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.
69 Constant *Op0 = 0, *Op1 = 0;
70 switch (I->getNumOperands()) {
73 Op1 = dyn_cast<Constant>(I->getOperand(1));
74 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 if (Constant *Op0 = dyn_cast<Constant>(I->getOperand(0)))
84 if (Constant *Op1 = dyn_cast<Constant>(I->getOperand(1)))
85 return ConstantExpr::get(I->getOpcode(), Op0, Op1);
86 return 0; // Operands not constants.
89 // Scan the operand list, checking to see if the are all constants, if so,
90 // hand off to ConstantFoldInstOperands.
91 std::vector<Constant*> Ops;
92 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
93 if (Constant *Op = dyn_cast<Constant>(I->getOperand(i)))
96 return 0; // All operands not constant!
98 return ConstantFoldInstOperands(I->getOpcode(), I->getType(), Ops);
101 /// ConstantFoldInstOperands - Attempt to constant fold an instruction with the
102 /// specified opcode and operands. If successful, the constant result is
103 /// returned, if not, null is returned. Note that this function can fail when
104 /// attempting to fold instructions like loads and stores, which have no
105 /// constant expression form.
107 Constant *llvm::ConstantFoldInstOperands(unsigned Opc, const Type *DestTy,
108 const std::vector<Constant*> &Ops) {
109 if (Opc >= Instruction::BinaryOpsBegin && Opc < Instruction::BinaryOpsEnd)
110 return ConstantExpr::get(Opc, Ops[0], Ops[1]);
114 case Instruction::Call:
115 if (Function *F = dyn_cast<Function>(Ops[0])) {
116 if (canConstantFoldCallTo(F)) {
117 std::vector<Constant*> Args(Ops.begin()+1, Ops.end());
118 return ConstantFoldCall(F, Args);
122 case Instruction::Shl:
123 case Instruction::Shr:
124 return ConstantExpr::get(Opc, Ops[0], Ops[1]);
125 case Instruction::Cast:
126 return ConstantExpr::getCast(Ops[0], DestTy);
127 case Instruction::Select:
128 return ConstantExpr::getSelect(Ops[0], Ops[1], Ops[2]);
129 case Instruction::ExtractElement:
130 return ConstantExpr::getExtractElement(Ops[0], Ops[1]);
131 case Instruction::InsertElement:
132 return ConstantExpr::getInsertElement(Ops[0], Ops[1], Ops[2]);
133 case Instruction::ShuffleVector:
134 return ConstantExpr::getShuffleVector(Ops[0], Ops[1], Ops[2]);
135 case Instruction::GetElementPtr:
136 return ConstantExpr::getGetElementPtr(Ops[0],
137 std::vector<Constant*>(Ops.begin()+1,
142 // ConstantFoldTerminator - If a terminator instruction is predicated on a
143 // constant value, convert it into an unconditional branch to the constant
146 bool llvm::ConstantFoldTerminator(BasicBlock *BB) {
147 TerminatorInst *T = BB->getTerminator();
149 // Branch - See if we are conditional jumping on constant
150 if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
151 if (BI->isUnconditional()) return false; // Can't optimize uncond branch
152 BasicBlock *Dest1 = cast<BasicBlock>(BI->getOperand(0));
153 BasicBlock *Dest2 = cast<BasicBlock>(BI->getOperand(1));
155 if (ConstantBool *Cond = dyn_cast<ConstantBool>(BI->getCondition())) {
156 // Are we branching on constant?
157 // YES. Change to unconditional branch...
158 BasicBlock *Destination = Cond->getValue() ? Dest1 : Dest2;
159 BasicBlock *OldDest = Cond->getValue() ? Dest2 : Dest1;
161 //cerr << "Function: " << T->getParent()->getParent()
162 // << "\nRemoving branch from " << T->getParent()
163 // << "\n\nTo: " << OldDest << endl;
165 // Let the basic block know that we are letting go of it. Based on this,
166 // it will adjust it's PHI nodes.
167 assert(BI->getParent() && "Terminator not inserted in block!");
168 OldDest->removePredecessor(BI->getParent());
170 // Set the unconditional destination, and change the insn to be an
171 // unconditional branch.
172 BI->setUnconditionalDest(Destination);
174 } else if (Dest2 == Dest1) { // Conditional branch to same location?
175 // This branch matches something like this:
176 // br bool %cond, label %Dest, label %Dest
177 // and changes it into: br label %Dest
179 // Let the basic block know that we are letting go of one copy of it.
180 assert(BI->getParent() && "Terminator not inserted in block!");
181 Dest1->removePredecessor(BI->getParent());
183 // Change a conditional branch to unconditional.
184 BI->setUnconditionalDest(Dest1);
187 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) {
188 // If we are switching on a constant, we can convert the switch into a
189 // single branch instruction!
190 ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition());
191 BasicBlock *TheOnlyDest = SI->getSuccessor(0); // The default dest
192 BasicBlock *DefaultDest = TheOnlyDest;
193 assert(TheOnlyDest == SI->getDefaultDest() &&
194 "Default destination is not successor #0?");
196 // Figure out which case it goes to...
197 for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) {
198 // Found case matching a constant operand?
199 if (SI->getSuccessorValue(i) == CI) {
200 TheOnlyDest = SI->getSuccessor(i);
204 // Check to see if this branch is going to the same place as the default
205 // dest. If so, eliminate it as an explicit compare.
206 if (SI->getSuccessor(i) == DefaultDest) {
207 // Remove this entry...
208 DefaultDest->removePredecessor(SI->getParent());
210 --i; --e; // Don't skip an entry...
214 // Otherwise, check to see if the switch only branches to one destination.
215 // We do this by reseting "TheOnlyDest" to null when we find two non-equal
217 if (SI->getSuccessor(i) != TheOnlyDest) TheOnlyDest = 0;
220 if (CI && !TheOnlyDest) {
221 // Branching on a constant, but not any of the cases, go to the default
223 TheOnlyDest = SI->getDefaultDest();
226 // If we found a single destination that we can fold the switch into, do so
229 // Insert the new branch..
230 new BranchInst(TheOnlyDest, SI);
231 BasicBlock *BB = SI->getParent();
233 // Remove entries from PHI nodes which we no longer branch to...
234 for (unsigned i = 0, e = SI->getNumSuccessors(); i != e; ++i) {
235 // Found case matching a constant operand?
236 BasicBlock *Succ = SI->getSuccessor(i);
237 if (Succ == TheOnlyDest)
238 TheOnlyDest = 0; // Don't modify the first branch to TheOnlyDest
240 Succ->removePredecessor(BB);
243 // Delete the old switch...
244 BB->getInstList().erase(SI);
246 } else if (SI->getNumSuccessors() == 2) {
247 // Otherwise, we can fold this switch into a conditional branch
248 // instruction if it has only one non-default destination.
249 Value *Cond = new SetCondInst(Instruction::SetEQ, SI->getCondition(),
250 SI->getSuccessorValue(1), "cond", SI);
251 // Insert the new branch...
252 new BranchInst(SI->getSuccessor(1), SI->getSuccessor(0), Cond, SI);
254 // Delete the old switch...
255 SI->getParent()->getInstList().erase(SI);
262 /// ConstantFoldLoadThroughGEPConstantExpr - Given a constant and a
263 /// getelementptr constantexpr, return the constant value being addressed by the
264 /// constant expression, or null if something is funny and we can't decide.
265 Constant *llvm::ConstantFoldLoadThroughGEPConstantExpr(Constant *C,
267 if (CE->getOperand(1) != Constant::getNullValue(CE->getOperand(1)->getType()))
268 return 0; // Do not allow stepping over the value!
270 // Loop over all of the operands, tracking down which value we are
272 gep_type_iterator I = gep_type_begin(CE), E = gep_type_end(CE);
273 for (++I; I != E; ++I)
274 if (const StructType *STy = dyn_cast<StructType>(*I)) {
275 ConstantUInt *CU = cast<ConstantUInt>(I.getOperand());
276 assert(CU->getValue() < STy->getNumElements() &&
277 "Struct index out of range!");
278 unsigned El = (unsigned)CU->getValue();
279 if (ConstantStruct *CS = dyn_cast<ConstantStruct>(C)) {
280 C = CS->getOperand(El);
281 } else if (isa<ConstantAggregateZero>(C)) {
282 C = Constant::getNullValue(STy->getElementType(El));
283 } else if (isa<UndefValue>(C)) {
284 C = UndefValue::get(STy->getElementType(El));
288 } else if (ConstantInt *CI = dyn_cast<ConstantInt>(I.getOperand())) {
289 if (const ArrayType *ATy = dyn_cast<ArrayType>(*I)) {
290 if ((uint64_t)CI->getRawValue() >= ATy->getNumElements())
292 if (ConstantArray *CA = dyn_cast<ConstantArray>(C))
293 C = CA->getOperand((unsigned)CI->getRawValue());
294 else if (isa<ConstantAggregateZero>(C))
295 C = Constant::getNullValue(ATy->getElementType());
296 else if (isa<UndefValue>(C))
297 C = UndefValue::get(ATy->getElementType());
300 } else if (const PackedType *PTy = dyn_cast<PackedType>(*I)) {
301 if ((uint64_t)CI->getRawValue() >= PTy->getNumElements())
303 if (ConstantPacked *CP = dyn_cast<ConstantPacked>(C))
304 C = CP->getOperand((unsigned)CI->getRawValue());
305 else if (isa<ConstantAggregateZero>(C))
306 C = Constant::getNullValue(PTy->getElementType());
307 else if (isa<UndefValue>(C))
308 C = UndefValue::get(PTy->getElementType());
321 //===----------------------------------------------------------------------===//
322 // Local dead code elimination...
325 bool llvm::isInstructionTriviallyDead(Instruction *I) {
326 if (!I->use_empty() || isa<TerminatorInst>(I)) return false;
328 if (!I->mayWriteToMemory()) return true;
330 if (CallInst *CI = dyn_cast<CallInst>(I))
331 if (Function *F = CI->getCalledFunction()) {
332 unsigned IntrinsicID = F->getIntrinsicID();
333 #define GET_SIDE_EFFECT_INFO
334 #include "llvm/Intrinsics.gen"
335 #undef GET_SIDE_EFFECT_INFO
340 // dceInstruction - Inspect the instruction at *BBI and figure out if it's
341 // [trivially] dead. If so, remove the instruction and update the iterator
342 // to point to the instruction that immediately succeeded the original
345 bool llvm::dceInstruction(BasicBlock::iterator &BBI) {
346 // Look for un"used" definitions...
347 if (isInstructionTriviallyDead(BBI)) {
348 BBI = BBI->getParent()->getInstList().erase(BBI); // Bye bye