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::LShr:
124 case Instruction::AShr:
125 return ConstantExpr::get(Opc, Ops[0], Ops[1]);
126 case Instruction::Cast:
127 return ConstantExpr::getCast(Ops[0], DestTy);
128 case Instruction::Select:
129 return ConstantExpr::getSelect(Ops[0], Ops[1], Ops[2]);
130 case Instruction::ExtractElement:
131 return ConstantExpr::getExtractElement(Ops[0], Ops[1]);
132 case Instruction::InsertElement:
133 return ConstantExpr::getInsertElement(Ops[0], Ops[1], Ops[2]);
134 case Instruction::ShuffleVector:
135 return ConstantExpr::getShuffleVector(Ops[0], Ops[1], Ops[2]);
136 case Instruction::GetElementPtr:
137 return ConstantExpr::getGetElementPtr(Ops[0],
138 std::vector<Constant*>(Ops.begin()+1,
143 // ConstantFoldTerminator - If a terminator instruction is predicated on a
144 // constant value, convert it into an unconditional branch to the constant
147 bool llvm::ConstantFoldTerminator(BasicBlock *BB) {
148 TerminatorInst *T = BB->getTerminator();
150 // Branch - See if we are conditional jumping on constant
151 if (BranchInst *BI = dyn_cast<BranchInst>(T)) {
152 if (BI->isUnconditional()) return false; // Can't optimize uncond branch
153 BasicBlock *Dest1 = cast<BasicBlock>(BI->getOperand(0));
154 BasicBlock *Dest2 = cast<BasicBlock>(BI->getOperand(1));
156 if (ConstantBool *Cond = dyn_cast<ConstantBool>(BI->getCondition())) {
157 // Are we branching on constant?
158 // YES. Change to unconditional branch...
159 BasicBlock *Destination = Cond->getValue() ? Dest1 : Dest2;
160 BasicBlock *OldDest = Cond->getValue() ? Dest2 : Dest1;
162 //cerr << "Function: " << T->getParent()->getParent()
163 // << "\nRemoving branch from " << T->getParent()
164 // << "\n\nTo: " << OldDest << endl;
166 // Let the basic block know that we are letting go of it. Based on this,
167 // it will adjust it's PHI nodes.
168 assert(BI->getParent() && "Terminator not inserted in block!");
169 OldDest->removePredecessor(BI->getParent());
171 // Set the unconditional destination, and change the insn to be an
172 // unconditional branch.
173 BI->setUnconditionalDest(Destination);
175 } else if (Dest2 == Dest1) { // Conditional branch to same location?
176 // This branch matches something like this:
177 // br bool %cond, label %Dest, label %Dest
178 // and changes it into: br label %Dest
180 // Let the basic block know that we are letting go of one copy of it.
181 assert(BI->getParent() && "Terminator not inserted in block!");
182 Dest1->removePredecessor(BI->getParent());
184 // Change a conditional branch to unconditional.
185 BI->setUnconditionalDest(Dest1);
188 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) {
189 // If we are switching on a constant, we can convert the switch into a
190 // single branch instruction!
191 ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition());
192 BasicBlock *TheOnlyDest = SI->getSuccessor(0); // The default dest
193 BasicBlock *DefaultDest = TheOnlyDest;
194 assert(TheOnlyDest == SI->getDefaultDest() &&
195 "Default destination is not successor #0?");
197 // Figure out which case it goes to...
198 for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) {
199 // Found case matching a constant operand?
200 if (SI->getSuccessorValue(i) == CI) {
201 TheOnlyDest = SI->getSuccessor(i);
205 // Check to see if this branch is going to the same place as the default
206 // dest. If so, eliminate it as an explicit compare.
207 if (SI->getSuccessor(i) == DefaultDest) {
208 // Remove this entry...
209 DefaultDest->removePredecessor(SI->getParent());
211 --i; --e; // Don't skip an entry...
215 // Otherwise, check to see if the switch only branches to one destination.
216 // We do this by reseting "TheOnlyDest" to null when we find two non-equal
218 if (SI->getSuccessor(i) != TheOnlyDest) TheOnlyDest = 0;
221 if (CI && !TheOnlyDest) {
222 // Branching on a constant, but not any of the cases, go to the default
224 TheOnlyDest = SI->getDefaultDest();
227 // If we found a single destination that we can fold the switch into, do so
230 // Insert the new branch..
231 new BranchInst(TheOnlyDest, SI);
232 BasicBlock *BB = SI->getParent();
234 // Remove entries from PHI nodes which we no longer branch to...
235 for (unsigned i = 0, e = SI->getNumSuccessors(); i != e; ++i) {
236 // Found case matching a constant operand?
237 BasicBlock *Succ = SI->getSuccessor(i);
238 if (Succ == TheOnlyDest)
239 TheOnlyDest = 0; // Don't modify the first branch to TheOnlyDest
241 Succ->removePredecessor(BB);
244 // Delete the old switch...
245 BB->getInstList().erase(SI);
247 } else if (SI->getNumSuccessors() == 2) {
248 // Otherwise, we can fold this switch into a conditional branch
249 // instruction if it has only one non-default destination.
250 Value *Cond = new SetCondInst(Instruction::SetEQ, SI->getCondition(),
251 SI->getSuccessorValue(1), "cond", SI);
252 // Insert the new branch...
253 new BranchInst(SI->getSuccessor(1), SI->getSuccessor(0), Cond, SI);
255 // Delete the old switch...
256 SI->getParent()->getInstList().erase(SI);
263 /// ConstantFoldLoadThroughGEPConstantExpr - Given a constant and a
264 /// getelementptr constantexpr, return the constant value being addressed by the
265 /// constant expression, or null if something is funny and we can't decide.
266 Constant *llvm::ConstantFoldLoadThroughGEPConstantExpr(Constant *C,
268 if (CE->getOperand(1) != Constant::getNullValue(CE->getOperand(1)->getType()))
269 return 0; // Do not allow stepping over the value!
271 // Loop over all of the operands, tracking down which value we are
273 gep_type_iterator I = gep_type_begin(CE), E = gep_type_end(CE);
274 for (++I; I != E; ++I)
275 if (const StructType *STy = dyn_cast<StructType>(*I)) {
276 ConstantInt *CU = cast<ConstantInt>(I.getOperand());
277 assert(CU->getZExtValue() < STy->getNumElements() &&
278 "Struct index out of range!");
279 unsigned El = (unsigned)CU->getZExtValue();
280 if (ConstantStruct *CS = dyn_cast<ConstantStruct>(C)) {
281 C = CS->getOperand(El);
282 } else if (isa<ConstantAggregateZero>(C)) {
283 C = Constant::getNullValue(STy->getElementType(El));
284 } else if (isa<UndefValue>(C)) {
285 C = UndefValue::get(STy->getElementType(El));
289 } else if (ConstantInt *CI = dyn_cast<ConstantInt>(I.getOperand())) {
290 if (const ArrayType *ATy = dyn_cast<ArrayType>(*I)) {
291 if (CI->getZExtValue() >= ATy->getNumElements())
293 if (ConstantArray *CA = dyn_cast<ConstantArray>(C))
294 C = CA->getOperand(CI->getZExtValue());
295 else if (isa<ConstantAggregateZero>(C))
296 C = Constant::getNullValue(ATy->getElementType());
297 else if (isa<UndefValue>(C))
298 C = UndefValue::get(ATy->getElementType());
301 } else if (const PackedType *PTy = dyn_cast<PackedType>(*I)) {
302 if (CI->getZExtValue() >= PTy->getNumElements())
304 if (ConstantPacked *CP = dyn_cast<ConstantPacked>(C))
305 C = CP->getOperand(CI->getZExtValue());
306 else if (isa<ConstantAggregateZero>(C))
307 C = Constant::getNullValue(PTy->getElementType());
308 else if (isa<UndefValue>(C))
309 C = UndefValue::get(PTy->getElementType());
322 //===----------------------------------------------------------------------===//
323 // Local dead code elimination...
326 bool llvm::isInstructionTriviallyDead(Instruction *I) {
327 if (!I->use_empty() || isa<TerminatorInst>(I)) return false;
329 if (!I->mayWriteToMemory()) return true;
331 if (CallInst *CI = dyn_cast<CallInst>(I))
332 if (Function *F = CI->getCalledFunction()) {
333 unsigned IntrinsicID = F->getIntrinsicID();
334 #define GET_SIDE_EFFECT_INFO
335 #include "llvm/Intrinsics.gen"
336 #undef GET_SIDE_EFFECT_INFO
341 // dceInstruction - Inspect the instruction at *BBI and figure out if it's
342 // [trivially] dead. If so, remove the instruction and update the iterator
343 // to point to the instruction that immediately succeeded the original
346 bool llvm::dceInstruction(BasicBlock::iterator &BBI) {
347 // Look for un"used" definitions...
348 if (isInstructionTriviallyDead(BBI)) {
349 BBI = BBI->getParent()->getInstList().erase(BBI); // Bye bye