return true;
}
+/// isProfitableToFoldUnconditional - Return true if it is safe and profitable
+/// to merge these two terminator instructions together, where SI1 is an
+/// unconditional branch. PhiNodes will store all PHI nodes in common
+/// successors.
+///
+static bool isProfitableToFoldUnconditional(BranchInst *SI1,
+ BranchInst *SI2,
+ Instruction* Cond,
+ SmallVectorImpl<PHINode*> &PhiNodes) {
+ if (SI1 == SI2) return false; // Can't merge with self!
+ assert(SI1->isUnconditional() && SI2->isConditional());
+
+ // We fold the unconditional branch if we can easily update all PHI nodes in
+ // common successors:
+ // 1> We have a constant incoming value for the conditional branch;
+ // 2> We have "Cond" as the incoming value for the unconditional branch;
+ // 3> SI2->getCondition() and Cond have same operands.
+ CmpInst *Ci2 = dyn_cast<CmpInst>(SI2->getCondition());
+ if (!Ci2) return false;
+ if (!(Cond->getOperand(0) == Ci2->getOperand(0) &&
+ Cond->getOperand(1) == Ci2->getOperand(1)) &&
+ !(Cond->getOperand(0) == Ci2->getOperand(1) &&
+ Cond->getOperand(1) == Ci2->getOperand(0)))
+ return false;
+
+ BasicBlock *SI1BB = SI1->getParent();
+ BasicBlock *SI2BB = SI2->getParent();
+ SmallPtrSet<BasicBlock*, 16> SI1Succs(succ_begin(SI1BB), succ_end(SI1BB));
+ for (succ_iterator I = succ_begin(SI2BB), E = succ_end(SI2BB); I != E; ++I)
+ if (SI1Succs.count(*I))
+ for (BasicBlock::iterator BBI = (*I)->begin();
+ isa<PHINode>(BBI); ++BBI) {
+ PHINode *PN = cast<PHINode>(BBI);
+ if (PN->getIncomingValueForBlock(SI1BB) != Cond ||
+ !isa<Constant>(PN->getIncomingValueForBlock(SI2BB)))
+ return false;
+ PhiNodes.push_back(PN);
+ }
+ 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
return Result;
}
+/// checkCSEInPredecessor - Return true if the given instruction is available
+/// in its predecessor block. If yes, the instruction will be removed.
+///
+bool checkCSEInPredecessor(Instruction *Inst, BasicBlock *PB) {
+ if (!isa<BinaryOperator>(Inst) && !isa<CmpInst>(Inst))
+ return false;
+ for (BasicBlock::iterator I = PB->begin(), E = PB->end(); I != E; I++) {
+ Instruction *PBI = &*I;
+ // Check whether Inst and PBI generate the same value.
+ if (Inst->isIdenticalTo(PBI)) {
+ Inst->replaceAllUsesWith(PBI);
+ Inst->eraseFromParent();
+ return true;
+ }
+ }
+ return false;
+}
/// FoldBranchToCommonDest - If this basic block is simple enough, and if a
/// predecessor branches to us and one of our successors, fold the block into
bool llvm::FoldBranchToCommonDest(BranchInst *BI) {
BasicBlock *BB = BI->getParent();
- Instruction *Cond = dyn_cast<Instruction>(BI->getCondition());
+ Instruction *Cond = 0;
+ if (BI->isConditional())
+ Cond = dyn_cast<Instruction>(BI->getCondition());
+ else {
+ // For unconditional branch, check for a simple CFG pattern, where
+ // BB has a single predecessor and BB's successor is also its predecessor's
+ // successor. If such pattern exisits, check for CSE between BB and its
+ // predecessor.
+ if (BasicBlock *PB = BB->getSinglePredecessor())
+ if (BranchInst *PBI = dyn_cast<BranchInst>(PB->getTerminator()))
+ if (PBI->isConditional() &&
+ (BI->getSuccessor(0) == PBI->getSuccessor(0) ||
+ BI->getSuccessor(0) == PBI->getSuccessor(1))) {
+ for (BasicBlock::iterator I = BB->begin(), E = BB->end();
+ I != E; ) {
+ Instruction *Curr = I++;
+ if (isa<CmpInst>(Curr)) {
+ Cond = Curr;
+ break;
+ }
+ // Quit if we can't remove this instruction.
+ if (!checkCSEInPredecessor(Curr, PB))
+ return false;
+ }
+ }
+
+ if (Cond == 0)
+ return false;
+ }
+
if (Cond == 0 || (!isa<CmpInst>(Cond) && !isa<BinaryOperator>(Cond)) ||
Cond->getParent() != BB || !Cond->hasOneUse())
return false;
// Finally, don't infinitely unroll conditional loops.
BasicBlock *TrueDest = BI->getSuccessor(0);
- BasicBlock *FalseDest = BI->getSuccessor(1);
+ BasicBlock *FalseDest = (BI->isConditional()) ? BI->getSuccessor(1) : 0;
if (TrueDest == BB || FalseDest == BB)
return false;
// Check that we have two conditional branches. If there is a PHI node in
// the common successor, verify that the same value flows in from both
// blocks.
- if (PBI == 0 || PBI->isUnconditional() || !SafeToMergeTerminators(BI, PBI))
+ SmallVector<PHINode*, 4> PHIs;
+ if (PBI == 0 || PBI->isUnconditional() ||
+ (BI->isConditional() &&
+ !SafeToMergeTerminators(BI, PBI)) ||
+ (!BI->isConditional() &&
+ !isProfitableToFoldUnconditional(BI, PBI, Cond, PHIs)))
continue;
// Determine if the two branches share a common destination.
Instruction::BinaryOps Opc;
bool InvertPredCond = false;
- if (PBI->getSuccessor(0) == TrueDest)
- Opc = Instruction::Or;
- else if (PBI->getSuccessor(1) == FalseDest)
- Opc = Instruction::And;
- else if (PBI->getSuccessor(0) == FalseDest)
- Opc = Instruction::And, InvertPredCond = true;
- else if (PBI->getSuccessor(1) == TrueDest)
- Opc = Instruction::Or, InvertPredCond = true;
- else
- continue;
+ if (BI->isConditional()) {
+ if (PBI->getSuccessor(0) == TrueDest)
+ Opc = Instruction::Or;
+ else if (PBI->getSuccessor(1) == FalseDest)
+ Opc = Instruction::And;
+ else if (PBI->getSuccessor(0) == FalseDest)
+ Opc = Instruction::And, InvertPredCond = true;
+ else if (PBI->getSuccessor(1) == TrueDest)
+ Opc = Instruction::Or, InvertPredCond = true;
+ else
+ continue;
+ } else {
+ if (PBI->getSuccessor(0) != TrueDest && PBI->getSuccessor(1) != TrueDest)
+ continue;
+ }
// Ensure that any values used in the bonus instruction are also used
// by the terminator of the predecessor. This means that those values
New->takeName(Cond);
Cond->setName(New->getName()+".old");
- Instruction *NewCond =
- cast<Instruction>(Builder.CreateBinOp(Opc, PBI->getCondition(),
+ if (BI->isConditional()) {
+ Instruction *NewCond =
+ cast<Instruction>(Builder.CreateBinOp(Opc, PBI->getCondition(),
New, "or.cond"));
- 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);
+ 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);
+ }
+ } else {
+ // Update PHI nodes in the common successors.
+ for (unsigned i = 0, e = PHIs.size(); i != e; ++i) {
+ ConstantInt *PBI_C = dyn_cast<ConstantInt>(
+ PHIs[i]->getIncomingValueForBlock(PBI->getParent()));
+ assert(PBI_C->getType()->isIntegerTy(1));
+ Instruction *MergedCond = 0;
+ if (PBI->getSuccessor(0) == TrueDest) {
+ // Create (PBI_Cond and PBI_C) or (!PBI_Cond and BI_Value)
+ // PBI_C is true: PBI_Cond or (!PBI_Cond and BI_Value)
+ // is false: !PBI_Cond and BI_Value
+ Instruction *NotCond =
+ cast<Instruction>(Builder.CreateNot(PBI->getCondition(),
+ "not.cond"));
+ MergedCond =
+ cast<Instruction>(Builder.CreateBinOp(Instruction::And,
+ NotCond, New,
+ "and.cond"));
+ if (PBI_C->isOne())
+ MergedCond =
+ cast<Instruction>(Builder.CreateBinOp(Instruction::Or,
+ PBI->getCondition(), MergedCond,
+ "or.cond"));
+ } else {
+ // Create (PBI_Cond and BI_Value) or (!PBI_Cond and PBI_C)
+ // PBI_C is true: (PBI_Cond and BI_Value) or (!PBI_Cond)
+ // is false: PBI_Cond and BI_Value
+ MergedCond =
+ cast<Instruction>(Builder.CreateBinOp(Instruction::And,
+ PBI->getCondition(), New,
+ "and.cond"));
+ if (PBI_C->isOne()) {
+ Instruction *NotCond =
+ cast<Instruction>(Builder.CreateNot(PBI->getCondition(),
+ "not.cond"));
+ MergedCond =
+ cast<Instruction>(Builder.CreateBinOp(Instruction::Or,
+ NotCond, MergedCond,
+ "or.cond"));
+ }
+ }
+ // Update PHI Node.
+ PHIs[i]->setIncomingValue(PHIs[i]->getBasicBlockIndex(PBI->getParent()),
+ MergedCond);
+ }
+ // Change PBI from Conditional to Unconditional.
+ BranchInst *New_PBI = BranchInst::Create(TrueDest, PBI);
+ EraseTerminatorInstAndDCECond(PBI);
+ PBI = New_PBI;
}
// TODO: If BB is reachable from all paths through PredBlock, then we
// Merge probability data into PredBlock's branch.
APInt A, B, C, D;
- if (ExtractBranchMetadata(PBI, C, D) && ExtractBranchMetadata(BI, A, B)) {
+ if (PBI->isConditional() && BI->isConditional() &&
+ ExtractBranchMetadata(PBI, C, D) && ExtractBranchMetadata(BI, A, B)) {
// Given IR which does:
// bbA:
// br i1 %x, label %bbB, label %bbC
return true;
}
+ // If this basic block is ONLY a compare and a branch, and if a predecessor
+ // branches to us and our successor, fold the comparison into the
+ // predecessor and use logical operations to update the incoming value
+ // for PHI nodes in common successor.
+ if (FoldBranchToCommonDest(BI))
+ return SimplifyCFG(BB) | true;
return false;
}
projects / oota-llvm.git / commitdiff