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/Transforms/Utils/Local.h"
16 #include "llvm/Constants.h"
17 #include "llvm/DerivedTypes.h"
18 #include "llvm/Instructions.h"
19 #include "llvm/Intrinsics.h"
20 #include "llvm/Analysis/ConstantFolding.h"
21 #include "llvm/Support/GetElementPtrTypeIterator.h"
22 #include "llvm/Support/MathExtras.h"
26 //===----------------------------------------------------------------------===//
27 // Local constant propagation...
30 /// doConstantPropagation - If an instruction references constants, try to fold
33 bool llvm::doConstantPropagation(BasicBlock::iterator &II) {
34 if (Constant *C = ConstantFoldInstruction(II)) {
35 // Replaces all of the uses of a variable with uses of the constant.
36 II->replaceAllUsesWith(C);
38 // Remove the instruction from the basic block...
39 II = II->getParent()->getInstList().erase(II);
46 /// ConstantFoldInstruction - Attempt to constant fold the specified
47 /// instruction. If successful, the constant result is returned, if not, null
48 /// is returned. Note that this function can only fail when attempting to fold
49 /// instructions like loads and stores, which have no constant expression form.
51 Constant *llvm::ConstantFoldInstruction(Instruction *I) {
52 if (PHINode *PN = dyn_cast<PHINode>(I)) {
53 if (PN->getNumIncomingValues() == 0)
54 return Constant::getNullValue(PN->getType());
56 Constant *Result = dyn_cast<Constant>(PN->getIncomingValue(0));
57 if (Result == 0) return 0;
59 // Handle PHI nodes specially here...
60 for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i)
61 if (PN->getIncomingValue(i) != Result && PN->getIncomingValue(i) != PN)
62 return 0; // Not all the same incoming constants...
64 // If we reach here, all incoming values are the same constant.
68 Constant *Op0 = 0, *Op1 = 0;
69 switch (I->getNumOperands()) {
72 Op1 = dyn_cast<Constant>(I->getOperand(1));
73 if (Op1 == 0) return 0; // Not a constant?, can't fold
76 Op0 = dyn_cast<Constant>(I->getOperand(0));
77 if (Op0 == 0) return 0; // Not a constant?, can't fold
82 if (isa<BinaryOperator>(I) || isa<ShiftInst>(I)) {
83 return ConstantExpr::get(I->getOpcode(), Op0, Op1);
84 } else if (isa<ICmpInst>(I)) {
85 return ConstantExpr::getICmp(cast<ICmpInst>(I)->getPredicate(), Op0, Op1);
86 } else if (isa<FCmpInst>(I)) {
87 return ConstantExpr::getFCmp(cast<FCmpInst>(I)->getPredicate(), Op0, Op1);
90 // Scan the operand list, checking to see if they are all constants, if so,
91 // hand off to ConstantFoldInstOperands.
92 std::vector<Constant*> Ops;
93 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
94 if (Constant *Op = dyn_cast<Constant>(I->getOperand(i)))
97 return 0; // All operands not constant!
99 return ConstantFoldInstOperands(I, Ops);
102 /// ConstantFoldInstOperands - Attempt to constant fold an instruction with the
103 /// specified opcode and operands. If successful, the constant result is
104 /// returned, if not, null is returned. Note that this function can fail when
105 /// attempting to fold instructions like loads and stores, which have no
106 /// constant expression form.
108 Constant *llvm::ConstantFoldInstOperands(const Instruction* I,
109 const std::vector<Constant*> &Ops) {
110 unsigned Opc = I->getOpcode();
111 const Type *DestTy = I->getType();
113 // Handle easy binops first
114 if (isa<BinaryOperator>(I))
115 return ConstantExpr::get(Opc, Ops[0], Ops[1]);
119 case Instruction::Call:
120 if (Function *F = dyn_cast<Function>(Ops[0])) {
121 if (canConstantFoldCallTo(F)) {
122 std::vector<Constant*> Args(Ops.begin()+1, Ops.end());
123 return ConstantFoldCall(F, Args);
127 case Instruction::ICmp:
128 case Instruction::FCmp:
129 return ConstantExpr::getCompare(cast<CmpInst>(I)->getPredicate(), Ops[0],
131 case Instruction::Shl:
132 case Instruction::LShr:
133 case Instruction::AShr:
134 return ConstantExpr::get(Opc, Ops[0], Ops[1]);
135 case Instruction::Trunc:
136 case Instruction::ZExt:
137 case Instruction::SExt:
138 case Instruction::FPTrunc:
139 case Instruction::FPExt:
140 case Instruction::UIToFP:
141 case Instruction::SIToFP:
142 case Instruction::FPToUI:
143 case Instruction::FPToSI:
144 case Instruction::PtrToInt:
145 case Instruction::IntToPtr:
146 case Instruction::BitCast:
147 return ConstantExpr::getCast(Opc, Ops[0], DestTy);
148 case Instruction::Select:
149 return ConstantExpr::getSelect(Ops[0], Ops[1], Ops[2]);
150 case Instruction::ExtractElement:
151 return ConstantExpr::getExtractElement(Ops[0], Ops[1]);
152 case Instruction::InsertElement:
153 return ConstantExpr::getInsertElement(Ops[0], Ops[1], Ops[2]);
154 case Instruction::ShuffleVector:
155 return ConstantExpr::getShuffleVector(Ops[0], Ops[1], Ops[2]);
156 case Instruction::GetElementPtr:
157 return ConstantExpr::getGetElementPtr(Ops[0],
158 std::vector<Constant*>(Ops.begin()+1,
163 // ConstantFoldTerminator - If a terminator instruction is predicated on a
164 // constant value, convert it into an unconditional branch to the constant
167 bool llvm::ConstantFoldTerminator(BasicBlock *BB) {
168 TerminatorInst *T = BB->getTerminator();
170 // Branch - See if we are conditional jumping on constant
171 if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
172 if (BI->isUnconditional()) return false; // Can't optimize uncond branch
173 BasicBlock *Dest1 = cast<BasicBlock>(BI->getOperand(0));
174 BasicBlock *Dest2 = cast<BasicBlock>(BI->getOperand(1));
176 if (ConstantInt *Cond = dyn_cast<ConstantInt>(BI->getCondition())) {
177 // Are we branching on constant?
178 // YES. Change to unconditional branch...
179 BasicBlock *Destination = Cond->getBoolValue() ? Dest1 : Dest2;
180 BasicBlock *OldDest = Cond->getBoolValue() ? Dest2 : Dest1;
182 //cerr << "Function: " << T->getParent()->getParent()
183 // << "\nRemoving branch from " << T->getParent()
184 // << "\n\nTo: " << OldDest << endl;
186 // Let the basic block know that we are letting go of it. Based on this,
187 // it will adjust it's PHI nodes.
188 assert(BI->getParent() && "Terminator not inserted in block!");
189 OldDest->removePredecessor(BI->getParent());
191 // Set the unconditional destination, and change the insn to be an
192 // unconditional branch.
193 BI->setUnconditionalDest(Destination);
195 } else if (Dest2 == Dest1) { // Conditional branch to same location?
196 // This branch matches something like this:
197 // br bool %cond, label %Dest, label %Dest
198 // and changes it into: br label %Dest
200 // Let the basic block know that we are letting go of one copy of it.
201 assert(BI->getParent() && "Terminator not inserted in block!");
202 Dest1->removePredecessor(BI->getParent());
204 // Change a conditional branch to unconditional.
205 BI->setUnconditionalDest(Dest1);
208 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) {
209 // If we are switching on a constant, we can convert the switch into a
210 // single branch instruction!
211 ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition());
212 BasicBlock *TheOnlyDest = SI->getSuccessor(0); // The default dest
213 BasicBlock *DefaultDest = TheOnlyDest;
214 assert(TheOnlyDest == SI->getDefaultDest() &&
215 "Default destination is not successor #0?");
217 // Figure out which case it goes to...
218 for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) {
219 // Found case matching a constant operand?
220 if (SI->getSuccessorValue(i) == CI) {
221 TheOnlyDest = SI->getSuccessor(i);
225 // Check to see if this branch is going to the same place as the default
226 // dest. If so, eliminate it as an explicit compare.
227 if (SI->getSuccessor(i) == DefaultDest) {
228 // Remove this entry...
229 DefaultDest->removePredecessor(SI->getParent());
231 --i; --e; // Don't skip an entry...
235 // Otherwise, check to see if the switch only branches to one destination.
236 // We do this by reseting "TheOnlyDest" to null when we find two non-equal
238 if (SI->getSuccessor(i) != TheOnlyDest) TheOnlyDest = 0;
241 if (CI && !TheOnlyDest) {
242 // Branching on a constant, but not any of the cases, go to the default
244 TheOnlyDest = SI->getDefaultDest();
247 // If we found a single destination that we can fold the switch into, do so
250 // Insert the new branch..
251 new BranchInst(TheOnlyDest, SI);
252 BasicBlock *BB = SI->getParent();
254 // Remove entries from PHI nodes which we no longer branch to...
255 for (unsigned i = 0, e = SI->getNumSuccessors(); i != e; ++i) {
256 // Found case matching a constant operand?
257 BasicBlock *Succ = SI->getSuccessor(i);
258 if (Succ == TheOnlyDest)
259 TheOnlyDest = 0; // Don't modify the first branch to TheOnlyDest
261 Succ->removePredecessor(BB);
264 // Delete the old switch...
265 BB->getInstList().erase(SI);
267 } else if (SI->getNumSuccessors() == 2) {
268 // Otherwise, we can fold this switch into a conditional branch
269 // instruction if it has only one non-default destination.
270 Value *Cond = new ICmpInst(ICmpInst::ICMP_EQ, SI->getCondition(),
271 SI->getSuccessorValue(1), "cond", SI);
272 // Insert the new branch...
273 new BranchInst(SI->getSuccessor(1), SI->getSuccessor(0), Cond, SI);
275 // Delete the old switch...
276 SI->getParent()->getInstList().erase(SI);
283 /// ConstantFoldLoadThroughGEPConstantExpr - Given a constant and a
284 /// getelementptr constantexpr, return the constant value being addressed by the
285 /// constant expression, or null if something is funny and we can't decide.
286 Constant *llvm::ConstantFoldLoadThroughGEPConstantExpr(Constant *C,
288 if (CE->getOperand(1) != Constant::getNullValue(CE->getOperand(1)->getType()))
289 return 0; // Do not allow stepping over the value!
291 // Loop over all of the operands, tracking down which value we are
293 gep_type_iterator I = gep_type_begin(CE), E = gep_type_end(CE);
294 for (++I; I != E; ++I)
295 if (const StructType *STy = dyn_cast<StructType>(*I)) {
296 ConstantInt *CU = cast<ConstantInt>(I.getOperand());
297 assert(CU->getZExtValue() < STy->getNumElements() &&
298 "Struct index out of range!");
299 unsigned El = (unsigned)CU->getZExtValue();
300 if (ConstantStruct *CS = dyn_cast<ConstantStruct>(C)) {
301 C = CS->getOperand(El);
302 } else if (isa<ConstantAggregateZero>(C)) {
303 C = Constant::getNullValue(STy->getElementType(El));
304 } else if (isa<UndefValue>(C)) {
305 C = UndefValue::get(STy->getElementType(El));
309 } else if (ConstantInt *CI = dyn_cast<ConstantInt>(I.getOperand())) {
310 if (const ArrayType *ATy = dyn_cast<ArrayType>(*I)) {
311 if (CI->getZExtValue() >= ATy->getNumElements())
313 if (ConstantArray *CA = dyn_cast<ConstantArray>(C))
314 C = CA->getOperand(CI->getZExtValue());
315 else if (isa<ConstantAggregateZero>(C))
316 C = Constant::getNullValue(ATy->getElementType());
317 else if (isa<UndefValue>(C))
318 C = UndefValue::get(ATy->getElementType());
321 } else if (const PackedType *PTy = dyn_cast<PackedType>(*I)) {
322 if (CI->getZExtValue() >= PTy->getNumElements())
324 if (ConstantPacked *CP = dyn_cast<ConstantPacked>(C))
325 C = CP->getOperand(CI->getZExtValue());
326 else if (isa<ConstantAggregateZero>(C))
327 C = Constant::getNullValue(PTy->getElementType());
328 else if (isa<UndefValue>(C))
329 C = UndefValue::get(PTy->getElementType());
342 //===----------------------------------------------------------------------===//
343 // Local dead code elimination...
346 bool llvm::isInstructionTriviallyDead(Instruction *I) {
347 if (!I->use_empty() || isa<TerminatorInst>(I)) return false;
349 if (!I->mayWriteToMemory()) return true;
351 if (CallInst *CI = dyn_cast<CallInst>(I))
352 if (Function *F = CI->getCalledFunction()) {
353 unsigned IntrinsicID = F->getIntrinsicID();
354 #define GET_SIDE_EFFECT_INFO
355 #include "llvm/Intrinsics.gen"
356 #undef GET_SIDE_EFFECT_INFO
361 // dceInstruction - Inspect the instruction at *BBI and figure out if it's
362 // [trivially] dead. If so, remove the instruction and update the iterator
363 // to point to the instruction that immediately succeeded the original
366 bool llvm::dceInstruction(BasicBlock::iterator &BBI) {
367 // Look for un"used" definitions...
368 if (isInstructionTriviallyDead(BBI)) {
369 BBI = BBI->getParent()->getInstList().erase(BBI); // Bye bye