1 //===- SCCP.cpp - Sparse Conditional Constant Propagation -----------------===//
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 file implements sparse conditional constant propagation and merging:
12 // Specifically, this:
13 // * Assumes values are constant unless proven otherwise
14 // * Assumes BasicBlocks are dead unless proven otherwise
15 // * Proves values to be constant, and replaces them with constants
16 // * Proves conditional branches to be unconditional
19 // * This pass has a habit of making definitions be dead. It is a good idea
20 // to to run a DCE pass sometime after running this pass.
22 //===----------------------------------------------------------------------===//
24 #include "llvm/Transforms/Scalar.h"
25 #include "llvm/Constants.h"
26 #include "llvm/Function.h"
27 #include "llvm/GlobalVariable.h"
28 #include "llvm/Instructions.h"
29 #include "llvm/Pass.h"
30 #include "llvm/Type.h"
31 #include "llvm/Support/InstVisitor.h"
32 #include "Support/Debug.h"
33 #include "Support/Statistic.h"
34 #include "Support/STLExtras.h"
39 // InstVal class - This class represents the different lattice values that an
40 // instruction may occupy. It is a simple class with value semantics.
43 Statistic<> NumInstRemoved("sccp", "Number of instructions removed");
47 undefined, // This instruction has no known value
48 constant, // This instruction has a constant value
49 overdefined // This instruction has an unknown value
50 } LatticeValue; // The current lattice position
51 Constant *ConstantVal; // If Constant value, the current value
53 inline InstVal() : LatticeValue(undefined), ConstantVal(0) {}
55 // markOverdefined - Return true if this is a new status to be in...
56 inline bool markOverdefined() {
57 if (LatticeValue != overdefined) {
58 LatticeValue = overdefined;
64 // markConstant - Return true if this is a new status for us...
65 inline bool markConstant(Constant *V) {
66 if (LatticeValue != constant) {
67 LatticeValue = constant;
71 assert(ConstantVal == V && "Marking constant with different value");
76 inline bool isUndefined() const { return LatticeValue == undefined; }
77 inline bool isConstant() const { return LatticeValue == constant; }
78 inline bool isOverdefined() const { return LatticeValue == overdefined; }
80 inline Constant *getConstant() const {
81 assert(isConstant() && "Cannot get the constant of a non-constant!");
86 } // end anonymous namespace
89 //===----------------------------------------------------------------------===//
92 // This class does all of the work of Sparse Conditional Constant Propagation.
95 class SCCP : public FunctionPass, public InstVisitor<SCCP> {
96 std::set<BasicBlock*> BBExecutable;// The basic blocks that are executable
97 std::map<Value*, InstVal> ValueState; // The state each value is in...
99 std::vector<Instruction*> InstWorkList;// The instruction work list
100 std::vector<BasicBlock*> BBWorkList; // The BasicBlock work list
102 /// UsersOfOverdefinedPHIs - Keep track of any users of PHI nodes that are not
103 /// overdefined, despite the fact that the PHI node is overdefined.
104 std::multimap<PHINode*, Instruction*> UsersOfOverdefinedPHIs;
106 /// KnownFeasibleEdges - Entries in this set are edges which have already had
107 /// PHI nodes retriggered.
108 typedef std::pair<BasicBlock*,BasicBlock*> Edge;
109 std::set<Edge> KnownFeasibleEdges;
112 // runOnFunction - Run the Sparse Conditional Constant Propagation algorithm,
113 // and return true if the function was modified.
115 bool runOnFunction(Function &F);
117 virtual void getAnalysisUsage(AnalysisUsage &AU) const {
118 AU.setPreservesCFG();
122 //===--------------------------------------------------------------------===//
123 // The implementation of this class
126 friend class InstVisitor<SCCP>; // Allow callbacks from visitor
128 // markValueOverdefined - Make a value be marked as "constant". If the value
129 // is not already a constant, add it to the instruction work list so that
130 // the users of the instruction are updated later.
132 inline void markConstant(InstVal &IV, Instruction *I, Constant *C) {
133 if (IV.markConstant(C)) {
134 DEBUG(std::cerr << "markConstant: " << *C << ": " << *I);
135 InstWorkList.push_back(I);
138 inline void markConstant(Instruction *I, Constant *C) {
139 markConstant(ValueState[I], I, C);
142 // markValueOverdefined - Make a value be marked as "overdefined". If the
143 // value is not already overdefined, add it to the instruction work list so
144 // that the users of the instruction are updated later.
146 inline void markOverdefined(InstVal &IV, Instruction *I) {
147 if (IV.markOverdefined()) {
148 DEBUG(std::cerr << "markOverdefined: " << *I);
149 InstWorkList.push_back(I); // Only instructions go on the work list
152 inline void markOverdefined(Instruction *I) {
153 markOverdefined(ValueState[I], I);
156 // getValueState - Return the InstVal object that corresponds to the value.
157 // This function is necessary because not all values should start out in the
158 // underdefined state... Argument's should be overdefined, and
159 // constants should be marked as constants. If a value is not known to be an
160 // Instruction object, then use this accessor to get its value from the map.
162 inline InstVal &getValueState(Value *V) {
163 std::map<Value*, InstVal>::iterator I = ValueState.find(V);
164 if (I != ValueState.end()) return I->second; // Common case, in the map
166 if (Constant *CPV = dyn_cast<Constant>(V)) { // Constants are constant
167 ValueState[CPV].markConstant(CPV);
168 } else if (isa<Argument>(V)) { // Arguments are overdefined
169 ValueState[V].markOverdefined();
170 } else if (GlobalValue *GV = dyn_cast<GlobalValue>(V)) {
171 // The address of a global is a constant...
172 ValueState[V].markConstant(ConstantPointerRef::get(GV));
174 // All others are underdefined by default...
175 return ValueState[V];
178 // markEdgeExecutable - Mark a basic block as executable, adding it to the BB
179 // work list if it is not already executable...
181 void markEdgeExecutable(BasicBlock *Source, BasicBlock *Dest) {
182 if (!KnownFeasibleEdges.insert(Edge(Source, Dest)).second)
183 return; // This edge is already known to be executable!
185 if (BBExecutable.count(Dest)) {
186 DEBUG(std::cerr << "Marking Edge Executable: " << Source->getName()
187 << " -> " << Dest->getName() << "\n");
189 // The destination is already executable, but we just made an edge
190 // feasible that wasn't before. Revisit the PHI nodes in the block
191 // because they have potentially new operands.
192 for (BasicBlock::iterator I = Dest->begin();
193 PHINode *PN = dyn_cast<PHINode>(I); ++I)
197 DEBUG(std::cerr << "Marking Block Executable: " << Dest->getName()<<"\n");
198 BBExecutable.insert(Dest); // Basic block is executable!
199 BBWorkList.push_back(Dest); // Add the block to the work list!
204 // visit implementations - Something changed in this instruction... Either an
205 // operand made a transition, or the instruction is newly executable. Change
206 // the value type of I to reflect these changes if appropriate.
208 void visitPHINode(PHINode &I);
211 void visitReturnInst(ReturnInst &I) { /*does not have an effect*/ }
212 void visitTerminatorInst(TerminatorInst &TI);
214 void visitCastInst(CastInst &I);
215 void visitSelectInst(SelectInst &I);
216 void visitBinaryOperator(Instruction &I);
217 void visitShiftInst(ShiftInst &I) { visitBinaryOperator(I); }
219 // Instructions that cannot be folded away...
220 void visitStoreInst (Instruction &I) { /*returns void*/ }
221 void visitLoadInst (LoadInst &I);
222 void visitGetElementPtrInst(GetElementPtrInst &I);
223 void visitCallInst (Instruction &I) { markOverdefined(&I); }
224 void visitInvokeInst (TerminatorInst &I) {
225 if (I.getType() != Type::VoidTy) markOverdefined(&I);
226 visitTerminatorInst(I);
228 void visitUnwindInst (TerminatorInst &I) { /*returns void*/ }
229 void visitAllocationInst(Instruction &I) { markOverdefined(&I); }
230 void visitVANextInst (Instruction &I) { markOverdefined(&I); }
231 void visitVAArgInst (Instruction &I) { markOverdefined(&I); }
232 void visitFreeInst (Instruction &I) { /*returns void*/ }
234 void visitInstruction(Instruction &I) {
235 // If a new instruction is added to LLVM that we don't handle...
236 std::cerr << "SCCP: Don't know how to handle: " << I;
237 markOverdefined(&I); // Just in case
240 // getFeasibleSuccessors - Return a vector of booleans to indicate which
241 // successors are reachable from a given terminator instruction.
243 void getFeasibleSuccessors(TerminatorInst &TI, std::vector<bool> &Succs);
245 // isEdgeFeasible - Return true if the control flow edge from the 'From' basic
246 // block to the 'To' basic block is currently feasible...
248 bool isEdgeFeasible(BasicBlock *From, BasicBlock *To);
250 // OperandChangedState - This method is invoked on all of the users of an
251 // instruction that was just changed state somehow.... Based on this
252 // information, we need to update the specified user of this instruction.
254 void OperandChangedState(User *U) {
255 // Only instructions use other variable values!
256 Instruction &I = cast<Instruction>(*U);
257 if (BBExecutable.count(I.getParent())) // Inst is executable?
262 RegisterOpt<SCCP> X("sccp", "Sparse Conditional Constant Propagation");
263 } // end anonymous namespace
266 // createSCCPPass - This is the public interface to this file...
267 Pass *llvm::createSCCPPass() {
272 //===----------------------------------------------------------------------===//
273 // SCCP Class Implementation
276 // runOnFunction() - Run the Sparse Conditional Constant Propagation algorithm,
277 // and return true if the function was modified.
279 bool SCCP::runOnFunction(Function &F) {
280 // Mark the first block of the function as being executable...
281 BBExecutable.insert(F.begin()); // Basic block is executable!
282 BBWorkList.push_back(F.begin()); // Add the block to the work list!
284 // Process the work lists until their are empty!
285 while (!BBWorkList.empty() || !InstWorkList.empty()) {
286 // Process the instruction work list...
287 while (!InstWorkList.empty()) {
288 Instruction *I = InstWorkList.back();
289 InstWorkList.pop_back();
291 DEBUG(std::cerr << "\nPopped off I-WL: " << I);
293 // "I" got into the work list because it either made the transition from
294 // bottom to constant, or to Overdefined.
296 // Update all of the users of this instruction's value...
298 for_each(I->use_begin(), I->use_end(),
299 bind_obj(this, &SCCP::OperandChangedState));
302 // Process the basic block work list...
303 while (!BBWorkList.empty()) {
304 BasicBlock *BB = BBWorkList.back();
305 BBWorkList.pop_back();
307 DEBUG(std::cerr << "\nPopped off BBWL: " << BB);
309 // Notify all instructions in this basic block that they are newly
316 for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I)
317 if (!BBExecutable.count(I))
318 std::cerr << "BasicBlock Dead:" << *I;
321 // Iterate over all of the instructions in a function, replacing them with
322 // constants if we have found them to be of constant values.
324 bool MadeChanges = false;
325 for (Function::iterator BB = F.begin(), BBE = F.end(); BB != BBE; ++BB)
326 for (BasicBlock::iterator BI = BB->begin(); BI != BB->end();) {
327 Instruction &Inst = *BI;
328 InstVal &IV = ValueState[&Inst];
329 if (IV.isConstant()) {
330 Constant *Const = IV.getConstant();
331 DEBUG(std::cerr << "Constant: " << Const << " = " << Inst);
333 // Replaces all of the uses of a variable with uses of the constant.
334 Inst.replaceAllUsesWith(Const);
336 // Remove the operator from the list of definitions... and delete it.
337 BI = BB->getInstList().erase(BI);
339 // Hey, we just changed something!
347 // Reset state so that the next invocation will have empty data structures
348 BBExecutable.clear();
350 std::vector<Instruction*>().swap(InstWorkList);
351 std::vector<BasicBlock*>().swap(BBWorkList);
357 // getFeasibleSuccessors - Return a vector of booleans to indicate which
358 // successors are reachable from a given terminator instruction.
360 void SCCP::getFeasibleSuccessors(TerminatorInst &TI, std::vector<bool> &Succs) {
361 Succs.resize(TI.getNumSuccessors());
362 if (BranchInst *BI = dyn_cast<BranchInst>(&TI)) {
363 if (BI->isUnconditional()) {
366 InstVal &BCValue = getValueState(BI->getCondition());
367 if (BCValue.isOverdefined() ||
368 (BCValue.isConstant() && !isa<ConstantBool>(BCValue.getConstant()))) {
369 // Overdefined condition variables, and branches on unfoldable constant
370 // conditions, mean the branch could go either way.
371 Succs[0] = Succs[1] = true;
372 } else if (BCValue.isConstant()) {
373 // Constant condition variables mean the branch can only go a single way
374 Succs[BCValue.getConstant() == ConstantBool::False] = true;
377 } else if (InvokeInst *II = dyn_cast<InvokeInst>(&TI)) {
378 // Invoke instructions successors are always executable.
379 Succs[0] = Succs[1] = true;
380 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(&TI)) {
381 InstVal &SCValue = getValueState(SI->getCondition());
382 if (SCValue.isOverdefined() || // Overdefined condition?
383 (SCValue.isConstant() && !isa<ConstantInt>(SCValue.getConstant()))) {
384 // All destinations are executable!
385 Succs.assign(TI.getNumSuccessors(), true);
386 } else if (SCValue.isConstant()) {
387 Constant *CPV = SCValue.getConstant();
388 // Make sure to skip the "default value" which isn't a value
389 for (unsigned i = 1, E = SI->getNumSuccessors(); i != E; ++i) {
390 if (SI->getSuccessorValue(i) == CPV) {// Found the right branch...
396 // Constant value not equal to any of the branches... must execute
397 // default branch then...
401 std::cerr << "SCCP: Don't know how to handle: " << TI;
402 Succs.assign(TI.getNumSuccessors(), true);
407 // isEdgeFeasible - Return true if the control flow edge from the 'From' basic
408 // block to the 'To' basic block is currently feasible...
410 bool SCCP::isEdgeFeasible(BasicBlock *From, BasicBlock *To) {
411 assert(BBExecutable.count(To) && "Dest should always be alive!");
413 // Make sure the source basic block is executable!!
414 if (!BBExecutable.count(From)) return false;
416 // Check to make sure this edge itself is actually feasible now...
417 TerminatorInst *TI = From->getTerminator();
418 if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
419 if (BI->isUnconditional())
422 InstVal &BCValue = getValueState(BI->getCondition());
423 if (BCValue.isOverdefined()) {
424 // Overdefined condition variables mean the branch could go either way.
426 } else if (BCValue.isConstant()) {
427 // Not branching on an evaluatable constant?
428 if (!isa<ConstantBool>(BCValue.getConstant())) return true;
430 // Constant condition variables mean the branch can only go a single way
431 return BI->getSuccessor(BCValue.getConstant() ==
432 ConstantBool::False) == To;
436 } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
437 // Invoke instructions successors are always executable.
439 } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
440 InstVal &SCValue = getValueState(SI->getCondition());
441 if (SCValue.isOverdefined()) { // Overdefined condition?
442 // All destinations are executable!
444 } else if (SCValue.isConstant()) {
445 Constant *CPV = SCValue.getConstant();
446 if (!isa<ConstantInt>(CPV))
447 return true; // not a foldable constant?
449 // Make sure to skip the "default value" which isn't a value
450 for (unsigned i = 1, E = SI->getNumSuccessors(); i != E; ++i)
451 if (SI->getSuccessorValue(i) == CPV) // Found the taken branch...
452 return SI->getSuccessor(i) == To;
454 // Constant value not equal to any of the branches... must execute
455 // default branch then...
456 return SI->getDefaultDest() == To;
460 std::cerr << "Unknown terminator instruction: " << *TI;
465 // visit Implementations - Something changed in this instruction... Either an
466 // operand made a transition, or the instruction is newly executable. Change
467 // the value type of I to reflect these changes if appropriate. This method
468 // makes sure to do the following actions:
470 // 1. If a phi node merges two constants in, and has conflicting value coming
471 // from different branches, or if the PHI node merges in an overdefined
472 // value, then the PHI node becomes overdefined.
473 // 2. If a phi node merges only constants in, and they all agree on value, the
474 // PHI node becomes a constant value equal to that.
475 // 3. If V <- x (op) y && isConstant(x) && isConstant(y) V = Constant
476 // 4. If V <- x (op) y && (isOverdefined(x) || isOverdefined(y)) V = Overdefined
477 // 5. If V <- MEM or V <- CALL or V <- (unknown) then V = Overdefined
478 // 6. If a conditional branch has a value that is constant, make the selected
479 // destination executable
480 // 7. If a conditional branch has a value that is overdefined, make all
481 // successors executable.
483 void SCCP::visitPHINode(PHINode &PN) {
484 InstVal &PNIV = getValueState(&PN);
485 if (PNIV.isOverdefined()) {
486 // There may be instructions using this PHI node that are not overdefined
487 // themselves. If so, make sure that they know that the PHI node operand
489 std::multimap<PHINode*, Instruction*>::iterator I, E;
490 tie(I, E) = UsersOfOverdefinedPHIs.equal_range(&PN);
492 std::vector<Instruction*> Users;
493 Users.reserve(std::distance(I, E));
494 for (; I != E; ++I) Users.push_back(I->second);
495 while (!Users.empty()) {
500 return; // Quick exit
503 // Look at all of the executable operands of the PHI node. If any of them
504 // are overdefined, the PHI becomes overdefined as well. If they are all
505 // constant, and they agree with each other, the PHI becomes the identical
506 // constant. If they are constant and don't agree, the PHI is overdefined.
507 // If there are no executable operands, the PHI remains undefined.
509 Constant *OperandVal = 0;
510 for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
511 InstVal &IV = getValueState(PN.getIncomingValue(i));
512 if (IV.isUndefined()) continue; // Doesn't influence PHI node.
514 if (isEdgeFeasible(PN.getIncomingBlock(i), PN.getParent())) {
515 if (IV.isOverdefined()) { // PHI node becomes overdefined!
516 markOverdefined(PNIV, &PN);
520 if (OperandVal == 0) { // Grab the first value...
521 OperandVal = IV.getConstant();
522 } else { // Another value is being merged in!
523 // There is already a reachable operand. If we conflict with it,
524 // then the PHI node becomes overdefined. If we agree with it, we
527 // Check to see if there are two different constants merging...
528 if (IV.getConstant() != OperandVal) {
529 // Yes there is. This means the PHI node is not constant.
530 // You must be overdefined poor PHI.
532 markOverdefined(PNIV, &PN); // The PHI node now becomes overdefined
533 return; // I'm done analyzing you
539 // If we exited the loop, this means that the PHI node only has constant
540 // arguments that agree with each other(and OperandVal is the constant) or
541 // OperandVal is null because there are no defined incoming arguments. If
542 // this is the case, the PHI remains undefined.
545 markConstant(PNIV, &PN, OperandVal); // Acquire operand value
548 void SCCP::visitTerminatorInst(TerminatorInst &TI) {
549 std::vector<bool> SuccFeasible;
550 getFeasibleSuccessors(TI, SuccFeasible);
552 BasicBlock *BB = TI.getParent();
554 // Mark all feasible successors executable...
555 for (unsigned i = 0, e = SuccFeasible.size(); i != e; ++i)
557 markEdgeExecutable(BB, TI.getSuccessor(i));
560 void SCCP::visitCastInst(CastInst &I) {
561 Value *V = I.getOperand(0);
562 InstVal &VState = getValueState(V);
563 if (VState.isOverdefined()) // Inherit overdefinedness of operand
565 else if (VState.isConstant()) // Propagate constant value
566 markConstant(&I, ConstantExpr::getCast(VState.getConstant(), I.getType()));
569 void SCCP::visitSelectInst(SelectInst &I) {
570 InstVal &CondValue = getValueState(I.getCondition());
571 if (CondValue.isOverdefined())
573 else if (CondValue.isConstant()) {
574 if (CondValue.getConstant() == ConstantBool::True) {
575 InstVal &Val = getValueState(I.getTrueValue());
576 if (Val.isOverdefined())
578 else if (Val.isConstant())
579 markConstant(&I, Val.getConstant());
580 } else if (CondValue.getConstant() == ConstantBool::False) {
581 InstVal &Val = getValueState(I.getFalseValue());
582 if (Val.isOverdefined())
584 else if (Val.isConstant())
585 markConstant(&I, Val.getConstant());
591 // Handle BinaryOperators and Shift Instructions...
592 void SCCP::visitBinaryOperator(Instruction &I) {
593 InstVal &IV = ValueState[&I];
594 if (IV.isOverdefined()) return;
596 InstVal &V1State = getValueState(I.getOperand(0));
597 InstVal &V2State = getValueState(I.getOperand(1));
599 if (V1State.isOverdefined() || V2State.isOverdefined()) {
600 // If both operands are PHI nodes, it is possible that this instruction has
601 // a constant value, despite the fact that the PHI node doesn't. Check for
602 // this condition now.
603 if (PHINode *PN1 = dyn_cast<PHINode>(I.getOperand(0)))
604 if (PHINode *PN2 = dyn_cast<PHINode>(I.getOperand(1)))
605 if (PN1->getParent() == PN2->getParent()) {
606 // Since the two PHI nodes are in the same basic block, they must have
607 // entries for the same predecessors. Walk the predecessor list, and
608 // if all of the incoming values are constants, and the result of
609 // evaluating this expression with all incoming value pairs is the
610 // same, then this expression is a constant even though the PHI node
611 // is not a constant!
613 for (unsigned i = 0, e = PN1->getNumIncomingValues(); i != e; ++i) {
614 InstVal &In1 = getValueState(PN1->getIncomingValue(i));
615 BasicBlock *InBlock = PN1->getIncomingBlock(i);
616 InstVal &In2 =getValueState(PN2->getIncomingValueForBlock(InBlock));
618 if (In1.isOverdefined() || In2.isOverdefined()) {
619 Result.markOverdefined();
620 break; // Cannot fold this operation over the PHI nodes!
621 } else if (In1.isConstant() && In2.isConstant()) {
622 Constant *V = ConstantExpr::get(I.getOpcode(), In1.getConstant(),
624 if (Result.isUndefined())
625 Result.markConstant(V);
626 else if (Result.isConstant() && Result.getConstant() != V) {
627 Result.markOverdefined();
633 // If we found a constant value here, then we know the instruction is
634 // constant despite the fact that the PHI nodes are overdefined.
635 if (Result.isConstant()) {
636 markConstant(IV, &I, Result.getConstant());
637 // Remember that this instruction is virtually using the PHI node
639 UsersOfOverdefinedPHIs.insert(std::make_pair(PN1, &I));
640 UsersOfOverdefinedPHIs.insert(std::make_pair(PN2, &I));
642 } else if (Result.isUndefined()) {
646 // Okay, this really is overdefined now. Since we might have
647 // speculatively thought that this was not overdefined before, and
648 // added ourselves to the UsersOfOverdefinedPHIs list for the PHIs,
649 // make sure to clean out any entries that we put there, for
651 std::multimap<PHINode*, Instruction*>::iterator It, E;
652 tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN1);
654 if (It->second == &I) {
655 UsersOfOverdefinedPHIs.erase(It++);
659 tie(It, E) = UsersOfOverdefinedPHIs.equal_range(PN2);
661 if (It->second == &I) {
662 UsersOfOverdefinedPHIs.erase(It++);
668 markOverdefined(IV, &I);
669 } else if (V1State.isConstant() && V2State.isConstant()) {
670 markConstant(IV, &I, ConstantExpr::get(I.getOpcode(), V1State.getConstant(),
671 V2State.getConstant()));
675 // Handle getelementptr instructions... if all operands are constants then we
676 // can turn this into a getelementptr ConstantExpr.
678 void SCCP::visitGetElementPtrInst(GetElementPtrInst &I) {
679 InstVal &IV = ValueState[&I];
680 if (IV.isOverdefined()) return;
682 std::vector<Constant*> Operands;
683 Operands.reserve(I.getNumOperands());
685 for (unsigned i = 0, e = I.getNumOperands(); i != e; ++i) {
686 InstVal &State = getValueState(I.getOperand(i));
687 if (State.isUndefined())
688 return; // Operands are not resolved yet...
689 else if (State.isOverdefined()) {
690 markOverdefined(IV, &I);
693 assert(State.isConstant() && "Unknown state!");
694 Operands.push_back(State.getConstant());
697 Constant *Ptr = Operands[0];
698 Operands.erase(Operands.begin()); // Erase the pointer from idx list...
700 markConstant(IV, &I, ConstantExpr::getGetElementPtr(Ptr, Operands));
703 /// GetGEPGlobalInitializer - Given a constant and a getelementptr constantexpr,
704 /// return the constant value being addressed by the constant expression, or
705 /// null if something is funny.
707 static Constant *GetGEPGlobalInitializer(Constant *C, ConstantExpr *CE) {
708 if (CE->getOperand(1) != Constant::getNullValue(Type::LongTy))
709 return 0; // Do not allow stepping over the value!
711 // Loop over all of the operands, tracking down which value we are
713 for (unsigned i = 2, e = CE->getNumOperands(); i != e; ++i)
714 if (ConstantUInt *CU = dyn_cast<ConstantUInt>(CE->getOperand(i))) {
715 ConstantStruct *CS = dyn_cast<ConstantStruct>(C);
716 if (CS == 0) return 0;
717 if (CU->getValue() >= CS->getValues().size()) return 0;
718 C = cast<Constant>(CS->getValues()[CU->getValue()]);
719 } else if (ConstantSInt *CS = dyn_cast<ConstantSInt>(CE->getOperand(i))) {
720 ConstantArray *CA = dyn_cast<ConstantArray>(C);
721 if (CA == 0) return 0;
722 if ((uint64_t)CS->getValue() >= CA->getValues().size()) return 0;
723 C = cast<Constant>(CA->getValues()[CS->getValue()]);
729 // Handle load instructions. If the operand is a constant pointer to a constant
730 // global, we can replace the load with the loaded constant value!
731 void SCCP::visitLoadInst(LoadInst &I) {
732 InstVal &IV = ValueState[&I];
733 if (IV.isOverdefined()) return;
735 InstVal &PtrVal = getValueState(I.getOperand(0));
736 if (PtrVal.isUndefined()) return; // The pointer is not resolved yet!
737 if (PtrVal.isConstant() && !I.isVolatile()) {
738 Value *Ptr = PtrVal.getConstant();
739 if (isa<ConstantPointerNull>(Ptr)) {
741 markConstant(IV, &I, Constant::getNullValue(I.getType()));
745 if (ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(Ptr))
746 Ptr = CPR->getValue();
748 // Transform load (constant global) into the value loaded.
749 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(Ptr))
750 if (GV->isConstant() && !GV->isExternal()) {
751 markConstant(IV, &I, GV->getInitializer());
755 // Transform load (constantexpr_GEP global, 0, ...) into the value loaded.
756 if (ConstantExpr *CE = dyn_cast<ConstantExpr>(Ptr))
757 if (CE->getOpcode() == Instruction::GetElementPtr)
758 if (ConstantPointerRef *G
759 = dyn_cast<ConstantPointerRef>(CE->getOperand(0)))
760 if (GlobalVariable *GV = dyn_cast<GlobalVariable>(G->getValue()))
761 if (GV->isConstant() && !GV->isExternal())
763 GetGEPGlobalInitializer(GV->getInitializer(), CE)) {
764 markConstant(IV, &I, V);
769 // Otherwise we cannot say for certain what value this load will produce.
771 markOverdefined(IV, &I);