1 //===- SimplifyCFG.cpp - Code to perform CFG simplification ---------------===//
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 // Peephole optimize the CFG.
12 //===----------------------------------------------------------------------===//
14 #include "llvm/Transforms/Utils/Local.h"
15 #include "llvm/Constants.h"
16 #include "llvm/Instructions.h"
17 #include "llvm/Type.h"
18 #include "llvm/Support/CFG.h"
23 // PropagatePredecessorsForPHIs - This gets "Succ" ready to have the
24 // predecessors from "BB". This is a little tricky because "Succ" has PHI
25 // nodes, which need to have extra slots added to them to hold the merge edges
26 // from BB's predecessors, and BB itself might have had PHI nodes in it. This
27 // function returns true (failure) if the Succ BB already has a predecessor that
28 // is a predecessor of BB and incoming PHI arguments would not be discernible.
30 // Assumption: Succ is the single successor for BB.
32 static bool PropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
33 assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
35 if (!isa<PHINode>(Succ->front()))
36 return false; // We can make the transformation, no problem.
38 // If there is more than one predecessor, and there are PHI nodes in
39 // the successor, then we need to add incoming edges for the PHI nodes
41 const std::vector<BasicBlock*> BBPreds(pred_begin(BB), pred_end(BB));
43 // Check to see if one of the predecessors of BB is already a predecessor of
44 // Succ. If so, we cannot do the transformation if there are any PHI nodes
45 // with incompatible values coming in from the two edges!
47 for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ); PI != PE; ++PI)
48 if (find(BBPreds.begin(), BBPreds.end(), *PI) != BBPreds.end()) {
49 // Loop over all of the PHI nodes checking to see if there are
50 // incompatible values coming in.
51 for (BasicBlock::iterator I = Succ->begin();
52 PHINode *PN = dyn_cast<PHINode>(I); ++I) {
53 // Loop up the entries in the PHI node for BB and for *PI if the values
54 // coming in are non-equal, we cannot merge these two blocks (instead we
55 // should insert a conditional move or something, then merge the
57 int Idx1 = PN->getBasicBlockIndex(BB);
58 int Idx2 = PN->getBasicBlockIndex(*PI);
59 assert(Idx1 != -1 && Idx2 != -1 &&
60 "Didn't have entries for my predecessors??");
61 if (PN->getIncomingValue(Idx1) != PN->getIncomingValue(Idx2))
62 return true; // Values are not equal...
66 // Loop over all of the PHI nodes in the successor BB
67 for (BasicBlock::iterator I = Succ->begin();
68 PHINode *PN = dyn_cast<PHINode>(I); ++I) {
69 Value *OldVal = PN->removeIncomingValue(BB, false);
70 assert(OldVal && "No entry in PHI for Pred BB!");
72 // If this incoming value is one of the PHI nodes in BB...
73 if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
74 PHINode *OldValPN = cast<PHINode>(OldVal);
75 for (std::vector<BasicBlock*>::const_iterator PredI = BBPreds.begin(),
76 End = BBPreds.end(); PredI != End; ++PredI) {
77 PN->addIncoming(OldValPN->getIncomingValueForBlock(*PredI), *PredI);
80 for (std::vector<BasicBlock*>::const_iterator PredI = BBPreds.begin(),
81 End = BBPreds.end(); PredI != End; ++PredI) {
82 // Add an incoming value for each of the new incoming values...
83 PN->addIncoming(OldVal, *PredI);
90 /// GetIfCondition - Given a basic block (BB) with two predecessors (and
91 /// presumably PHI nodes in it), check to see if the merge at this block is due
92 /// to an "if condition". If so, return the boolean condition that determines
93 /// which entry into BB will be taken. Also, return by references the block
94 /// that will be entered from if the condition is true, and the block that will
95 /// be entered if the condition is false.
98 static Value *GetIfCondition(BasicBlock *BB,
99 BasicBlock *&IfTrue, BasicBlock *&IfFalse) {
100 assert(std::distance(pred_begin(BB), pred_end(BB)) == 2 &&
101 "Function can only handle blocks with 2 predecessors!");
102 BasicBlock *Pred1 = *pred_begin(BB);
103 BasicBlock *Pred2 = *++pred_begin(BB);
105 // We can only handle branches. Other control flow will be lowered to
106 // branches if possible anyway.
107 if (!isa<BranchInst>(Pred1->getTerminator()) ||
108 !isa<BranchInst>(Pred2->getTerminator()))
110 BranchInst *Pred1Br = cast<BranchInst>(Pred1->getTerminator());
111 BranchInst *Pred2Br = cast<BranchInst>(Pred2->getTerminator());
113 // Eliminate code duplication by ensuring that Pred1Br is conditional if
115 if (Pred2Br->isConditional()) {
116 // If both branches are conditional, we don't have an "if statement". In
117 // reality, we could transform this case, but since the condition will be
118 // required anyway, we stand no chance of eliminating it, so the xform is
119 // probably not profitable.
120 if (Pred1Br->isConditional())
123 std::swap(Pred1, Pred2);
124 std::swap(Pred1Br, Pred2Br);
127 if (Pred1Br->isConditional()) {
128 // If we found a conditional branch predecessor, make sure that it branches
129 // to BB and Pred2Br. If it doesn't, this isn't an "if statement".
130 if (Pred1Br->getSuccessor(0) == BB &&
131 Pred1Br->getSuccessor(1) == Pred2) {
134 } else if (Pred1Br->getSuccessor(0) == Pred2 &&
135 Pred1Br->getSuccessor(1) == BB) {
139 // We know that one arm of the conditional goes to BB, so the other must
140 // go somewhere unrelated, and this must not be an "if statement".
144 // The only thing we have to watch out for here is to make sure that Pred2
145 // doesn't have incoming edges from other blocks. If it does, the condition
146 // doesn't dominate BB.
147 if (++pred_begin(Pred2) != pred_end(Pred2))
150 return Pred1Br->getCondition();
153 // Ok, if we got here, both predecessors end with an unconditional branch to
154 // BB. Don't panic! If both blocks only have a single (identical)
155 // predecessor, and THAT is a conditional branch, then we're all ok!
156 if (pred_begin(Pred1) == pred_end(Pred1) ||
157 ++pred_begin(Pred1) != pred_end(Pred1) ||
158 pred_begin(Pred2) == pred_end(Pred2) ||
159 ++pred_begin(Pred2) != pred_end(Pred2) ||
160 *pred_begin(Pred1) != *pred_begin(Pred2))
163 // Otherwise, if this is a conditional branch, then we can use it!
164 BasicBlock *CommonPred = *pred_begin(Pred1);
165 if (BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator())) {
166 assert(BI->isConditional() && "Two successors but not conditional?");
167 if (BI->getSuccessor(0) == Pred1) {
174 return BI->getCondition();
180 // If we have a merge point of an "if condition" as accepted above, return true
181 // if the specified value dominates the block. We don't handle the true
182 // generality of domination here, just a special case which works well enough
184 static bool DominatesMergePoint(Value *V, BasicBlock *BB) {
185 if (Instruction *I = dyn_cast<Instruction>(V)) {
186 BasicBlock *PBB = I->getParent();
187 // If this instruction is defined in a block that contains an unconditional
188 // branch to BB, then it must be in the 'conditional' part of the "if
190 if (isa<BranchInst>(PBB->getTerminator()) &&
191 cast<BranchInst>(PBB->getTerminator())->isUnconditional() &&
192 cast<BranchInst>(PBB->getTerminator())->getSuccessor(0) == BB)
195 // We also don't want to allow wierd loops that might have the "if
196 // condition" in the bottom of this block.
197 if (PBB == BB) return false;
200 // Non-instructions all dominate instructions.
204 // GatherConstantSetEQs - Given a potentially 'or'd together collection of seteq
205 // instructions that compare a value against a constant, return the value being
206 // compared, and stick the constant into the Values vector.
207 static Value *GatherConstantSetEQs(Value *V, std::vector<Constant*> &Values) {
208 if (Instruction *Inst = dyn_cast<Instruction>(V))
209 if (Inst->getOpcode() == Instruction::SetEQ) {
210 if (Constant *C = dyn_cast<Constant>(Inst->getOperand(1))) {
212 return Inst->getOperand(0);
213 } else if (Constant *C = dyn_cast<Constant>(Inst->getOperand(0))) {
215 return Inst->getOperand(1);
217 } else if (Inst->getOpcode() == Instruction::Or) {
218 if (Value *LHS = GatherConstantSetEQs(Inst->getOperand(0), Values))
219 if (Value *RHS = GatherConstantSetEQs(Inst->getOperand(1), Values))
226 // GatherConstantSetNEs - Given a potentially 'and'd together collection of
227 // setne instructions that compare a value against a constant, return the value
228 // being compared, and stick the constant into the Values vector.
229 static Value *GatherConstantSetNEs(Value *V, std::vector<Constant*> &Values) {
230 if (Instruction *Inst = dyn_cast<Instruction>(V))
231 if (Inst->getOpcode() == Instruction::SetNE) {
232 if (Constant *C = dyn_cast<Constant>(Inst->getOperand(1))) {
234 return Inst->getOperand(0);
235 } else if (Constant *C = dyn_cast<Constant>(Inst->getOperand(0))) {
237 return Inst->getOperand(1);
239 } else if (Inst->getOpcode() == Instruction::Cast) {
240 // Cast of X to bool is really a comparison against zero.
241 assert(Inst->getType() == Type::BoolTy && "Can only handle bool values!");
242 Values.push_back(Constant::getNullValue(Inst->getOperand(0)->getType()));
243 return Inst->getOperand(0);
244 } else if (Inst->getOpcode() == Instruction::And) {
245 if (Value *LHS = GatherConstantSetNEs(Inst->getOperand(0), Values))
246 if (Value *RHS = GatherConstantSetNEs(Inst->getOperand(1), Values))
255 /// GatherValueComparisons - If the specified Cond is an 'and' or 'or' of a
256 /// bunch of comparisons of one value against constants, return the value and
257 /// the constants being compared.
258 static bool GatherValueComparisons(Instruction *Cond, Value *&CompVal,
259 std::vector<Constant*> &Values) {
260 if (Cond->getOpcode() == Instruction::Or) {
261 CompVal = GatherConstantSetEQs(Cond, Values);
263 // Return true to indicate that the condition is true if the CompVal is
264 // equal to one of the constants.
266 } else if (Cond->getOpcode() == Instruction::And) {
267 CompVal = GatherConstantSetNEs(Cond, Values);
269 // Return false to indicate that the condition is false if the CompVal is
270 // equal to one of the constants.
276 /// ErasePossiblyDeadInstructionTree - If the specified instruction is dead and
277 /// has no side effects, nuke it. If it uses any instructions that become dead
278 /// because the instruction is now gone, nuke them too.
279 static void ErasePossiblyDeadInstructionTree(Instruction *I) {
280 if (isInstructionTriviallyDead(I)) {
281 std::vector<Value*> Operands(I->op_begin(), I->op_end());
282 I->getParent()->getInstList().erase(I);
283 for (unsigned i = 0, e = Operands.size(); i != e; ++i)
284 if (Instruction *OpI = dyn_cast<Instruction>(Operands[i]))
285 ErasePossiblyDeadInstructionTree(OpI);
289 // SimplifyCFG - This function is used to do simplification of a CFG. For
290 // example, it adjusts branches to branches to eliminate the extra hop, it
291 // eliminates unreachable basic blocks, and does other "peephole" optimization
292 // of the CFG. It returns true if a modification was made.
294 // WARNING: The entry node of a function may not be simplified.
296 bool llvm::SimplifyCFG(BasicBlock *BB) {
297 bool Changed = false;
298 Function *M = BB->getParent();
300 assert(BB && BB->getParent() && "Block not embedded in function!");
301 assert(BB->getTerminator() && "Degenerate basic block encountered!");
302 assert(&BB->getParent()->front() != BB && "Can't Simplify entry block!");
304 // Remove basic blocks that have no predecessors... which are unreachable.
305 if (pred_begin(BB) == pred_end(BB)) {
306 //cerr << "Removing BB: \n" << BB;
308 // Loop through all of our successors and make sure they know that one
309 // of their predecessors is going away.
310 for_each(succ_begin(BB), succ_end(BB),
311 std::bind2nd(std::mem_fun(&BasicBlock::removePredecessor), BB));
313 while (!BB->empty()) {
314 Instruction &I = BB->back();
315 // If this instruction is used, replace uses with an arbitrary
316 // constant value. Because control flow can't get here, we don't care
317 // what we replace the value with. Note that since this block is
318 // unreachable, and all values contained within it must dominate their
319 // uses, that all uses will eventually be removed.
321 // Make all users of this instruction reference the constant instead
322 I.replaceAllUsesWith(Constant::getNullValue(I.getType()));
324 // Remove the instruction from the basic block
325 BB->getInstList().pop_back();
327 M->getBasicBlockList().erase(BB);
331 // Check to see if we can constant propagate this terminator instruction
333 Changed |= ConstantFoldTerminator(BB);
335 // Check to see if this block has no non-phi instructions and only a single
336 // successor. If so, replace references to this basic block with references
338 succ_iterator SI(succ_begin(BB));
339 if (SI != succ_end(BB) && ++SI == succ_end(BB)) { // One succ?
341 BasicBlock::iterator BBI = BB->begin(); // Skip over phi nodes...
342 while (isa<PHINode>(*BBI)) ++BBI;
344 if (BBI->isTerminator()) { // Terminator is the only non-phi instruction!
345 BasicBlock *Succ = *succ_begin(BB); // There is exactly one successor
347 if (Succ != BB) { // Arg, don't hurt infinite loops!
348 // If our successor has PHI nodes, then we need to update them to
349 // include entries for BB's predecessors, not for BB itself.
350 // Be careful though, if this transformation fails (returns true) then
351 // we cannot do this transformation!
353 if (!PropagatePredecessorsForPHIs(BB, Succ)) {
354 //cerr << "Killing Trivial BB: \n" << BB;
355 std::string OldName = BB->getName();
357 std::vector<BasicBlock*>
358 OldSuccPreds(pred_begin(Succ), pred_end(Succ));
360 // Move all PHI nodes in BB to Succ if they are alive, otherwise
362 while (PHINode *PN = dyn_cast<PHINode>(&BB->front()))
364 BB->getInstList().erase(BB->begin()); // Nuke instruction...
366 // The instruction is alive, so this means that Succ must have
367 // *ONLY* had BB as a predecessor, and the PHI node is still valid
368 // now. Simply move it into Succ, because we know that BB
369 // strictly dominated Succ.
370 BB->getInstList().remove(BB->begin());
371 Succ->getInstList().push_front(PN);
373 // We need to add new entries for the PHI node to account for
374 // predecessors of Succ that the PHI node does not take into
375 // account. At this point, since we know that BB dominated succ,
376 // this means that we should any newly added incoming edges should
377 // use the PHI node as the value for these edges, because they are
380 for (unsigned i = 0, e = OldSuccPreds.size(); i != e; ++i)
381 if (OldSuccPreds[i] != BB)
382 PN->addIncoming(PN, OldSuccPreds[i]);
385 // Everything that jumped to BB now goes to Succ...
386 BB->replaceAllUsesWith(Succ);
388 // Delete the old basic block...
389 M->getBasicBlockList().erase(BB);
391 if (!OldName.empty() && !Succ->hasName()) // Transfer name if we can
392 Succ->setName(OldName);
394 //cerr << "Function after removal: \n" << M;
401 // If this is a returning block with only PHI nodes in it, fold the return
402 // instruction into any unconditional branch predecessors.
403 if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
404 BasicBlock::iterator BBI = BB->getTerminator();
405 if (BBI == BB->begin() || isa<PHINode>(--BBI)) {
406 // Find predecessors that end with unconditional branches.
407 std::vector<BasicBlock*> UncondBranchPreds;
408 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
409 TerminatorInst *PTI = (*PI)->getTerminator();
410 if (BranchInst *BI = dyn_cast<BranchInst>(PTI))
411 if (BI->isUnconditional())
412 UncondBranchPreds.push_back(*PI);
415 // If we found some, do the transformation!
416 if (!UncondBranchPreds.empty()) {
417 while (!UncondBranchPreds.empty()) {
418 BasicBlock *Pred = UncondBranchPreds.back();
419 UncondBranchPreds.pop_back();
420 Instruction *UncondBranch = Pred->getTerminator();
421 // Clone the return and add it to the end of the predecessor.
422 Instruction *NewRet = RI->clone();
423 Pred->getInstList().push_back(NewRet);
425 // If the return instruction returns a value, and if the value was a
426 // PHI node in "BB", propagate the right value into the return.
427 if (NewRet->getNumOperands() == 1)
428 if (PHINode *PN = dyn_cast<PHINode>(NewRet->getOperand(0)))
429 if (PN->getParent() == BB)
430 NewRet->setOperand(0, PN->getIncomingValueForBlock(Pred));
431 // Update any PHI nodes in the returning block to realize that we no
432 // longer branch to them.
433 BB->removePredecessor(Pred);
434 Pred->getInstList().erase(UncondBranch);
437 // If we eliminated all predecessors of the block, delete the block now.
438 if (pred_begin(BB) == pred_end(BB))
439 // We know there are no successors, so just nuke the block.
440 M->getBasicBlockList().erase(BB);
446 } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->begin())) {
447 // Check to see if the first instruction in this block is just an unwind.
448 // If so, replace any invoke instructions which use this as an exception
449 // destination with call instructions.
451 std::vector<BasicBlock*> Preds(pred_begin(BB), pred_end(BB));
452 while (!Preds.empty()) {
453 BasicBlock *Pred = Preds.back();
454 if (InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator()))
455 if (II->getUnwindDest() == BB) {
456 // Insert a new branch instruction before the invoke, because this
457 // is now a fall through...
458 BranchInst *BI = new BranchInst(II->getNormalDest(), II);
459 Pred->getInstList().remove(II); // Take out of symbol table
461 // Insert the call now...
462 std::vector<Value*> Args(II->op_begin()+3, II->op_end());
463 CallInst *CI = new CallInst(II->getCalledValue(), Args,
465 // If the invoke produced a value, the Call now does instead
466 II->replaceAllUsesWith(CI);
475 // Merge basic blocks into their predecessor if there is only one distinct
476 // pred, and if there is only one distinct successor of the predecessor, and
477 // if there are no PHI nodes.
479 pred_iterator PI(pred_begin(BB)), PE(pred_end(BB));
480 BasicBlock *OnlyPred = *PI++;
481 for (; PI != PE; ++PI) // Search all predecessors, see if they are all same
482 if (*PI != OnlyPred) {
483 OnlyPred = 0; // There are multiple different predecessors...
487 BasicBlock *OnlySucc = 0;
488 if (OnlyPred && OnlyPred != BB && // Don't break self loops
489 OnlyPred->getTerminator()->getOpcode() != Instruction::Invoke) {
490 // Check to see if there is only one distinct successor...
491 succ_iterator SI(succ_begin(OnlyPred)), SE(succ_end(OnlyPred));
493 for (; SI != SE; ++SI)
494 if (*SI != OnlySucc) {
495 OnlySucc = 0; // There are multiple distinct successors!
501 //cerr << "Merging: " << BB << "into: " << OnlyPred;
502 TerminatorInst *Term = OnlyPred->getTerminator();
504 // Resolve any PHI nodes at the start of the block. They are all
505 // guaranteed to have exactly one entry if they exist, unless there are
506 // multiple duplicate (but guaranteed to be equal) entries for the
507 // incoming edges. This occurs when there are multiple edges from
508 // OnlyPred to OnlySucc.
510 while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
511 PN->replaceAllUsesWith(PN->getIncomingValue(0));
512 BB->getInstList().pop_front(); // Delete the phi node...
515 // Delete the unconditional branch from the predecessor...
516 OnlyPred->getInstList().pop_back();
518 // Move all definitions in the successor to the predecessor...
519 OnlyPred->getInstList().splice(OnlyPred->end(), BB->getInstList());
521 // Make all PHI nodes that referred to BB now refer to Pred as their
523 BB->replaceAllUsesWith(OnlyPred);
525 std::string OldName = BB->getName();
527 // Erase basic block from the function...
528 M->getBasicBlockList().erase(BB);
530 // Inherit predecessors name if it exists...
531 if (!OldName.empty() && !OnlyPred->hasName())
532 OnlyPred->setName(OldName);
537 for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
538 if (BranchInst *BI = dyn_cast<BranchInst>((*PI)->getTerminator()))
539 // Change br (X == 0 | X == 1), T, F into a switch instruction.
540 if (BI->isConditional() && isa<Instruction>(BI->getCondition())) {
541 Instruction *Cond = cast<Instruction>(BI->getCondition());
542 // If this is a bunch of seteq's or'd together, or if it's a bunch of
543 // 'setne's and'ed together, collect them.
545 std::vector<Constant*> Values;
546 bool TrueWhenEqual = GatherValueComparisons(Cond, CompVal, Values);
547 if (CompVal && CompVal->getType()->isInteger()) {
548 // There might be duplicate constants in the list, which the switch
549 // instruction can't handle, remove them now.
550 std::sort(Values.begin(), Values.end());
551 Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
553 // Figure out which block is which destination.
554 BasicBlock *DefaultBB = BI->getSuccessor(1);
555 BasicBlock *EdgeBB = BI->getSuccessor(0);
556 if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
558 // Create the new switch instruction now.
559 SwitchInst *New = new SwitchInst(CompVal, DefaultBB, BI);
561 // Add all of the 'cases' to the switch instruction.
562 for (unsigned i = 0, e = Values.size(); i != e; ++i)
563 New->addCase(Values[i], EdgeBB);
565 // We added edges from PI to the EdgeBB. As such, if there were any
566 // PHI nodes in EdgeBB, they need entries to be added corresponding to
567 // the number of edges added.
568 for (BasicBlock::iterator BBI = EdgeBB->begin();
569 PHINode *PN = dyn_cast<PHINode>(BBI); ++BBI) {
570 Value *InVal = PN->getIncomingValueForBlock(*PI);
571 for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
572 PN->addIncoming(InVal, *PI);
575 // Erase the old branch instruction.
576 (*PI)->getInstList().erase(BI);
578 // Erase the potentially condition tree that was used to computed the
580 ErasePossiblyDeadInstructionTree(Cond);
585 // If there is a trivial two-entry PHI node in this basic block, and we can
586 // eliminate it, do so now.
587 if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
588 if (PN->getNumIncomingValues() == 2) {
589 // Ok, this is a two entry PHI node. Check to see if this is a simple "if
590 // statement", which has a very simple dominance structure. Basically, we
591 // are trying to find the condition that is being branched on, which
592 // subsequently causes this merge to happen. We really want control
593 // dependence information for this check, but simplifycfg can't keep it up
594 // to date, and this catches most of the cases we care about anyway.
596 BasicBlock *IfTrue, *IfFalse;
597 if (Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse)) {
598 //std::cerr << "FOUND IF CONDITION! " << *IfCond << " T: "
599 // << IfTrue->getName() << " F: " << IfFalse->getName() << "\n";
601 // Figure out where to insert instructions as necessary.
602 BasicBlock::iterator AfterPHIIt = BB->begin();
603 while (isa<PHINode>(AfterPHIIt)) ++AfterPHIIt;
605 BasicBlock::iterator I = BB->begin();
606 while (PHINode *PN = dyn_cast<PHINode>(I)) {
609 // If we can eliminate this PHI by directly computing it based on the
610 // condition, do so now. We can't eliminate PHI nodes where the
611 // incoming values are defined in the conditional parts of the branch,
612 // so check for this.
614 if (DominatesMergePoint(PN->getIncomingValue(0), BB) &&
615 DominatesMergePoint(PN->getIncomingValue(1), BB)) {
617 PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
619 PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
621 // FIXME: when we have a 'select' statement, we can be completely
622 // generic and clean here and let the instcombine pass clean up
623 // after us, by folding the select instructions away when possible.
625 if (TrueVal == FalseVal) {
626 // Degenerate case...
627 PN->replaceAllUsesWith(TrueVal);
628 BB->getInstList().erase(PN);
630 } else if (isa<ConstantBool>(TrueVal) &&
631 isa<ConstantBool>(FalseVal)) {
632 if (TrueVal == ConstantBool::True) {
633 // The PHI node produces the same thing as the condition.
634 PN->replaceAllUsesWith(IfCond);
636 // The PHI node produces the inverse of the condition. Insert a
637 // "NOT" instruction, which is really a XOR.
639 BinaryOperator::createNot(IfCond, IfCond->getName()+".inv",
641 PN->replaceAllUsesWith(InverseCond);
643 BB->getInstList().erase(PN);
645 } else if (isa<ConstantInt>(TrueVal) && isa<ConstantInt>(FalseVal)){
646 // If this is a PHI of two constant integers, we insert a cast of
647 // the boolean to the integer type in question, giving us 0 or 1.
648 // Then we multiply this by the difference of the two constants,
649 // giving us 0 if false, and the difference if true. We add this
650 // result to the base constant, giving us our final value. We
651 // rely on the instruction combiner to eliminate many special
652 // cases, like turning multiplies into shifts when possible.
653 std::string Name = PN->getName(); PN->setName("");
654 Value *TheCast = new CastInst(IfCond, TrueVal->getType(),
656 Constant *TheDiff = ConstantExpr::get(Instruction::Sub,
657 cast<Constant>(TrueVal),
658 cast<Constant>(FalseVal));
660 if (TheDiff != ConstantInt::get(TrueVal->getType(), 1))
661 V = BinaryOperator::create(Instruction::Mul, TheCast,
662 TheDiff, TheCast->getName()+".scale",
664 if (!cast<Constant>(FalseVal)->isNullValue())
665 V = BinaryOperator::create(Instruction::Add, V, FalseVal,
666 V->getName()+".offs", AfterPHIIt);
667 PN->replaceAllUsesWith(V);
668 BB->getInstList().erase(PN);
670 } else if (isa<ConstantInt>(FalseVal) &&
671 cast<Constant>(FalseVal)->isNullValue()) {
672 // If the false condition is an integral zero value, we can
673 // compute the PHI by multiplying the condition by the other
675 std::string Name = PN->getName(); PN->setName("");
676 Value *TheCast = new CastInst(IfCond, TrueVal->getType(),
677 Name+".c", AfterPHIIt);
678 Value *V = BinaryOperator::create(Instruction::Mul, TrueVal,
679 TheCast, Name, AfterPHIIt);
680 PN->replaceAllUsesWith(V);
681 BB->getInstList().erase(PN);
683 } else if (isa<ConstantInt>(TrueVal) &&
684 cast<Constant>(TrueVal)->isNullValue()) {
685 // If the true condition is an integral zero value, we can compute
686 // the PHI by multiplying the inverse condition by the other
688 std::string Name = PN->getName(); PN->setName("");
689 Value *NotCond = BinaryOperator::createNot(IfCond, Name+".inv",
691 Value *TheCast = new CastInst(NotCond, TrueVal->getType(),
692 Name+".inv", AfterPHIIt);
693 Value *V = BinaryOperator::create(Instruction::Mul, FalseVal,
694 TheCast, Name, AfterPHIIt);
695 PN->replaceAllUsesWith(V);
696 BB->getInstList().erase(PN);