(ATy->getElementType());
292 } else if (const PackedType *PTy = dyn_cast<PackedType>(*I)) {
293 if (CI->getZExtValue() >= PTy->getNumElements())
295 if (ConstantPacked *CP = dyn_cast<ConstantPacked>(C))
296 C = CP->getOperand(CI->getZExtValue());
297 else if (isa<ConstantAggregateZero>(C))
298 C = Constant::getNullValue(PTy->getElementType());
299 else if (isa<UndefValue>(C))
300 C = UndefValue::get(PTy->getElementType());
313 //===----------------------------------------------------------------------===//
314 // Constant Folding for Calls
317 /// canConstantFoldCallTo - Return true if its even possible to fold a call to
318 /// the specified function.
320 llvm::canConstantFoldCallTo(Function *F) {
321 const std::string &Name = F->getName();
323 switch (F->getIntrinsicID()) {
324 case Intrinsic::sqrt_f32:
325 case Intrinsic::sqrt_f64:
326 case Intrinsic::bswap_i16:
327 case Intrinsic::bswap_i32:
328 case Intrinsic::bswap_i64:
329 case Intrinsic::powi_f32:
330 case Intrinsic::powi_f64:
331 // FIXME: these should be constant folded as well
332 //case Intrinsic::ctpop_i8:
333 //case Intrinsic::ctpop_i16:
334 //case Intrinsic::ctpop_i32:
335 //case Intrinsic::ctpop_i64:
336 //case Intrinsic::ctlz_i8:
337 //case Intrinsic::ctlz_i16:
338 //case Intrinsic::ctlz_i32:
339 //case Intrinsic::ctlz_i64:
340 //case Intrinsic::cttz_i8:
341 //case Intrinsic::cttz_i16:
342 //case Intrinsic::cttz_i32:
343 //case Intrinsic::cttz_i64:
351 return Name == "acos" || Name == "asin" || Name == "atan" ||
354 return Name == "ceil" || Name == "cos" || Name == "cosf" ||
357 return Name == "exp";
359 return Name == "fabs" || Name == "fmod" || Name == "floor";
361 return Name == "log" || Name == "log10";
363 return Name == "pow";
365 return Name == "sin" || Name == "sinh" ||
366 Name == "sqrt" || Name == "sqrtf";
368 return Name == "tan" || Name == "tanh";
374 static Constant *ConstantFoldFP(double (*NativeFP)(double), double V,
379 return ConstantFP::get(Ty, V);
384 /// ConstantFoldCall - Attempt to constant fold a call to the specified function
385 /// with the specified arguments, returning null if unsuccessful.
387 llvm::ConstantFoldCall(Function *F, Constant** Operands, unsigned NumOperands) {
388 const std::string &Name = F->getName();
389 const Type *Ty = F->getReturnType();
391 if (NumOperands == 1) {
392 if (ConstantFP *Op = dyn_cast<ConstantFP>(Operands[0])) {
393 double V = Op->getValue();
398 return ConstantFoldFP(acos, V, Ty);
399 else if (Name == "asin")
400 return ConstantFoldFP(asin, V, Ty);
401 else if (Name == "atan")
402 return ConstantFP::get(Ty, atan(V));
406 return ConstantFoldFP(ceil, V, Ty);
407 else if (Name == "cos")
408 return ConstantFP::get(Ty, cos(V));
409 else if (Name == "cosh")
410 return ConstantFP::get(Ty, cosh(V));
414 return ConstantFP::get(Ty, exp(V));
418 return ConstantFP::get(Ty, fabs(V));
419 else if (Name == "floor")
420 return ConstantFoldFP(floor, V, Ty);
423 if (Name == "log" && V > 0)
424 return ConstantFP::get(Ty, log(V));
425 else if (Name == "log10" && V > 0)
426 return ConstantFoldFP(log10, V, Ty);
427 else if (Name == "llvm.sqrt.f32" || Name == "llvm.sqrt.f64") {
429 return ConstantFP::get(Ty, sqrt(V));
431 return ConstantFP::get(Ty, 0.0);
436 return ConstantFP::get(Ty, sin(V));
437 else if (Name == "sinh")
438 return ConstantFP::get(Ty, sinh(V));
439 else if (Name == "sqrt" && V >= 0)
440 return ConstantFP::get(Ty, sqrt(V));
441 else if (Name == "sqrtf" && V >= 0)
442 return ConstantFP::get(Ty, sqrt((float)V));
446 return ConstantFP::get(Ty, tan(V));
447 else if (Name == "tanh")
448 return ConstantFP::get(Ty, tanh(V));
453 } else if (ConstantInt *Op = dyn_cast<ConstantInt>(Operands[0])) {
454 uint64_t V = Op->getZExtValue();
455 if (Name == "llvm.bswap.i16")
456 return ConstantInt::get(Ty, ByteSwap_16(V));
457 else if (Name == "llvm.bswap.i32")
458 return ConstantInt::get(Ty, ByteSwap_32(V));
459 else if (Name == "llvm.bswap.i64")
460 return ConstantInt::get(Ty, ByteSwap_64(V));
462 } else if (NumOperands == 2) {
463 if (ConstantFP *Op1 = dyn_cast<ConstantFP>(Operands[0])) {
464 double Op1V = Op1->getValue();
465 if (ConstantFP *Op2 = dyn_cast<ConstantFP>(Operands[1])) {
466 double Op2V = Op2->getValue();
470 double V = pow(Op1V, Op2V);
472 return ConstantFP::get(Ty, V);
473 } else if (Name == "fmod") {
475 double V = fmod(Op1V, Op2V);
477 return ConstantFP::get(Ty, V);
478 } else if (Name == "atan2") {
479 return ConstantFP::get(Ty, atan2(Op1V,Op2V));
481 } else if (ConstantInt *Op2C = dyn_cast<ConstantInt>(Operands[1])) {
482 if (Name == "llvm.powi.f32") {
483 return ConstantFP::get(Ty, std::pow((float)Op1V,
484 (int)Op2C->getZExtValue()));
485 } else if (Name == "llvm.powi.f64") {
486 return ConstantFP::get(Ty, std::pow((double)Op1V,
487 (int)Op2C->getZExtValue()));