//
//===----------------------------------------------------------------------===//
+#define DEBUG_TYPE "simplifycfg"
#include "llvm/Transforms/Utils/Local.h"
#include "llvm/Constants.h"
#include "llvm/Instructions.h"
+#include "llvm/Type.h"
#include "llvm/Support/CFG.h"
+#include "llvm/Support/Debug.h"
#include <algorithm>
#include <functional>
+#include <set>
+#include <map>
using namespace llvm;
-// PropagatePredecessors - This gets "Succ" ready to have the predecessors from
-// "BB". This is a little tricky because "Succ" has PHI nodes, which need to
-// have extra slots added to them to hold the merge edges from BB's
-// predecessors, and BB itself might have had PHI nodes in it. This function
-// returns true (failure) if the Succ BB already has a predecessor that is a
-// predecessor of BB and incoming PHI arguments would not be discernible.
+// PropagatePredecessorsForPHIs - This gets "Succ" ready to have the
+// predecessors from "BB". This is a little tricky because "Succ" has PHI
+// nodes, which need to have extra slots added to them to hold the merge edges
+// from BB's predecessors, and BB itself might have had PHI nodes in it. This
+// function returns true (failure) if the Succ BB already has a predecessor that
+// is a predecessor of BB and incoming PHI arguments would not be discernible.
//
// Assumption: Succ is the single successor for BB.
//
// with incompatible values coming in from the two edges!
//
for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ); PI != PE; ++PI)
- if (find(BBPreds.begin(), BBPreds.end(), *PI) != BBPreds.end()) {
+ if (std::find(BBPreds.begin(), BBPreds.end(), *PI) != BBPreds.end()) {
// Loop over all of the PHI nodes checking to see if there are
// incompatible values coming in.
- for (BasicBlock::iterator I = Succ->begin();
- PHINode *PN = dyn_cast<PHINode>(I); ++I) {
+ for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
+ PHINode *PN = cast<PHINode>(I);
// Loop up the entries in the PHI node for BB and for *PI if the values
// coming in are non-equal, we cannot merge these two blocks (instead we
// should insert a conditional move or something, then merge the
}
}
- // Loop over all of the PHI nodes in the successor BB
- for (BasicBlock::iterator I = Succ->begin();
- PHINode *PN = dyn_cast<PHINode>(I); ++I) {
+ // Loop over all of the PHI nodes in the successor BB.
+ for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
+ PHINode *PN = cast<PHINode>(I);
Value *OldVal = PN->removeIncomingValue(BB, false);
assert(OldVal && "No entry in PHI for Pred BB!");
- // If this incoming value is one of the PHI nodes in BB...
+ // If this incoming value is one of the PHI nodes in BB, the new entries in
+ // the PHI node are the entries from the old PHI.
if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
PHINode *OldValPN = cast<PHINode>(OldVal);
- for (std::vector<BasicBlock*>::const_iterator PredI = BBPreds.begin(),
- End = BBPreds.end(); PredI != End; ++PredI) {
- PN->addIncoming(OldValPN->getIncomingValueForBlock(*PredI), *PredI);
- }
+ for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i)
+ PN->addIncoming(OldValPN->getIncomingValue(i),
+ OldValPN->getIncomingBlock(i));
} else {
for (std::vector<BasicBlock*>::const_iterator PredI = BBPreds.begin(),
End = BBPreds.end(); PredI != End; ++PredI) {
// if the specified value dominates the block. We don't handle the true
// generality of domination here, just a special case which works well enough
// for us.
-static bool DominatesMergePoint(Value *V, BasicBlock *BB) {
- if (Instruction *I = dyn_cast<Instruction>(V)) {
- BasicBlock *PBB = I->getParent();
- // If this instruction is defined in a block that contains an unconditional
- // branch to BB, then it must be in the 'conditional' part of the "if
- // statement".
- if (isa<BranchInst>(PBB->getTerminator()) &&
- cast<BranchInst>(PBB->getTerminator())->isUnconditional() &&
- cast<BranchInst>(PBB->getTerminator())->getSuccessor(0) == BB)
- return false;
-
- // We also don't want to allow wierd loops that might have the "if
- // condition" in the bottom of this block.
- if (PBB == BB) return false;
+//
+// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
+// see if V (which must be an instruction) is cheap to compute and is
+// non-trapping. If both are true, the instruction is inserted into the set and
+// true is returned.
+static bool DominatesMergePoint(Value *V, BasicBlock *BB,
+ std::set<Instruction*> *AggressiveInsts) {
+ Instruction *I = dyn_cast<Instruction>(V);
+ if (!I) return true; // Non-instructions all dominate instructions.
+ BasicBlock *PBB = I->getParent();
+
+ // We don't want to allow wierd loops that might have the "if condition" in
+ // the bottom of this block.
+ if (PBB == BB) return false;
+
+ // If this instruction is defined in a block that contains an unconditional
+ // branch to BB, then it must be in the 'conditional' part of the "if
+ // statement".
+ if (BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator()))
+ if (BI->isUnconditional() && BI->getSuccessor(0) == BB) {
+ if (!AggressiveInsts) return false;
+ // Okay, it looks like the instruction IS in the "condition". Check to
+ // see if its a cheap instruction to unconditionally compute, and if it
+ // only uses stuff defined outside of the condition. If so, hoist it out.
+ switch (I->getOpcode()) {
+ default: return false; // Cannot hoist this out safely.
+ case Instruction::Load:
+ // We can hoist loads that are non-volatile and obviously cannot trap.
+ if (cast<LoadInst>(I)->isVolatile())
+ return false;
+ if (!isa<AllocaInst>(I->getOperand(0)) &&
+ !isa<Constant>(I->getOperand(0)))
+ return false;
+
+ // Finally, we have to check to make sure there are no instructions
+ // before the load in its basic block, as we are going to hoist the loop
+ // out to its predecessor.
+ if (PBB->begin() != BasicBlock::iterator(I))
+ return false;
+ break;
+ case Instruction::Add:
+ case Instruction::Sub:
+ case Instruction::And:
+ case Instruction::Or:
+ case Instruction::Xor:
+ case Instruction::Shl:
+ case Instruction::Shr:
+ break; // These are all cheap and non-trapping instructions.
+ }
+
+ // Okay, we can only really hoist these out if their operands are not
+ // defined in the conditional region.
+ for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
+ if (!DominatesMergePoint(I->getOperand(i), BB, 0))
+ return false;
+ // Okay, it's safe to do this! Remember this instruction.
+ AggressiveInsts->insert(I);
+ }
+
+ return true;
+}
+
+// GatherConstantSetEQs - Given a potentially 'or'd together collection of seteq
+// instructions that compare a value against a constant, return the value being
+// compared, and stick the constant into the Values vector.
+static Value *GatherConstantSetEQs(Value *V, std::vector<ConstantInt*> &Values){
+ if (Instruction *Inst = dyn_cast<Instruction>(V))
+ if (Inst->getOpcode() == Instruction::SetEQ) {
+ if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
+ Values.push_back(C);
+ return Inst->getOperand(0);
+ } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
+ Values.push_back(C);
+ return Inst->getOperand(1);
+ }
+ } else if (Inst->getOpcode() == Instruction::Or) {
+ if (Value *LHS = GatherConstantSetEQs(Inst->getOperand(0), Values))
+ if (Value *RHS = GatherConstantSetEQs(Inst->getOperand(1), Values))
+ if (LHS == RHS)
+ return LHS;
+ }
+ return 0;
+}
+
+// GatherConstantSetNEs - Given a potentially 'and'd together collection of
+// setne instructions that compare a value against a constant, return the value
+// being compared, and stick the constant into the Values vector.
+static Value *GatherConstantSetNEs(Value *V, std::vector<ConstantInt*> &Values){
+ if (Instruction *Inst = dyn_cast<Instruction>(V))
+ if (Inst->getOpcode() == Instruction::SetNE) {
+ if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
+ Values.push_back(C);
+ return Inst->getOperand(0);
+ } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
+ Values.push_back(C);
+ return Inst->getOperand(1);
+ }
+ } else if (Inst->getOpcode() == Instruction::Cast) {
+ // Cast of X to bool is really a comparison against zero.
+ assert(Inst->getType() == Type::BoolTy && "Can only handle bool values!");
+ Values.push_back(ConstantInt::get(Inst->getOperand(0)->getType(), 0));
+ return Inst->getOperand(0);
+ } else if (Inst->getOpcode() == Instruction::And) {
+ if (Value *LHS = GatherConstantSetNEs(Inst->getOperand(0), Values))
+ if (Value *RHS = GatherConstantSetNEs(Inst->getOperand(1), Values))
+ if (LHS == RHS)
+ return LHS;
+ }
+ return 0;
+}
+
+
+
+/// GatherValueComparisons - If the specified Cond is an 'and' or 'or' of a
+/// bunch of comparisons of one value against constants, return the value and
+/// the constants being compared.
+static bool GatherValueComparisons(Instruction *Cond, Value *&CompVal,
+ std::vector<ConstantInt*> &Values) {
+ if (Cond->getOpcode() == Instruction::Or) {
+ CompVal = GatherConstantSetEQs(Cond, Values);
+
+ // Return true to indicate that the condition is true if the CompVal is
+ // equal to one of the constants.
+ return true;
+ } else if (Cond->getOpcode() == Instruction::And) {
+ CompVal = GatherConstantSetNEs(Cond, Values);
+
+ // Return false to indicate that the condition is false if the CompVal is
+ // equal to one of the constants.
+ return false;
}
+ return false;
+}
+
+/// ErasePossiblyDeadInstructionTree - If the specified instruction is dead and
+/// has no side effects, nuke it. If it uses any instructions that become dead
+/// because the instruction is now gone, nuke them too.
+static void ErasePossiblyDeadInstructionTree(Instruction *I) {
+ if (isInstructionTriviallyDead(I)) {
+ std::vector<Value*> Operands(I->op_begin(), I->op_end());
+ I->getParent()->getInstList().erase(I);
+ for (unsigned i = 0, e = Operands.size(); i != e; ++i)
+ if (Instruction *OpI = dyn_cast<Instruction>(Operands[i]))
+ ErasePossiblyDeadInstructionTree(OpI);
+ }
+}
- // Non-instructions all dominate instructions.
+/// SafeToMergeTerminators - Return true if it is safe to merge these two
+/// terminator instructions together.
+///
+static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
+ if (SI1 == SI2) return false; // Can't merge with self!
+
+ // It is not safe to merge these two switch instructions if they have a common
+ // successor, and if that successor has a PHI node, and if *that* PHI node has
+ // conflicting incoming values from the two switch blocks.
+ BasicBlock *SI1BB = SI1->getParent();
+ BasicBlock *SI2BB = SI2->getParent();
+ std::set<BasicBlock*> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
+
+ for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
+ if (SI1Succs.count(*I))
+ for (BasicBlock::iterator BBI = (*I)->begin();
+ isa<PHINode>(BBI); ++BBI) {
+ PHINode *PN = cast<PHINode>(BBI);
+ if (PN->getIncomingValueForBlock(SI1BB) !=
+ PN->getIncomingValueForBlock(SI2BB))
+ return false;
+ }
+
return true;
}
+/// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
+/// now be entries in it from the 'NewPred' block. The values that will be
+/// flowing into the PHI nodes will be the same as those coming in from
+/// ExistPred, an existing predecessor of Succ.
+static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
+ BasicBlock *ExistPred) {
+ assert(std::find(succ_begin(ExistPred), succ_end(ExistPred), Succ) !=
+ succ_end(ExistPred) && "ExistPred is not a predecessor of Succ!");
+ if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
+
+ for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
+ PHINode *PN = cast<PHINode>(I);
+ Value *V = PN->getIncomingValueForBlock(ExistPred);
+ PN->addIncoming(V, NewPred);
+ }
+}
+
+// isValueEqualityComparison - Return true if the specified terminator checks to
+// see if a value is equal to constant integer value.
+static Value *isValueEqualityComparison(TerminatorInst *TI) {
+ if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
+ // Do not permit merging of large switch instructions into their
+ // predecessors unless there is only one predecessor.
+ if (SI->getNumSuccessors() * std::distance(pred_begin(SI->getParent()),
+ pred_end(SI->getParent())) > 128)
+ return 0;
+
+ return SI->getCondition();
+ }
+ if (BranchInst *BI = dyn_cast<BranchInst>(TI))
+ if (BI->isConditional() && BI->getCondition()->hasOneUse())
+ if (SetCondInst *SCI = dyn_cast<SetCondInst>(BI->getCondition()))
+ if ((SCI->getOpcode() == Instruction::SetEQ ||
+ SCI->getOpcode() == Instruction::SetNE) &&
+ isa<ConstantInt>(SCI->getOperand(1)))
+ return SCI->getOperand(0);
+ return 0;
+}
+
+// Given a value comparison instruction, decode all of the 'cases' that it
+// represents and return the 'default' block.
+static BasicBlock *
+GetValueEqualityComparisonCases(TerminatorInst *TI,
+ std::vector<std::pair<ConstantInt*,
+ BasicBlock*> > &Cases) {
+ if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
+ Cases.reserve(SI->getNumCases());
+ for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
+ Cases.push_back(std::make_pair(cast<ConstantInt>(SI->getCaseValue(i)),
+ SI->getSuccessor(i)));
+ return SI->getDefaultDest();
+ }
+
+ BranchInst *BI = cast<BranchInst>(TI);
+ SetCondInst *SCI = cast<SetCondInst>(BI->getCondition());
+ Cases.push_back(std::make_pair(cast<ConstantInt>(SCI->getOperand(1)),
+ BI->getSuccessor(SCI->getOpcode() ==
+ Instruction::SetNE)));
+ return BI->getSuccessor(SCI->getOpcode() == Instruction::SetEQ);
+}
+
+
+// FoldValueComparisonIntoPredecessors - The specified terminator is a value
+// equality comparison instruction (either a switch or a branch on "X == c").
+// See if any of the predecessors of the terminator block are value comparisons
+// on the same value. If so, and if safe to do so, fold them together.
+static bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI) {
+ BasicBlock *BB = TI->getParent();
+ Value *CV = isValueEqualityComparison(TI); // CondVal
+ assert(CV && "Not a comparison?");
+ bool Changed = false;
+
+ std::vector<BasicBlock*> Preds(pred_begin(BB), pred_end(BB));
+ while (!Preds.empty()) {
+ BasicBlock *Pred = Preds.back();
+ Preds.pop_back();
+
+ // See if the predecessor is a comparison with the same value.
+ TerminatorInst *PTI = Pred->getTerminator();
+ Value *PCV = isValueEqualityComparison(PTI); // PredCondVal
+
+ if (PCV == CV && SafeToMergeTerminators(TI, PTI)) {
+ // Figure out which 'cases' to copy from SI to PSI.
+ std::vector<std::pair<ConstantInt*, BasicBlock*> > BBCases;
+ BasicBlock *BBDefault = GetValueEqualityComparisonCases(TI, BBCases);
+
+ std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
+ BasicBlock *PredDefault = GetValueEqualityComparisonCases(PTI, PredCases);
+
+ // Based on whether the default edge from PTI goes to BB or not, fill in
+ // PredCases and PredDefault with the new switch cases we would like to
+ // build.
+ std::vector<BasicBlock*> NewSuccessors;
+
+ if (PredDefault == BB) {
+ // If this is the default destination from PTI, only the edges in TI
+ // that don't occur in PTI, or that branch to BB will be activated.
+ std::set<ConstantInt*> PTIHandled;
+ for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
+ if (PredCases[i].second != BB)
+ PTIHandled.insert(PredCases[i].first);
+ else {
+ // The default destination is BB, we don't need explicit targets.
+ std::swap(PredCases[i], PredCases.back());
+ PredCases.pop_back();
+ --i; --e;
+ }
+
+ // Reconstruct the new switch statement we will be building.
+ if (PredDefault != BBDefault) {
+ PredDefault->removePredecessor(Pred);
+ PredDefault = BBDefault;
+ NewSuccessors.push_back(BBDefault);
+ }
+ for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
+ if (!PTIHandled.count(BBCases[i].first) &&
+ BBCases[i].second != BBDefault) {
+ PredCases.push_back(BBCases[i]);
+ NewSuccessors.push_back(BBCases[i].second);
+ }
+
+ } else {
+ // If this is not the default destination from PSI, only the edges
+ // in SI that occur in PSI with a destination of BB will be
+ // activated.
+ std::set<ConstantInt*> PTIHandled;
+ for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
+ if (PredCases[i].second == BB) {
+ PTIHandled.insert(PredCases[i].first);
+ std::swap(PredCases[i], PredCases.back());
+ PredCases.pop_back();
+ --i; --e;
+ }
+
+ // Okay, now we know which constants were sent to BB from the
+ // predecessor. Figure out where they will all go now.
+ for (unsigned i = 0, e = BBCases.size(); i != e; ++i)
+ if (PTIHandled.count(BBCases[i].first)) {
+ // If this is one we are capable of getting...
+ PredCases.push_back(BBCases[i]);
+ NewSuccessors.push_back(BBCases[i].second);
+ PTIHandled.erase(BBCases[i].first);// This constant is taken care of
+ }
+
+ // If there are any constants vectored to BB that TI doesn't handle,
+ // they must go to the default destination of TI.
+ for (std::set<ConstantInt*>::iterator I = PTIHandled.begin(),
+ E = PTIHandled.end(); I != E; ++I) {
+ PredCases.push_back(std::make_pair(*I, BBDefault));
+ NewSuccessors.push_back(BBDefault);
+ }
+ }
+
+ // Okay, at this point, we know which new successor Pred will get. Make
+ // sure we update the number of entries in the PHI nodes for these
+ // successors.
+ for (unsigned i = 0, e = NewSuccessors.size(); i != e; ++i)
+ AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
+
+ // Now that the successors are updated, create the new Switch instruction.
+ SwitchInst *NewSI = new SwitchInst(CV, PredDefault, PTI);
+ for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
+ NewSI->addCase(PredCases[i].first, PredCases[i].second);
+ Pred->getInstList().erase(PTI);
+
+ // Okay, last check. If BB is still a successor of PSI, then we must
+ // have an infinite loop case. If so, add an infinitely looping block
+ // to handle the case to preserve the behavior of the code.
+ BasicBlock *InfLoopBlock = 0;
+ for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
+ if (NewSI->getSuccessor(i) == BB) {
+ if (InfLoopBlock == 0) {
+ // Insert it at the end of the loop, because it's either code,
+ // or it won't matter if it's hot. :)
+ InfLoopBlock = new BasicBlock("infloop", BB->getParent());
+ new BranchInst(InfLoopBlock, InfLoopBlock);
+ }
+ NewSI->setSuccessor(i, InfLoopBlock);
+ }
+
+ Changed = true;
+ }
+ }
+ return Changed;
+}
+
+/// HoistThenElseCodeToIf - Given a conditional branch that codes to BB1 and
+/// BB2, hoist any common code in the two blocks up into the branch block. The
+/// caller of this function guarantees that BI's block dominates BB1 and BB2.
+static bool HoistThenElseCodeToIf(BranchInst *BI) {
+ // This does very trivial matching, with limited scanning, to find identical
+ // instructions in the two blocks. In particular, we don't want to get into
+ // O(M*N) situations here where M and N are the sizes of BB1 and BB2. As
+ // such, we currently just scan for obviously identical instructions in an
+ // identical order.
+ BasicBlock *BB1 = BI->getSuccessor(0); // The true destination.
+ BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
+
+ Instruction *I1 = BB1->begin(), *I2 = BB2->begin();
+ if (I1->getOpcode() != I2->getOpcode() || !I1->isIdenticalTo(I2))
+ return false;
+
+ // If we get here, we can hoist at least one instruction.
+ BasicBlock *BIParent = BI->getParent();
+
+ do {
+ // If we are hoisting the terminator instruction, don't move one (making a
+ // broken BB), instead clone it, and remove BI.
+ if (isa<TerminatorInst>(I1))
+ goto HoistTerminator;
+
+ // For a normal instruction, we just move one to right before the branch,
+ // then replace all uses of the other with the first. Finally, we remove
+ // the now redundant second instruction.
+ BIParent->getInstList().splice(BI, BB1->getInstList(), I1);
+ if (!I2->use_empty())
+ I2->replaceAllUsesWith(I1);
+ BB2->getInstList().erase(I2);
+
+ I1 = BB1->begin();
+ I2 = BB2->begin();
+ } while (I1->getOpcode() == I2->getOpcode() && I1->isIdenticalTo(I2));
+
+ return true;
+
+HoistTerminator:
+ // Okay, it is safe to hoist the terminator.
+ Instruction *NT = I1->clone();
+ BIParent->getInstList().insert(BI, NT);
+ if (NT->getType() != Type::VoidTy) {
+ I1->replaceAllUsesWith(NT);
+ I2->replaceAllUsesWith(NT);
+ NT->setName(I1->getName());
+ }
+
+ // Hoisting one of the terminators from our successor is a great thing.
+ // Unfortunately, the successors of the if/else blocks may have PHI nodes in
+ // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
+ // nodes, so we insert select instruction to compute the final result.
+ std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
+ for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
+ PHINode *PN;
+ for (BasicBlock::iterator BBI = SI->begin();
+ (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
+ Value *BB1V = PN->getIncomingValueForBlock(BB1);
+ Value *BB2V = PN->getIncomingValueForBlock(BB2);
+ if (BB1V != BB2V) {
+ // These values do not agree. Insert a select instruction before NT
+ // that determines the right value.
+ SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
+ if (SI == 0)
+ SI = new SelectInst(BI->getCondition(), BB1V, BB2V,
+ BB1V->getName()+"."+BB2V->getName(), NT);
+ // Make the PHI node use the select for all incoming values for BB1/BB2
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
+ if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
+ PN->setIncomingValue(i, SI);
+ }
+ }
+ }
+
+ // Update any PHI nodes in our new successors.
+ for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
+ AddPredecessorToBlock(*SI, BIParent, BB1);
+
+ BI->eraseFromParent();
+ return true;
+}
+
+namespace {
+ /// ConstantIntOrdering - This class implements a stable ordering of constant
+ /// integers that does not depend on their address. This is important for
+ /// applications that sort ConstantInt's to ensure uniqueness.
+ struct ConstantIntOrdering {
+ bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
+ return LHS->getRawValue() < RHS->getRawValue();
+ }
+ };
+}
+
+
// SimplifyCFG - This function is used to do simplification of a CFG. For
// example, it adjusts branches to branches to eliminate the extra hop, it
// eliminates unreachable basic blocks, and does other "peephole" optimization
assert(BB->getTerminator() && "Degenerate basic block encountered!");
assert(&BB->getParent()->front() != BB && "Can't Simplify entry block!");
- // Check to see if the first instruction in this block is just an unwind. If
- // so, replace any invoke instructions which use this as an exception
- // destination with call instructions.
- //
- if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator()))
- if (BB->begin() == BasicBlock::iterator(UI)) { // Empty block?
- std::vector<BasicBlock*> Preds(pred_begin(BB), pred_end(BB));
- while (!Preds.empty()) {
- BasicBlock *Pred = Preds.back();
- if (InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator()))
- if (II->getUnwindDest() == BB) {
- // Insert a new branch instruction before the invoke, because this
- // is now a fall through...
- BranchInst *BI = new BranchInst(II->getNormalDest(), II);
- Pred->getInstList().remove(II); // Take out of symbol table
-
- // Insert the call now...
- std::vector<Value*> Args(II->op_begin()+3, II->op_end());
- CallInst *CI = new CallInst(II->getCalledValue(), Args,
- II->getName(), BI);
- // If the invoke produced a value, the Call now does instead
- II->replaceAllUsesWith(CI);
- delete II;
- Changed = true;
- }
-
- Preds.pop_back();
- }
- }
-
// Remove basic blocks that have no predecessors... which are unreachable.
- if (pred_begin(BB) == pred_end(BB)) {
- //cerr << "Removing BB: \n" << BB;
+ if (pred_begin(BB) == pred_end(BB) ||
+ *pred_begin(BB) == BB && ++pred_begin(BB) == pred_end(BB)) {
+ DEBUG(std::cerr << "Removing BB: \n" << *BB);
// Loop through all of our successors and make sure they know that one
// of their predecessors is going away.
// to the successor.
succ_iterator SI(succ_begin(BB));
if (SI != succ_end(BB) && ++SI == succ_end(BB)) { // One succ?
-
BasicBlock::iterator BBI = BB->begin(); // Skip over phi nodes...
while (isa<PHINode>(*BBI)) ++BBI;
- if (BBI->isTerminator()) { // Terminator is the only non-phi instruction!
- BasicBlock *Succ = *succ_begin(BB); // There is exactly one successor
-
- if (Succ != BB) { // Arg, don't hurt infinite loops!
- // If our successor has PHI nodes, then we need to update them to
- // include entries for BB's predecessors, not for BB itself.
- // Be careful though, if this transformation fails (returns true) then
- // we cannot do this transformation!
- //
- if (!PropagatePredecessorsForPHIs(BB, Succ)) {
- //cerr << "Killing Trivial BB: \n" << BB;
- std::string OldName = BB->getName();
-
+ BasicBlock *Succ = *succ_begin(BB); // There is exactly one successor.
+ if (BBI->isTerminator() && // Terminator is the only non-phi instruction!
+ Succ != BB) { // Don't hurt infinite loops!
+ // If our successor has PHI nodes, then we need to update them to include
+ // entries for BB's predecessors, not for BB itself. Be careful though,
+ // if this transformation fails (returns true) then we cannot do this
+ // transformation!
+ //
+ if (!PropagatePredecessorsForPHIs(BB, Succ)) {
+ DEBUG(std::cerr << "Killing Trivial BB: \n" << *BB);
+
+ if (isa<PHINode>(&BB->front())) {
std::vector<BasicBlock*>
OldSuccPreds(pred_begin(Succ), pred_end(Succ));
-
+
// Move all PHI nodes in BB to Succ if they are alive, otherwise
// delete them.
while (PHINode *PN = dyn_cast<PHINode>(&BB->front()))
if (PN->use_empty())
- BB->getInstList().erase(BB->begin()); // Nuke instruction...
+ BB->getInstList().erase(BB->begin()); // Nuke instruction.
else {
// The instruction is alive, so this means that Succ must have
// *ONLY* had BB as a predecessor, and the PHI node is still valid
// strictly dominated Succ.
BB->getInstList().remove(BB->begin());
Succ->getInstList().push_front(PN);
-
+
// We need to add new entries for the PHI node to account for
// predecessors of Succ that the PHI node does not take into
// account. At this point, since we know that BB dominated succ,
// this means that we should any newly added incoming edges should
// use the PHI node as the value for these edges, because they are
// loop back edges.
-
for (unsigned i = 0, e = OldSuccPreds.size(); i != e; ++i)
if (OldSuccPreds[i] != BB)
PN->addIncoming(PN, OldSuccPreds[i]);
}
+ }
+
+ // Everything that jumped to BB now goes to Succ.
+ std::string OldName = BB->getName();
+ BB->replaceAllUsesWith(Succ);
+ BB->eraseFromParent(); // Delete the old basic block.
+
+ if (!OldName.empty() && !Succ->hasName()) // Transfer name if we can
+ Succ->setName(OldName);
+ return true;
+ }
+ }
+ }
- // Everything that jumped to BB now goes to Succ...
- BB->replaceAllUsesWith(Succ);
+ // If this is a returning block with only PHI nodes in it, fold the return
+ // instruction into any unconditional branch predecessors.
+ //
+ // If any predecessor is a conditional branch that just selects among
+ // different return values, fold the replace the branch/return with a select
+ // and return.
+ if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
+ BasicBlock::iterator BBI = BB->getTerminator();
+ if (BBI == BB->begin() || isa<PHINode>(--BBI)) {
+ // Find predecessors that end with branches.
+ std::vector<BasicBlock*> UncondBranchPreds;
+ std::vector<BranchInst*> CondBranchPreds;
+ for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
+ TerminatorInst *PTI = (*PI)->getTerminator();
+ if (BranchInst *BI = dyn_cast<BranchInst>(PTI))
+ if (BI->isUnconditional())
+ UncondBranchPreds.push_back(*PI);
+ else
+ CondBranchPreds.push_back(BI);
+ }
+
+ // If we found some, do the transformation!
+ if (!UncondBranchPreds.empty()) {
+ while (!UncondBranchPreds.empty()) {
+ BasicBlock *Pred = UncondBranchPreds.back();
+ UncondBranchPreds.pop_back();
+ Instruction *UncondBranch = Pred->getTerminator();
+ // Clone the return and add it to the end of the predecessor.
+ Instruction *NewRet = RI->clone();
+ Pred->getInstList().push_back(NewRet);
- // Delete the old basic block...
+ // If the return instruction returns a value, and if the value was a
+ // PHI node in "BB", propagate the right value into the return.
+ if (NewRet->getNumOperands() == 1)
+ if (PHINode *PN = dyn_cast<PHINode>(NewRet->getOperand(0)))
+ if (PN->getParent() == BB)
+ NewRet->setOperand(0, PN->getIncomingValueForBlock(Pred));
+ // Update any PHI nodes in the returning block to realize that we no
+ // longer branch to them.
+ BB->removePredecessor(Pred);
+ Pred->getInstList().erase(UncondBranch);
+ }
+
+ // If we eliminated all predecessors of the block, delete the block now.
+ if (pred_begin(BB) == pred_end(BB))
+ // We know there are no successors, so just nuke the block.
M->getBasicBlockList().erase(BB);
-
- if (!OldName.empty() && !Succ->hasName()) // Transfer name if we can
- Succ->setName(OldName);
+
+ return true;
+ }
+
+ // Check out all of the conditional branches going to this return
+ // instruction. If any of them just select between returns, change the
+ // branch itself into a select/return pair.
+ while (!CondBranchPreds.empty()) {
+ BranchInst *BI = CondBranchPreds.back();
+ CondBranchPreds.pop_back();
+ BasicBlock *TrueSucc = BI->getSuccessor(0);
+ BasicBlock *FalseSucc = BI->getSuccessor(1);
+ BasicBlock *OtherSucc = TrueSucc == BB ? FalseSucc : TrueSucc;
+
+ // Check to see if the non-BB successor is also a return block.
+ if (isa<ReturnInst>(OtherSucc->getTerminator())) {
+ // Check to see if there are only PHI instructions in this block.
+ BasicBlock::iterator OSI = OtherSucc->getTerminator();
+ if (OSI == OtherSucc->begin() || isa<PHINode>(--OSI)) {
+ // Okay, we found a branch that is going to two return nodes. If
+ // there is no return value for this function, just change the
+ // branch into a return.
+ if (RI->getNumOperands() == 0) {
+ TrueSucc->removePredecessor(BI->getParent());
+ FalseSucc->removePredecessor(BI->getParent());
+ new ReturnInst(0, BI);
+ BI->getParent()->getInstList().erase(BI);
+ return true;
+ }
+
+ // Otherwise, figure out what the true and false return values are
+ // so we can insert a new select instruction.
+ Value *TrueValue = TrueSucc->getTerminator()->getOperand(0);
+ Value *FalseValue = FalseSucc->getTerminator()->getOperand(0);
+
+ // Unwrap any PHI nodes in the return blocks.
+ if (PHINode *TVPN = dyn_cast<PHINode>(TrueValue))
+ if (TVPN->getParent() == TrueSucc)
+ TrueValue = TVPN->getIncomingValueForBlock(BI->getParent());
+ if (PHINode *FVPN = dyn_cast<PHINode>(FalseValue))
+ if (FVPN->getParent() == FalseSucc)
+ FalseValue = FVPN->getIncomingValueForBlock(BI->getParent());
+
+ TrueSucc->removePredecessor(BI->getParent());
+ FalseSucc->removePredecessor(BI->getParent());
+
+ // Insert a new select instruction.
+ Value *NewRetVal;
+ Value *BrCond = BI->getCondition();
+ if (TrueValue != FalseValue)
+ NewRetVal = new SelectInst(BrCond, TrueValue,
+ FalseValue, "retval", BI);
+ else
+ NewRetVal = TrueValue;
+
+ new ReturnInst(NewRetVal, BI);
+ BI->getParent()->getInstList().erase(BI);
+ if (BrCond->use_empty())
+ if (Instruction *BrCondI = dyn_cast<Instruction>(BrCond))
+ BrCondI->getParent()->getInstList().erase(BrCondI);
+ return true;
+ }
+ }
+ }
+ }
+ } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->begin())) {
+ // Check to see if the first instruction in this block is just an unwind.
+ // If so, replace any invoke instructions which use this as an exception
+ // destination with call instructions, and any unconditional branch
+ // predecessor with an unwind.
+ //
+ std::vector<BasicBlock*> Preds(pred_begin(BB), pred_end(BB));
+ while (!Preds.empty()) {
+ BasicBlock *Pred = Preds.back();
+ if (BranchInst *BI = dyn_cast<BranchInst>(Pred->getTerminator())) {
+ if (BI->isUnconditional()) {
+ Pred->getInstList().pop_back(); // nuke uncond branch
+ new UnwindInst(Pred); // Use unwind.
+ Changed = true;
+ }
+ } else if (InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator()))
+ if (II->getUnwindDest() == BB) {
+ // Insert a new branch instruction before the invoke, because this
+ // is now a fall through...
+ BranchInst *BI = new BranchInst(II->getNormalDest(), II);
+ Pred->getInstList().remove(II); // Take out of symbol table
- //cerr << "Function after removal: \n" << M;
- return true;
- }
+ // Insert the call now...
+ std::vector<Value*> Args(II->op_begin()+3, II->op_end());
+ CallInst *CI = new CallInst(II->getCalledValue(), Args,
+ II->getName(), BI);
+ // If the invoke produced a value, the Call now does instead
+ II->replaceAllUsesWith(CI);
+ delete II;
+ Changed = true;
+ }
+
+ Preds.pop_back();
+ }
+
+ // If this block is now dead, remove it.
+ if (pred_begin(BB) == pred_end(BB)) {
+ // We know there are no successors, so just nuke the block.
+ M->getBasicBlockList().erase(BB);
+ return true;
+ }
+
+ } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->begin())) {
+ if (isValueEqualityComparison(SI))
+ if (FoldValueComparisonIntoPredecessors(SI))
+ return SimplifyCFG(BB) || 1;
+ } else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
+ if (BI->isConditional()) {
+ if (Value *CompVal = isValueEqualityComparison(BI)) {
+ // This block must be empty, except for the setcond inst, if it exists.
+ BasicBlock::iterator I = BB->begin();
+ if (&*I == BI ||
+ (&*I == cast<Instruction>(BI->getCondition()) &&
+ &*++I == BI))
+ if (FoldValueComparisonIntoPredecessors(BI))
+ return SimplifyCFG(BB) | true;
+ }
+
+ // If this basic block is ONLY a setcc and a branch, and if a predecessor
+ // branches to us and one of our successors, fold the setcc into the
+ // predecessor and use logical operations to pick the right destination.
+ BasicBlock *TrueDest = BI->getSuccessor(0);
+ BasicBlock *FalseDest = BI->getSuccessor(1);
+ if (BinaryOperator *Cond = dyn_cast<BinaryOperator>(BI->getCondition()))
+ if (Cond->getParent() == BB && &BB->front() == Cond &&
+ Cond->getNext() == BI && Cond->hasOneUse() &&
+ TrueDest != BB && FalseDest != BB)
+ for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI!=E; ++PI)
+ if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
+ if (PBI->isConditional() && SafeToMergeTerminators(BI, PBI)) {
+ BasicBlock *PredBlock = *PI;
+ if (PBI->getSuccessor(0) == FalseDest ||
+ PBI->getSuccessor(1) == TrueDest) {
+ // Invert the predecessors condition test (xor it with true),
+ // which allows us to write this code once.
+ Value *NewCond =
+ BinaryOperator::createNot(PBI->getCondition(),
+ PBI->getCondition()->getName()+".not", PBI);
+ PBI->setCondition(NewCond);
+ BasicBlock *OldTrue = PBI->getSuccessor(0);
+ BasicBlock *OldFalse = PBI->getSuccessor(1);
+ PBI->setSuccessor(0, OldFalse);
+ PBI->setSuccessor(1, OldTrue);
+ }
+
+ if (PBI->getSuccessor(0) == TrueDest ||
+ PBI->getSuccessor(1) == FalseDest) {
+ // Clone Cond into the predecessor basic block, and or/and the
+ // two conditions together.
+ Instruction *New = Cond->clone();
+ New->setName(Cond->getName());
+ Cond->setName(Cond->getName()+".old");
+ PredBlock->getInstList().insert(PBI, New);
+ Instruction::BinaryOps Opcode =
+ PBI->getSuccessor(0) == TrueDest ?
+ Instruction::Or : Instruction::And;
+ Value *NewCond =
+ BinaryOperator::create(Opcode, PBI->getCondition(),
+ New, "bothcond", PBI);
+ PBI->setCondition(NewCond);
+ if (PBI->getSuccessor(0) == BB) {
+ AddPredecessorToBlock(TrueDest, PredBlock, BB);
+ PBI->setSuccessor(0, TrueDest);
+ }
+ if (PBI->getSuccessor(1) == BB) {
+ AddPredecessorToBlock(FalseDest, PredBlock, BB);
+ PBI->setSuccessor(1, FalseDest);
+ }
+ return SimplifyCFG(BB) | 1;
+ }
+ }
+
+ // If this block ends with a branch instruction, and if there is one
+ // predecessor, see if the previous block ended with a branch on the same
+ // condition, which makes this conditional branch redundant.
+ pred_iterator PI(pred_begin(BB)), PE(pred_end(BB));
+ BasicBlock *OnlyPred = *PI++;
+ for (; PI != PE; ++PI)// Search all predecessors, see if they are all same
+ if (*PI != OnlyPred) {
+ OnlyPred = 0; // There are multiple different predecessors...
+ break;
+ }
+
+ if (OnlyPred)
+ if (BranchInst *PBI = dyn_cast<BranchInst>(OnlyPred->getTerminator()))
+ if (PBI->isConditional() &&
+ PBI->getCondition() == BI->getCondition() &&
+ (PBI->getSuccessor(0) != BB || PBI->getSuccessor(1) != BB)) {
+ // Okay, the outcome of this conditional branch is statically
+ // knowable. Delete the outgoing CFG edge that is impossible to
+ // execute.
+ bool CondIsTrue = PBI->getSuccessor(0) == BB;
+ BI->getSuccessor(CondIsTrue)->removePredecessor(BB);
+ new BranchInst(BI->getSuccessor(!CondIsTrue), BB);
+ BB->getInstList().erase(BI);
+ return SimplifyCFG(BB) | true;
+ }
+ }
+ } else if (isa<UnreachableInst>(BB->getTerminator())) {
+ // If there are any instructions immediately before the unreachable that can
+ // be removed, do so.
+ Instruction *Unreachable = BB->getTerminator();
+ while (Unreachable != BB->begin()) {
+ BasicBlock::iterator BBI = Unreachable;
+ --BBI;
+ if (isa<CallInst>(BBI)) break;
+ // Delete this instruction
+ BB->getInstList().erase(BBI);
+ Changed = true;
+ }
+
+ // If the unreachable instruction is the first in the block, take a gander
+ // at all of the predecessors of this instruction, and simplify them.
+ if (&BB->front() == Unreachable) {
+ std::vector<BasicBlock*> Preds(pred_begin(BB), pred_end(BB));
+ for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
+ TerminatorInst *TI = Preds[i]->getTerminator();
+
+ if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
+ if (BI->isUnconditional()) {
+ if (BI->getSuccessor(0) == BB) {
+ new UnreachableInst(TI);
+ TI->eraseFromParent();
+ Changed = true;
+ }
+ } else {
+ if (BI->getSuccessor(0) == BB) {
+ new BranchInst(BI->getSuccessor(1), BI);
+ BI->eraseFromParent();
+ } else if (BI->getSuccessor(1) == BB) {
+ new BranchInst(BI->getSuccessor(0), BI);
+ BI->eraseFromParent();
+ Changed = true;
+ }
+ }
+ } else if (SwitchInst *SI = dyn_cast<SwitchInst>(TI)) {
+ for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
+ if (SI->getSuccessor(i) == BB) {
+ SI->removeCase(i);
+ --i; --e;
+ Changed = true;
+ }
+ // If the default value is unreachable, figure out the most popular
+ // destination and make it the default.
+ if (SI->getSuccessor(0) == BB) {
+ std::map<BasicBlock*, unsigned> Popularity;
+ for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
+ Popularity[SI->getSuccessor(i)]++;
+
+ // Find the most popular block.
+ unsigned MaxPop = 0;
+ BasicBlock *MaxBlock = 0;
+ for (std::map<BasicBlock*, unsigned>::iterator
+ I = Popularity.begin(), E = Popularity.end(); I != E; ++I) {
+ if (I->second > MaxPop) {
+ MaxPop = I->second;
+ MaxBlock = I->first;
+ }
+ }
+ if (MaxBlock) {
+ // Make this the new default, allowing us to delete any explicit
+ // edges to it.
+ SI->setSuccessor(0, MaxBlock);
+ Changed = true;
+
+ for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
+ if (SI->getSuccessor(i) == MaxBlock) {
+ SI->removeCase(i);
+ --i; --e;
+ }
+ }
+ }
+ } else if (InvokeInst *II = dyn_cast<InvokeInst>(TI)) {
+ if (II->getUnwindDest() == BB) {
+ // Convert the invoke to a call instruction. This would be a good
+ // place to note that the call does not throw though.
+ BranchInst *BI = new BranchInst(II->getNormalDest(), II);
+ II->removeFromParent(); // Take out of symbol table
+
+ // Insert the call now...
+ std::vector<Value*> Args(II->op_begin()+3, II->op_end());
+ CallInst *CI = new CallInst(II->getCalledValue(), Args,
+ II->getName(), BI);
+ // If the invoke produced a value, the Call does now instead.
+ II->replaceAllUsesWith(CI);
+ delete II;
+ Changed = true;
+ }
+ }
+ }
+
+ // If this block is now dead, remove it.
+ if (pred_begin(BB) == pred_end(BB)) {
+ // We know there are no successors, so just nuke the block.
+ M->getBasicBlockList().erase(BB);
+ return true;
}
}
}
OnlyPred = 0; // There are multiple different predecessors...
break;
}
-
+
BasicBlock *OnlySucc = 0;
if (OnlyPred && OnlyPred != BB && // Don't break self loops
OnlyPred->getTerminator()->getOpcode() != Instruction::Invoke) {
}
if (OnlySucc) {
- //cerr << "Merging: " << BB << "into: " << OnlyPred;
+ DEBUG(std::cerr << "Merging: " << *BB << "into: " << *OnlyPred);
TerminatorInst *Term = OnlyPred->getTerminator();
// Resolve any PHI nodes at the start of the block. They are all
return true;
}
+ // Otherwise, if this block only has a single predecessor, and if that block
+ // is a conditional branch, see if we can hoist any code from this block up
+ // into our predecessor.
+ if (OnlyPred)
+ if (BranchInst *BI = dyn_cast<BranchInst>(OnlyPred->getTerminator())) {
+ // This is guaranteed to be a condbr at this point.
+ assert(BI->isConditional() && "Should have folded bb into pred!");
+ // Get the other block.
+ BasicBlock *OtherBB = BI->getSuccessor(BI->getSuccessor(0) == BB);
+ PI = pred_begin(OtherBB);
+ ++PI;
+ if (PI == pred_end(OtherBB)) {
+ // We have a conditional branch to two blocks that are only reachable
+ // from the condbr. We know that the condbr dominates the two blocks,
+ // so see if there is any identical code in the "then" and "else"
+ // blocks. If so, we can hoist it up to the branching block.
+ Changed |= HoistThenElseCodeToIf(BI);
+ }
+ }
+
+ for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
+ if (BranchInst *BI = dyn_cast<BranchInst>((*PI)->getTerminator()))
+ // Change br (X == 0 | X == 1), T, F into a switch instruction.
+ if (BI->isConditional() && isa<Instruction>(BI->getCondition())) {
+ Instruction *Cond = cast<Instruction>(BI->getCondition());
+ // If this is a bunch of seteq's or'd together, or if it's a bunch of
+ // 'setne's and'ed together, collect them.
+ Value *CompVal = 0;
+ std::vector<ConstantInt*> Values;
+ bool TrueWhenEqual = GatherValueComparisons(Cond, CompVal, Values);
+ if (CompVal && CompVal->getType()->isInteger()) {
+ // There might be duplicate constants in the list, which the switch
+ // instruction can't handle, remove them now.
+ std::sort(Values.begin(), Values.end(), ConstantIntOrdering());
+ Values.erase(std::unique(Values.begin(), Values.end()), Values.end());
+
+ // Figure out which block is which destination.
+ BasicBlock *DefaultBB = BI->getSuccessor(1);
+ BasicBlock *EdgeBB = BI->getSuccessor(0);
+ if (!TrueWhenEqual) std::swap(DefaultBB, EdgeBB);
+
+ // Create the new switch instruction now.
+ SwitchInst *New = new SwitchInst(CompVal, DefaultBB, BI);
+
+ // Add all of the 'cases' to the switch instruction.
+ for (unsigned i = 0, e = Values.size(); i != e; ++i)
+ New->addCase(Values[i], EdgeBB);
+
+ // We added edges from PI to the EdgeBB. As such, if there were any
+ // PHI nodes in EdgeBB, they need entries to be added corresponding to
+ // the number of edges added.
+ for (BasicBlock::iterator BBI = EdgeBB->begin();
+ isa<PHINode>(BBI); ++BBI) {
+ PHINode *PN = cast<PHINode>(BBI);
+ Value *InVal = PN->getIncomingValueForBlock(*PI);
+ for (unsigned i = 0, e = Values.size()-1; i != e; ++i)
+ PN->addIncoming(InVal, *PI);
+ }
+
+ // Erase the old branch instruction.
+ (*PI)->getInstList().erase(BI);
+
+ // Erase the potentially condition tree that was used to computed the
+ // branch condition.
+ ErasePossiblyDeadInstructionTree(Cond);
+ return true;
+ }
+ }
+
// If there is a trivial two-entry PHI node in this basic block, and we can
// eliminate it, do so now.
if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
//
BasicBlock *IfTrue, *IfFalse;
if (Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse)) {
- //std::cerr << "FOUND IF CONDITION! " << *IfCond << " T: "
- // << IfTrue->getName() << " F: " << IfFalse->getName() << "\n";
+ DEBUG(std::cerr << "FOUND IF CONDITION! " << *IfCond << " T: "
+ << IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
+
+ // Loop over the PHI's seeing if we can promote them all to select
+ // instructions. While we are at it, keep track of the instructions
+ // that need to be moved to the dominating block.
+ std::set<Instruction*> AggressiveInsts;
+ bool CanPromote = true;
- // Figure out where to insert instructions as necessary.
BasicBlock::iterator AfterPHIIt = BB->begin();
- while (isa<PHINode>(AfterPHIIt)) ++AfterPHIIt;
+ while (isa<PHINode>(AfterPHIIt)) {
+ PHINode *PN = cast<PHINode>(AfterPHIIt++);
+ if (PN->getIncomingValue(0) == PN->getIncomingValue(1))
+ PN->replaceAllUsesWith(PN->getIncomingValue(0));
+ else if (!DominatesMergePoint(PN->getIncomingValue(0), BB,
+ &AggressiveInsts) ||
+ !DominatesMergePoint(PN->getIncomingValue(1), BB,
+ &AggressiveInsts)) {
+ CanPromote = false;
+ break;
+ }
+ }
- BasicBlock::iterator I = BB->begin();
- while (PHINode *PN = dyn_cast<PHINode>(I)) {
- ++I;
-
- // If we can eliminate this PHI by directly computing it based on the
- // condition, do so now. We can't eliminate PHI nodes where the
- // incoming values are defined in the conditional parts of the branch,
- // so check for this.
- //
- if (DominatesMergePoint(PN->getIncomingValue(0), BB) &&
- DominatesMergePoint(PN->getIncomingValue(1), BB)) {
+ // Did we eliminate all PHI's?
+ CanPromote |= AfterPHIIt == BB->begin();
+
+ // If we all PHI nodes are promotable, check to make sure that all
+ // instructions in the predecessor blocks can be promoted as well. If
+ // not, we won't be able to get rid of the control flow, so it's not
+ // worth promoting to select instructions.
+ BasicBlock *DomBlock = 0, *IfBlock1 = 0, *IfBlock2 = 0;
+ if (CanPromote) {
+ PN = cast<PHINode>(BB->begin());
+ BasicBlock *Pred = PN->getIncomingBlock(0);
+ if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
+ IfBlock1 = Pred;
+ DomBlock = *pred_begin(Pred);
+ for (BasicBlock::iterator I = Pred->begin();
+ !isa<TerminatorInst>(I); ++I)
+ if (!AggressiveInsts.count(I)) {
+ // This is not an aggressive instruction that we can promote.
+ // Because of this, we won't be able to get rid of the control
+ // flow, so the xform is not worth it.
+ CanPromote = false;
+ break;
+ }
+ }
+
+ Pred = PN->getIncomingBlock(1);
+ if (CanPromote &&
+ cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
+ IfBlock2 = Pred;
+ DomBlock = *pred_begin(Pred);
+ for (BasicBlock::iterator I = Pred->begin();
+ !isa<TerminatorInst>(I); ++I)
+ if (!AggressiveInsts.count(I)) {
+ // This is not an aggressive instruction that we can promote.
+ // Because of this, we won't be able to get rid of the control
+ // flow, so the xform is not worth it.
+ CanPromote = false;
+ break;
+ }
+ }
+ }
+
+ // If we can still promote the PHI nodes after this gauntlet of tests,
+ // do all of the PHI's now.
+ if (CanPromote) {
+ // Move all 'aggressive' instructions, which are defined in the
+ // conditional parts of the if's up to the dominating block.
+ if (IfBlock1) {
+ DomBlock->getInstList().splice(DomBlock->getTerminator(),
+ IfBlock1->getInstList(),
+ IfBlock1->begin(),
+ IfBlock1->getTerminator());
+ }
+ if (IfBlock2) {
+ DomBlock->getInstList().splice(DomBlock->getTerminator(),
+ IfBlock2->getInstList(),
+ IfBlock2->begin(),
+ IfBlock2->getTerminator());
+ }
+
+ while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
+ // Change the PHI node into a select instruction.
Value *TrueVal =
PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
Value *FalseVal =
PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
- // FIXME: when we have a 'select' statement, we can be completely
- // generic and clean here and let the instcombine pass clean up
- // after us, by folding the select instructions away when possible.
- //
- if (TrueVal == FalseVal) {
- // Degenerate case...
- PN->replaceAllUsesWith(TrueVal);
- BB->getInstList().erase(PN);
- Changed = true;
- } else if (isa<ConstantBool>(TrueVal) &&
- isa<ConstantBool>(FalseVal)) {
- if (TrueVal == ConstantBool::True) {
- // The PHI node produces the same thing as the condition.
- PN->replaceAllUsesWith(IfCond);
- } else {
- // The PHI node produces the inverse of the condition. Insert a
- // "NOT" instruction, which is really a XOR.
- Value *InverseCond =
- BinaryOperator::createNot(IfCond, IfCond->getName()+".inv",
- AfterPHIIt);
- PN->replaceAllUsesWith(InverseCond);
- }
- BB->getInstList().erase(PN);
- Changed = true;
- } else if (isa<ConstantInt>(TrueVal) && isa<ConstantInt>(FalseVal)){
- // If this is a PHI of two constant integers, we insert a cast of
- // the boolean to the integer type in question, giving us 0 or 1.
- // Then we multiply this by the difference of the two constants,
- // giving us 0 if false, and the difference if true. We add this
- // result to the base constant, giving us our final value. We
- // rely on the instruction combiner to eliminate many special
- // cases, like turning multiplies into shifts when possible.
- std::string Name = PN->getName(); PN->setName("");
- Value *TheCast = new CastInst(IfCond, TrueVal->getType(),
- Name, AfterPHIIt);
- Constant *TheDiff = ConstantExpr::get(Instruction::Sub,
- cast<Constant>(TrueVal),
- cast<Constant>(FalseVal));
- Value *V = TheCast;
- if (TheDiff != ConstantInt::get(TrueVal->getType(), 1))
- V = BinaryOperator::create(Instruction::Mul, TheCast,
- TheDiff, TheCast->getName()+".scale",
- AfterPHIIt);
- if (!cast<Constant>(FalseVal)->isNullValue())
- V = BinaryOperator::create(Instruction::Add, V, FalseVal,
- V->getName()+".offs", AfterPHIIt);
- PN->replaceAllUsesWith(V);
- BB->getInstList().erase(PN);
- Changed = true;
- } else if (isa<ConstantInt>(FalseVal) &&
- cast<Constant>(FalseVal)->isNullValue()) {
- // If the false condition is an integral zero value, we can
- // compute the PHI by multiplying the condition by the other
- // value.
- std::string Name = PN->getName(); PN->setName("");
- Value *TheCast = new CastInst(IfCond, TrueVal->getType(),
- Name+".c", AfterPHIIt);
- Value *V = BinaryOperator::create(Instruction::Mul, TrueVal,
- TheCast, Name, AfterPHIIt);
- PN->replaceAllUsesWith(V);
- BB->getInstList().erase(PN);
- Changed = true;
- } else if (isa<ConstantInt>(TrueVal) &&
- cast<Constant>(TrueVal)->isNullValue()) {
- // If the true condition is an integral zero value, we can compute
- // the PHI by multiplying the inverse condition by the other
- // value.
- std::string Name = PN->getName(); PN->setName("");
- Value *NotCond = BinaryOperator::createNot(IfCond, Name+".inv",
- AfterPHIIt);
- Value *TheCast = new CastInst(NotCond, TrueVal->getType(),
- Name+".inv", AfterPHIIt);
- Value *V = BinaryOperator::create(Instruction::Mul, FalseVal,
- TheCast, Name, AfterPHIIt);
- PN->replaceAllUsesWith(V);
- BB->getInstList().erase(PN);
- Changed = true;
- }
+ std::string Name = PN->getName(); PN->setName("");
+ PN->replaceAllUsesWith(new SelectInst(IfCond, TrueVal, FalseVal,
+ Name, AfterPHIIt));
+ BB->getInstList().erase(PN);
}
+ Changed = true;
}
}
}
projects / oota-llvm.git / blobdiff