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
75 Op0 = dyn_cast<Constant>(I->getOperand(0));
76 if (Op0 == 0) return 0; // Not a constant?, can't fold
81 if (isa<BinaryOperator>(I) || isa<ShiftInst>(I)) {
82 if (Constant *Op0 = dyn_cast<Constant>(I->getOperand(0)))
83 if (Constant *Op1 = dyn_cast<Constant>(I->getOperand(1)))
84 return ConstantExpr::get(I->getOpcode(), Op0, Op1);
85 return 0; // Operands not constants.
88 // Scan the operand list, checking to see if the are all constants, if so,
89 // hand off to ConstantFoldInstOperands.
90 std::vector<Constant*> Ops;
91 for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
92 if (Constant *Op = dyn_cast<Constant>(I->getOperand(i)))
95 return 0; // All operands not constant!
97 return ConstantFoldInstOperands(I->getOpcode(), I->getType(), Ops);
100 /// ConstantFoldInstOperands - Attempt to constant fold an instruction with the
101 /// specified opcode and operands. If successful, the constant result is
102 /// returned, if not, null is returned. Note that this function can fail when
103 /// attempting to fold instructions like loads and stores, which have no
104 /// constant expression form.
106 Constant *llvm::ConstantFoldInstOperands(unsigned Opc, const Type *DestTy,
107 const std::vector<Constant*> &Ops) {
108 if (Opc >= Instruction::BinaryOpsBegin && Opc < Instruction::BinaryOpsEnd)
109 return ConstantExpr::get(Opc, Ops[0], Ops[1]);
113 case Instruction::Call:
114 if (Function *F = dyn_cast<Function>(Ops[0])) {
115 if (canConstantFoldCallTo(F)) {
116 std::vector<Constant*> Args(Ops.begin()+1, Ops.end());
117 return ConstantFoldCall(F, Args);
121 case Instruction::Shl:
122 case Instruction::LShr:
123 case Instruction::AShr:
124 return ConstantExpr::get(Opc, Ops[0], Ops[1]);
125 case Instruction::Trunc:
126 case Instruction::ZExt:
127 case Instruction::SExt:
128 case Instruction::FPTrunc:
129 case Instruction::FPExt:
130 case Instruction::UIToFP:
131 case Instruction::SIToFP:
132 case Instruction::FPToUI:
133 case Instruction::FPToSI:
134 case Instruction::PtrToInt:
135 case Instruction::IntToPtr:
136 case Instruction::BitCast:
137 return ConstantExpr::getCast(Opc, Ops[0], DestTy);
138 case Instruction::Select:
139 return ConstantExpr::getSelect(Ops[0], Ops[1], Ops[2]);
140 case Instruction::ExtractElement:
141 return ConstantExpr::getExtractElement(Ops[0], Ops[1]);
142 case Instruction::InsertElement:
143 return ConstantExpr::getInsertElement(Ops[0], Ops[1], Ops[2]);
144 case Instruction::ShuffleVector:
145 return ConstantExpr::getShuffleVector(Ops[0], Ops[1], Ops[2]);
146 case Instruction::GetElementPtr:
147 return ConstantExpr::getGetElementPtr(Ops[0],
148 std::vector<Constant*>(Ops.begin()+1,
153 // ConstantFoldTerminator - If a terminator instruction is predicated on a
154 // constant value, convert it into an unconditional branch to the constant
157 bool llvm::ConstantFoldTerminator(BasicBlock *BB) {
158 TerminatorInst *T = BB->getTerminator();
160 // Branch - See if we are conditional jumping on constant
161 if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
162 if (BI->isUnconditional()) return false; // Can't optimize uncond branch
163 BasicBlock *Dest1 = cast<BasicBlock>(BI->getOperand(0));
164 BasicBlock *Dest2 = cast<BasicBlock>(BI->getOperand(1));
166 if (ConstantBool *Cond = dyn_cast<ConstantBool>(BI->getCondition())) {
167 // Are we branching on constant?
168 // YES. Change to unconditional branch...
169 BasicBlock *Destination = Cond->getValue() ? Dest1 : Dest2;
170 BasicBlock *OldDest = Cond->getValue() ? Dest2 : Dest1;
172 //cerr << "Function: " << T->getParent()->getParent()
173 // << "\nRemoving branch from " << T->getParent()
174 // << "\n\nTo: " << OldDest << endl;
176 // Let the basic block know that we are letting go of it. Based on this,
177 // it will adjust it's PHI nodes.
178 assert(BI->getParent() && "Terminator not inserted in block!");
179 OldDest->removePredecessor(BI->getParent());
181 // Set the unconditional destination, and change the insn to be an
182 // unconditional branch.
183 BI->setUnconditionalDest(Destination);
185 } else if (Dest2 == Dest1) { // Conditional branch to same location?
186 // This branch matches something like this:
187 // br bool %cond, label %Dest, label %Dest
188 // and changes it into: br label %Dest
190 // Let the basic block know that we are letting go of one copy of it.
191 assert(BI->getParent() && "Terminator not inserted in block!");
192 Dest1->removePredecessor(BI->getParent());
194 // Change a conditional branch to unconditional.
195 BI->setUnconditionalDest(Dest1);
198 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) {
199 // If we are switching on a constant, we can convert the switch into a
200 // single branch instruction!
201 ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition());
202 BasicBlock *TheOnlyDest = SI->getSuccessor(0); // The default dest
203 BasicBlock *DefaultDest = TheOnlyDest;
204 assert(TheOnlyDest == SI->getDefaultDest() &&
205 "Default destination is not successor #0?");
207 // Figure out which case it goes to...
208 for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) {
209 // Found case matching a constant operand?
210 if (SI->getSuccessorValue(i) == CI) {
211 TheOnlyDest = SI->getSuccessor(i);
215 // Check to see if this branch is going to the same place as the default
216 // dest. If so, eliminate it as an explicit compare.
217 if (SI->getSuccessor(i) == DefaultDest) {
218 // Remove this entry...
219 DefaultDest->removePredecessor(SI->getParent());
221 --i; --e; // Don't skip an entry...
225 // Otherwise, check to see if the switch only branches to one destination.
226 // We do this by reseting "TheOnlyDest" to null when we find two non-equal
228 if (SI->getSuccessor(i) != TheOnlyDest) TheOnlyDest = 0;
231 if (CI && !TheOnlyDest) {
232 // Branching on a constant, but not any of the cases, go to the default
234 TheOnlyDest = SI->getDefaultDest();
237 // If we found a single destination that we can fold the switch into, do so
240 // Insert the new branch..
241 new BranchInst(TheOnlyDest, SI);
242 BasicBlock *BB = SI->getParent();
244 // Remove entries from PHI nodes which we no longer branch to...
245 for (unsigned i = 0, e = SI->getNumSuccessors(); i != e; ++i) {
246 // Found case matching a constant operand?
247 BasicBlock *Succ = SI->getSuccessor(i);
248 if (Succ == TheOnlyDest)
249 TheOnlyDest = 0; // Don't modify the first branch to TheOnlyDest
251 Succ->removePredecessor(BB);
254 // Delete the old switch...
255 BB->getInstList().erase(SI);
257 } else if (SI->getNumSuccessors() == 2) {
258 // Otherwise, we can fold this switch into a conditional branch
259 // instruction if it has only one non-default destination.
260 Value *Cond = new SetCondInst(Instruction::SetEQ, SI->getCondition(),
261 SI->getSuccessorValue(1), "cond", SI);
262 // Insert the new branch...
263 new BranchInst(SI->getSuccessor(1), SI->getSuccessor(0), Cond, SI);
265 // Delete the old switch...
266 SI->getParent()->getInstList().erase(SI);
273 /// ConstantFoldLoadThroughGEPConstantExpr - Given a constant and a
274 /// getelementptr constantexpr, return the constant value being addressed by the
275 /// constant expression, or null if something is funny and we can't decide.
276 Constant *llvm::ConstantFoldLoadThroughGEPConstantExpr(Constant *C,
278 if (CE->getOperand(1) != Constant::getNullValue(CE->getOperand(1)->getType()))
279 return 0; // Do not allow stepping over the value!
281 // Loop over all of the operands, tracking down which value we are
283 gep_type_iterator I = gep_type_begin(CE), E = gep_type_end(CE);
284 for (++I; I != E; ++I)
285 if (const StructType *STy = dyn_cast<StructType>(*I)) {
286 ConstantInt *CU = cast<ConstantInt>(I.getOperand());
287 assert(CU->getZExtValue() < STy->getNumElements() &&
288 "Struct index out of range!");
289 unsigned El = (unsigned)CU->getZExtValue();
290 if (ConstantStruct *CS = dyn_cast<ConstantStruct>(C)) {
291 C = CS->getOperand(El);
292 } else if (isa<ConstantAggregateZero>(C)) {
293 C = Constant::getNullValue(STy->getElementType(El));
294 } else if (isa<UndefValue>(C)) {
295 C = UndefValue::get(STy->getElementType(El));
299 } else if (ConstantInt *CI = dyn_cast<ConstantInt>(I.getOperand())) {
300 if (const ArrayType *ATy = dyn_cast<ArrayType>(*I)) {
301 if (CI->getZExtValue() >= ATy->getNumElements())
303 if (ConstantArray *CA = dyn_cast<ConstantArray>(C))
304 C = CA->getOperand(CI->getZExtValue());
305 else if (isa<ConstantAggregateZero>(C))
306 C = Constant::getNullValue(ATy->getElementType());
307 else if (isa<UndefValue>(C))
308 C = UndefValue::get(ATy->getElementType());
311 } else if (const PackedType *PTy = dyn_cast<PackedType>(*I)) {
312 if (CI->getZExtValue() >= PTy->getNumElements())
314 if (ConstantPacked *CP = dyn_cast<ConstantPacked>(C))
315 C = CP->getOperand(CI->getZExtValue());
316 else if (isa<ConstantAggregateZero>(C))
317 C = Constant::getNullValue(PTy->getElementType());
318 else if (isa<UndefValue>(C))
319 C = UndefValue::get(PTy->getElementType());
332 //===----------------------------------------------------------------------===//
333 // Local dead code elimination...
336 bool llvm::isInstructionTriviallyDead(Instruction *I) {
337 if (!I->use_empty() || isa<TerminatorInst>(I)) return false;
339 if (!I->mayWriteToMemory()) return true;
341 if (CallInst *CI = dyn_cast<CallInst>(I))
342 if (Function *F = CI->getCalledFunction()) {
343 unsigned IntrinsicID = F->getIntrinsicID();
344 #define GET_SIDE_EFFECT_INFO
345 #include "llvm/Intrinsics.gen"
346 #undef GET_SIDE_EFFECT_INFO
351 // dceInstruction - Inspect the instruction at *BBI and figure out if it's
352 // [trivially] dead. If so, remove the instruction and update the iterator
353 // to point to the instruction that immediately succeeded the original
356 bool llvm::dceInstruction(BasicBlock::iterator &BBI) {
357 // Look for un"used" definitions...
358 if (isInstructionTriviallyDead(BBI)) {
359 BBI = BBI->getParent()->getInstList().erase(BBI); // Bye bye