//===- SimplifyCFG.cpp - Code to perform CFG simplification ---------------===//
-//
+//
// The LLVM Compiler Infrastructure
//
-// This file was developed by the LLVM research group and is distributed under
-// the University of Illinois Open Source License. See LICENSE.TXT for details.
-//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
//===----------------------------------------------------------------------===//
//
// Peephole optimize the CFG.
#include "llvm/Constants.h"
#include "llvm/Instructions.h"
#include "llvm/Type.h"
+#include "llvm/DerivedTypes.h"
#include "llvm/Support/CFG.h"
#include "llvm/Support/Debug.h"
+#include "llvm/Analysis/ConstantFolding.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/SmallPtrSet.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();
+ SmallPtrSet<BasicBlock*, 16> 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 (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) {
- // 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())) {
+ SmallPtrSet<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
+ for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ);
+ PI != PE; ++PI)
+ if (BBPreds.count(*PI)) {
+ // 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, handle it.
+ bool IsSafe = true;
+ for (pred_iterator PI = pred_begin(Succ), E = pred_end(Succ); PI != E; ++PI)
+ if (*PI != BB) {
+ IsSafe = false;
+ break;
}
+ 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);
+ 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.
+ SmallPtrSet<BasicBlock*, 16> 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;
+}
- // 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, 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);
+/// 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 SmallVector<BasicBlock*, 16> 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 {
+ // Add an incoming value for each of the new incoming values.
+ for (unsigned i = 0, e = BBPreds.size(); i != e; ++i)
+ PN->addIncoming(OldVal, BBPreds[i]);
}
}
}
- return false;
+
+ if (isa<PHINode>(&BB->front())) {
+ SmallVector<BasicBlock*, 16>
+ 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.
+ BB->replaceAllUsesWith(Succ);
+ if (!Succ->hasName()) Succ->takeName(BB);
+ BB->eraseFromParent(); // Delete the old basic block.
+ return true;
}
/// GetIfCondition - Given a basic block (BB) with two predecessors (and
/// which entry into BB will be taken. Also, return by references the block
/// that will be entered from if the condition is true, and the block that will
/// be entered if the condition is false.
-///
+///
///
static Value *GetIfCondition(BasicBlock *BB,
BasicBlock *&IfTrue, BasicBlock *&IfFalse) {
// 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, bool AllowAggressive){
+//
+// 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.
+ 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 wierd loops that might have the "if condition" in
+ // We don't want to allow weird loops that might have the "if condition" in
// the bottom of this block.
if (PBB == BB) return false;
// statement".
if (BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator()))
if (BI->isUnconditional() && BI->getSuccessor(0) == BB) {
- if (!AllowAggressive) return false;
+ 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.
case Instruction::Or:
case Instruction::Xor:
case Instruction::Shl:
- case Instruction::Shr:
+ case Instruction::LShr:
+ case Instruction::AShr:
+ case Instruction::ICmp:
+ case Instruction::FCmp:
+ if (I->getOperand(0)->getType()->isFPOrFPVector())
+ return false; // FP arithmetic might trap.
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))
+ if (!DominatesMergePoint(I->getOperand(i), BB, 0))
return false;
- // Okay, it's safe to do this!
+ // 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.
+// 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 (Instruction *Inst = dyn_cast<Instruction>(V)) {
+ 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);
if (LHS == RHS)
return LHS;
}
+ }
return 0;
}
// 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 (Instruction *Inst = dyn_cast<Instruction>(V)) {
+ 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))
if (LHS == RHS)
return LHS;
}
+ }
return 0;
}
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;
/// 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);
- }
-}
+ if (!isInstructionTriviallyDead(I)) return;
+
+ SmallVector<Instruction*, 16> InstrsToInspect;
+ InstrsToInspect.push_back(I);
-/// 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!
+ while (!InstrsToInspect.empty()) {
+ I = InstrsToInspect.back();
+ InstrsToInspect.pop_back();
- // 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));
+ if (!isInstructionTriviallyDead(I)) continue;
- for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
- if (SI1Succs.count(*I))
- for (BasicBlock::iterator BBI = (*I)->begin();
- PHINode *PN = dyn_cast<PHINode>(BBI); ++BBI)
- if (PN->getIncomingValueForBlock(SI1BB) !=
- PN->getIncomingValueForBlock(SI2BB))
- return false;
-
- return true;
-}
+ // 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;
+ }
-/// 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
+ // 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);
- for (BasicBlock::iterator I = Succ->begin();
- PHINode *PN = dyn_cast<PHINode>(I); ++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;
}
// Given a value comparison instruction, decode all of the 'cases' that it
// represents and return the 'default' block.
static BasicBlock *
-GetValueEqualityComparisonCases(TerminatorInst *TI,
+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)));
+ Cases.push_back(std::make_pair(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);
+ 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);
+}
+
+
+// EliminateBlockCases - Given a vector of bb/value pairs, remove any entries
+// in the list that match the specified block.
+static void EliminateBlockCases(BasicBlock *BB,
+ std::vector<std::pair<ConstantInt*, BasicBlock*> > &Cases) {
+ for (unsigned i = 0, e = Cases.size(); i != e; ++i)
+ if (Cases[i].second == BB) {
+ Cases.erase(Cases.begin()+i);
+ --i; --e;
+ }
+}
+
+// ValuesOverlap - Return true if there are any keys in C1 that exist in C2 as
+// well.
+static bool
+ValuesOverlap(std::vector<std::pair<ConstantInt*, BasicBlock*> > &C1,
+ std::vector<std::pair<ConstantInt*, BasicBlock*> > &C2) {
+ std::vector<std::pair<ConstantInt*, BasicBlock*> > *V1 = &C1, *V2 = &C2;
+
+ // Make V1 be smaller than V2.
+ if (V1->size() > V2->size())
+ std::swap(V1, V2);
+
+ if (V1->size() == 0) return false;
+ if (V1->size() == 1) {
+ // Just scan V2.
+ ConstantInt *TheVal = (*V1)[0].first;
+ for (unsigned i = 0, e = V2->size(); i != e; ++i)
+ if (TheVal == (*V2)[i].first)
+ return true;
+ }
+
+ // Otherwise, just sort both lists and compare element by element.
+ std::sort(V1->begin(), V1->end());
+ std::sort(V2->begin(), V2->end());
+ unsigned i1 = 0, i2 = 0, e1 = V1->size(), e2 = V2->size();
+ while (i1 != e1 && i2 != e2) {
+ if ((*V1)[i1].first == (*V2)[i2].first)
+ return true;
+ if ((*V1)[i1].first < (*V2)[i2].first)
+ ++i1;
+ else
+ ++i2;
+ }
+ return false;
}
+// SimplifyEqualityComparisonWithOnlyPredecessor - If TI is known to be a
+// terminator instruction and its block is known to only have a single
+// predecessor block, check to see if that predecessor is also a value
+// comparison with the same value, and if that comparison determines the outcome
+// of this comparison. If so, simplify TI. This does a very limited form of
+// jump threading.
+static bool SimplifyEqualityComparisonWithOnlyPredecessor(TerminatorInst *TI,
+ BasicBlock *Pred) {
+ Value *PredVal = isValueEqualityComparison(Pred->getTerminator());
+ if (!PredVal) return false; // Not a value comparison in predecessor.
+
+ Value *ThisVal = isValueEqualityComparison(TI);
+ assert(ThisVal && "This isn't a value comparison!!");
+ if (ThisVal != PredVal) return false; // Different predicates.
+
+ // Find out information about when control will move from Pred to TI's block.
+ std::vector<std::pair<ConstantInt*, BasicBlock*> > PredCases;
+ BasicBlock *PredDef = GetValueEqualityComparisonCases(Pred->getTerminator(),
+ PredCases);
+ EliminateBlockCases(PredDef, PredCases); // Remove default from cases.
+
+ // Find information about how control leaves this block.
+ std::vector<std::pair<ConstantInt*, BasicBlock*> > ThisCases;
+ BasicBlock *ThisDef = GetValueEqualityComparisonCases(TI, ThisCases);
+ EliminateBlockCases(ThisDef, ThisCases); // Remove default from cases.
+
+ // If TI's block is the default block from Pred's comparison, potentially
+ // simplify TI based on this knowledge.
+ if (PredDef == TI->getParent()) {
+ // If we are here, we know that the value is none of those cases listed in
+ // PredCases. If there are any cases in ThisCases that are in PredCases, we
+ // can simplify TI.
+ if (ValuesOverlap(PredCases, ThisCases)) {
+ if (BranchInst *BTI = dyn_cast<BranchInst>(TI)) {
+ // Okay, one of the successors of this condbr is dead. Convert it to a
+ // uncond br.
+ assert(ThisCases.size() == 1 && "Branch can only have one case!");
+ Value *Cond = BTI->getCondition();
+ // Insert the new branch.
+ Instruction *NI = BranchInst::Create(ThisDef, TI);
+
+ // Remove PHI node entries for the dead edge.
+ ThisCases[0].second->removePredecessor(TI->getParent());
+
+ 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.
+ if (Instruction *CondI = dyn_cast<Instruction>(Cond))
+ ErasePossiblyDeadInstructionTree(CondI);
+ return true;
+
+ } else {
+ SwitchInst *SI = cast<SwitchInst>(TI);
+ // Okay, TI has cases that are statically dead, prune them away.
+ SmallPtrSet<Constant*, 16> DeadCases;
+ for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
+ DeadCases.insert(PredCases[i].first);
+
+ 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->getSuccessor(i)->removePredecessor(TI->getParent());
+ SI->removeCase(i);
+ }
+
+ DOUT << "Leaving: " << *TI << "\n";
+ return true;
+ }
+ }
+
+ } else {
+ // Otherwise, TI's block must correspond to some matched value. Find out
+ // which value (or set of values) this is.
+ ConstantInt *TIV = 0;
+ BasicBlock *TIBB = TI->getParent();
+ for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
+ if (PredCases[i].second == TIBB) {
+ if (TIV == 0)
+ TIV = PredCases[i].first;
+ else
+ return false; // Cannot handle multiple values coming to this block.
+ }
+ assert(TIV && "No edge from pred to succ?");
+
+ // Okay, we found the one constant that our value can be if we get into TI's
+ // BB. Find out which successor will unconditionally be branched to.
+ BasicBlock *TheRealDest = 0;
+ for (unsigned i = 0, e = ThisCases.size(); i != e; ++i)
+ if (ThisCases[i].first == TIV) {
+ TheRealDest = ThisCases[i].second;
+ break;
+ }
+
+ // If not handled by any explicit cases, it is handled by the default case.
+ if (TheRealDest == 0) TheRealDest = ThisDef;
+
+ // Remove PHI node entries for dead edges.
+ BasicBlock *CheckEdge = TheRealDest;
+ for (succ_iterator SI = succ_begin(TIBB), e = succ_end(TIBB); SI != e; ++SI)
+ if (*SI != CheckEdge)
+ (*SI)->removePredecessor(TIBB);
+ else
+ CheckEdge = 0;
+
+ // Insert the new branch.
+ Instruction *NI = BranchInst::Create(TheRealDest, TI);
+
+ 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());
+ TI->eraseFromParent(); // Nuke the old one.
+
+ if (Cond) ErasePossiblyDeadInstructionTree(Cond);
+ return true;
+ }
+ return false;
+}
// FoldValueComparisonIntoPredecessors - The specified terminator is a value
// equality comparison instruction (either a switch or a branch on "X == c").
assert(CV && "Not a comparison?");
bool Changed = false;
- std::vector<BasicBlock*> Preds(pred_begin(BB), pred_end(BB));
+ SmallVector<BasicBlock*, 16> 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
// 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;
+ SmallVector<BasicBlock*, 8> NewSuccessors;
if (PredDefault == BB) {
// If this is the default destination from PTI, only the edges in TI
AddPredecessorToBlock(NewSuccessors[i], Pred, BB);
// Now that the successors are updated, create the new Switch instruction.
- SwitchInst *NewSI = new SwitchInst(CV, PredDefault, PTI);
+ SwitchInst *NewSI = SwitchInst::Create(CV, PredDefault, PredCases.size(), PTI);
for (unsigned i = 0, e = PredCases.size(); i != e; ++i)
NewSI->addCase(PredCases[i].first, PredCases[i].second);
+
+ Instruction *DeadCond = 0;
+ if (BranchInst *BI = dyn_cast<BranchInst>(PTI))
+ // If PTI is a branch, remember the condition.
+ DeadCond = dyn_cast<Instruction>(BI->getCondition());
Pred->getInstList().erase(PTI);
+ // If the condition is dead now, remove the instruction tree.
+ if (DeadCond) ErasePossiblyDeadInstructionTree(DeadCond);
+
// 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.
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);
+ InfLoopBlock = BasicBlock::Create("infloop", BB->getParent());
+ BranchInst::Create(InfLoopBlock, InfLoopBlock);
}
NewSI->setSuccessor(i, InfLoopBlock);
}
-
+
Changed = true;
}
}
return Changed;
}
+/// 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) {
+ // 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() || isa<PHINode>(I1) ||
+ isa<InvokeInst>(I1) || !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->takeName(I1);
+ }
+
+ // 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 = SelectInst::Create(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;
+}
+
+/// 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 = BasicBlock::Create(RealDest->getName()+".critedge",
+ RealDest->getParent(), RealDest);
+ BranchInst::Create(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);
+
+ Value *NV = SelectInst::Create(IfCond, TrueVal, FalseVal, "", AfterPHIIt);
+ PN->replaceAllUsesWith(NV);
+ NV->takeName(PN);
+
+ BB->getInstList().erase(PN);
+ }
+ return true;
+}
+
+/// SimplifyCondBranchToTwoReturns - If we found a conditional branch that goes
+/// to two returning blocks, try to merge them together into one return,
+/// introducing a select if the return values disagree.
+static bool SimplifyCondBranchToTwoReturns(BranchInst *BI) {
+ assert(BI->isConditional() && "Must be a conditional branch");
+ BasicBlock *TrueSucc = BI->getSuccessor(0);
+ BasicBlock *FalseSucc = BI->getSuccessor(1);
+ ReturnInst *TrueRet = cast<ReturnInst>(TrueSucc->getTerminator());
+ ReturnInst *FalseRet = cast<ReturnInst>(FalseSucc->getTerminator());
+
+ // Check to ensure both blocks are empty (just a return) or optionally empty
+ // with PHI nodes. If there are other instructions, merging would cause extra
+ // computation on one path or the other.
+ BasicBlock::iterator BBI = TrueRet;
+ if (BBI != TrueSucc->begin() && !isa<PHINode>(--BBI))
+ return false; // Not empty with optional phi nodes.
+ BBI = FalseRet;
+ if (BBI != FalseSucc->begin() && !isa<PHINode>(--BBI))
+ return false; // Not empty with optional phi nodes.
+
+ // 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 (FalseRet->getNumOperands() == 0) {
+ TrueSucc->removePredecessor(BI->getParent());
+ FalseSucc->removePredecessor(BI->getParent());
+ ReturnInst::Create(0, BI);
+ BI->eraseFromParent();
+ return true;
+ }
+
+ // Otherwise, build up the result values for the new return.
+ SmallVector<Value*, 4> TrueResult;
+ SmallVector<Value*, 4> FalseResult;
+
+ for (unsigned i = 0, e = TrueRet->getNumOperands(); i != e; ++i) {
+ // Otherwise, figure out what the true and false return values are
+ // so we can insert a new select instruction.
+ Value *TrueValue = TrueRet->getOperand(i);
+ Value *FalseValue = FalseRet->getOperand(i);
+
+ // 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());
+
+ // 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 (ConstantExpr *TCV = dyn_cast<ConstantExpr>(TrueValue))
+ if (TCV->canTrap())
+ return false;
+ if (ConstantExpr *FCV = dyn_cast<ConstantExpr>(FalseValue))
+ if (FCV->canTrap())
+ return false;
+
+ TrueResult.push_back(TrueValue);
+ FalseResult.push_back(FalseValue);
+ }
+
+ // Okay, we collected all the mapped values and checked them for sanity, and
+ // defined to really do this transformation. First, update the CFG.
+ TrueSucc->removePredecessor(BI->getParent());
+ FalseSucc->removePredecessor(BI->getParent());
+
+ // Insert select instructions where needed.
+ Value *BrCond = BI->getCondition();
+ for (unsigned i = 0, e = TrueRet->getNumOperands(); i != e; ++i) {
+ // Insert a select if the results differ.
+ if (TrueResult[i] == FalseResult[i] || isa<UndefValue>(FalseResult[i]))
+ continue;
+ if (isa<UndefValue>(TrueResult[i])) {
+ TrueResult[i] = FalseResult[i];
+ continue;
+ }
+
+ TrueResult[i] = SelectInst::Create(BrCond, TrueResult[i],
+ FalseResult[i], "retval", BI);
+ }
+
+ Value *RI = ReturnInst::Create(&TrueResult[0], TrueResult.size(), BI);
+
+ DOUT << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
+ << "\n " << *BI << "NewRet = " << *RI
+ << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc;
+
+ BI->eraseFromParent();
+
+ if (Instruction *BrCondI = dyn_cast<Instruction>(BrCond))
+ ErasePossiblyDeadInstructionTree(BrCondI);
+ 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->getValue().ult(RHS->getValue());
}
};
}
-
// 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 && BB->getParent() && "Block not embedded in function!");
assert(BB->getTerminator() && "Degenerate basic block encountered!");
- assert(&BB->getParent()->front() != BB && "Can't Simplify entry block!");
+ assert(&BB->getParent()->getEntryBlock() != BB &&
+ "Can't Simplify entry block!");
// 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);
+ if ((pred_begin(BB) == pred_end(BB)) ||
+ (*pred_begin(BB) == BB && ++pred_begin(BB) == pred_end(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.
- for_each(succ_begin(BB), succ_end(BB),
- std::bind2nd(std::mem_fun(&BasicBlock::removePredecessor), BB));
+ for (succ_iterator SI = succ_begin(BB), E = succ_end(BB); SI != E; ++SI)
+ SI->removePredecessor(BB);
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
- // what we replace the value with. Note that since this block is
+ // 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()));
-
+ if (!I.use_empty())
+ // 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;
-
- 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)) {
- DEBUG(std::cerr << "Killing Trivial BB: \n" << *BB);
- std::string OldName = BB->getName();
-
- 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...
- 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...
- BB->replaceAllUsesWith(Succ);
-
- // Delete the old basic block...
- M->getBasicBlockList().erase(BB);
-
- if (!OldName.empty() && !Succ->hasName()) // Transfer name if we can
- Succ->setName(OldName);
- 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()))
+ if (PN->getNumIncomingValues() == 2)
+ Changed |= FoldTwoEntryPHINode(PN);
// If this is a returning block with only PHI nodes in it, fold the return
// instruction into any unconditional branch predecessors.
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;
+ SmallVector<BasicBlock*, 8> UncondBranchPreds;
+ SmallVector<BranchInst*, 8> 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 (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();
+ 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.
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;
- }
- }
+ if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
+ isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
+ SimplifyCondBranchToTwoReturns(BI))
+ 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
// predecessor with an unwind.
//
- std::vector<BasicBlock*> Preds(pred_begin(BB), pred_end(BB));
+ SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
while (!Preds.empty()) {
BasicBlock *Pred = Preds.back();
if (BranchInst *BI = dyn_cast<BranchInst>(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);
+ BranchInst *BI = BranchInst::Create(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);
+ SmallVector<Value*,8> Args(II->op_begin()+3, II->op_end());
+ CallInst *CI = CallInst::Create(II->getCalledValue(),
+ Args.begin(), Args.end(), II->getName(), BI);
+ CI->setCallingConv(II->getCallingConv());
+ CI->setParamAttrs(II->getParamAttrs());
// If the invoke produced a value, the Call now does instead
II->replaceAllUsesWith(CI);
delete II;
Changed = true;
}
-
+
Preds.pop_back();
}
return true;
}
- } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->begin())) {
- if (isValueEqualityComparison(SI))
- if (FoldValueComparisonIntoPredecessors(SI))
- return SimplifyCFG(BB) || 1;
+ } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
+ if (isValueEqualityComparison(SI)) {
+ // 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 (BasicBlock *OnlyPred = BB->getSinglePredecessor())
+ if (SimplifyEqualityComparisonWithOnlyPredecessor(SI, OnlyPred))
+ return SimplifyCFG(BB) || 1;
+
+ // If the block only contains the switch, see if we can fold the block
+ // away into any preds.
+ if (SI == &BB->front())
+ if (FoldValueComparisonIntoPredecessors(SI))
+ 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 (BasicBlock *OnlyPred = BB->getSinglePredecessor())
+ if (SimplifyEqualityComparisonWithOnlyPredecessor(BI, OnlyPred))
+ return SimplifyCFG(BB) || 1;
+
// This block must be empty, except for the setcond inst, if it exists.
BasicBlock::iterator I = BB->begin();
if (&*I == BI ||
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 &&
- Cond->getNext() == BI && Cond->hasOneUse() &&
+ if (Instruction *Cond = dyn_cast<Instruction>(BI->getCondition())) {
+ BasicBlock::iterator CondIt = Cond;
+ if ((isa<CmpInst>(Cond) || isa<BinaryOperator>(Cond)) &&
+ Cond->getParent() == BB && &BB->front() == Cond &&
+ &*++CondIt == 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()))
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();
- New->setName(Cond->getName());
- Cond->setName(Cond->getName()+".old");
PredBlock->getInstList().insert(PBI, New);
+ New->takeName(Cond);
+ Cond->setName(New->getName()+".old");
Instruction::BinaryOps Opcode =
PBI->getSuccessor(0) == TrueDest ?
Instruction::Or : Instruction::And;
- Value *NewCond =
+ Value *NewCond =
BinaryOperator::create(Opcode, PBI->getCondition(),
New, "bothcond", PBI);
PBI->setCondition(NewCond);
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;
+ // Scan predessor blocks for conditional branches.
+ 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 = PHINode::Create(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;
+ }
+ }
+ }
+
+ // 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 = SelectInst::Create(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 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) {
+ SmallVector<BasicBlock*, 8> 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) {
+ BranchInst::Create(BI->getSuccessor(1), BI);
+ BI->eraseFromParent();
+ } else if (BI->getSuccessor(1) == BB) {
+ BranchInst::Create(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) {
+ BB->removePredecessor(SI->getParent());
+ 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;
+
+ // If MaxBlock has phinodes in it, remove MaxPop-1 entries from
+ // it.
+ if (isa<PHINode>(MaxBlock->begin()))
+ for (unsigned i = 0; i != MaxPop-1; ++i)
+ MaxBlock->removePredecessor(SI->getParent());
+
+ 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 = BranchInst::Create(II->getNormalDest(), II);
+ II->removeFromParent(); // Take out of symbol table
+
+ // Insert the call now...
+ SmallVector<Value*, 8> Args(II->op_begin()+3, II->op_end());
+ CallInst *CI = CallInst::Create(II->getCalledValue(),
+ Args.begin(), Args.end(),
+ II->getName(), BI);
+ CI->setCallingConv(II->getCallingConv());
+ CI->setParamAttrs(II->getParamAttrs());
+ // 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;
+ }
+ }
}
// Merge basic blocks into their predecessor if there is only one distinct
}
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
//
while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
PN->replaceAllUsesWith(PN->getIncomingValue(0));
- BB->getInstList().pop_front(); // Delete the phi node...
+ BB->getInstList().pop_front(); // Delete the phi node.
}
- // Delete the unconditional branch from the predecessor...
+ // Delete the unconditional branch from the predecessor.
OnlyPred->getInstList().pop_back();
-
- // Move all definitions in the successor to the predecessor...
+
+ // Move all definitions in the successor to the predecessor.
OnlyPred->getInstList().splice(OnlyPred->end(), BB->getInstList());
-
+
// Make all PHI nodes that referred to BB now refer to Pred as their
- // source...
+ // source.
BB->replaceAllUsesWith(OnlyPred);
- std::string OldName = BB->getName();
-
- // Erase basic block from the function...
+ // Inherit predecessors name if it exists.
+ if (!OnlyPred->hasName())
+ OnlyPred->takeName(BB);
+
+ // Erase basic block from the function.
M->getBasicBlockList().erase(BB);
- // Inherit predecessors name if it exists...
- if (!OldName.empty() && !OnlyPred->hasName())
- OnlyPred->setName(OldName);
-
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()))
+ if (BI->isConditional()) {
+ // 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.
// 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);
-
+ SwitchInst *New = SwitchInst::Create(CompVal, DefaultBB,Values.size(),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();
- PHINode *PN = dyn_cast<PHINode>(BBI); ++BBI) {
+ 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);
}
}
- // 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");
-
- // Figure out where to insert instructions as necessary.
- BasicBlock::iterator AfterPHIIt = BB->begin();
- while (isa<PHINode>(AfterPHIIt)) ++AfterPHIIt;
-
- 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, true) &&
- DominatesMergePoint(PN->getIncomingValue(1), BB, true)) {
- Value *TrueVal =
- PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
- Value *FalseVal =
- PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
-
- // 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;
- }
- }
- }
- }
-
return Changed;
}
projects / oota-llvm.git / blobdiff