1 //===-- Local.cpp - Functions to perform local transformations ------------===//
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 perform various local transformations to the
13 //===----------------------------------------------------------------------===//
15 #include "llvm/Support/MathExtras.h"
16 #include "llvm/Transforms/Utils/Local.h"
17 #include "llvm/Constants.h"
18 #include "llvm/Instructions.h"
19 #include "llvm/Intrinsics.h"
24 //===----------------------------------------------------------------------===//
25 // Local constant propagation...
28 /// doConstantPropagation - If an instruction references constants, try to fold
31 bool llvm::doConstantPropagation(BasicBlock::iterator &II) {
32 if (Constant *C = ConstantFoldInstruction(II)) {
33 // Replaces all of the uses of a variable with uses of the constant.
34 II->replaceAllUsesWith(C);
36 // Remove the instruction from the basic block...
37 II = II->getParent()->getInstList().erase(II);
44 /// ConstantFoldInstruction - Attempt to constant fold the specified
45 /// instruction. If successful, the constant result is returned, if not, null
46 /// is returned. Note that this function can only fail when attempting to fold
47 /// instructions like loads and stores, which have no constant expression form.
49 Constant *llvm::ConstantFoldInstruction(Instruction *I) {
50 if (PHINode *PN = dyn_cast<PHINode>(I)) {
51 if (PN->getNumIncomingValues() == 0)
52 return Constant::getNullValue(PN->getType());
54 Constant *Result = dyn_cast<Constant>(PN->getIncomingValue(0));
55 if (Result == 0) return 0;
57 // Handle PHI nodes specially here...
58 for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i)
59 if (PN->getIncomingValue(i) != Result && PN->getIncomingValue(i) != PN)
60 return 0; // Not all the same incoming constants...
62 // If we reach here, all incoming values are the same constant.
64 } else if (CallInst *CI = dyn_cast<CallInst>(I)) {
65 if (Function *F = CI->getCalledFunction())
66 if (canConstantFoldCallTo(F)) {
67 std::vector<Constant*> Args;
68 for (unsigned i = 1, e = CI->getNumOperands(); i != e; ++i)
69 if (Constant *Op = dyn_cast<Constant>(CI->getOperand(i)))
73 return ConstantFoldCall(F, Args);
78 Constant *Op0 = 0, *Op1 = 0;
79 switch (I->getNumOperands()) {
82 Op1 = dyn_cast<Constant>(I->getOperand(1));
83 if (Op1 == 0) return 0; // Not a constant?, can't fold
85 Op0 = dyn_cast<Constant>(I->getOperand(0));
86 if (Op0 == 0) return 0; // Not a constant?, can't fold
91 if (isa<BinaryOperator>(I) || isa<ShiftInst>(I))
92 return ConstantExpr::get(I->getOpcode(), Op0, Op1);
94 switch (I->getOpcode()) {
96 case Instruction::Cast:
97 return ConstantExpr::getCast(Op0, I->getType());
98 case Instruction::Select:
99 if (Constant *Op2 = dyn_cast<Constant>(I->getOperand(2)))
100 return ConstantExpr::getSelect(Op0, Op1, Op2);
102 case Instruction::GetElementPtr:
103 std::vector<Constant*> IdxList;
104 IdxList.reserve(I->getNumOperands()-1);
105 if (Op1) IdxList.push_back(Op1);
106 for (unsigned i = 2, e = I->getNumOperands(); i != e; ++i)
107 if (Constant *C = dyn_cast<Constant>(I->getOperand(i)))
108 IdxList.push_back(C);
110 return 0; // Non-constant operand
111 return ConstantExpr::getGetElementPtr(Op0, IdxList);
115 // ConstantFoldTerminator - If a terminator instruction is predicated on a
116 // constant value, convert it into an unconditional branch to the constant
119 bool llvm::ConstantFoldTerminator(BasicBlock *BB) {
120 TerminatorInst *T = BB->getTerminator();
122 // Branch - See if we are conditional jumping on constant
123 if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
124 if (BI->isUnconditional()) return false; // Can't optimize uncond branch
125 BasicBlock *Dest1 = cast<BasicBlock>(BI->getOperand(0));
126 BasicBlock *Dest2 = cast<BasicBlock>(BI->getOperand(1));
128 if (ConstantBool *Cond = dyn_cast<ConstantBool>(BI->getCondition())) {
129 // Are we branching on constant?
130 // YES. Change to unconditional branch...
131 BasicBlock *Destination = Cond->getValue() ? Dest1 : Dest2;
132 BasicBlock *OldDest = Cond->getValue() ? Dest2 : Dest1;
134 //cerr << "Function: " << T->getParent()->getParent()
135 // << "\nRemoving branch from " << T->getParent()
136 // << "\n\nTo: " << OldDest << endl;
138 // Let the basic block know that we are letting go of it. Based on this,
139 // it will adjust it's PHI nodes.
140 assert(BI->getParent() && "Terminator not inserted in block!");
141 OldDest->removePredecessor(BI->getParent());
143 // Set the unconditional destination, and change the insn to be an
144 // unconditional branch.
145 BI->setUnconditionalDest(Destination);
147 } else if (Dest2 == Dest1) { // Conditional branch to same location?
148 // This branch matches something like this:
149 // br bool %cond, label %Dest, label %Dest
150 // and changes it into: br label %Dest
152 // Let the basic block know that we are letting go of one copy of it.
153 assert(BI->getParent() && "Terminator not inserted in block!");
154 Dest1->removePredecessor(BI->getParent());
156 // Change a conditional branch to unconditional.
157 BI->setUnconditionalDest(Dest1);
160 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) {
161 // If we are switching on a constant, we can convert the switch into a
162 // single branch instruction!
163 ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition());
164 BasicBlock *TheOnlyDest = SI->getSuccessor(0); // The default dest
165 BasicBlock *DefaultDest = TheOnlyDest;
166 assert(TheOnlyDest == SI->getDefaultDest() &&
167 "Default destination is not successor #0?");
169 // Figure out which case it goes to...
170 for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) {
171 // Found case matching a constant operand?
172 if (SI->getSuccessorValue(i) == CI) {
173 TheOnlyDest = SI->getSuccessor(i);
177 // Check to see if this branch is going to the same place as the default
178 // dest. If so, eliminate it as an explicit compare.
179 if (SI->getSuccessor(i) == DefaultDest) {
180 // Remove this entry...
181 DefaultDest->removePredecessor(SI->getParent());
183 --i; --e; // Don't skip an entry...
187 // Otherwise, check to see if the switch only branches to one destination.
188 // We do this by reseting "TheOnlyDest" to null when we find two non-equal
190 if (SI->getSuccessor(i) != TheOnlyDest) TheOnlyDest = 0;
193 if (CI && !TheOnlyDest) {
194 // Branching on a constant, but not any of the cases, go to the default
196 TheOnlyDest = SI->getDefaultDest();
199 // If we found a single destination that we can fold the switch into, do so
202 // Insert the new branch..
203 new BranchInst(TheOnlyDest, SI);
204 BasicBlock *BB = SI->getParent();
206 // Remove entries from PHI nodes which we no longer branch to...
207 for (unsigned i = 0, e = SI->getNumSuccessors(); i != e; ++i) {
208 // Found case matching a constant operand?
209 BasicBlock *Succ = SI->getSuccessor(i);
210 if (Succ == TheOnlyDest)
211 TheOnlyDest = 0; // Don't modify the first branch to TheOnlyDest
213 Succ->removePredecessor(BB);
216 // Delete the old switch...
217 BB->getInstList().erase(SI);
219 } else if (SI->getNumSuccessors() == 2) {
220 // Otherwise, we can fold this switch into a conditional branch
221 // instruction if it has only one non-default destination.
222 Value *Cond = new SetCondInst(Instruction::SetEQ, SI->getCondition(),
223 SI->getSuccessorValue(1), "cond", SI);
224 // Insert the new branch...
225 new BranchInst(SI->getSuccessor(1), SI->getSuccessor(0), Cond, SI);
227 // Delete the old switch...
228 SI->getParent()->getInstList().erase(SI);
235 /// canConstantFoldCallTo - Return true if its even possible to fold a call to
236 /// the specified function.
237 bool llvm::canConstantFoldCallTo(Function *F) {
238 const std::string &Name = F->getName();
240 switch (F->getIntrinsicID()) {
241 case Intrinsic::isunordered: return true;
248 return Name == "acos" || Name == "asin" || Name == "atan" ||
251 return Name == "ceil" || Name == "cos" || Name == "cosf" ||
254 return Name == "exp";
256 return Name == "fabs" || Name == "fmod" || Name == "floor";
258 return Name == "log" || Name == "log10";
260 return Name == "pow";
262 return Name == "sin" || Name == "sinh" || Name == "sqrt";
264 return Name == "tan" || Name == "tanh";
270 static Constant *ConstantFoldFP(double (*NativeFP)(double), double V,
275 return ConstantFP::get(Ty, V);
279 /// ConstantFoldCall - Attempt to constant fold a call to the specified function
280 /// with the specified arguments, returning null if unsuccessful.
281 Constant *llvm::ConstantFoldCall(Function *F,
282 const std::vector<Constant*> &Operands) {
283 const std::string &Name = F->getName();
284 const Type *Ty = F->getReturnType();
286 if (Operands.size() == 1) {
287 if (ConstantFP *Op = dyn_cast<ConstantFP>(Operands[0])) {
288 double V = Op->getValue();
293 return ConstantFoldFP(acos, V, Ty);
294 else if (Name == "asin")
295 return ConstantFoldFP(asin, V, Ty);
296 else if (Name == "atan")
297 return ConstantFP::get(Ty, atan(V));
301 return ConstantFoldFP(ceil, V, Ty);
302 else if (Name == "cos")
303 return ConstantFP::get(Ty, cos(V));
304 else if (Name == "cosh")
305 return ConstantFP::get(Ty, cosh(V));
309 return ConstantFP::get(Ty, exp(V));
313 return ConstantFP::get(Ty, fabs(V));
314 else if (Name == "floor")
315 return ConstantFoldFP(floor, V, Ty);
318 if (Name == "log" && V > 0)
319 return ConstantFP::get(Ty, log(V));
320 else if (Name == "log10" && V > 0)
321 return ConstantFoldFP(log10, V, Ty);
325 return ConstantFP::get(Ty, sin(V));
326 else if (Name == "sinh")
327 return ConstantFP::get(Ty, sinh(V));
328 else if (Name == "sqrt" && V >= 0)
329 return ConstantFP::get(Ty, sqrt(V));
333 return ConstantFP::get(Ty, tan(V));
334 else if (Name == "tanh")
335 return ConstantFP::get(Ty, tanh(V));
341 } else if (Operands.size() == 2) {
342 if (ConstantFP *Op1 = dyn_cast<ConstantFP>(Operands[0])) {
343 double Op1V = Op1->getValue();
344 if (ConstantFP *Op2 = dyn_cast<ConstantFP>(Operands[1])) {
345 double Op2V = Op2->getValue();
347 if (Name == "llvm.isunordered")
348 return ConstantBool::get(IsNAN(Op1V) || IsNAN(Op2V));
352 double V = pow(Op1V, Op2V);
354 return ConstantFP::get(Ty, V);
355 } else if (Name == "fmod") {
357 double V = fmod(Op1V, Op2V);
359 return ConstantFP::get(Ty, V);
360 } else if (Name == "atan2")
361 return ConstantFP::get(Ty, atan2(Op1V,Op2V));
371 //===----------------------------------------------------------------------===//
372 // Local dead code elimination...
375 bool llvm::isInstructionTriviallyDead(Instruction *I) {
376 if (!I->use_empty() || isa<TerminatorInst>(I)) return false;
378 if (!I->mayWriteToMemory()) return true;
380 if (CallInst *CI = dyn_cast<CallInst>(I))
381 if (Function *F = CI->getCalledFunction())
382 switch (F->getIntrinsicID()) {
384 case Intrinsic::vastart:
385 case Intrinsic::vacopy:
386 case Intrinsic::returnaddress:
387 case Intrinsic::frameaddress:
388 case Intrinsic::isunordered:
389 case Intrinsic::ctpop:
390 case Intrinsic::ctlz:
391 case Intrinsic::cttz:
392 case Intrinsic::sqrt:
393 return true; // These intrinsics have no side effects.
398 // dceInstruction - Inspect the instruction at *BBI and figure out if it's
399 // [trivially] dead. If so, remove the instruction and update the iterator
400 // to point to the instruction that immediately succeeded the original
403 bool llvm::dceInstruction(BasicBlock::iterator &BBI) {
404 // Look for un"used" definitions...
405 if (isInstructionTriviallyDead(BBI)) {
406 BBI = BBI->getParent()->getInstList().erase(BBI); // Bye bye
412 //===----------------------------------------------------------------------===//
413 // PHI Instruction Simplification
416 /// hasConstantValue - If the specified PHI node always merges together the same
417 /// value, return the value, otherwise return null.
419 Value *llvm::hasConstantValue(PHINode *PN) {
420 // If the PHI node only has one incoming value, eliminate the PHI node...
421 if (PN->getNumIncomingValues() == 1)
422 return PN->getIncomingValue(0);
424 // Otherwise if all of the incoming values are the same for the PHI, replace
425 // the PHI node with the incoming value.
428 for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
429 if (PN->getIncomingValue(i) != PN && // Not the PHI node itself...
430 !isa<UndefValue>(PN->getIncomingValue(i)))
431 if (InVal && PN->getIncomingValue(i) != InVal)
432 return 0; // Not the same, bail out.
434 InVal = PN->getIncomingValue(i);
436 // The only case that could cause InVal to be null is if we have a PHI node
437 // that only has entries for itself. In this case, there is no entry into the
438 // loop, so kill the PHI.
440 if (InVal == 0) InVal = UndefValue::get(PN->getType());
442 // All of the incoming values are the same, return the value now.