#include "llvm/Type.h"
#include "llvm/DerivedTypes.h"
#include "llvm/GlobalVariable.h"
-#include "llvm/Support/CFG.h"
-#include "llvm/Support/Debug.h"
-#include "llvm/Support/raw_ostream.h"
-#include "llvm/Analysis/ConstantFolding.h"
+#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Target/TargetData.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
#include "llvm/ADT/STLExtras.h"
+#include "llvm/Support/CFG.h"
+#include "llvm/Support/CommandLine.h"
+#include "llvm/Support/ConstantRange.h"
+#include "llvm/Support/Debug.h"
+#include "llvm/Support/raw_ostream.h"
#include <algorithm>
#include <set>
#include <map>
using namespace llvm;
+static cl::opt<bool>
+DupRet("simplifycfg-dup-ret", cl::Hidden, cl::init(false),
+ cl::desc("Duplicate return instructions into unconditional branches"));
+
STATISTIC(NumSpeculations, "Number of speculative executed instructions");
namespace {
BasicBlock *Pred);
bool FoldValueComparisonIntoPredecessors(TerminatorInst *TI);
+ bool SimplifyReturn(ReturnInst *RI);
+ bool SimplifyUnwind(UnwindInst *UI);
+ bool SimplifyUnreachable(UnreachableInst *UI);
+ bool SimplifySwitch(SwitchInst *SI);
+ bool SimplifyIndirectBr(IndirectBrInst *IBI);
+ bool SimplifyUncondBranch(BranchInst *BI);
+ bool SimplifyCondBranch(BranchInst *BI);
+
public:
explicit SimplifyCFGOpt(const TargetData *td) : TD(td) {}
bool run(BasicBlock *BB);
/// 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
PHINode *PN;
}
-/// GetIfCondition - Given a basic block (BB) with two predecessors (and
-/// presumably PHI nodes in it), check to see if the merge at this block is due
+/// GetIfCondition - Given a basic block (BB) with two predecessors (and at
+/// least one PHI node in it), check to see if the merge at this block is due
/// to an "if condition". If so, return the boolean condition that determines
/// 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) {
- assert(std::distance(pred_begin(BB), pred_end(BB)) == 2 &&
+/// This does no checking to see if the true/false blocks have large or unsavory
+/// instructions in them.
+static Value *GetIfCondition(BasicBlock *BB, BasicBlock *&IfTrue,
+ BasicBlock *&IfFalse) {
+ PHINode *SomePHI = cast<PHINode>(BB->begin());
+ assert(SomePHI->getNumIncomingValues() == 2 &&
"Function can only handle blocks with 2 predecessors!");
- BasicBlock *Pred1 = *pred_begin(BB);
- BasicBlock *Pred2 = *++pred_begin(BB);
+ BasicBlock *Pred1 = SomePHI->getIncomingBlock(0);
+ BasicBlock *Pred2 = SomePHI->getIncomingBlock(1);
// We can only handle branches. Other control flow will be lowered to
// branches if possible anyway.
- if (!isa<BranchInst>(Pred1->getTerminator()) ||
- !isa<BranchInst>(Pred2->getTerminator()))
+ BranchInst *Pred1Br = dyn_cast<BranchInst>(Pred1->getTerminator());
+ BranchInst *Pred2Br = dyn_cast<BranchInst>(Pred2->getTerminator());
+ if (Pred1Br == 0 || Pred2Br == 0)
return 0;
- BranchInst *Pred1Br = cast<BranchInst>(Pred1->getTerminator());
- BranchInst *Pred2Br = cast<BranchInst>(Pred2->getTerminator());
// Eliminate code duplication by ensuring that Pred1Br is conditional if
// either are.
}
if (Pred1Br->isConditional()) {
+ // The only thing we have to watch out for here is to make sure that Pred2
+ // doesn't have incoming edges from other blocks. If it does, the condition
+ // doesn't dominate BB.
+ if (Pred2->getSinglePredecessor() == 0)
+ return 0;
+
// If we found a conditional branch predecessor, make sure that it branches
// to BB and Pred2Br. If it doesn't, this isn't an "if statement".
if (Pred1Br->getSuccessor(0) == BB &&
return 0;
}
- // The only thing we have to watch out for here is to make sure that Pred2
- // doesn't have incoming edges from other blocks. If it does, the condition
- // doesn't dominate BB.
- if (++pred_begin(Pred2) != pred_end(Pred2))
- return 0;
-
return Pred1Br->getCondition();
}
// Ok, if we got here, both predecessors end with an unconditional branch to
// BB. Don't panic! If both blocks only have a single (identical)
// predecessor, and THAT is a conditional branch, then we're all ok!
- if (pred_begin(Pred1) == pred_end(Pred1) ||
- ++pred_begin(Pred1) != pred_end(Pred1) ||
- pred_begin(Pred2) == pred_end(Pred2) ||
- ++pred_begin(Pred2) != pred_end(Pred2) ||
- *pred_begin(Pred1) != *pred_begin(Pred2))
+ BasicBlock *CommonPred = Pred1->getSinglePredecessor();
+ if (CommonPred == 0 || CommonPred != Pred2->getSinglePredecessor())
return 0;
// Otherwise, if this is a conditional branch, then we can use it!
- BasicBlock *CommonPred = *pred_begin(Pred1);
- if (BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator())) {
- assert(BI->isConditional() && "Two successors but not conditional?");
- if (BI->getSuccessor(0) == Pred1) {
- IfTrue = Pred1;
- IfFalse = Pred2;
- } else {
- IfTrue = Pred2;
- IfFalse = Pred1;
- }
- return BI->getCondition();
+ BranchInst *BI = dyn_cast<BranchInst>(CommonPred->getTerminator());
+ if (BI == 0) return 0;
+
+ assert(BI->isConditional() && "Two successors but not conditional?");
+ if (BI->getSuccessor(0) == Pred1) {
+ IfTrue = Pred1;
+ IfFalse = Pred2;
+ } else {
+ IfTrue = Pred2;
+ IfFalse = Pred1;
}
- return 0;
+ return BI->getCondition();
}
/// DominatesMergePoint - If we have a merge point of an "if condition" as
/// 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) {
+ SmallPtrSet<Instruction*, 4> *AggressiveInsts) {
Instruction *I = dyn_cast<Instruction>(V);
if (!I) {
// Non-instructions all dominate instructions, but not all constantexprs
// 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 it's a cheap instruction to unconditionally compute, and if it
- // only uses stuff defined outside of the condition. If so, hoist it out.
- if (!I->isSafeToSpeculativelyExecute())
- return false;
+ // statement". If not, it definitely dominates the region.
+ BranchInst *BI = dyn_cast<BranchInst>(PBB->getTerminator());
+ if (BI == 0 || BI->isConditional() || BI->getSuccessor(0) != BB)
+ return true;
- switch (I->getOpcode()) {
- default: return false; // Cannot hoist this out safely.
- case Instruction::Load: {
- // 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.
- BasicBlock::iterator IP = PBB->begin();
- while (isa<DbgInfoIntrinsic>(IP))
- IP++;
- if (IP != 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:
- break; // These are all cheap and non-trapping instructions.
- }
+ // If we aren't allowing aggressive promotion anymore, then don't consider
+ // instructions in the 'if region'.
+ if (AggressiveInsts == 0) return false;
+
+ // Okay, it looks like the instruction IS in the "condition". Check to
+ // see if it's a cheap instruction to unconditionally compute, and if it
+ // only uses stuff defined outside of the condition. If so, hoist it out.
+ if (!I->isSafeToSpeculativelyExecute())
+ return false;
- // Okay, we can only really hoist these out if their operands are not
- // defined in the conditional region.
- for (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
- if (!DominatesMergePoint(*i, BB, 0))
- return false;
- // Okay, it's safe to do this! Remember this instruction.
- AggressiveInsts->insert(I);
- }
+ switch (I->getOpcode()) {
+ default: return false; // Cannot hoist this out safely.
+ case Instruction::Load:
+ // 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 load out to its
+ // predecessor.
+ if (PBB->getFirstNonPHIOrDbg() != 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:
+ 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 (User::op_iterator i = I->op_begin(), e = I->op_end(); i != e; ++i)
+ if (!DominatesMergePoint(*i, BB, 0))
+ return false;
+ // Okay, it's safe to do this! Remember this instruction.
+ AggressiveInsts->insert(I);
return true;
}
// If this is an icmp against a constant, handle this as one of the cases.
if (ICmpInst *ICI = dyn_cast<ICmpInst>(I)) {
- if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ : ICmpInst::ICMP_NE))
- if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) {
+ if (ConstantInt *C = GetConstantInt(I->getOperand(1), TD)) {
+ if (ICI->getPredicate() == (isEQ ? ICmpInst::ICMP_EQ:ICmpInst::ICMP_NE)) {
Vals.push_back(C);
return I->getOperand(0);
}
+
+ // If we have "x ult 3" comparison, for example, then we can add 0,1,2 to
+ // the set.
+ ConstantRange Span =
+ ConstantRange::makeICmpRegion(ICI->getPredicate(), C->getValue());
+
+ // If this is an and/!= check then we want to optimize "x ugt 2" into
+ // x != 0 && x != 1.
+ if (!isEQ)
+ Span = Span.inverse();
+
+ // If there are a ton of values, we don't want to make a ginormous switch.
+ if (Span.getSetSize().ugt(8) || Span.isEmptySet() ||
+ // We don't handle wrapped sets yet.
+ Span.isWrappedSet())
+ return 0;
+
+ for (APInt Tmp = Span.getLower(); Tmp != Span.getUpper(); ++Tmp)
+ Vals.push_back(ConstantInt::get(V->getContext(), Tmp));
+ return I->getOperand(0);
+ }
return 0;
}
isEQ)) {
if (LHS == RHS)
return LHS;
+ Vals.resize(NumVals);
}
- Vals.resize(NumVals);
// The RHS of the or/and can't be folded in and we haven't used "Extra" yet,
// set it and return success.
// If the LHS can't be folded in, but Extra is available and RHS can, try to
// use LHS as Extra.
if (Extra == 0 || Extra == I->getOperand(0)) {
+ Value *OldExtra = Extra;
Extra = I->getOperand(0);
if (Value *RHS = GatherConstantCompares(I->getOperand(1), Vals, Extra, TD,
isEQ))
return RHS;
- Vals.resize(NumValsBeforeLHS);
- Extra = 0;
+ assert(Vals.size() == NumValsBeforeLHS);
+ Extra = OldExtra;
}
return 0;
static int ConstantIntSortPredicate(const void *P1, const void *P2) {
const ConstantInt *LHS = *(const ConstantInt**)P1;
const ConstantInt *RHS = *(const ConstantInt**)P2;
- return LHS->getValue().ult(RHS->getValue());
+ if (LHS->getValue().ult(RHS->getValue()))
+ return 1;
+ if (LHS->getValue() == RHS->getValue())
+ return 0;
+ return -1;
}
/// FoldValueComparisonIntoPredecessors - The specified terminator is a value
if (!I2->use_empty())
I2->replaceAllUsesWith(I1);
I1->intersectOptionalDataWith(I2);
- BB2->getInstList().erase(I2);
+ I2->eraseFromParent();
I1 = BB1_Itr++;
while (isa<DbgInfoIntrinsic>(I1))
/// 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) {
+static bool FoldCondBranchOnPHI(BranchInst *BI, const TargetData *TD) {
BasicBlock *BB = BI->getParent();
PHINode *PN = dyn_cast<PHINode>(BI->getCondition());
// NOTE: we currently cannot transform this case if the PHI node is used
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);
- }
+
+ // Update PHI nodes.
+ AddPredecessorToBlock(RealDest, EdgeBB, BB);
// BB may have instructions that are being threaded over. Clone these
// instructions into EdgeBB. We know that there will be no uses of the
}
// Check for trivial simplification.
- if (Constant *C = ConstantFoldInstruction(N)) {
- TranslateMap[BBI] = C;
- delete N; // Constant folded away, don't need actual inst
+ if (Value *V = SimplifyInstruction(N, TD)) {
+ TranslateMap[BBI] = V;
+ delete N; // Instruction folded away, don't need actual inst
} else {
// Insert the new instruction into its new home.
EdgeBB->getInstList().insert(InsertPt, N);
}
// Recurse, simplifying any other constants.
- return FoldCondBranchOnPHI(BI) | true;
+ return FoldCondBranchOnPHI(BI, TD) | 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) {
+static bool FoldTwoEntryPHINode(PHINode *PN, const TargetData *TD) {
// 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;
+ if (!IfCond ||
+ // Don't bother if the branch will be constant folded trivially.
+ isa<ConstantInt>(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.
if (NumPhis > 2)
return false;
- DEBUG(dbgs() << "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;
+ SmallPtrSet<Instruction*, 4> AggressiveInsts;
+
+ for (BasicBlock::iterator II = BB->begin(); isa<PHINode>(II);) {
+ PHINode *PN = cast<PHINode>(II++);
+ if (Value *V = SimplifyInstruction(PN, TD)) {
+ PN->replaceAllUsesWith(V);
+ PN->eraseFromParent();
+ continue;
}
+
+ if (!DominatesMergePoint(PN->getIncomingValue(0), BB, &AggressiveInsts) ||
+ !DominatesMergePoint(PN->getIncomingValue(1), BB, &AggressiveInsts))
+ return false;
}
+ // If we folded the the first phi, PN dangles at this point. Refresh it. If
+ // we ran out of PHIs then we simplified them all.
+ PN = dyn_cast<PHINode>(BB->begin());
+ if (PN == 0) return true;
+
+ // Don't fold i1 branches on PHIs which contain binary operators. These can
+ // often be turned into switches and other things.
+ if (PN->getType()->isIntegerTy(1) &&
+ (isa<BinaryOperator>(PN->getIncomingValue(0)) ||
+ isa<BinaryOperator>(PN->getIncomingValue(1)) ||
+ isa<BinaryOperator>(IfCond)))
+ 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)
+ BasicBlock *DomBlock = 0;
+ BasicBlock *IfBlock1 = PN->getIncomingBlock(0);
+ BasicBlock *IfBlock2 = PN->getIncomingBlock(1);
+ if (cast<BranchInst>(IfBlock1->getTerminator())->isConditional()) {
+ IfBlock1 = 0;
+ } else {
+ DomBlock = *pred_begin(IfBlock1);
+ for (BasicBlock::iterator I = IfBlock1->begin();!isa<TerminatorInst>(I);++I)
if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(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
}
}
- 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 (cast<BranchInst>(IfBlock2->getTerminator())->isConditional()) {
+ IfBlock2 = 0;
+ } else {
+ DomBlock = *pred_begin(IfBlock2);
+ for (BasicBlock::iterator I = IfBlock2->begin();!isa<TerminatorInst>(I);++I)
if (!AggressiveInsts.count(I) && !isa<DbgInfoIntrinsic>(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
return false;
}
}
+
+ DEBUG(dbgs() << "FOUND IF CONDITION! " << *IfCond << " T: "
+ << IfTrue->getName() << " F: " << IfFalse->getName() << "\n");
// If we can still promote the PHI nodes after this gauntlet of tests,
// do all of the PHI's now.
-
+ Instruction *InsertPt = DomBlock->getTerminator();
+
// 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(),
+ DomBlock->getInstList().splice(InsertPt,
IfBlock1->getInstList(), IfBlock1->begin(),
IfBlock1->getTerminator());
if (IfBlock2)
- DomBlock->getInstList().splice(DomBlock->getTerminator(),
+ DomBlock->getInstList().splice(InsertPt,
IfBlock2->getInstList(), IfBlock2->begin(),
IfBlock2->getTerminator());
Value *TrueVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfFalse);
Value *FalseVal = PN->getIncomingValue(PN->getIncomingBlock(0) == IfTrue);
- Value *NV = SelectInst::Create(IfCond, TrueVal, FalseVal, "", AfterPHIIt);
+ Value *NV = SelectInst::Create(IfCond, TrueVal, FalseVal, "", InsertPt);
PN->replaceAllUsesWith(NV);
NV->takeName(PN);
-
- BB->getInstList().erase(PN);
+ PN->eraseFromParent();
}
+
+ // At this point, IfBlock1 and IfBlock2 are both empty, so our if statement
+ // has been flattened. Change DomBlock to jump directly to our new block to
+ // avoid other simplifycfg's kicking in on the diamond.
+ TerminatorInst *OldTI = DomBlock->getTerminator();
+ BranchInst::Create(BB, OldTI);
+ OldTI->eraseFromParent();
return true;
}
// must be at the front of the block.
BasicBlock::iterator FrontIt = BB->front();
// Ignore dbg intrinsics.
- while(isa<DbgInfoIntrinsic>(FrontIt))
+ while (isa<DbgInfoIntrinsic>(FrontIt))
++FrontIt;
// Allow a single instruction to be hoisted in addition to the compare
UsedValues.erase(Pair.first);
if (UsedValues.empty()) break;
- if (Instruction* I = dyn_cast<Instruction>(Pair.first)) {
+ if (Instruction *I = dyn_cast<Instruction>(Pair.first)) {
for (Instruction::op_iterator OI = I->op_begin(), OE = I->op_end();
OI != OE; ++OI)
Worklist.push_back(std::make_pair(OI->get(), Pair.second+1));
// If we need to invert the condition in the pred block to match, do so now.
if (InvertPredCond) {
- Value *NewCond =
- BinaryOperator::CreateNot(PBI->getCondition(),
+ Value *NewCond = PBI->getCondition();
+
+ if (NewCond->hasOneUse() && isa<CmpInst>(NewCond)) {
+ CmpInst *CI = cast<CmpInst>(NewCond);
+ CI->setPredicate(CI->getInversePredicate());
+ } else {
+ NewCond = BinaryOperator::CreateNot(NewCond,
PBI->getCondition()->getName()+".not", PBI);
+ }
+
PBI->setCondition(NewCond);
BasicBlock *OldTrue = PBI->getSuccessor(0);
BasicBlock *OldFalse = PBI->getSuccessor(1);
// 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());
- }
+ AddPredecessorToBlock(OtherDest, PBI->getParent(), BB);
// 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.
+ PHINode *PN;
for (BasicBlock::iterator II = CommonDest->begin();
(PN = dyn_cast<PHINode>(II)); ++II) {
Value *BIV = PN->getIncomingValueForBlock(BB);
return true;
}
-// SimplifyIndirectBrOnSelect - Replaces
-// (indirectbr (select cond, blockaddress(@fn, BlockA),
-// blockaddress(@fn, BlockB)))
-// with
-// (br cond, BlockA, BlockB).
-static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) {
- // Check that both operands of the select are block addresses.
- BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
- BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
- if (!TBA || !FBA)
- return false;
-
- // Extract the actual blocks.
- BasicBlock *TrueBB = TBA->getBasicBlock();
- BasicBlock *FalseBB = FBA->getBasicBlock();
-
+// SimplifyTerminatorOnSelect - Simplifies a terminator by replacing it with a
+// branch to TrueBB if Cond is true or to FalseBB if Cond is false.
+// Takes care of updating the successors and removing the old terminator.
+// Also makes sure not to introduce new successors by assuming that edges to
+// non-successor TrueBBs and FalseBBs aren't reachable.
+static bool SimplifyTerminatorOnSelect(TerminatorInst *OldTerm, Value *Cond,
+ BasicBlock *TrueBB, BasicBlock *FalseBB){
// Remove any superfluous successor edges from the CFG.
// First, figure out which successors to preserve.
// If TrueBB and FalseBB are equal, only try to preserve one copy of that
BasicBlock *KeepEdge2 = TrueBB != FalseBB ? FalseBB : 0;
// Then remove the rest.
- for (unsigned I = 0, E = IBI->getNumSuccessors(); I != E; ++I) {
- BasicBlock *Succ = IBI->getSuccessor(I);
+ for (unsigned I = 0, E = OldTerm->getNumSuccessors(); I != E; ++I) {
+ BasicBlock *Succ = OldTerm->getSuccessor(I);
// Make sure only to keep exactly one copy of each edge.
if (Succ == KeepEdge1)
KeepEdge1 = 0;
else if (Succ == KeepEdge2)
KeepEdge2 = 0;
else
- Succ->removePredecessor(IBI->getParent());
+ Succ->removePredecessor(OldTerm->getParent());
}
// Insert an appropriate new terminator.
if (TrueBB == FalseBB)
// We were only looking for one successor, and it was present.
// Create an unconditional branch to it.
- BranchInst::Create(TrueBB, IBI);
+ BranchInst::Create(TrueBB, OldTerm);
else
// We found both of the successors we were looking for.
// Create a conditional branch sharing the condition of the select.
- BranchInst::Create(TrueBB, FalseBB, SI->getCondition(), IBI);
+ BranchInst::Create(TrueBB, FalseBB, Cond, OldTerm);
} else if (KeepEdge1 && (KeepEdge2 || TrueBB == FalseBB)) {
// Neither of the selected blocks were successors, so this
- // indirectbr must be unreachable.
- new UnreachableInst(IBI->getContext(), IBI);
+ // terminator must be unreachable.
+ new UnreachableInst(OldTerm->getContext(), OldTerm);
} else {
// One of the selected values was a successor, but the other wasn't.
// Insert an unconditional branch to the one that was found;
// the edge to the one that wasn't must be unreachable.
if (KeepEdge1 == 0)
// Only TrueBB was found.
- BranchInst::Create(TrueBB, IBI);
+ BranchInst::Create(TrueBB, OldTerm);
else
// Only FalseBB was found.
- BranchInst::Create(FalseBB, IBI);
+ BranchInst::Create(FalseBB, OldTerm);
}
- EraseTerminatorInstAndDCECond(IBI);
+ EraseTerminatorInstAndDCECond(OldTerm);
return true;
}
+// SimplifyIndirectBrOnSelect - Replaces
+// (indirectbr (select cond, blockaddress(@fn, BlockA),
+// blockaddress(@fn, BlockB)))
+// with
+// (br cond, BlockA, BlockB).
+static bool SimplifyIndirectBrOnSelect(IndirectBrInst *IBI, SelectInst *SI) {
+ // Check that both operands of the select are block addresses.
+ BlockAddress *TBA = dyn_cast<BlockAddress>(SI->getTrueValue());
+ BlockAddress *FBA = dyn_cast<BlockAddress>(SI->getFalseValue());
+ if (!TBA || !FBA)
+ return false;
+
+ // Extract the actual blocks.
+ BasicBlock *TrueBB = TBA->getBasicBlock();
+ BasicBlock *FalseBB = FBA->getBasicBlock();
+
+ // Perform the actual simplification.
+ return SimplifyTerminatorOnSelect(IBI, SI->getCondition(), TrueBB, FalseBB);
+}
+
/// TryToSimplifyUncondBranchWithICmpInIt - This is called when we find an icmp
/// instruction (a seteq/setne with a constant) as the only instruction in a
/// block that ends with an uncond branch. We are looking for a very specific
///
/// We prefer to split the edge to 'end' so that there is a true/false entry to
/// the PHI, merging the third icmp into the switch.
-static bool TryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI) {
+static bool TryToSimplifyUncondBranchWithICmpInIt(ICmpInst *ICI,
+ const TargetData *TD) {
BasicBlock *BB = ICI->getParent();
// If the block has any PHIs in it or the icmp has multiple uses, it is too
// complex.
assert(VVal && "Should have a unique destination value");
ICI->setOperand(0, VVal);
- if (Constant *C = ConstantFoldInstruction(ICI)) {
- ICI->replaceAllUsesWith(C);
+ if (Value *V = SimplifyInstruction(ICI, TD)) {
+ ICI->replaceAllUsesWith(V);
ICI->eraseFromParent();
}
// BB is now empty, so it is likely to simplify away.
BasicBlock *BB = BI->getParent();
+ DEBUG(dbgs() << "Converting 'icmp' chain with " << Values.size()
+ << " cases into SWITCH. BB is:\n" << *BB);
+
// If there are any extra values that couldn't be folded into the switch
// then we evaluate them with an explicit branch first. Split the block
// right before the condbr to handle it.
// Remove the uncond branch added to the old block.
TerminatorInst *OldTI = BB->getTerminator();
- BranchInst::Create(EdgeBB, NewBB, ExtraCase, OldTI);
+ if (TrueWhenEqual)
+ BranchInst::Create(EdgeBB, NewBB, ExtraCase, OldTI);
+ else
+ BranchInst::Create(NewBB, EdgeBB, ExtraCase, OldTI);
+
OldTI->eraseFromParent();
+
+ // If there are PHI nodes in EdgeBB, then we need to add a new entry to them
+ // for the edge we just added.
+ AddPredecessorToBlock(EdgeBB, BB, NewBB);
+
+ DEBUG(dbgs() << " ** 'icmp' chain unhandled condition: " << *ExtraCase
+ << "\nEXTRABB = " << *BB);
BB = NewBB;
}
}
// Create the new switch instruction now.
- SwitchInst *New =
- SwitchInst::Create(CompVal, DefaultBB, Values.size(), 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)
// Erase the old branch instruction.
EraseTerminatorInstAndDCECond(BI);
+
+ DEBUG(dbgs() << " ** 'icmp' chain result is:\n" << *BB << '\n');
return true;
}
-bool SimplifyCFGOpt::run(BasicBlock *BB) {
- bool Changed = false;
- Function *Fn = BB->getParent();
-
- assert(BB && Fn && "Block not embedded in function!");
- assert(BB->getTerminator() && "Degenerate basic block encountered!");
-
- // Remove basic blocks that have no predecessors (except the entry block)...
- // or that just have themself as a predecessor. These are unreachable.
- if ((pred_begin(BB) == pred_end(BB) && BB != &Fn->getEntryBlock()) ||
- BB->getSinglePredecessor() == BB) {
- DEBUG(dbgs() << "Removing BB: \n" << *BB);
- DeleteDeadBlock(BB);
+bool SimplifyCFGOpt::SimplifyReturn(ReturnInst *RI) {
+ BasicBlock *BB = RI->getParent();
+ if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
+
+ // Find predecessors that end with branches.
+ SmallVector<BasicBlock*, 8> UncondBranchPreds;
+ SmallVector<BranchInst*, 8> CondBranchPreds;
+ for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
+ BasicBlock *P = *PI;
+ TerminatorInst *PTI = P->getTerminator();
+ if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
+ if (BI->isUnconditional())
+ UncondBranchPreds.push_back(P);
+ else
+ CondBranchPreds.push_back(BI);
+ }
+ }
+
+ // If we found some, do the transformation!
+ if (!UncondBranchPreds.empty() && DupRet) {
+ while (!UncondBranchPreds.empty()) {
+ BasicBlock *Pred = UncondBranchPreds.pop_back_val();
+ DEBUG(dbgs() << "FOLDING: " << *BB
+ << "INTO UNCOND BRANCH PRED: " << *Pred);
+ (void)FoldReturnIntoUncondBranch(RI, BB, Pred);
+ }
+
+ // If we eliminated all predecessors of the block, delete the block now.
+ if (pred_begin(BB) == pred_end(BB))
+ // We know there are no successors, so just nuke the block.
+ BB->eraseFromParent();
+
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.pop_back_val();
+
+ // Check to see if the non-BB successor is also a return block.
+ if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
+ isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
+ SimplifyCondBranchToTwoReturns(BI))
+ return true;
+ }
+ return false;
+}
- // Check to see if we can constant propagate this terminator instruction
- // away...
- Changed |= ConstantFoldTerminator(BB);
-
- // Check for and eliminate duplicate PHI nodes in this block.
- Changed |= EliminateDuplicatePHINodes(BB);
+bool SimplifyCFGOpt::SimplifyUnwind(UnwindInst *UI) {
+ // 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.
+ BasicBlock *BB = UI->getParent();
+ if (!BB->getFirstNonPHIOrDbg()->isTerminator()) return false;
- // Merge basic blocks into their predecessor if there is only one distinct
- // pred, and if there is only one distinct successor of the predecessor, and
- // if there are no PHI nodes.
- //
- if (MergeBlockIntoPredecessor(BB))
+ bool Changed = false;
+ SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
+ while (!Preds.empty()) {
+ BasicBlock *Pred = Preds.back();
+ InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator());
+ if (II && II->getUnwindDest() == BB) {
+ // Insert a new branch instruction before the invoke, because this
+ // is now a fall through.
+ BranchInst *BI = BranchInst::Create(II->getNormalDest(), II);
+ Pred->getInstList().remove(II); // Take out of symbol table
+
+ // Insert the call now.
+ SmallVector<Value*,8> Args(II->op_begin(), II->op_end()-3);
+ CallInst *CI = CallInst::Create(II->getCalledValue(),
+ Args.begin(), Args.end(),
+ II->getName(), BI);
+ CI->setCallingConv(II->getCallingConv());
+ CI->setAttributes(II->getAttributes());
+ // If the invoke produced a value, the Call now does instead.
+ II->replaceAllUsesWith(CI);
+ delete II;
+ Changed = true;
+ }
+
+ Preds.pop_back();
+ }
+
+ // If this block is now dead (and isn't the entry block), remove it.
+ if (pred_begin(BB) == pred_end(BB) &&
+ BB != &BB->getParent()->getEntryBlock()) {
+ // We know there are no successors, so just nuke the block.
+ BB->eraseFromParent();
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);
+ return Changed;
+}
- // 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())) {
- if (BB->getFirstNonPHIOrDbg()->isTerminator()) {
- // Find predecessors that end with branches.
- SmallVector<BasicBlock*, 8> UncondBranchPreds;
- SmallVector<BranchInst*, 8> CondBranchPreds;
- for (pred_iterator PI = pred_begin(BB), E = pred_end(BB); PI != E; ++PI) {
- BasicBlock *P = *PI;
- TerminatorInst *PTI = P->getTerminator();
- if (BranchInst *BI = dyn_cast<BranchInst>(PTI)) {
- if (BI->isUnconditional())
- UncondBranchPreds.push_back(P);
- else
- CondBranchPreds.push_back(BI);
+bool SimplifyCFGOpt::SimplifyUnreachable(UnreachableInst *UI) {
+ BasicBlock *BB = UI->getParent();
+
+ bool Changed = false;
+
+ // If there are any instructions immediately before the unreachable that can
+ // be removed, do so.
+ while (UI != BB->begin()) {
+ BasicBlock::iterator BBI = UI;
+ --BBI;
+ // Do not delete instructions that can have side effects, like calls
+ // (which may never return) and volatile loads and stores.
+ if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
+
+ if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
+ if (SI->isVolatile())
+ break;
+
+ if (LoadInst *LI = dyn_cast<LoadInst>(BBI))
+ if (LI->isVolatile())
+ break;
+
+ // Delete this instruction
+ BBI->eraseFromParent();
+ 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() != UI) return Changed;
+
+ 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->getContext(), TI);
+ TI->eraseFromParent();
+ Changed = true;
+ }
+ } else {
+ if (BI->getSuccessor(0) == BB) {
+ BranchInst::Create(BI->getSuccessor(1), BI);
+ EraseTerminatorInstAndDCECond(BI);
+ } else if (BI->getSuccessor(1) == BB) {
+ BranchInst::Create(BI->getSuccessor(0), BI);
+ EraseTerminatorInstAndDCECond(BI);
+ Changed = true;
}
}
-
- // If we found some, do the transformation!
- if (!UncondBranchPreds.empty()) {
- while (!UncondBranchPreds.empty()) {
- BasicBlock *Pred = UncondBranchPreds.pop_back_val();
- DEBUG(dbgs() << "FOLDING: " << *BB
- << "INTO UNCOND BRANCH PRED: " << *Pred);
- Instruction *UncondBranch = Pred->getTerminator();
- // Clone the return and add it to the end of the predecessor.
- Instruction *NewRet = RI->clone();
- Pred->getInstList().push_back(NewRet);
-
- // If the return instruction returns a value, and if the value was a
- // PHI node in "BB", propagate the right value into the return.
- for (User::op_iterator i = NewRet->op_begin(), e = NewRet->op_end();
- i != e; ++i)
- if (PHINode *PN = dyn_cast<PHINode>(*i))
- if (PN->getParent() == BB)
- *i = PN->getIncomingValueForBlock(Pred);
+ } 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());
- // Update any PHI nodes in the returning block to realize that we no
- // longer branch to them.
- BB->removePredecessor(Pred);
- Pred->getInstList().erase(UncondBranch);
+ for (unsigned i = 1, e = SI->getNumCases(); i != e; ++i)
+ if (SI->getSuccessor(i) == MaxBlock) {
+ SI->removeCase(i);
+ --i; --e;
+ }
}
-
- // If we eliminated all predecessors of the block, delete the block now.
- if (pred_begin(BB) == pred_end(BB))
- // We know there are no successors, so just nuke the block.
- Fn->getBasicBlockList().erase(BB);
-
- 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.pop_back_val();
-
- // Check to see if the non-BB successor is also a return block.
- if (isa<ReturnInst>(BI->getSuccessor(0)->getTerminator()) &&
- isa<ReturnInst>(BI->getSuccessor(1)->getTerminator()) &&
- SimplifyCondBranchToTwoReturns(BI))
- return true;
}
- }
- } 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.
- //
- SmallVector<BasicBlock*, 8> Preds(pred_begin(BB), pred_end(BB));
- while (!Preds.empty()) {
- BasicBlock *Pred = Preds.back();
- InvokeInst *II = dyn_cast<InvokeInst>(Pred->getTerminator());
- if (II && II->getUnwindDest() == BB) {
- // Insert a new branch instruction before the invoke, because this
- // is now a fall through.
+ } 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);
- Pred->getInstList().remove(II); // Take out of symbol table
-
- // Insert the call now.
- SmallVector<Value*,8> Args(II->op_begin(), II->op_end()-3);
+ II->removeFromParent(); // Take out of symbol table
+
+ // Insert the call now...
+ SmallVector<Value*, 8> Args(II->op_begin(), II->op_end()-3);
CallInst *CI = CallInst::Create(II->getCalledValue(),
Args.begin(), Args.end(),
II->getName(), BI);
CI->setCallingConv(II->getCallingConv());
CI->setAttributes(II->getAttributes());
- // If the invoke produced a value, the Call now does instead.
+ // If the invoke produced a value, the call does now instead.
II->replaceAllUsesWith(CI);
delete II;
Changed = true;
}
-
- Preds.pop_back();
}
+ }
+
+ // If this block is now dead, remove it.
+ if (pred_begin(BB) == pred_end(BB) &&
+ BB != &BB->getParent()->getEntryBlock()) {
+ // We know there are no successors, so just nuke the block.
+ BB->eraseFromParent();
+ return true;
+ }
- // If this block is now dead (and isn't the entry block), remove it.
- if (pred_begin(BB) == pred_end(BB) && BB != &Fn->getEntryBlock()) {
- // We know there are no successors, so just nuke the block.
- Fn->getBasicBlockList().erase(BB);
- return true;
- }
+ return Changed;
+}
- } 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.
- BasicBlock::iterator BBI = BB->begin();
- // Ignore dbg intrinsics.
- while (isa<DbgInfoIntrinsic>(BBI))
- ++BBI;
- if (SI == &*BBI)
- if (FoldValueComparisonIntoPredecessors(SI))
- return SimplifyCFG(BB) || 1;
- }
- } else if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
- if (BI->isUnconditional()) {
- // If the Terminator is the only non-phi instruction, simplify the block.
- BasicBlock::iterator I = BB->getFirstNonPHIOrDbg();
- if (I->isTerminator() && BB != &Fn->getEntryBlock() &&
- TryToSimplifyUncondBranchFromEmptyBlock(BB))
- return true;
-
- // If the only instruction in the block is a seteq/setne comparison
- // against a constant, try to simplify the block.
- if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
- if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) {
- for (++I; isa<DbgInfoIntrinsic>(I); ++I)
- ;
- if (I->isTerminator() &&
- TryToSimplifyUncondBranchWithICmpInIt(ICI))
- return true;
- }
-
- } 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) | true;
-
- // This block must be empty, except for the setcond inst, if it exists.
- // Ignore dbg intrinsics.
- BasicBlock::iterator I = BB->begin();
- // Ignore dbg intrinsics.
- while (isa<DbgInfoIntrinsic>(I))
- ++I;
- if (&*I == BI) {
- if (FoldValueComparisonIntoPredecessors(BI))
- return SimplifyCFG(BB) | true;
- } else if (&*I == cast<Instruction>(BI->getCondition())){
- ++I;
- // Ignore dbg intrinsics.
- while (isa<DbgInfoIntrinsic>(I))
- ++I;
- if (&*I == BI && FoldValueComparisonIntoPredecessors(BI))
- return SimplifyCFG(BB) | true;
- }
- }
- // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction.
- if (SimplifyBranchOnICmpChain(BI, TD))
- return true;
-
-
- // We have a conditional branch to two blocks that are only reachable
- // from BI. 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.
- if (BI->getSuccessor(0)->getSinglePredecessor() != 0) {
- if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
- if (HoistThenElseCodeToIf(BI))
- return SimplifyCFG(BB) | true;
- } else {
- // If Successor #1 has multiple preds, we may be able to conditionally
- // execute Successor #0 if it branches to successor #1.
- TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator();
- if (Succ0TI->getNumSuccessors() == 1 &&
- Succ0TI->getSuccessor(0) == BI->getSuccessor(1))
- if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0)))
- return SimplifyCFG(BB) | true;
- }
- } else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
- // If Successor #0 has multiple preds, we may be able to conditionally
- // execute Successor #1 if it branches to successor #0.
- TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator();
- if (Succ1TI->getNumSuccessors() == 1 &&
- Succ1TI->getSuccessor(0) == BI->getSuccessor(0))
- if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1)))
- 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.
- if (FoldBranchToCommonDest(BI))
- return SimplifyCFG(BB) | true;
+bool SimplifyCFGOpt::SimplifySwitch(SwitchInst *SI) {
+ // If this switch is too complex to want to look at, ignore it.
+ if (!isValueEqualityComparison(SI))
+ return false;
- // Scan predecessor 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 (SimplifyCondBranchToCondBranch(PBI, BI))
- return SimplifyCFG(BB) | true;
- }
- } else if (isa<UnreachableInst>(BB->getTerminator())) {
- // If there are any instructions immediately before the unreachable that can
- // be removed, do so.
- Instruction *Unreachable = BB->getTerminator();
- while (Unreachable != BB->begin()) {
- BasicBlock::iterator BBI = Unreachable;
- --BBI;
- // Do not delete instructions that can have side effects, like calls
- // (which may never return) and volatile loads and stores.
- if (isa<CallInst>(BBI) && !isa<DbgInfoIntrinsic>(BBI)) break;
-
- if (StoreInst *SI = dyn_cast<StoreInst>(BBI))
- if (SI->isVolatile())
- break;
-
- if (LoadInst *LI = dyn_cast<LoadInst>(BBI))
- if (LI->isVolatile())
- break;
-
- // Delete this instruction
- BB->getInstList().erase(BBI);
+ BasicBlock *BB = SI->getParent();
+
+ // 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) | true;
+
+ // If the block only contains the switch, see if we can fold the block
+ // away into any preds.
+ BasicBlock::iterator BBI = BB->begin();
+ // Ignore dbg intrinsics.
+ while (isa<DbgInfoIntrinsic>(BBI))
+ ++BBI;
+ if (SI == &*BBI)
+ if (FoldValueComparisonIntoPredecessors(SI))
+ return SimplifyCFG(BB) | true;
+
+ return false;
+}
+
+bool SimplifyCFGOpt::SimplifyIndirectBr(IndirectBrInst *IBI) {
+ BasicBlock *BB = IBI->getParent();
+ bool Changed = false;
+
+ // Eliminate redundant destinations.
+ SmallPtrSet<Value *, 8> Succs;
+ for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
+ BasicBlock *Dest = IBI->getDestination(i);
+ if (!Dest->hasAddressTaken() || !Succs.insert(Dest)) {
+ Dest->removePredecessor(BB);
+ IBI->removeDestination(i);
+ --i; --e;
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->getContext(), TI);
- TI->eraseFromParent();
- Changed = true;
- }
- } else {
- if (BI->getSuccessor(0) == BB) {
- BranchInst::Create(BI->getSuccessor(1), BI);
- EraseTerminatorInstAndDCECond(BI);
- } else if (BI->getSuccessor(1) == BB) {
- BranchInst::Create(BI->getSuccessor(0), BI);
- EraseTerminatorInstAndDCECond(BI);
- 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(), II->op_end()-3);
- CallInst *CI = CallInst::Create(II->getCalledValue(),
- Args.begin(), Args.end(),
- II->getName(), BI);
- CI->setCallingConv(II->getCallingConv());
- CI->setAttributes(II->getAttributes());
- // If the invoke produced a value, the call does now instead.
- II->replaceAllUsesWith(CI);
- delete II;
- Changed = true;
- }
- }
- }
+ if (IBI->getNumDestinations() == 0) {
+ // If the indirectbr has no successors, change it to unreachable.
+ new UnreachableInst(IBI->getContext(), IBI);
+ EraseTerminatorInstAndDCECond(IBI);
+ return true;
+ }
+
+ if (IBI->getNumDestinations() == 1) {
+ // If the indirectbr has one successor, change it to a direct branch.
+ BranchInst::Create(IBI->getDestination(0), IBI);
+ EraseTerminatorInstAndDCECond(IBI);
+ return true;
+ }
+
+ if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
+ if (SimplifyIndirectBrOnSelect(IBI, SI))
+ return SimplifyCFG(BB) | true;
+ }
+ return Changed;
+}
- // If this block is now dead, remove it.
- if (pred_begin(BB) == pred_end(BB) && BB != &Fn->getEntryBlock()) {
- // We know there are no successors, so just nuke the block.
- Fn->getBasicBlockList().erase(BB);
+bool SimplifyCFGOpt::SimplifyUncondBranch(BranchInst *BI) {
+ BasicBlock *BB = BI->getParent();
+
+ // If the Terminator is the only non-phi instruction, simplify the block.
+ BasicBlock::iterator I = BB->getFirstNonPHIOrDbg();
+ if (I->isTerminator() && BB != &BB->getParent()->getEntryBlock() &&
+ TryToSimplifyUncondBranchFromEmptyBlock(BB))
+ return true;
+
+ // If the only instruction in the block is a seteq/setne comparison
+ // against a constant, try to simplify the block.
+ if (ICmpInst *ICI = dyn_cast<ICmpInst>(I))
+ if (ICI->isEquality() && isa<ConstantInt>(ICI->getOperand(1))) {
+ for (++I; isa<DbgInfoIntrinsic>(I); ++I)
+ ;
+ if (I->isTerminator() && TryToSimplifyUncondBranchWithICmpInIt(ICI, TD))
return true;
- }
}
- } else if (IndirectBrInst *IBI =
- dyn_cast<IndirectBrInst>(BB->getTerminator())) {
- // Eliminate redundant destinations.
- SmallPtrSet<Value *, 8> Succs;
- for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
- BasicBlock *Dest = IBI->getDestination(i);
- if (!Dest->hasAddressTaken() || !Succs.insert(Dest)) {
- Dest->removePredecessor(BB);
- IBI->removeDestination(i);
- --i; --e;
- Changed = true;
- }
- }
+
+ return false;
+}
- if (IBI->getNumDestinations() == 0) {
- // If the indirectbr has no successors, change it to unreachable.
- new UnreachableInst(IBI->getContext(), IBI);
- EraseTerminatorInstAndDCECond(IBI);
- Changed = true;
- } else if (IBI->getNumDestinations() == 1) {
- // If the indirectbr has one successor, change it to a direct branch.
- BranchInst::Create(IBI->getDestination(0), IBI);
- EraseTerminatorInstAndDCECond(IBI);
- Changed = true;
- } else if (SelectInst *SI = dyn_cast<SelectInst>(IBI->getAddress())) {
- if (SimplifyIndirectBrOnSelect(IBI, SI))
+
+bool SimplifyCFGOpt::SimplifyCondBranch(BranchInst *BI) {
+ BasicBlock *BB = BI->getParent();
+
+ // 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) | true;
+
+ // This block must be empty, except for the setcond inst, if it exists.
+ // Ignore dbg intrinsics.
+ BasicBlock::iterator I = BB->begin();
+ // Ignore dbg intrinsics.
+ while (isa<DbgInfoIntrinsic>(I))
+ ++I;
+ if (&*I == BI) {
+ if (FoldValueComparisonIntoPredecessors(BI))
+ return SimplifyCFG(BB) | true;
+ } else if (&*I == cast<Instruction>(BI->getCondition())){
+ ++I;
+ // Ignore dbg intrinsics.
+ while (isa<DbgInfoIntrinsic>(I))
+ ++I;
+ if (&*I == BI && FoldValueComparisonIntoPredecessors(BI))
+ return SimplifyCFG(BB) | true;
+ }
+ }
+
+ // Try to turn "br (X == 0 | X == 1), T, F" into a switch instruction.
+ if (SimplifyBranchOnICmpChain(BI, TD))
+ return true;
+
+ // We have a conditional branch to two blocks that are only reachable
+ // from BI. 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.
+ if (BI->getSuccessor(0)->getSinglePredecessor() != 0) {
+ if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
+ if (HoistThenElseCodeToIf(BI))
+ return SimplifyCFG(BB) | true;
+ } else {
+ // If Successor #1 has multiple preds, we may be able to conditionally
+ // execute Successor #0 if it branches to successor #1.
+ TerminatorInst *Succ0TI = BI->getSuccessor(0)->getTerminator();
+ if (Succ0TI->getNumSuccessors() == 1 &&
+ Succ0TI->getSuccessor(0) == BI->getSuccessor(1))
+ if (SpeculativelyExecuteBB(BI, BI->getSuccessor(0)))
+ return SimplifyCFG(BB) | true;
+ }
+ } else if (BI->getSuccessor(1)->getSinglePredecessor() != 0) {
+ // If Successor #0 has multiple preds, we may be able to conditionally
+ // execute Successor #1 if it branches to successor #0.
+ TerminatorInst *Succ1TI = BI->getSuccessor(1)->getTerminator();
+ if (Succ1TI->getNumSuccessors() == 1 &&
+ Succ1TI->getSuccessor(0) == BI->getSuccessor(0))
+ if (SpeculativelyExecuteBB(BI, BI->getSuccessor(1)))
+ 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, TD))
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.
+ if (FoldBranchToCommonDest(BI))
+ return SimplifyCFG(BB) | true;
+
+ // Scan predecessor 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 (SimplifyCondBranchToCondBranch(PBI, BI))
+ return SimplifyCFG(BB) | true;
+
+ return false;
+}
+
+bool SimplifyCFGOpt::run(BasicBlock *BB) {
+ bool Changed = false;
+
+ assert(BB && BB->getParent() && "Block not embedded in function!");
+ assert(BB->getTerminator() && "Degenerate basic block encountered!");
+
+ // Remove basic blocks that have no predecessors (except the entry block)...
+ // or that just have themself as a predecessor. These are unreachable.
+ if ((pred_begin(BB) == pred_end(BB) &&
+ BB != &BB->getParent()->getEntryBlock()) ||
+ BB->getSinglePredecessor() == BB) {
+ DEBUG(dbgs() << "Removing BB: \n" << *BB);
+ DeleteDeadBlock(BB);
+ return true;
+ }
+
+ // Check to see if we can constant propagate this terminator instruction
+ // away...
+ Changed |= ConstantFoldTerminator(BB);
+
+ // Check for and eliminate duplicate PHI nodes in this block.
+ Changed |= EliminateDuplicatePHINodes(BB);
+
+ // Merge basic blocks into their predecessor if there is only one distinct
+ // pred, and if there is only one distinct successor of the predecessor, and
+ // if there are no PHI nodes.
+ //
+ if (MergeBlockIntoPredecessor(BB))
+ 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, TD);
+
+ if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
+ if (BI->isUnconditional()) {
+ if (SimplifyUncondBranch(BI)) return true;
+ } else {
+ if (SimplifyCondBranch(BI)) return true;
}
+ } else if (ReturnInst *RI = dyn_cast<ReturnInst>(BB->getTerminator())) {
+ if (SimplifyReturn(RI)) return true;
+ } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
+ if (SimplifySwitch(SI)) return true;
+ } else if (UnreachableInst *UI =
+ dyn_cast<UnreachableInst>(BB->getTerminator())) {
+ if (SimplifyUnreachable(UI)) return true;
+ } else if (UnwindInst *UI = dyn_cast<UnwindInst>(BB->getTerminator())) {
+ if (SimplifyUnwind(UI)) return true;
+ } else if (IndirectBrInst *IBI =
+ dyn_cast<IndirectBrInst>(BB->getTerminator())) {
+ if (SimplifyIndirectBr(IBI)) return true;
}
return Changed;
projects / oota-llvm.git / blobdiff