#include "llvm/Type.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/Debug.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include <algorithm>
#include <functional>
#include <set>
#include <map>
using namespace llvm;
-// 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.
+/// 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);
+ }
+}
+
+// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
+// almost-empty BB ending in an unconditional branch to Succ, into succ.
//
// Assumption: Succ is the single successor for BB.
//
-static bool PropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
+static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
- if (!isa<PHINode>(Succ->front()))
- return false; // We can make the transformation, no problem.
-
- // If there is more than one predecessor, and there are PHI nodes in
- // the successor, then we need to add incoming edges for the PHI nodes
- //
- const std::vector<BasicBlock*> BBPreds(pred_begin(BB), pred_end(BB));
-
// Check to see if one of the predecessors of BB is already a predecessor of
// Succ. If so, we cannot do the transformation if there are any PHI nodes
// with incompatible values coming in from the two edges!
//
- for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ); PI != PE; ++PI)
- 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(); 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
- // blocks).
- int Idx1 = PN->getBasicBlockIndex(BB);
- int Idx2 = PN->getBasicBlockIndex(*PI);
- assert(Idx1 != -1 && Idx2 != -1 &&
- "Didn't have entries for my predecessors??");
- if (PN->getIncomingValue(Idx1) != PN->getIncomingValue(Idx2))
- return true; // Values are not equal...
+ if (isa<PHINode>(Succ->front())) {
+ std::set<BasicBlock*> BBPreds(pred_begin(BB), pred_end(BB));
+ for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ);
+ PI != PE; ++PI)
+ 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(); 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 blocks).
+ if (PN->getIncomingValueForBlock(BB) !=
+ PN->getIncomingValueForBlock(*PI))
+ return false; // Values are not equal...
+ }
}
+ }
+
+ // Finally, if BB has PHI nodes that are used by things other than the PHIs in
+ // Succ and Succ has predecessors that are not Succ and not Pred, we cannot
+ // fold these blocks, as we don't know whether BB dominates Succ or not to
+ // update the PHI nodes correctly.
+ if (!isa<PHINode>(BB->begin()) || Succ->getSinglePredecessor()) return true;
+
+ // If the predecessors of Succ are only BB and Succ itself, we can handle this.
+ bool IsSafe = true;
+ for (pred_iterator PI = pred_begin(Succ), E = pred_end(Succ); PI != E; ++PI)
+ if (*PI != Succ && *PI != BB) {
+ IsSafe = false;
+ break;
}
-
- // Loop over all of the PHI nodes in the successor BB.
- for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
+ if (IsSafe) return true;
+
+ // If the PHI nodes in BB are only used by instructions in Succ, we are ok if
+ // BB and Succ have no common predecessors.
+ for (BasicBlock::iterator I = BB->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, 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 (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(),
+ for (Value::use_iterator UI = PN->use_begin(), E = PN->use_end(); UI != E;
+ ++UI)
+ if (cast<Instruction>(*UI)->getParent() != Succ)
+ return false;
+ }
+
+ // Scan the predecessor sets of BB and Succ, making sure there are no common
+ // predecessors. Common predecessors would cause us to build a phi node with
+ // differing incoming values, which is not legal.
+ std::set<BasicBlock*> BBPreds(pred_begin(BB), pred_end(BB));
+ for (pred_iterator PI = pred_begin(Succ), E = pred_end(Succ); PI != E; ++PI)
+ if (BBPreds.count(*PI))
+ return false;
+
+ return true;
+}
+
+/// TryToSimplifyUncondBranchFromEmptyBlock - BB contains an unconditional
+/// branch to Succ, and contains no instructions other than PHI nodes and the
+/// branch. If possible, eliminate BB.
+static bool TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB,
+ BasicBlock *Succ) {
+ // 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 (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
+
+ DOUT << "Killing Trivial BB: \n" << *BB;
+
+ if (isa<PHINode>(Succ->begin())) {
+ // If there is more than one pred of succ, and there are PHI nodes in
+ // the successor, then we need to add incoming edges for the PHI nodes
+ //
+ const std::vector<BasicBlock*> BBPreds(pred_begin(BB), pred_end(BB));
+
+ // Loop over all of the PHI nodes in the successor of 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, 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 (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) {
- // Add an incoming value for each of the new incoming values...
- PN->addIncoming(OldVal, *PredI);
+ // Add an incoming value for each of the new incoming values...
+ PN->addIncoming(OldVal, *PredI);
+ }
}
}
}
- return false;
+
+ 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()) {
+ // Just remove the dead phi. This happens if Succ's PHIs were the only
+ // users of the PHI nodes.
+ PN->eraseFromParent();
+ } 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
+ // now. Simply move it into Succ, because we know that BB
+ // strictly dominated Succ.
+ Succ->getInstList().splice(Succ->begin(),
+ BB->getInstList(), BB->begin());
+
+ // 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;
}
/// GetIfCondition - Given a basic block (BB) with two predecessors (and
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.
+ if (!I) {
+ // Non-instructions all dominate instructions, but not all constantexprs
+ // can be executed unconditionally.
+ if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
+ if (C->canTrap())
+ return false;
+ return true;
+ }
BasicBlock *PBB = I->getParent();
// We don't want to allow weird loops that might have the "if condition" in
case Instruction::Or:
case Instruction::Xor:
case Instruction::Shl:
- case Instruction::Shr:
- case Instruction::SetEQ:
- case Instruction::SetNE:
- case Instruction::SetLT:
- case Instruction::SetGT:
- case Instruction::SetLE:
- case Instruction::SetGE:
+ case Instruction::LShr:
+ case Instruction::AShr:
+ case Instruction::ICmp:
+ case Instruction::FCmp:
break; // These are all cheap and non-trapping instructions.
}
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.
+// GatherConstantSetEQs - Given a potentially 'or'd together collection of
+// icmp_eq 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 (Inst->getOpcode() == Instruction::ICmp &&
+ cast<ICmpInst>(Inst)->getPredicate() == ICmpInst::ICMP_EQ) {
if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
Values.push_back(C);
return Inst->getOperand(0);
// 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 (Inst->getOpcode() == Instruction::ICmp &&
+ cast<ICmpInst>(Inst)->getPredicate() == ICmpInst::ICMP_NE) {
if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
Values.push_back(C);
return 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))
/// 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);
- }
-}
-
-/// 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;
+ if (!isInstructionTriviallyDead(I)) return;
+
+ std::vector<Instruction*> InstrsToInspect;
+ InstrsToInspect.push_back(I);
+
+ while (!InstrsToInspect.empty()) {
+ I = InstrsToInspect.back();
+ InstrsToInspect.pop_back();
+
+ if (!isInstructionTriviallyDead(I)) continue;
+
+ // If I is in the work list multiple times, remove previous instances.
+ for (unsigned i = 0, e = InstrsToInspect.size(); i != e; ++i)
+ if (InstrsToInspect[i] == I) {
+ InstrsToInspect.erase(InstrsToInspect.begin()+i);
+ --i, --e;
}
- return true;
-}
+ // Add operands of dead instruction to worklist.
+ for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
+ if (Instruction *OpI = dyn_cast<Instruction>(I->getOperand(i)))
+ InstrsToInspect.push_back(OpI);
-/// 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);
+ // Remove dead instruction.
+ I->eraseFromParent();
}
}
}
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);
+ if (ICmpInst *ICI = dyn_cast<ICmpInst>(BI->getCondition()))
+ if ((ICI->getPredicate() == ICmpInst::ICMP_EQ ||
+ ICI->getPredicate() == ICmpInst::ICMP_NE) &&
+ isa<ConstantInt>(ICI->getOperand(1)))
+ return ICI->getOperand(0);
return 0;
}
}
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);
+ ICmpInst *ICI = cast<ICmpInst>(BI->getCondition());
+ Cases.push_back(std::make_pair(cast<ConstantInt>(ICI->getOperand(1)),
+ BI->getSuccessor(ICI->getPredicate() ==
+ ICmpInst::ICMP_NE)));
+ return BI->getSuccessor(ICI->getPredicate() == ICmpInst::ICMP_EQ);
}
// Remove PHI node entries for the dead edge.
ThisCases[0].second->removePredecessor(TI->getParent());
- DEBUG(std::cerr << "Threading pred instr: " << *Pred->getTerminator()
- << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
+ DOUT << "Threading pred instr: " << *Pred->getTerminator()
+ << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n";
TI->eraseFromParent(); // Nuke the old one.
// If condition is now dead, nuke it.
for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
DeadCases.insert(PredCases[i].first);
- DEBUG(std::cerr << "Threading pred instr: " << *Pred->getTerminator()
- << "Through successor TI: " << *TI);
+ DOUT << "Threading pred instr: " << *Pred->getTerminator()
+ << "Through successor TI: " << *TI;
for (unsigned i = SI->getNumCases()-1; i != 0; --i)
if (DeadCases.count(SI->getCaseValue(i))) {
SI->removeCase(i);
}
- DEBUG(std::cerr << "Leaving: " << *TI << "\n");
+ DOUT << "Leaving: " << *TI << "\n";
return true;
}
}
// Insert the new branch.
Instruction *NI = new BranchInst(TheRealDest, TI);
- DEBUG(std::cerr << "Threading pred instr: " << *Pred->getTerminator()
- << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n");
+ DOUT << "Threading pred instr: " << *Pred->getTerminator()
+ << "Through successor TI: " << *TI << "Leaving: " << *NI << "\n";
Instruction *Cond = 0;
if (BranchInst *BI = dyn_cast<BranchInst>(TI))
Cond = dyn_cast<Instruction>(BI->getCondition());
return Changed;
}
-/// HoistThenElseCodeToIf - Given a conditional branch that codes to BB1 and
+/// HoistThenElseCodeToIf - Given a conditional branch that goes 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) {
BasicBlock *BB2 = BI->getSuccessor(1); // The false destination
Instruction *I1 = BB1->begin(), *I2 = BB2->begin();
- if (I1->getOpcode() != I2->getOpcode() || !I1->isIdenticalTo(I2))
+ if (I1->getOpcode() != I2->getOpcode() || isa<PHINode>(I1) ||
+ isa<InvokeInst>(I1) || !I1->isIdenticalTo(I2))
return false;
// If we get here, we can hoist at least one instruction.
return true;
}
+/// BlockIsSimpleEnoughToThreadThrough - Return true if we can thread a branch
+/// across this block.
+static bool BlockIsSimpleEnoughToThreadThrough(BasicBlock *BB) {
+ BranchInst *BI = cast<BranchInst>(BB->getTerminator());
+ unsigned Size = 0;
+
+ // If this basic block contains anything other than a PHI (which controls the
+ // branch) and branch itself, bail out. FIXME: improve this in the future.
+ for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI, ++Size) {
+ if (Size > 10) return false; // Don't clone large BB's.
+
+ // We can only support instructions that are do not define values that are
+ // live outside of the current basic block.
+ for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
+ UI != E; ++UI) {
+ Instruction *U = cast<Instruction>(*UI);
+ if (U->getParent() != BB || isa<PHINode>(U)) return false;
+ }
+
+ // Looks ok, continue checking.
+ }
+
+ return true;
+}
+
+/// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
+/// that is defined in the same block as the branch and if any PHI entries are
+/// constants, thread edges corresponding to that entry to be branches to their
+/// ultimate destination.
+static bool FoldCondBranchOnPHI(BranchInst *BI) {
+ BasicBlock *BB = BI->getParent();
+ PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
+ // NOTE: we currently cannot transform this case if the PHI node is used
+ // outside of the block.
+ if (!PN || PN->getParent() != BB || !PN->hasOneUse())
+ return false;
+
+ // Degenerate case of a single entry PHI.
+ if (PN->getNumIncomingValues() == 1) {
+ if (PN->getIncomingValue(0) != PN)
+ PN->replaceAllUsesWith(PN->getIncomingValue(0));
+ else
+ PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
+ PN->eraseFromParent();
+ return true;
+ }
+
+ // Now we know that this block has multiple preds and two succs.
+ if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
+
+ // Okay, this is a simple enough basic block. See if any phi values are
+ // constants.
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
+ ConstantInt *CB;
+ if ((CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i))) &&
+ CB->getType() == Type::Int1Ty) {
+ // Okay, we now know that all edges from PredBB should be revectored to
+ // branch to RealDest.
+ BasicBlock *PredBB = PN->getIncomingBlock(i);
+ BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
+
+ if (RealDest == BB) continue; // Skip self loops.
+
+ // The dest block might have PHI nodes, other predecessors and other
+ // difficult cases. Instead of being smart about this, just insert a new
+ // block that jumps to the destination block, effectively splitting
+ // the edge we are about to create.
+ BasicBlock *EdgeBB = new BasicBlock(RealDest->getName()+".critedge",
+ RealDest->getParent(), RealDest);
+ new BranchInst(RealDest, EdgeBB);
+ PHINode *PN;
+ for (BasicBlock::iterator BBI = RealDest->begin();
+ (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
+ Value *V = PN->getIncomingValueForBlock(BB);
+ PN->addIncoming(V, EdgeBB);
+ }
+
+ // BB may have instructions that are being threaded over. Clone these
+ // instructions into EdgeBB. We know that there will be no uses of the
+ // cloned instructions outside of EdgeBB.
+ BasicBlock::iterator InsertPt = EdgeBB->begin();
+ std::map<Value*, Value*> TranslateMap; // Track translated values.
+ for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
+ if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
+ TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
+ } else {
+ // Clone the instruction.
+ Instruction *N = BBI->clone();
+ if (BBI->hasName()) N->setName(BBI->getName()+".c");
+
+ // Update operands due to translation.
+ for (unsigned i = 0, e = N->getNumOperands(); i != e; ++i) {
+ std::map<Value*, Value*>::iterator PI =
+ TranslateMap.find(N->getOperand(i));
+ if (PI != TranslateMap.end())
+ N->setOperand(i, PI->second);
+ }
+
+ // Check for trivial simplification.
+ if (Constant *C = ConstantFoldInstruction(N)) {
+ TranslateMap[BBI] = C;
+ delete N; // Constant folded away, don't need actual inst
+ } else {
+ // Insert the new instruction into its new home.
+ EdgeBB->getInstList().insert(InsertPt, N);
+ if (!BBI->use_empty())
+ TranslateMap[BBI] = N;
+ }
+ }
+ }
+
+ // Loop over all of the edges from PredBB to BB, changing them to branch
+ // to EdgeBB instead.
+ TerminatorInst *PredBBTI = PredBB->getTerminator();
+ for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
+ if (PredBBTI->getSuccessor(i) == BB) {
+ BB->removePredecessor(PredBB);
+ PredBBTI->setSuccessor(i, EdgeBB);
+ }
+
+ // Recurse, simplifying any other constants.
+ return FoldCondBranchOnPHI(BI) | true;
+ }
+ }
+
+ return false;
+}
+
+/// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
+/// PHI node, see if we can eliminate it.
+static bool FoldTwoEntryPHINode(PHINode *PN) {
+ // Ok, this is a two entry PHI node. Check to see if this is a simple "if
+ // statement", which has a very simple dominance structure. Basically, we
+ // are trying to find the condition that is being branched on, which
+ // subsequently causes this merge to happen. We really want control
+ // dependence information for this check, but simplifycfg can't keep it up
+ // to date, and this catches most of the cases we care about anyway.
+ //
+ BasicBlock *BB = PN->getParent();
+ BasicBlock *IfTrue, *IfFalse;
+ Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
+ if (!IfCond) return false;
+
+ // Okay, we found that we can merge this two-entry phi node into a select.
+ // Doing so would require us to fold *all* two entry phi nodes in this block.
+ // At some point this becomes non-profitable (particularly if the target
+ // doesn't support cmov's). Only do this transformation if there are two or
+ // fewer PHI nodes in this block.
+ unsigned NumPhis = 0;
+ for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
+ if (NumPhis > 2)
+ return false;
+
+ DOUT << "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;
+
+ BasicBlock::iterator AfterPHIIt = BB->begin();
+ while (isa<PHINode>(AfterPHIIt)) {
+ PHINode *PN = cast<PHINode>(AfterPHIIt++);
+ if (PN->getIncomingValue(0) == PN->getIncomingValue(1)) {
+ if (PN->getIncomingValue(0) != PN)
+ PN->replaceAllUsesWith(PN->getIncomingValue(0));
+ else
+ PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
+ } else if (!DominatesMergePoint(PN->getIncomingValue(0), BB,
+ &AggressiveInsts) ||
+ !DominatesMergePoint(PN->getIncomingValue(1), BB,
+ &AggressiveInsts)) {
+ return false;
+ }
+ }
+
+ // 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;
+ 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.
+ return false;
+ }
+ }
+
+ Pred = PN->getIncomingBlock(1);
+ if (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.
+ return false;
+ }
+ }
+
+ // If we can still promote the PHI nodes after this gauntlet of tests,
+ // do all of the PHI's now.
+
+ // 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);
+
+ std::string Name = PN->getName(); PN->setName("");
+ PN->replaceAllUsesWith(new SelectInst(IfCond, TrueVal, FalseVal,
+ Name, AfterPHIIt));
+ BB->getInstList().erase(PN);
+ }
+ 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();
+ return LHS->getZExtValue() < RHS->getZExtValue();
}
};
}
-
// 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
// Remove basic blocks that have no predecessors... which are unreachable.
if (pred_begin(BB) == pred_end(BB) ||
*pred_begin(BB) == BB && ++pred_begin(BB) == pred_end(BB)) {
- DEBUG(std::cerr << "Removing BB: \n" << *BB);
+ DOUT << "Removing BB: \n" << *BB;
// Loop through all of our successors and make sure they know that one
// of their predecessors is going away.
while (!BB->empty()) {
Instruction &I = BB->back();
// If this instruction is used, replace uses with an arbitrary
- // constant value. Because control flow can't get here, we don't care
+ // value. Because control flow can't get here, we don't care
// what we replace the value with. Note that since this block is
// unreachable, and all values contained within it must dominate their
// uses, that all uses will eventually be removed.
if (!I.use_empty())
- // Make all users of this instruction reference the constant instead
- I.replaceAllUsesWith(Constant::getNullValue(I.getType()));
+ // Make all users of this instruction use undef instead
+ I.replaceAllUsesWith(UndefValue::get(I.getType()));
// Remove the instruction from the basic block
BB->getInstList().pop_back();
// away...
Changed |= ConstantFoldTerminator(BB);
- // Check to see if this block has no non-phi instructions and only a single
- // successor. If so, replace references to this basic block with references
- // 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;
-
- 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() || Succ->getSinglePredecessor() == 0) {
- // We can only move the PHI node into Succ if BB dominates Succ.
- // Since BB only has a single successor (Succ), the PHI nodes
- // will dominate Succ, unless Succ has multiple predecessors. In
- // this case, the PHIs are either dead, or have references in dead
- // blocks. In either case, we can just remove them.
- if (!PN->use_empty()) // Uses in dead block?
- PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
- PN->eraseFromParent(); // 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
- // now. Simply move it into Succ, because we know that BB
- // 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;
- }
- }
- }
-
// If this is a returning block with only PHI nodes in it, fold the return
// instruction into any unconditional branch predecessors.
//
if (!UncondBranchPreds.empty()) {
while (!UncondBranchPreds.empty()) {
BasicBlock *Pred = UncondBranchPreds.back();
+ DOUT << "FOLDING: " << *BB
+ << "INTO UNCOND BRANCH PRED: " << *Pred;
UncondBranchPreds.pop_back();
Instruction *UncondBranch = Pred->getTerminator();
// Clone the return and add it to the end of the predecessor.
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())
+ // In order for this transformation to be safe, we must be able to
+ // unconditionally execute both operands to the return. This is
+ // normally the case, but we could have a potentially-trapping
+ // constant expression that prevents this transformation from being
+ // safe.
+ if ((!isa<ConstantExpr>(TrueValue) ||
+ !cast<ConstantExpr>(TrueValue)->canTrap()) &&
+ (!isa<ConstantExpr>(TrueValue) ||
+ !cast<ConstantExpr>(TrueValue)->canTrap())) {
+ 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;
+
+ DOUT << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
+ << "\n " << *BI << "Select = " << *NewRetVal
+ << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc;
+
+ new ReturnInst(NewRetVal, BI);
+ BI->eraseFromParent();
if (Instruction *BrCondI = dyn_cast<Instruction>(BrCond))
- BrCondI->getParent()->getInstList().erase(BrCondI);
- return true;
+ if (isInstructionTriviallyDead(BrCondI))
+ BrCondI->eraseFromParent();
+ return true;
+ }
}
}
}
}
- } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->begin())) {
+ } else if (isa<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
return SimplifyCFG(BB) || 1;
}
} else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
- if (BI->isConditional()) {
- if (Value *CompVal = isValueEqualityComparison(BI)) {
+ if (BI->isUnconditional()) {
+ BasicBlock::iterator BBI = BB->begin(); // Skip over phi nodes...
+ while (isa<PHINode>(*BBI)) ++BBI;
+
+ BasicBlock *Succ = BI->getSuccessor(0);
+ if (BBI->isTerminator() && // Terminator is the only non-phi instruction!
+ Succ != BB) // Don't hurt infinite loops!
+ if (TryToSimplifyUncondBranchFromEmptyBlock(BB, Succ))
+ return 1;
+
+ } else { // Conditional branch
+ if (isValueEqualityComparison(BI)) {
// If we only have one predecessor, and if it is a branch on this value,
// see if that predecessor totally determines the outcome of this
// switch.
if (FoldValueComparisonIntoPredecessors(BI))
return SimplifyCFG(BB) | true;
}
+
+ // If this is a branch on a phi node in the current block, thread control
+ // through this block if any PHI node entries are constants.
+ if (PHINode *PN = dyn_cast<PHINode>(BI->getCondition()))
+ if (PN->getParent() == BI->getParent())
+ if (FoldCondBranchOnPHI(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 &&
+ if (Instruction *Cond = dyn_cast<Instruction>(BI->getCondition()))
+ if ((isa<CmpInst>(Cond) || isa<BinaryOperator>(Cond)) &&
+ 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)
PBI->setSuccessor(1, OldTrue);
}
- if (PBI->getSuccessor(0) == TrueDest ||
- PBI->getSuccessor(1) == FalseDest) {
+ if ((PBI->getSuccessor(0) == TrueDest && FalseDest != BB) ||
+ (PBI->getSuccessor(1) == FalseDest && TrueDest != BB)) {
// Clone Cond into the predecessor basic block, and or/and the
// two conditions together.
Instruction *New = Cond->clone();
}
}
- // 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;
- }
+ // Scan predessor blocks for conditional branchs.
+ for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
+ if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
+ if (PBI != BI && PBI->isConditional()) {
+
+ // If this block ends with a branch instruction, and if there is a
+ // predecessor that ends on a branch of the same condition, make
+ // this conditional branch redundant.
+ if (PBI->getCondition() == BI->getCondition() &&
+ PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
+ // Okay, the outcome of this conditional branch is statically
+ // knowable. If this block had a single pred, handle specially.
+ if (BB->getSinglePredecessor()) {
+ // Turn this into a branch on constant.
+ bool CondIsTrue = PBI->getSuccessor(0) == BB;
+ BI->setCondition(ConstantInt::get(Type::Int1Ty, CondIsTrue));
+ return SimplifyCFG(BB); // Nuke the branch on constant.
+ }
+
+ // Otherwise, if there are multiple predecessors, insert a PHI
+ // that merges in the constant and simplify the block result.
+ if (BlockIsSimpleEnoughToThreadThrough(BB)) {
+ PHINode *NewPN = new PHINode(Type::Int1Ty,
+ BI->getCondition()->getName()+".pr",
+ BB->begin());
+ for (PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
+ if ((PBI = dyn_cast<BranchInst>((*PI)->getTerminator())) &&
+ PBI != BI && PBI->isConditional() &&
+ PBI->getCondition() == BI->getCondition() &&
+ PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
+ bool CondIsTrue = PBI->getSuccessor(0) == BB;
+ NewPN->addIncoming(ConstantInt::get(Type::Int1Ty,
+ CondIsTrue), *PI);
+ } else {
+ NewPN->addIncoming(BI->getCondition(), *PI);
+ }
+
+ BI->setCondition(NewPN);
+ // This will thread the branch.
+ return SimplifyCFG(BB) | true;
+ }
+ }
+
+ // If this is a conditional branch in an empty block, and if any
+ // predecessors is a conditional branch to one of our destinations,
+ // fold the conditions into logical ops and one cond br.
+ if (&BB->front() == BI) {
+ int PBIOp, BIOp;
+ if (PBI->getSuccessor(0) == BI->getSuccessor(0)) {
+ PBIOp = BIOp = 0;
+ } else if (PBI->getSuccessor(0) == BI->getSuccessor(1)) {
+ PBIOp = 0; BIOp = 1;
+ } else if (PBI->getSuccessor(1) == BI->getSuccessor(0)) {
+ PBIOp = 1; BIOp = 0;
+ } else if (PBI->getSuccessor(1) == BI->getSuccessor(1)) {
+ PBIOp = BIOp = 1;
+ } else {
+ PBIOp = BIOp = -1;
+ }
+
+ // Check to make sure that the other destination of this branch
+ // isn't BB itself. If so, this is an infinite loop that will
+ // keep getting unwound.
+ if (PBIOp != -1 && PBI->getSuccessor(PBIOp) == BB)
+ PBIOp = BIOp = -1;
+
+ // Do not perform this transformation if it would require
+ // insertion of a large number of select instructions. For targets
+ // without predication/cmovs, this is a big pessimization.
+ if (PBIOp != -1) {
+ BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
+
+ unsigned NumPhis = 0;
+ for (BasicBlock::iterator II = CommonDest->begin();
+ isa<PHINode>(II); ++II, ++NumPhis) {
+ if (NumPhis > 2) {
+ // Disable this xform.
+ PBIOp = -1;
+ 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;
+ // Finally, if everything is ok, fold the branches to logical ops.
+ if (PBIOp != -1) {
+ BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
+ BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
+
+ // If OtherDest *is* BB, then this is a basic block with just
+ // a conditional branch in it, where one edge (OtherDesg) goes
+ // back to the block. We know that the program doesn't get
+ // stuck in the infinite loop, so the condition must be such
+ // that OtherDest isn't branched through. Forward to CommonDest,
+ // and avoid an infinite loop at optimizer time.
+ if (OtherDest == BB)
+ OtherDest = CommonDest;
+
+ DOUT << "FOLDING BRs:" << *PBI->getParent()
+ << "AND: " << *BI->getParent();
+
+ // BI may have other predecessors. Because of this, we leave
+ // it alone, but modify PBI.
+
+ // Make sure we get to CommonDest on True&True directions.
+ Value *PBICond = PBI->getCondition();
+ if (PBIOp)
+ PBICond = BinaryOperator::createNot(PBICond,
+ PBICond->getName()+".not",
+ PBI);
+ Value *BICond = BI->getCondition();
+ if (BIOp)
+ BICond = BinaryOperator::createNot(BICond,
+ BICond->getName()+".not",
+ PBI);
+ // Merge the conditions.
+ Value *Cond =
+ BinaryOperator::createOr(PBICond, BICond, "brmerge", PBI);
+
+ // Modify PBI to branch on the new condition to the new dests.
+ PBI->setCondition(Cond);
+ PBI->setSuccessor(0, CommonDest);
+ PBI->setSuccessor(1, OtherDest);
+
+ // OtherDest may have phi nodes. If so, add an entry from PBI's
+ // block that are identical to the entries for BI's block.
+ PHINode *PN;
+ for (BasicBlock::iterator II = OtherDest->begin();
+ (PN = dyn_cast<PHINode>(II)); ++II) {
+ Value *V = PN->getIncomingValueForBlock(BB);
+ PN->addIncoming(V, PBI->getParent());
+ }
+
+ // We know that the CommonDest already had an edge from PBI to
+ // it. If it has PHIs though, the PHIs may have different
+ // entries for BB and PBI's BB. If so, insert a select to make
+ // them agree.
+ for (BasicBlock::iterator II = CommonDest->begin();
+ (PN = dyn_cast<PHINode>(II)); ++II) {
+ Value * BIV = PN->getIncomingValueForBlock(BB);
+ unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
+ Value *PBIV = PN->getIncomingValue(PBBIdx);
+ if (BIV != PBIV) {
+ // Insert a select in PBI to pick the right value.
+ Value *NV = new SelectInst(PBICond, PBIV, BIV,
+ PBIV->getName()+".mux", PBI);
+ PN->setIncomingValue(PBBIdx, NV);
+ }
+ }
+
+ DOUT << "INTO: " << *PBI->getParent();
+
+ // This basic block is probably dead. We know it has at least
+ // one fewer predecessor.
+ return SimplifyCFG(BB) | true;
+ }
+ }
}
}
} else if (isa<UnreachableInst>(BB->getTerminator())) {
}
if (OnlySucc) {
- DEBUG(std::cerr << "Merging: " << *BB << "into: " << *OnlyPred);
- TerminatorInst *Term = OnlyPred->getTerminator();
+ DOUT << "Merging: " << *BB << "into: " << *OnlyPred;
// Resolve any PHI nodes at the start of the block. They are all
// guaranteed to have exactly one entry if they exist, unless there are
Value *CompVal = 0;
std::vector<ConstantInt*> Values;
bool TrueWhenEqual = GatherValueComparisons(Cond, CompVal, Values);
- if (CompVal && CompVal->getType()->isInteger()) {
+ if (CompVal && CompVal->getType()->isIntegral()) {
// 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());
// 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()))
- if (PN->getNumIncomingValues() == 2) {
- // Ok, this is a two entry PHI node. Check to see if this is a simple "if
- // statement", which has a very simple dominance structure. Basically, we
- // are trying to find the condition that is being branched on, which
- // subsequently causes this merge to happen. We really want control
- // dependence information for this check, but simplifycfg can't keep it up
- // to date, and this catches most of the cases we care about anyway.
- //
- BasicBlock *IfTrue, *IfFalse;
- if (Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse)) {
- 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;
-
- BasicBlock::iterator AfterPHIIt = BB->begin();
- while (isa<PHINode>(AfterPHIIt)) {
- PHINode *PN = cast<PHINode>(AfterPHIIt++);
- if (PN->getIncomingValue(0) == PN->getIncomingValue(1)) {
- if (PN->getIncomingValue(0) != PN)
- PN->replaceAllUsesWith(PN->getIncomingValue(0));
- else
- PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
- } else if (!DominatesMergePoint(PN->getIncomingValue(0), BB,
- &AggressiveInsts) ||
- !DominatesMergePoint(PN->getIncomingValue(1), BB,
- &AggressiveInsts)) {
- CanPromote = false;
- break;
- }
- }
-
- // 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);
-
- std::string Name = PN->getName(); PN->setName("");
- PN->replaceAllUsesWith(new SelectInst(IfCond, TrueVal, FalseVal,
- Name, AfterPHIIt));
- BB->getInstList().erase(PN);
- }
- Changed = true;
- }
- }
- }
+ if (PN->getNumIncomingValues() == 2)
+ Changed |= FoldTwoEntryPHINode(PN);
return Changed;
}
projects / oota-llvm.git / blobdiff