//
//===----------------------------------------------------------------------===//
+#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>
+
using namespace llvm;
// PropagatePredecessorsForPHIs - This gets "Succ" ready to have the
}
}
- // Loop over all of the PHI nodes in the successor BB
+ // Loop over all of the PHI nodes in the successor BB.
for (BasicBlock::iterator I = Succ->begin();
PHINode *PN = dyn_cast<PHINode>(I); ++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;
- }
+static bool DominatesMergePoint(Value *V, BasicBlock *BB, bool AllowAggressive){
+ 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 (!AllowAggressive) 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, false))
+ return false;
+ // Okay, it's safe to do this!
+ }
- // Non-instructions all dominate 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.
-static Value *GatherConstantSetEQs(Value *V, std::vector<Constant*> &Values) {
+static Value *GatherConstantSetEQs(Value *V, std::vector<ConstantInt*> &Values){
if (Instruction *Inst = dyn_cast<Instruction>(V))
if (Inst->getOpcode() == Instruction::SetEQ) {
- if (Constant *C = dyn_cast<Constant>(Inst->getOperand(1))) {
+ if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
Values.push_back(C);
return Inst->getOperand(0);
- } else if (Constant *C = dyn_cast<Constant>(Inst->getOperand(0))) {
+ } else if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(0))) {
Values.push_back(C);
return Inst->getOperand(1);
}
// 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<Constant*> &Values) {
+static Value *GatherConstantSetNEs(Value *V, std::vector<ConstantInt*> &Values){
if (Instruction *Inst = dyn_cast<Instruction>(V))
if (Inst->getOpcode() == Instruction::SetNE) {
- if (Constant *C = dyn_cast<Constant>(Inst->getOperand(1))) {
+ if (ConstantInt *C = dyn_cast<ConstantInt>(Inst->getOperand(1))) {
Values.push_back(C);
return Inst->getOperand(0);
- } else if (Constant *C = dyn_cast<Constant>(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(Constant::getNullValue(Inst->getOperand(0)->getType()));
+ 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))
/// 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<Constant*> &Values) {
+ std::vector<ConstantInt*> &Values) {
if (Cond->getOpcode() == Instruction::Or) {
CompVal = GatherConstantSetEQs(Cond, Values);
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
+ // 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();
/// 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, and existing predecessor of Succ.
+/// 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) !=
}
}
+// 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;
+}
+
+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
// 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)) {
- //cerr << "Removing BB: \n" << 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.
// we cannot do this transformation!
//
if (!PropagatePredecessorsForPHIs(BB, Succ)) {
- //cerr << "Killing Trivial BB: \n" << BB;
+ DEBUG(std::cerr << "Killing Trivial BB: \n" << *BB);
std::string OldName = BB->getName();
std::vector<BasicBlock*>
// 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]);
if (!OldName.empty() && !Succ->hasName()) // Transfer name if we can
Succ->setName(OldName);
-
- //cerr << "Function after removal: \n" << M;
return true;
}
}
// 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 unconditional branches.
+ // 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!
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 = new SelectInst(BI->getCondition(), TrueValue,
+ FalseValue, "retval", BI);
+ new ReturnInst(NewRetVal, BI);
+ BI->getParent()->getInstList().erase(BI);
+ 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.
+ // 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 (InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator()))
+ 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...
Preds.pop_back();
}
- } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->begin())) {
- // If the only instruction in this block is a switch instruction, see if we
- // can fold the switch instruction into a switch in a predecessor block.
- std::vector<BasicBlock*> Preds(pred_begin(BB), pred_end(BB));
- while (!Preds.empty()) {
- BasicBlock *Pred = Preds.back();
- Preds.pop_back();
-
- // If the two blocks are switching on the same value, we can merge this
- // switch into the predecessor's switch.
- if (SwitchInst *PSI = dyn_cast<SwitchInst>(Pred->getTerminator()))
- if (PSI->getCondition() == SI->getCondition() &&
- SafeToMergeTerminators(SI, PSI)) {
- // Figure out which 'cases' to copy from SI to PSI.
- std::vector<std::pair<Constant*, BasicBlock*> > Cases;
- BasicBlock *NewDefault = 0;
- if (PSI->getDefaultDest() == BB) {
- // If this is the default destination from PSI, only the edges in SI
- // that don't occur in PSI, or that branch to BB will be activated.
- std::set<Constant*> PSIHandled;
- for (unsigned i = 1, e = PSI->getNumSuccessors(); i != e; ++i)
- if (PSI->getSuccessor(i) != BB)
- PSIHandled.insert(PSI->getCaseValue(i));
- else {
- // This entry will be replaced.
- PSI->removeCase(i);
- --i; --e;
- }
- NewDefault = SI->getDefaultDest();
- for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) {
- Constant *C = SI->getCaseValue(i);
- if (!PSIHandled.count(C))
- Cases.push_back(std::make_pair(C, SI->getSuccessor(i)));
- }
+ // 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 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<Constant*> PSIHandled;
- for (unsigned i = 1, e = PSI->getNumSuccessors(); i != e; ++i)
- if (PSI->getSuccessor(i) == BB) {
- // We know that BB doesn't have any PHI nodes in it, so just
- // drop the edges.
- PSIHandled.insert(PSI->getCaseValue(i));
- PSI->removeCase(i);
- --i; --e;
- }
+ } 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;
+ }
- // Okay, now we know which constants were sent to BB from the
- // predecessor. Figure out where they will all go now.
- for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) {
- Constant *C = SI->getCaseValue(i);
- if (PSIHandled.count(C)) {
- // If this is one we are capable of getting...
- Cases.push_back(std::make_pair(C, SI->getSuccessor(i)));
- PSIHandled.erase(C); // This constant is taken care of
+ // 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 there are any constants vectored to BB that SI doesn't handle,
- // they must go to the default destination of SI.
- for (std::set<Constant*>::iterator I = PSIHandled.begin(),
- E = PSIHandled.end(); I != E; ++I)
- Cases.push_back(std::make_pair(*I, SI->getDefaultDest()));
- }
- // Okay, at this point, we know which cases need to be added to the
- // PSI switch and which destinations they go to. If PSI needs its
- // default destination changed, NewDefault is set. Start changing
- // stuff now.
- if (NewDefault) {
- AddPredecessorToBlock(NewDefault, Pred, BB);
- PSI->setSuccessor(0, NewDefault);
- }
-
- // Okay, add all of the cases now.
- for (unsigned i = 0, e = Cases.size(); i != e; ++i) {
- AddPredecessorToBlock(Cases[i].second, Pred, BB);
- PSI->addCase(Cases[i].first, Cases[i].second);
- }
-
- // 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 = PSI->getNumSuccessors(); i != e; ++i)
- if (PSI->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);
- }
- PSI->setSuccessor(i, InfLoopBlock);
- }
-
- Changed = true;
+ // 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;
+ }
}
-
- // If we removed all predecessors of this block, recursively call
- // SimplifyCFG to remove it.
- if (pred_begin(BB) == pred_end(BB))
- return SimplifyCFG(BB);
}
// Merge basic blocks into their predecessor if there is only one distinct
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
// 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<Constant*> Values;
+ 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());
+ 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 *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");
// Figure out where to insert instructions as necessary.
BasicBlock::iterator AfterPHIIt = BB->begin();
// 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)) {
+ if (DominatesMergePoint(PN->getIncomingValue(0), BB, true) &&
+ DominatesMergePoint(PN->getIncomingValue(1), BB, true)) {
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;
+ // If one of the incoming values is defined in the conditional
+ // region, move it into it's predecessor block, which we know is
+ // safe.
+ if (!DominatesMergePoint(TrueVal, BB, false)) {
+ Instruction *TrueI = cast<Instruction>(TrueVal);
+ BasicBlock *OldBB = TrueI->getParent();
+ OldBB->getInstList().remove(TrueI);
+ BasicBlock *NewBB = *pred_begin(OldBB);
+ NewBB->getInstList().insert(NewBB->getTerminator(), TrueI);
+ }
+ if (!DominatesMergePoint(FalseVal, BB, false)) {
+ Instruction *FalseI = cast<Instruction>(FalseVal);
+ BasicBlock *OldBB = FalseI->getParent();
+ OldBB->getInstList().remove(FalseI);
+ BasicBlock *NewBB = *pred_begin(OldBB);
+ NewBB->getInstList().insert(NewBB->getTerminator(), FalseI);
}
+
+ // Change the PHI node into a select instruction.
+ BasicBlock::iterator InsertPos = PN;
+ while (isa<PHINode>(InsertPos)) ++InsertPos;
+
+ std::string Name = PN->getName(); PN->setName("");
+ PN->replaceAllUsesWith(new SelectInst(IfCond, TrueVal, FalseVal,
+ Name, InsertPos));
+ BB->getInstList().erase(PN);
+ Changed = true;
}
}
}
projects / oota-llvm.git / blobdiff