//===- 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.
-//
+//
//===----------------------------------------------------------------------===//
//
// Peephole optimize the CFG.
//
//===----------------------------------------------------------------------===//
+#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 "llvm/Transforms/Utils/BasicBlockUtils.h"
#include <algorithm>
#include <functional>
#include <set>
+#include <map>
using namespace llvm;
-// PropagatePredecessorsForPHIs - This gets "Succ" ready to have the
-// predecessors from "BB". This is a little tricky because "Succ" has PHI
-// nodes, which need to have extra slots added to them to hold the merge edges
-// from BB's predecessors, and BB itself might have had PHI nodes in it. This
-// function returns true (failure) if the Succ BB already has a predecessor that
-// is a predecessor of BB and incoming PHI arguments would not be discernible.
+/// SafeToMergeTerminators - Return true if it is safe to merge these two
+/// terminator instructions together.
+///
+static bool SafeToMergeTerminators(TerminatorInst *SI1, TerminatorInst *SI2) {
+ if (SI1 == SI2) return false; // Can't merge with self!
+
+ // It is not safe to merge these two switch instructions if they have a common
+ // successor, and if that successor has a PHI node, and if *that* PHI node has
+ // conflicting incoming values from the two switch blocks.
+ BasicBlock *SI1BB = SI1->getParent();
+ BasicBlock *SI2BB = SI2->getParent();
+ std::set<BasicBlock*> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
+
+ for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
+ if (SI1Succs.count(*I))
+ for (BasicBlock::iterator BBI = (*I)->begin();
+ isa<PHINode>(BBI); ++BBI) {
+ PHINode *PN = cast<PHINode>(BBI);
+ if (PN->getIncomingValueForBlock(SI1BB) !=
+ PN->getIncomingValueForBlock(SI2BB))
+ return false;
+ }
+
+ return true;
+}
+
+/// AddPredecessorToBlock - Update PHI nodes in Succ to indicate that there will
+/// now be entries in it from the 'NewPred' block. The values that will be
+/// flowing into the PHI nodes will be the same as those coming in from
+/// ExistPred, an existing predecessor of Succ.
+static void AddPredecessorToBlock(BasicBlock *Succ, BasicBlock *NewPred,
+ BasicBlock *ExistPred) {
+ assert(std::find(succ_begin(ExistPred), succ_end(ExistPred), Succ) !=
+ succ_end(ExistPred) && "ExistPred is not a predecessor of Succ!");
+ if (!isa<PHINode>(Succ->begin())) return; // Quick exit if nothing to do
+
+ for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
+ PHINode *PN = cast<PHINode>(I);
+ Value *V = PN->getIncomingValueForBlock(ExistPred);
+ PN->addIncoming(V, NewPred);
+ }
+}
+
+// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
+// almost-empty BB ending in an unconditional branch to Succ, into succ.
//
// Assumption: Succ is the single successor for BB.
//
-static bool PropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
+static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
- if (!isa<PHINode>(Succ->front()))
- return false; // We can make the transformation, no problem.
-
- // If there is more than one predecessor, and there are PHI nodes in
- // the successor, then we need to add incoming edges for the PHI nodes
- //
- const std::vector<BasicBlock*> BBPreds(pred_begin(BB), pred_end(BB));
-
// Check to see if one of the predecessors of BB is already a predecessor of
// Succ. If so, we cannot do the transformation if there are any PHI nodes
// with incompatible values coming in from the two edges!
//
- for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ); PI != PE; ++PI)
- if (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())) {
+ std::set<BasicBlock*> BBPreds(pred_begin(BB), pred_end(BB));
+ for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ);
+ PI != PE; ++PI)
+ if (std::find(BBPreds.begin(), BBPreds.end(), *PI) != BBPreds.end()) {
+ // Loop over all of the PHI nodes checking to see if there are
+ // incompatible values coming in.
+ for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
+ PHINode *PN = cast<PHINode>(I);
+ // Loop up the entries in the PHI node for BB and for *PI if the
+ // values coming in are non-equal, we cannot merge these two blocks
+ // (instead we should insert a conditional move or something, then
+ // merge the blocks).
+ if (PN->getIncomingValueForBlock(BB) !=
+ PN->getIncomingValueForBlock(*PI))
+ return false; // Values are not equal...
+ }
}
+ }
+
+ // Finally, if BB has PHI nodes that are used by things other than the PHIs in
+ // Succ and Succ has predecessors that are not Succ and not Pred, we cannot
+ // fold these blocks, as we don't know whether BB dominates Succ or not to
+ // update the PHI nodes correctly.
+ if (!isa<PHINode>(BB->begin()) || Succ->getSinglePredecessor()) return true;
+
+ // If the predecessors of Succ are only BB and Succ itself, we can handle this.
+ bool IsSafe = true;
+ for (pred_iterator PI = pred_begin(Succ), E = pred_end(Succ); PI != E; ++PI)
+ if (*PI != Succ && *PI != BB) {
+ IsSafe = false;
+ break;
}
+ 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.
+ std::set<BasicBlock*> BBPreds(pred_begin(BB), pred_end(BB));
+ for (pred_iterator PI = pred_begin(Succ), E = pred_end(Succ); PI != E; ++PI)
+ if (BBPreds.count(*PI))
+ return false;
+
+ return true;
+}
- // 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 (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);
- }
- } else {
- for (std::vector<BasicBlock*>::const_iterator PredI = BBPreds.begin(),
+/// TryToSimplifyUncondBranchFromEmptyBlock - BB contains an unconditional
+/// branch to Succ, and contains no instructions other than PHI nodes and the
+/// branch. If possible, eliminate BB.
+static bool TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB,
+ BasicBlock *Succ) {
+ // If our successor has PHI nodes, then we need to update them to include
+ // entries for BB's predecessors, not for BB itself. Be careful though,
+ // if this transformation fails (returns true) then we cannot do this
+ // transformation!
+ //
+ if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
+
+ DOUT << "Killing Trivial BB: \n" << *BB;
+
+ if (isa<PHINode>(Succ->begin())) {
+ // If there is more than one pred of succ, and there are PHI nodes in
+ // the successor, then we need to add incoming edges for the PHI nodes
+ //
+ const std::vector<BasicBlock*> BBPreds(pred_begin(BB), pred_end(BB));
+
+ // Loop over all of the PHI nodes in the successor of BB.
+ for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
+ PHINode *PN = cast<PHINode>(I);
+ Value *OldVal = PN->removeIncomingValue(BB, false);
+ assert(OldVal && "No entry in PHI for Pred BB!");
+
+ // If this incoming value is one of the PHI nodes in BB, the new entries
+ // in the PHI node are the entries from the old PHI.
+ if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
+ PHINode *OldValPN = cast<PHINode>(OldVal);
+ for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i)
+ PN->addIncoming(OldValPN->getIncomingValue(i),
+ OldValPN->getIncomingBlock(i));
+ } else {
+ for (std::vector<BasicBlock*>::const_iterator PredI = BBPreds.begin(),
End = BBPreds.end(); PredI != End; ++PredI) {
- // Add an incoming value for each of the new incoming values...
- PN->addIncoming(OldVal, *PredI);
+ // Add an incoming value for each of the new incoming values...
+ PN->addIncoming(OldVal, *PredI);
+ }
}
}
}
- return false;
+
+ if (isa<PHINode>(&BB->front())) {
+ std::vector<BasicBlock*>
+ OldSuccPreds(pred_begin(Succ), pred_end(Succ));
+
+ // Move all PHI nodes in BB to Succ if they are alive, otherwise
+ // delete them.
+ while (PHINode *PN = dyn_cast<PHINode>(&BB->front()))
+ if (PN->use_empty()) {
+ // Just remove the dead phi. This happens if Succ's PHIs were the only
+ // users of the PHI nodes.
+ PN->eraseFromParent();
+ } else {
+ // The instruction is alive, so this means that Succ must have
+ // *ONLY* had BB as a predecessor, and the PHI node is still valid
+ // now. Simply move it into Succ, because we know that BB
+ // strictly dominated Succ.
+ Succ->getInstList().splice(Succ->begin(),
+ BB->getInstList(), BB->begin());
+
+ // We need to add new entries for the PHI node to account for
+ // predecessors of Succ that the PHI node does not take into
+ // account. At this point, since we know that BB dominated succ,
+ // this means that we should any newly added incoming edges should
+ // use the PHI node as the value for these edges, because they are
+ // loop back edges.
+ for (unsigned i = 0, e = OldSuccPreds.size(); i != e; ++i)
+ if (OldSuccPreds[i] != BB)
+ PN->addIncoming(PN, OldSuccPreds[i]);
+ }
+ }
+
+ // Everything that jumped to BB now goes to Succ.
+ std::string OldName = BB->getName();
+ BB->replaceAllUsesWith(Succ);
+ BB->eraseFromParent(); // Delete the old basic block.
+
+ if (!OldName.empty() && !Succ->hasName()) // Transfer name if we can
+ Succ->setName(OldName);
+ return true;
}
/// GetIfCondition - Given a basic block (BB) with two predecessors (and
/// 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) {
- if (Instruction *I = dyn_cast<Instruction>(V)) {
- BasicBlock *PBB = I->getParent();
- // If this instruction is defined in a block that contains an unconditional
- // branch to BB, then it must be in the 'conditional' part of the "if
- // statement".
- if (isa<BranchInst>(PBB->getTerminator()) &&
- cast<BranchInst>(PBB->getTerminator())->isUnconditional() &&
- cast<BranchInst>(PBB->getTerminator())->getSuccessor(0) == BB)
- return false;
-
- // We also don't want to allow wierd loops that might have the "if
- // condition" in the bottom of this block.
- if (PBB == BB) return false;
+//
+// If AggressiveInsts is non-null, and if V does not dominate BB, we check to
+// see if V (which must be an instruction) is cheap to compute and is
+// non-trapping. If both are true, the instruction is inserted into the set and
+// true is returned.
+static bool DominatesMergePoint(Value *V, BasicBlock *BB,
+ std::set<Instruction*> *AggressiveInsts) {
+ Instruction *I = dyn_cast<Instruction>(V);
+ if (!I) {
+ // Non-instructions all dominate instructions, but not all constantexprs
+ // can be executed unconditionally.
+ if (ConstantExpr *C = dyn_cast<ConstantExpr>(V))
+ if (C->canTrap())
+ return false;
+ return true;
}
+ BasicBlock *PBB = I->getParent();
+
+ // We don't want to allow weird loops that might have the "if condition" in
+ // the bottom of this block.
+ if (PBB == BB) return false;
+
+ // If this instruction is defined in a block that contains an unconditional
+ // branch to BB, then it must be in the 'conditional' part of the "if
+ // statement".
+ if (BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator()))
+ if (BI->isUnconditional() && BI->getSuccessor(0) == BB) {
+ if (!AggressiveInsts) return false;
+ // Okay, it looks like the instruction IS in the "condition". Check to
+ // see if its a cheap instruction to unconditionally compute, and if it
+ // only uses stuff defined outside of the condition. If so, hoist it out.
+ switch (I->getOpcode()) {
+ default: return false; // Cannot hoist this out safely.
+ case Instruction::Load:
+ // We can hoist loads that are non-volatile and obviously cannot trap.
+ if (cast<LoadInst>(I)->isVolatile())
+ return false;
+ if (!isa<AllocaInst>(I->getOperand(0)) &&
+ !isa<Constant>(I->getOperand(0)))
+ return false;
+
+ // Finally, we have to check to make sure there are no instructions
+ // before the load in its basic block, as we are going to hoist the loop
+ // out to its predecessor.
+ if (PBB->begin() != BasicBlock::iterator(I))
+ return false;
+ break;
+ case Instruction::Add:
+ case Instruction::Sub:
+ case Instruction::And:
+ case Instruction::Or:
+ case Instruction::Xor:
+ case Instruction::Shl:
+ case Instruction::LShr:
+ case Instruction::AShr:
+ case Instruction::ICmp:
+ case Instruction::FCmp:
+ break; // These are all cheap and non-trapping instructions.
+ }
+
+ // Okay, we can only really hoist these out if their operands are not
+ // defined in the conditional region.
+ for (unsigned i = 0, e = I->getNumOperands(); i != e; ++i)
+ if (!DominatesMergePoint(I->getOperand(i), BB, 0))
+ return false;
+ // Okay, it's safe to do this! Remember this instruction.
+ AggressiveInsts->insert(I);
+ }
- // 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) {
+// 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 (Constant *C = dyn_cast<Constant>(Inst->getOperand(1))) {
+ 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);
- } 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 (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);
- } 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()));
- 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))
/// 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);
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;
+
+ std::vector<Instruction*> InstrsToInspect;
+ InstrsToInspect.push_back(I);
+
+ while (!InstrsToInspect.empty()) {
+ I = InstrsToInspect.back();
+ InstrsToInspect.pop_back();
+
+ if (!isInstructionTriviallyDead(I)) continue;
+
+ // If I is in the work list multiple times, remove previous instances.
+ for (unsigned i = 0, e = InstrsToInspect.size(); i != e; ++i)
+ if (InstrsToInspect[i] == I) {
+ InstrsToInspect.erase(InstrsToInspect.begin()+i);
+ --i, --e;
+ }
+
+ // 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);
+
+ // Remove dead instruction.
+ I->eraseFromParent();
}
}
-/// 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!
+// 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;
- // 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));
+ return SI->getCondition();
+ }
+ if (BranchInst *BI = dyn_cast<BranchInst>(TI))
+ if (BI->isConditional() && BI->getCondition()->hasOneUse())
+ 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;
+}
- 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;
-
+// 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(SI->getCaseValue(i), SI->getSuccessor(i)));
+ return SI->getDefaultDest();
+ }
+
+ BranchInst *BI = cast<BranchInst>(TI);
+ 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 an 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 = new BranchInst(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.
+ std::set<Constant*> 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 = new BranchInst(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").
+// 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, 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.
+ BasicBlock *InfLoopBlock = 0;
+ for (unsigned i = 0, e = NewSI->getNumSuccessors(); i != e; ++i)
+ if (NewSI->getSuccessor(i) == BB) {
+ if (InfLoopBlock == 0) {
+ // Insert it at the end of the loop, because it's either code,
+ // or it won't matter if it's hot. :)
+ InfLoopBlock = new BasicBlock("infloop", BB->getParent());
+ new BranchInst(InfLoopBlock, InfLoopBlock);
+ }
+ NewSI->setSuccessor(i, InfLoopBlock);
+ }
+
+ Changed = true;
+ }
+ }
+ return Changed;
+}
+
+/// HoistThenElseCodeToIf - Given a conditional branch that 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->setName(I1->getName());
+ }
+
+ // Hoisting one of the terminators from our successor is a great thing.
+ // Unfortunately, the successors of the if/else blocks may have PHI nodes in
+ // them. If they do, all PHI entries for BB1/BB2 must agree for all PHI
+ // nodes, so we insert select instruction to compute the final result.
+ std::map<std::pair<Value*,Value*>, SelectInst*> InsertedSelects;
+ for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI) {
+ PHINode *PN;
+ for (BasicBlock::iterator BBI = SI->begin();
+ (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
+ Value *BB1V = PN->getIncomingValueForBlock(BB1);
+ Value *BB2V = PN->getIncomingValueForBlock(BB2);
+ if (BB1V != BB2V) {
+ // These values do not agree. Insert a select instruction before NT
+ // that determines the right value.
+ SelectInst *&SI = InsertedSelects[std::make_pair(BB1V, BB2V)];
+ if (SI == 0)
+ SI = new SelectInst(BI->getCondition(), BB1V, BB2V,
+ BB1V->getName()+"."+BB2V->getName(), NT);
+ // Make the PHI node use the select for all incoming values for BB1/BB2
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
+ if (PN->getIncomingBlock(i) == BB1 || PN->getIncomingBlock(i) == BB2)
+ PN->setIncomingValue(i, SI);
+ }
+ }
+ }
+
+ // Update any PHI nodes in our new successors.
+ for (succ_iterator SI = succ_begin(BB1), E = succ_end(BB1); SI != E; ++SI)
+ AddPredecessorToBlock(*SI, BIParent, BB1);
+
+ BI->eraseFromParent();
return true;
}
-/// 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.
-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
+/// 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.
+ }
- for (BasicBlock::iterator I = Succ->begin();
- PHINode *PN = dyn_cast<PHINode>(I); ++I) {
- Value *V = PN->getIncomingValueForBlock(ExistPred);
- PN->addIncoming(V, NewPred);
+ return true;
+}
+
+/// FoldCondBranchOnPHI - If we have a conditional branch on a PHI node value
+/// that is defined in the same block as the branch and if any PHI entries are
+/// constants, thread edges corresponding to that entry to be branches to their
+/// ultimate destination.
+static bool FoldCondBranchOnPHI(BranchInst *BI) {
+ BasicBlock *BB = BI->getParent();
+ PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
+ // NOTE: we currently cannot transform this case if the PHI node is used
+ // outside of the block.
+ if (!PN || PN->getParent() != BB || !PN->hasOneUse())
+ return false;
+
+ // Degenerate case of a single entry PHI.
+ if (PN->getNumIncomingValues() == 1) {
+ if (PN->getIncomingValue(0) != PN)
+ PN->replaceAllUsesWith(PN->getIncomingValue(0));
+ else
+ PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
+ PN->eraseFromParent();
+ return true;
+ }
+
+ // Now we know that this block has multiple preds and two succs.
+ if (!BlockIsSimpleEnoughToThreadThrough(BB)) return false;
+
+ // Okay, this is a simple enough basic block. See if any phi values are
+ // constants.
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
+ ConstantInt *CB;
+ if ((CB = dyn_cast<ConstantInt>(PN->getIncomingValue(i))) &&
+ CB->getType() == Type::Int1Ty) {
+ // Okay, we now know that all edges from PredBB should be revectored to
+ // branch to RealDest.
+ BasicBlock *PredBB = PN->getIncomingBlock(i);
+ BasicBlock *RealDest = BI->getSuccessor(!CB->getZExtValue());
+
+ if (RealDest == BB) continue; // Skip self loops.
+
+ // The dest block might have PHI nodes, other predecessors and other
+ // difficult cases. Instead of being smart about this, just insert a new
+ // block that jumps to the destination block, effectively splitting
+ // the edge we are about to create.
+ BasicBlock *EdgeBB = new BasicBlock(RealDest->getName()+".critedge",
+ RealDest->getParent(), RealDest);
+ new BranchInst(RealDest, EdgeBB);
+ PHINode *PN;
+ for (BasicBlock::iterator BBI = RealDest->begin();
+ (PN = dyn_cast<PHINode>(BBI)); ++BBI) {
+ Value *V = PN->getIncomingValueForBlock(BB);
+ PN->addIncoming(V, EdgeBB);
+ }
+
+ // BB may have instructions that are being threaded over. Clone these
+ // instructions into EdgeBB. We know that there will be no uses of the
+ // cloned instructions outside of EdgeBB.
+ BasicBlock::iterator InsertPt = EdgeBB->begin();
+ std::map<Value*, Value*> TranslateMap; // Track translated values.
+ for (BasicBlock::iterator BBI = BB->begin(); &*BBI != BI; ++BBI) {
+ if (PHINode *PN = dyn_cast<PHINode>(BBI)) {
+ TranslateMap[PN] = PN->getIncomingValueForBlock(PredBB);
+ } else {
+ // Clone the instruction.
+ Instruction *N = BBI->clone();
+ if (BBI->hasName()) N->setName(BBI->getName()+".c");
+
+ // Update operands due to translation.
+ for (unsigned i = 0, e = N->getNumOperands(); i != e; ++i) {
+ std::map<Value*, Value*>::iterator PI =
+ TranslateMap.find(N->getOperand(i));
+ if (PI != TranslateMap.end())
+ N->setOperand(i, PI->second);
+ }
+
+ // Check for trivial simplification.
+ if (Constant *C = ConstantFoldInstruction(N)) {
+ TranslateMap[BBI] = C;
+ delete N; // Constant folded away, don't need actual inst
+ } else {
+ // Insert the new instruction into its new home.
+ EdgeBB->getInstList().insert(InsertPt, N);
+ if (!BBI->use_empty())
+ TranslateMap[BBI] = N;
+ }
+ }
+ }
+
+ // Loop over all of the edges from PredBB to BB, changing them to branch
+ // to EdgeBB instead.
+ TerminatorInst *PredBBTI = PredBB->getTerminator();
+ for (unsigned i = 0, e = PredBBTI->getNumSuccessors(); i != e; ++i)
+ if (PredBBTI->getSuccessor(i) == BB) {
+ BB->removePredecessor(PredBB);
+ PredBBTI->setSuccessor(i, EdgeBB);
+ }
+
+ // Recurse, simplifying any other constants.
+ return FoldCondBranchOnPHI(BI) | true;
+ }
}
+
+ return false;
+}
+
+/// FoldTwoEntryPHINode - Given a BB that starts with the specified two-entry
+/// PHI node, see if we can eliminate it.
+static bool FoldTwoEntryPHINode(PHINode *PN) {
+ // Ok, this is a two entry PHI node. Check to see if this is a simple "if
+ // statement", which has a very simple dominance structure. Basically, we
+ // are trying to find the condition that is being branched on, which
+ // subsequently causes this merge to happen. We really want control
+ // dependence information for this check, but simplifycfg can't keep it up
+ // to date, and this catches most of the cases we care about anyway.
+ //
+ BasicBlock *BB = PN->getParent();
+ BasicBlock *IfTrue, *IfFalse;
+ Value *IfCond = GetIfCondition(BB, IfTrue, IfFalse);
+ if (!IfCond) return false;
+
+ // Okay, we found that we can merge this two-entry phi node into a select.
+ // Doing so would require us to fold *all* two entry phi nodes in this block.
+ // At some point this becomes non-profitable (particularly if the target
+ // doesn't support cmov's). Only do this transformation if there are two or
+ // fewer PHI nodes in this block.
+ unsigned NumPhis = 0;
+ for (BasicBlock::iterator I = BB->begin(); isa<PHINode>(I); ++NumPhis, ++I)
+ if (NumPhis > 2)
+ return false;
+
+ DOUT << "FOUND IF CONDITION! " << *IfCond << " T: "
+ << IfTrue->getName() << " F: " << IfFalse->getName() << "\n";
+
+ // Loop over the PHI's seeing if we can promote them all to select
+ // instructions. While we are at it, keep track of the instructions
+ // that need to be moved to the dominating block.
+ std::set<Instruction*> AggressiveInsts;
+
+ BasicBlock::iterator AfterPHIIt = BB->begin();
+ while (isa<PHINode>(AfterPHIIt)) {
+ PHINode *PN = cast<PHINode>(AfterPHIIt++);
+ if (PN->getIncomingValue(0) == PN->getIncomingValue(1)) {
+ if (PN->getIncomingValue(0) != PN)
+ PN->replaceAllUsesWith(PN->getIncomingValue(0));
+ else
+ PN->replaceAllUsesWith(UndefValue::get(PN->getType()));
+ } else if (!DominatesMergePoint(PN->getIncomingValue(0), BB,
+ &AggressiveInsts) ||
+ !DominatesMergePoint(PN->getIncomingValue(1), BB,
+ &AggressiveInsts)) {
+ return false;
+ }
+ }
+
+ // If we all PHI nodes are promotable, check to make sure that all
+ // instructions in the predecessor blocks can be promoted as well. If
+ // not, we won't be able to get rid of the control flow, so it's not
+ // worth promoting to select instructions.
+ BasicBlock *DomBlock = 0, *IfBlock1 = 0, *IfBlock2 = 0;
+ PN = cast<PHINode>(BB->begin());
+ BasicBlock *Pred = PN->getIncomingBlock(0);
+ if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
+ IfBlock1 = Pred;
+ DomBlock = *pred_begin(Pred);
+ for (BasicBlock::iterator I = Pred->begin();
+ !isa<TerminatorInst>(I); ++I)
+ if (!AggressiveInsts.count(I)) {
+ // This is not an aggressive instruction that we can promote.
+ // Because of this, we won't be able to get rid of the control
+ // flow, so the xform is not worth it.
+ return false;
+ }
+ }
+
+ Pred = PN->getIncomingBlock(1);
+ if (cast<BranchInst>(Pred->getTerminator())->isUnconditional()) {
+ IfBlock2 = Pred;
+ DomBlock = *pred_begin(Pred);
+ for (BasicBlock::iterator I = Pred->begin();
+ !isa<TerminatorInst>(I); ++I)
+ if (!AggressiveInsts.count(I)) {
+ // This is not an aggressive instruction that we can promote.
+ // Because of this, we won't be able to get rid of the control
+ // flow, so the xform is not worth it.
+ return false;
+ }
+ }
+
+ // If we can still promote the PHI nodes after this gauntlet of tests,
+ // do all of the PHI's now.
+
+ // Move all 'aggressive' instructions, which are defined in the
+ // conditional parts of the if's up to the dominating block.
+ if (IfBlock1) {
+ DomBlock->getInstList().splice(DomBlock->getTerminator(),
+ IfBlock1->getInstList(),
+ IfBlock1->begin(),
+ IfBlock1->getTerminator());
+ }
+ if (IfBlock2) {
+ DomBlock->getInstList().splice(DomBlock->getTerminator(),
+ IfBlock2->getInstList(),
+ IfBlock2->begin(),
+ IfBlock2->getTerminator());
+ }
+
+ while (PHINode *PN = dyn_cast<PHINode>(BB->begin())) {
+ // Change the PHI node into a select instruction.
+ Value *TrueVal =
+ PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
+ Value *FalseVal =
+ PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
+
+ std::string Name = PN->getName(); PN->setName("");
+ PN->replaceAllUsesWith(new SelectInst(IfCond, TrueVal, FalseVal,
+ Name, AfterPHIIt));
+ BB->getInstList().erase(PN);
+ }
+ return true;
+}
+
+namespace {
+ /// ConstantIntOrdering - This class implements a stable ordering of constant
+ /// integers that does not depend on their address. This is important for
+ /// applications that sort ConstantInt's to ensure uniqueness.
+ struct ConstantIntOrdering {
+ bool operator()(const ConstantInt *LHS, const ConstantInt *RHS) const {
+ return LHS->getZExtValue() < RHS->getZExtValue();
+ }
+ };
}
// SimplifyCFG - This function is used to do simplification of a CFG. For
// 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;
+ 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)) {
- //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);
-
- //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!
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.
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());
+
+ // In order for this transformation to be safe, we must be able to
+ // unconditionally execute both operands to the return. This is
+ // normally the case, but we could have a potentially-trapping
+ // constant expression that prevents this transformation from being
+ // safe.
+ if ((!isa<ConstantExpr>(TrueValue) ||
+ !cast<ConstantExpr>(TrueValue)->canTrap()) &&
+ (!isa<ConstantExpr>(TrueValue) ||
+ !cast<ConstantExpr>(TrueValue)->canTrap())) {
+ TrueSucc->removePredecessor(BI->getParent());
+ FalseSucc->removePredecessor(BI->getParent());
+
+ // Insert a new select instruction.
+ Value *NewRetVal;
+ Value *BrCond = BI->getCondition();
+ if (TrueValue != FalseValue)
+ NewRetVal = new SelectInst(BrCond, TrueValue,
+ FalseValue, "retval", BI);
+ else
+ NewRetVal = TrueValue;
+
+ DOUT << "\nCHANGING BRANCH TO TWO RETURNS INTO SELECT:"
+ << "\n " << *BI << "Select = " << *NewRetVal
+ << "TRUEBLOCK: " << *TrueSucc << "FALSEBLOCK: "<< *FalseSucc;
+
+ new ReturnInst(NewRetVal, BI);
+ BI->eraseFromParent();
+ if (Instruction *BrCondI = dyn_cast<Instruction>(BrCond))
+ if (isInstructionTriviallyDead(BrCondI))
+ BrCondI->eraseFromParent();
+ return true;
+ }
+ }
+ }
+ }
}
- } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->begin())) {
+ } else if (isa<UnwindInst>(BB->begin())) {
// Check to see if the first instruction in this block is just an unwind.
// If so, replace any invoke instructions which use this as an exception
- // destination with call instructions.
+ // 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...
BranchInst *BI = new BranchInst(II->getNormalDest(), II);
Pred->getInstList().remove(II); // Take out of symbol table
-
+
// Insert the call now...
std::vector<Value*> Args(II->op_begin()+3, II->op_end());
CallInst *CI = new CallInst(II->getCalledValue(), Args,
II->getName(), BI);
+ CI->setCallingConv(II->getCallingConv());
// 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 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;
+ } 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->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 ||
+ (&*I == cast<Instruction>(BI->getCondition()) &&
+ &*++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 (Instruction *Cond = dyn_cast<Instruction>(BI->getCondition()))
+ if ((isa<CmpInst>(Cond) || isa<BinaryOperator>(Cond)) &&
+ Cond->getParent() == BB && &BB->front() == Cond &&
+ Cond->getNext() == BI && Cond->hasOneUse() &&
+ TrueDest != BB && FalseDest != BB)
+ for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI!=E; ++PI)
+ 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 && 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);
+ 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;
+ }
}
- 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)));
+ // Scan predessor blocks for conditional branchs.
+ for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
+ if (BranchInst *PBI = dyn_cast<BranchInst>((*PI)->getTerminator()))
+ if (PBI != BI && PBI->isConditional()) {
+
+ // If this block ends with a branch instruction, and if there is a
+ // predecessor that ends on a branch of the same condition, make
+ // this conditional branch redundant.
+ if (PBI->getCondition() == BI->getCondition() &&
+ PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
+ // Okay, the outcome of this conditional branch is statically
+ // knowable. If this block had a single pred, handle specially.
+ if (BB->getSinglePredecessor()) {
+ // Turn this into a branch on constant.
+ bool CondIsTrue = PBI->getSuccessor(0) == BB;
+ BI->setCondition(ConstantInt::get(Type::Int1Ty, CondIsTrue));
+ return SimplifyCFG(BB); // Nuke the branch on constant.
+ }
+
+ // Otherwise, if there are multiple predecessors, insert a PHI
+ // that merges in the constant and simplify the block result.
+ if (BlockIsSimpleEnoughToThreadThrough(BB)) {
+ PHINode *NewPN = new PHINode(Type::Int1Ty,
+ BI->getCondition()->getName()+".pr",
+ BB->begin());
+ for (PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI)
+ if ((PBI = dyn_cast<BranchInst>((*PI)->getTerminator())) &&
+ PBI != BI && PBI->isConditional() &&
+ PBI->getCondition() == BI->getCondition() &&
+ PBI->getSuccessor(0) != PBI->getSuccessor(1)) {
+ bool CondIsTrue = PBI->getSuccessor(0) == BB;
+ NewPN->addIncoming(ConstantInt::get(Type::Int1Ty,
+ CondIsTrue), *PI);
+ } else {
+ NewPN->addIncoming(BI->getCondition(), *PI);
+ }
+
+ BI->setCondition(NewPN);
+ // This will thread the branch.
+ return SimplifyCFG(BB) | true;
+ }
}
-
- } 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;
+
+ // 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;
+ }
+ }
}
- // 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
+ // Finally, if everything is ok, fold the branches to logical ops.
+ if (PBIOp != -1) {
+ BasicBlock *CommonDest = PBI->getSuccessor(PBIOp);
+ BasicBlock *OtherDest = BI->getSuccessor(BIOp ^ 1);
+
+ // If OtherDest *is* BB, then this is a basic block with just
+ // a conditional branch in it, where one edge (OtherDesg) goes
+ // back to the block. We know that the program doesn't get
+ // stuck in the infinite loop, so the condition must be such
+ // that OtherDest isn't branched through. Forward to CommonDest,
+ // and avoid an infinite loop at optimizer time.
+ if (OtherDest == BB)
+ OtherDest = CommonDest;
+
+ DOUT << "FOLDING BRs:" << *PBI->getParent()
+ << "AND: " << *BI->getParent();
+
+ // BI may have other predecessors. Because of this, we leave
+ // it alone, but modify PBI.
+
+ // Make sure we get to CommonDest on True&True directions.
+ Value *PBICond = PBI->getCondition();
+ if (PBIOp)
+ PBICond = BinaryOperator::createNot(PBICond,
+ PBICond->getName()+".not",
+ PBI);
+ Value *BICond = BI->getCondition();
+ if (BIOp)
+ BICond = BinaryOperator::createNot(BICond,
+ BICond->getName()+".not",
+ PBI);
+ // Merge the conditions.
+ Value *Cond =
+ BinaryOperator::createOr(PBICond, BICond, "brmerge", PBI);
+
+ // Modify PBI to branch on the new condition to the new dests.
+ PBI->setCondition(Cond);
+ PBI->setSuccessor(0, CommonDest);
+ PBI->setSuccessor(1, OtherDest);
+
+ // OtherDest may have phi nodes. If so, add an entry from PBI's
+ // block that are identical to the entries for BI's block.
+ PHINode *PN;
+ for (BasicBlock::iterator II = OtherDest->begin();
+ (PN = dyn_cast<PHINode>(II)); ++II) {
+ Value *V = PN->getIncomingValueForBlock(BB);
+ PN->addIncoming(V, PBI->getParent());
+ }
+
+ // We know that the CommonDest already had an edge from PBI to
+ // it. If it has PHIs though, the PHIs may have different
+ // entries for BB and PBI's BB. If so, insert a select to make
+ // them agree.
+ for (BasicBlock::iterator II = CommonDest->begin();
+ (PN = dyn_cast<PHINode>(II)); ++II) {
+ Value * BIV = PN->getIncomingValueForBlock(BB);
+ unsigned PBBIdx = PN->getBasicBlockIndex(PBI->getParent());
+ Value *PBIV = PN->getIncomingValue(PBBIdx);
+ if (BIV != PBIV) {
+ // Insert a select in PBI to pick the right value.
+ Value *NV = new SelectInst(PBICond, PBIV, BIV,
+ PBIV->getName()+".mux", PBI);
+ PN->setIncomingValue(PBBIdx, NV);
+ }
+ }
+
+ DOUT << "INTO: " << *PBI->getParent();
+
+ // This basic block is probably dead. We know it has at least
+ // one fewer predecessor.
+ return SimplifyCFG(BB) | true;
}
}
-
- // 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);
}
+ }
+ } 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;
+ }
- // 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);
+ // If the unreachable instruction is the first in the block, take a gander
+ // at all of the predecessors of this instruction, and simplify them.
+ if (&BB->front() == Unreachable) {
+ std::vector<BasicBlock*> Preds(pred_begin(BB), pred_end(BB));
+ for (unsigned i = 0, e = Preds.size(); i != e; ++i) {
+ TerminatorInst *TI = Preds[i]->getTerminator();
+
+ if (BranchInst *BI = dyn_cast<BranchInst>(TI)) {
+ if (BI->isUnconditional()) {
+ if (BI->getSuccessor(0) == BB) {
+ new UnreachableInst(TI);
+ TI->eraseFromParent();
+ Changed = true;
+ }
+ } else {
+ if (BI->getSuccessor(0) == BB) {
+ new BranchInst(BI->getSuccessor(1), BI);
+ BI->eraseFromParent();
+ } else if (BI->getSuccessor(1) == BB) {
+ new BranchInst(BI->getSuccessor(0), BI);
+ BI->eraseFromParent();
+ Changed = true;
+ }
}
-
- // 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);
+ } 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;
}
- PSI->setSuccessor(i, InfLoopBlock);
}
-
- Changed = true;
+ 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 = new BranchInst(II->getNormalDest(), II);
+ II->removeFromParent(); // Take out of symbol table
+
+ // Insert the call now...
+ std::vector<Value*> Args(II->op_begin()+3, II->op_end());
+ CallInst *CI = new CallInst(II->getCalledValue(), Args,
+ II->getName(), BI);
+ CI->setCallingConv(II->getCallingConv());
+ // If the invoke produced a value, the Call does now instead.
+ II->replaceAllUsesWith(CI);
+ delete II;
+ Changed = 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);
+ // 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
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;
- 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
// Delete the unconditional branch from the predecessor...
OnlyPred->getInstList().pop_back();
-
+
// 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...
BB->replaceAllUsesWith(OnlyPred);
std::string OldName = BB->getName();
- // Erase basic block from the function...
+ // 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.
// 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 *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 = new SwitchInst(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)) {
- //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;
+ if (PN->getNumIncomingValues() == 2)
+ Changed |= FoldTwoEntryPHINode(PN);
- BasicBlock::iterator I = BB->begin();
- while (PHINode *PN = dyn_cast<PHINode>(I)) {
- ++I;
-
- // If we can eliminate this PHI by directly computing it based on the
- // condition, do so now. We can't eliminate PHI nodes where the
- // incoming values are defined in the conditional parts of the branch,
- // so check for this.
- //
- if (DominatesMergePoint(PN->getIncomingValue(0), BB) &&
- DominatesMergePoint(PN->getIncomingValue(1), BB)) {
- 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;
- }
- }
- }
- }
- }
-
return Changed;
}
projects / oota-llvm.git / blobdiff