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"
27 //===----------------------------------------------------------------------===//
28 // Local constant propagation...
31 /// doConstantPropagation - If an instruction references constants, try to fold
34 bool llvm::doConstantPropagation(BasicBlock::iterator &II) {
35 if (Constant *C = ConstantFoldInstruction(II)) {
36 // Replaces all of the uses of a variable with uses of the constant.
37 II->replaceAllUsesWith(C);
39 // Remove the instruction from the basic block...
40 II = II->getParent()->getInstList().erase(II);
47 /// ConstantFoldInstruction - Attempt to constant fold the specified
48 /// instruction. If successful, the constant result is returned, if not, null
49 /// is returned. Note that this function can only fail when attempting to fold
50 /// instructions like loads and stores, which have no constant expression form.
52 Constant *llvm::ConstantFoldInstruction(Instruction *I) {
53 if (PHINode *PN = dyn_cast<PHINode>(I)) {
54 if (PN->getNumIncomingValues() == 0)
55 return Constant::getNullValue(PN->getType());
57 Constant *Result = dyn_cast<Constant>(PN->getIncomingValue(0));
58 if (Result == 0) return 0;
60 // Handle PHI nodes specially here...
61 for (unsigned i = 1, e = PN->getNumIncomingValues(); i != e; ++i)
62 if (PN->getIncomingValue(i) != Result && PN->getIncomingValue(i) != PN)
63 return 0; // Not all the same incoming constants...
65 // If we reach here, all incoming values are the same constant.
67 } else if (CallInst *CI = dyn_cast<CallInst>(I)) {
68 if (Function *F = CI->getCalledFunction())
69 if (canConstantFoldCallTo(F)) {
70 std::vector<Constant*> Args;
71 for (unsigned i = 1, e = CI->getNumOperands(); i != e; ++i)
72 if (Constant *Op = dyn_cast<Constant>(CI->getOperand(i)))
76 return ConstantFoldCall(F, Args);
81 Constant *Op0 = 0, *Op1 = 0;
82 switch (I->getNumOperands()) {
85 Op1 = dyn_cast<Constant>(I->getOperand(1));
86 if (Op1 == 0) return 0; // Not a constant?, can't fold
88 Op0 = dyn_cast<Constant>(I->getOperand(0));
89 if (Op0 == 0) return 0; // Not a constant?, can't fold
94 if (isa<BinaryOperator>(I) || isa<ShiftInst>(I))
95 return ConstantExpr::get(I->getOpcode(), Op0, Op1);
97 switch (I->getOpcode()) {
99 case Instruction::Cast:
100 return ConstantExpr::getCast(Op0, I->getType());
101 case Instruction::Select:
102 if (Constant *Op2 = dyn_cast<Constant>(I->getOperand(2)))
103 return ConstantExpr::getSelect(Op0, Op1, Op2);
105 case Instruction::ExtractElement:
106 return ConstantExpr::getExtractElement(Op0, Op1);
107 case Instruction::InsertElement:
108 if (Constant *Op2 = dyn_cast<Constant>(I->getOperand(2)))
109 return ConstantExpr::getInsertElement(Op0, Op1, Op2);
111 case Instruction::ShuffleVector:
112 if (Constant *Op2 = dyn_cast<Constant>(I->getOperand(2)))
113 return ConstantExpr::getShuffleVector(Op0, Op1, Op2);
115 case Instruction::GetElementPtr:
116 std::vector<Constant*> IdxList;
117 IdxList.reserve(I->getNumOperands()-1);
118 if (Op1) IdxList.push_back(Op1);
119 for (unsigned i = 2, e = I->getNumOperands(); i != e; ++i)
120 if (Constant *C = dyn_cast<Constant>(I->getOperand(i)))
121 IdxList.push_back(C);
123 return 0; // Non-constant operand
124 return ConstantExpr::getGetElementPtr(Op0, IdxList);
128 // ConstantFoldTerminator - If a terminator instruction is predicated on a
129 // constant value, convert it into an unconditional branch to the constant
132 bool llvm::ConstantFoldTerminator(BasicBlock *BB) {
133 TerminatorInst *T = BB->getTerminator();
135 // Branch - See if we are conditional jumping on constant
136 if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
137 if (BI->isUnconditional()) return false; // Can't optimize uncond branch
138 BasicBlock *Dest1 = cast<BasicBlock>(BI->getOperand(0));
139 BasicBlock *Dest2 = cast<BasicBlock>(BI->getOperand(1));
141 if (ConstantBool *Cond = dyn_cast<ConstantBool>(BI->getCondition())) {
142 // Are we branching on constant?
143 // YES. Change to unconditional branch...
144 BasicBlock *Destination = Cond->getValue() ? Dest1 : Dest2;
145 BasicBlock *OldDest = Cond->getValue() ? Dest2 : Dest1;
147 //cerr << "Function: " << T->getParent()->getParent()
148 // << "\nRemoving branch from " << T->getParent()
149 // << "\n\nTo: " << OldDest << endl;
151 // Let the basic block know that we are letting go of it. Based on this,
152 // it will adjust it's PHI nodes.
153 assert(BI->getParent() && "Terminator not inserted in block!");
154 OldDest->removePredecessor(BI->getParent());
156 // Set the unconditional destination, and change the insn to be an
157 // unconditional branch.
158 BI->setUnconditionalDest(Destination);
160 } else if (Dest2 == Dest1) { // Conditional branch to same location?
161 // This branch matches something like this:
162 // br bool %cond, label %Dest, label %Dest
163 // and changes it into: br label %Dest
165 // Let the basic block know that we are letting go of one copy of it.
166 assert(BI->getParent() && "Terminator not inserted in block!");
167 Dest1->removePredecessor(BI->getParent());
169 // Change a conditional branch to unconditional.
170 BI->setUnconditionalDest(Dest1);
173 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) {
174 // If we are switching on a constant, we can convert the switch into a
175 // single branch instruction!
176 ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition());
177 BasicBlock *TheOnlyDest = SI->getSuccessor(0); // The default dest
178 BasicBlock *DefaultDest = TheOnlyDest;
179 assert(TheOnlyDest == SI->getDefaultDest() &&
180 "Default destination is not successor #0?");
182 // Figure out which case it goes to...
183 for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) {
184 // Found case matching a constant operand?
185 if (SI->getSuccessorValue(i) == CI) {
186 TheOnlyDest = SI->getSuccessor(i);
190 // Check to see if this branch is going to the same place as the default
191 // dest. If so, eliminate it as an explicit compare.
192 if (SI->getSuccessor(i) == DefaultDest) {
193 // Remove this entry...
194 DefaultDest->removePredecessor(SI->getParent());
196 --i; --e; // Don't skip an entry...
200 // Otherwise, check to see if the switch only branches to one destination.
201 // We do this by reseting "TheOnlyDest" to null when we find two non-equal
203 if (SI->getSuccessor(i) != TheOnlyDest) TheOnlyDest = 0;
206 if (CI && !TheOnlyDest) {
207 // Branching on a constant, but not any of the cases, go to the default
209 TheOnlyDest = SI->getDefaultDest();
212 // If we found a single destination that we can fold the switch into, do so
215 // Insert the new branch..
216 new BranchInst(TheOnlyDest, SI);
217 BasicBlock *BB = SI->getParent();
219 // Remove entries from PHI nodes which we no longer branch to...
220 for (unsigned i = 0, e = SI->getNumSuccessors(); i != e; ++i) {
221 // Found case matching a constant operand?
222 BasicBlock *Succ = SI->getSuccessor(i);
223 if (Succ == TheOnlyDest)
224 TheOnlyDest = 0; // Don't modify the first branch to TheOnlyDest
226 Succ->removePredecessor(BB);
229 // Delete the old switch...
230 BB->getInstList().erase(SI);
232 } else if (SI->getNumSuccessors() == 2) {
233 // Otherwise, we can fold this switch into a conditional branch
234 // instruction if it has only one non-default destination.
235 Value *Cond = new SetCondInst(Instruction::SetEQ, SI->getCondition(),
236 SI->getSuccessorValue(1), "cond", SI);
237 // Insert the new branch...
238 new BranchInst(SI->getSuccessor(1), SI->getSuccessor(0), Cond, SI);
240 // Delete the old switch...
241 SI->getParent()->getInstList().erase(SI);
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 ConstantUInt *CU = cast<ConstantUInt>(I.getOperand());
262 assert(CU->getValue() < STy->getNumElements() &&
263 "Struct index out of range!");
264 unsigned El = (unsigned)CU->getValue();
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 ((uint64_t)CI->getRawValue() >= ATy->getNumElements()) return 0;
277 if (ConstantArray *CA = dyn_cast<ConstantArray>(C))
278 C = CA->getOperand((unsigned)CI->getRawValue());
279 else if (isa<ConstantAggregateZero>(C))
280 C = Constant::getNullValue(ATy->getElementType());
281 else if (isa<UndefValue>(C))
282 C = UndefValue::get(ATy->getElementType());
285 } else if (const PackedType *PTy = dyn_cast<PackedType>(*I)) {
286 if ((uint64_t)CI->getRawValue() >= PTy->getNumElements()) return 0;
287 if (ConstantPacked *CP = dyn_cast<ConstantPacked>(C))
288 C = CP->getOperand((unsigned)CI->getRawValue());
289 else if (isa<ConstantAggregateZero>(C))
290 C = Constant::getNullValue(PTy->getElementType());
291 else if (isa<UndefValue>(C))
292 C = UndefValue::get(PTy->getElementType());
305 //===----------------------------------------------------------------------===//
306 // Local dead code elimination...
309 bool llvm::isInstructionTriviallyDead(Instruction *I) {
310 if (!I->use_empty() || isa<TerminatorInst>(I)) return false;
312 if (!I->mayWriteToMemory()) return true;
314 if (CallInst *CI = dyn_cast<CallInst>(I))
315 if (Function *F = CI->getCalledFunction()) {
316 unsigned IntrinsicID = F->getIntrinsicID();
317 #define GET_SIDE_EFFECT_INFO
318 #include "llvm/Intrinsics.gen"
319 #undef GET_SIDE_EFFECT_INFO
324 // dceInstruction - Inspect the instruction at *BBI and figure out if it's
325 // [trivially] dead. If so, remove the instruction and update the iterator
326 // to point to the instruction that immediately succeeded the original
329 bool llvm::dceInstruction(BasicBlock::iterator &BBI) {
330 // Look for un"used" definitions...
331 if (isInstructionTriviallyDead(BBI)) {
332 BBI = BBI->getParent()->getInstList().erase(BBI); // Bye bye