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-rw-r--r--lib/Transforms/Scalar/CondPropagate.cpp289
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diff --git a/lib/Transforms/Scalar/CondPropagate.cpp b/lib/Transforms/Scalar/CondPropagate.cpp
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--- a/lib/Transforms/Scalar/CondPropagate.cpp
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-//===-- CondPropagate.cpp - Propagate Conditional Expressions -------------===//
-//
-// The LLVM Compiler Infrastructure
-//
-// This file is distributed under the University of Illinois Open Source
-// License. See LICENSE.TXT for details.
-//
-//===----------------------------------------------------------------------===//
-//
-// This pass propagates information about conditional expressions through the
-// program, allowing it to eliminate conditional branches in some cases.
-//
-//===----------------------------------------------------------------------===//
-
-#define DEBUG_TYPE "condprop"
-#include "llvm/Transforms/Scalar.h"
-#include "llvm/Instructions.h"
-#include "llvm/IntrinsicInst.h"
-#include "llvm/Pass.h"
-#include "llvm/Type.h"
-#include "llvm/Transforms/Utils/BasicBlockUtils.h"
-#include "llvm/Transforms/Utils/Local.h"
-#include "llvm/ADT/Statistic.h"
-#include "llvm/ADT/SmallVector.h"
-using namespace llvm;
-
-STATISTIC(NumBrThread, "Number of CFG edges threaded through branches");
-STATISTIC(NumSwThread, "Number of CFG edges threaded through switches");
-
-namespace {
- struct CondProp : public FunctionPass {
- static char ID; // Pass identification, replacement for typeid
- CondProp() : FunctionPass(&ID) {}
-
- virtual bool runOnFunction(Function &F);
-
- virtual void getAnalysisUsage(AnalysisUsage &AU) const {
- AU.addRequiredID(BreakCriticalEdgesID);
- //AU.addRequired<DominanceFrontier>();
- }
-
- private:
- bool MadeChange;
- SmallVector<BasicBlock *, 4> DeadBlocks;
- void SimplifyBlock(BasicBlock *BB);
- void SimplifyPredecessors(BranchInst *BI);
- void SimplifyPredecessors(SwitchInst *SI);
- void RevectorBlockTo(BasicBlock *FromBB, BasicBlock *ToBB);
- bool RevectorBlockTo(BasicBlock *FromBB, Value *Cond, BranchInst *BI);
- };
-}
-
-char CondProp::ID = 0;
-static RegisterPass<CondProp> X("condprop", "Conditional Propagation");
-
-FunctionPass *llvm::createCondPropagationPass() {
- return new CondProp();
-}
-
-bool CondProp::runOnFunction(Function &F) {
- bool EverMadeChange = false;
- DeadBlocks.clear();
-
- // While we are simplifying blocks, keep iterating.
- do {
- MadeChange = false;
- for (Function::iterator BB = F.begin(), E = F.end(); BB != E;)
- SimplifyBlock(BB++);
- EverMadeChange = EverMadeChange || MadeChange;
- } while (MadeChange);
-
- if (EverMadeChange) {
- while (!DeadBlocks.empty()) {
- BasicBlock *BB = DeadBlocks.back(); DeadBlocks.pop_back();
- DeleteDeadBlock(BB);
- }
- }
- return EverMadeChange;
-}
-
-void CondProp::SimplifyBlock(BasicBlock *BB) {
- if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator())) {
- // If this is a conditional branch based on a phi node that is defined in
- // this block, see if we can simplify predecessors of this block.
- if (BI->isConditional() && isa<PHINode>(BI->getCondition()) &&
- cast<PHINode>(BI->getCondition())->getParent() == BB)
- SimplifyPredecessors(BI);
-
- } else if (SwitchInst *SI = dyn_cast<SwitchInst>(BB->getTerminator())) {
- if (isa<PHINode>(SI->getCondition()) &&
- cast<PHINode>(SI->getCondition())->getParent() == BB)
- SimplifyPredecessors(SI);
- }
-
- // If possible, simplify the terminator of this block.
- if (ConstantFoldTerminator(BB))
- MadeChange = true;
-
- // If this block ends with an unconditional branch and the only successor has
- // only this block as a predecessor, merge the two blocks together.
- if (BranchInst *BI = dyn_cast<BranchInst>(BB->getTerminator()))
- if (BI->isUnconditional() && BI->getSuccessor(0)->getSinglePredecessor() &&
- BB != BI->getSuccessor(0)) {
- BasicBlock *Succ = BI->getSuccessor(0);
-
- // If Succ has any PHI nodes, they are all single-entry PHI's. Eliminate
- // them.
- FoldSingleEntryPHINodes(Succ);
-
- // Remove BI.
- BI->eraseFromParent();
-
- // Move over all of the instructions.
- BB->getInstList().splice(BB->end(), Succ->getInstList());
-
- // Any phi nodes that had entries for Succ now have entries from BB.
- Succ->replaceAllUsesWith(BB);
-
- // Succ is now dead, but we cannot delete it without potentially
- // invalidating iterators elsewhere. Just insert an unreachable
- // instruction in it and delete this block later on.
- new UnreachableInst(BB->getContext(), Succ);
- DeadBlocks.push_back(Succ);
- MadeChange = true;
- }
-}
-
-// SimplifyPredecessors(branches) - We know that BI is a conditional branch
-// based on a PHI node defined in this block. If the phi node contains constant
-// operands, then the blocks corresponding to those operands can be modified to
-// jump directly to the destination instead of going through this block.
-void CondProp::SimplifyPredecessors(BranchInst *BI) {
- // TODO: We currently only handle the most trival case, where the PHI node has
- // one use (the branch), and is the only instruction besides the branch and dbg
- // intrinsics in the block.
- PHINode *PN = cast<PHINode>(BI->getCondition());
-
- if (PN->getNumIncomingValues() == 1) {
- // Eliminate single-entry PHI nodes.
- FoldSingleEntryPHINodes(PN->getParent());
- return;
- }
-
-
- if (!PN->hasOneUse()) return;
-
- BasicBlock *BB = BI->getParent();
- if (&*BB->begin() != PN)
- return;
- BasicBlock::iterator BBI = BB->begin();
- BasicBlock::iterator BBE = BB->end();
- while (BBI != BBE && isa<DbgInfoIntrinsic>(++BBI)) /* empty */;
- if (&*BBI != BI)
- return;
-
- // Ok, we have this really simple case, walk the PHI operands, looking for
- // constants. Walk from the end to remove operands from the end when
- // possible, and to avoid invalidating "i".
- for (unsigned i = PN->getNumIncomingValues(); i != 0; --i) {
- Value *InVal = PN->getIncomingValue(i-1);
- if (!RevectorBlockTo(PN->getIncomingBlock(i-1), InVal, BI))
- continue;
-
- ++NumBrThread;
-
- // If there were two predecessors before this simplification, or if the
- // PHI node contained all the same value except for the one we just
- // substituted, the PHI node may be deleted. Don't iterate through it the
- // last time.
- if (BI->getCondition() != PN) return;
- }
-}
-
-// SimplifyPredecessors(switch) - We know that SI is switch based on a PHI node
-// defined in this block. If the phi node contains constant operands, then the
-// blocks corresponding to those operands can be modified to jump directly to
-// the destination instead of going through this block.
-void CondProp::SimplifyPredecessors(SwitchInst *SI) {
- // TODO: We currently only handle the most trival case, where the PHI node has
- // one use (the branch), and is the only instruction besides the branch and
- // dbg intrinsics in the block.
- PHINode *PN = cast<PHINode>(SI->getCondition());
- if (!PN->hasOneUse()) return;
-
- BasicBlock *BB = SI->getParent();
- if (&*BB->begin() != PN)
- return;
- BasicBlock::iterator BBI = BB->begin();
- BasicBlock::iterator BBE = BB->end();
- while (BBI != BBE && isa<DbgInfoIntrinsic>(++BBI)) /* empty */;
- if (&*BBI != SI)
- return;
-
- // Ok, we have this really simple case, walk the PHI operands, looking for
- // constants. Walk from the end to remove operands from the end when
- // possible, and to avoid invalidating "i".
- for (unsigned i = PN->getNumIncomingValues(); i != 0; --i)
- if (ConstantInt *CI = dyn_cast<ConstantInt>(PN->getIncomingValue(i-1))) {
- BasicBlock *PredBB = PN->getIncomingBlock(i-1);
- if (isa<BranchInst>(PredBB->getTerminator())) {
- // If we have a constant, forward the edge from its current to its
- // ultimate destination.
- unsigned DestCase = SI->findCaseValue(CI);
- RevectorBlockTo(PredBB, SI->getSuccessor(DestCase));
- ++NumSwThread;
-
- // If there were two predecessors before this simplification, or if the
- // PHI node contained all the same value except for the one we just
- // substituted, the PHI node may be deleted. Don't iterate through it the
- // last time.
- if (SI->getCondition() != PN) return;
- }
- }
-}
-
-
-// RevectorBlockTo - Revector the unconditional branch at the end of FromBB to
-// the ToBB block, which is one of the successors of its current successor.
-void CondProp::RevectorBlockTo(BasicBlock *FromBB, BasicBlock *ToBB) {
- BranchInst *FromBr = cast<BranchInst>(FromBB->getTerminator());
- assert(FromBr->isUnconditional() && "FromBB should end with uncond br!");
-
- // Get the old block we are threading through.
- BasicBlock *OldSucc = FromBr->getSuccessor(0);
-
- // OldSucc had multiple successors. If ToBB has multiple predecessors, then
- // the edge between them would be critical, which we already took care of.
- // If ToBB has single operand PHI node then take care of it here.
- FoldSingleEntryPHINodes(ToBB);
-
- // Update PHI nodes in OldSucc to know that FromBB no longer branches to it.
- OldSucc->removePredecessor(FromBB);
-
- // Change FromBr to branch to the new destination.
- FromBr->setSuccessor(0, ToBB);
-
- MadeChange = true;
-}
-
-bool CondProp::RevectorBlockTo(BasicBlock *FromBB, Value *Cond, BranchInst *BI){
- BranchInst *FromBr = cast<BranchInst>(FromBB->getTerminator());
- if (!FromBr->isUnconditional())
- return false;
-
- // Get the old block we are threading through.
- BasicBlock *OldSucc = FromBr->getSuccessor(0);
-
- // If the condition is a constant, simply revector the unconditional branch at
- // the end of FromBB to one of the successors of its current successor.
- if (ConstantInt *CB = dyn_cast<ConstantInt>(Cond)) {
- BasicBlock *ToBB = BI->getSuccessor(CB->isZero());
-
- // OldSucc had multiple successors. If ToBB has multiple predecessors, then
- // the edge between them would be critical, which we already took care of.
- // If ToBB has single operand PHI node then take care of it here.
- FoldSingleEntryPHINodes(ToBB);
-
- // Update PHI nodes in OldSucc to know that FromBB no longer branches to it.
- OldSucc->removePredecessor(FromBB);
-
- // Change FromBr to branch to the new destination.
- FromBr->setSuccessor(0, ToBB);
- } else {
- BasicBlock *Succ0 = BI->getSuccessor(0);
- // Do not perform transform if the new destination has PHI nodes. The
- // transform will add new preds to the PHI's.
- if (isa<PHINode>(Succ0->begin()))
- return false;
-
- BasicBlock *Succ1 = BI->getSuccessor(1);
- if (isa<PHINode>(Succ1->begin()))
- return false;
-
- // Insert the new conditional branch.
- BranchInst::Create(Succ0, Succ1, Cond, FromBr);
-
- FoldSingleEntryPHINodes(Succ0);
- FoldSingleEntryPHINodes(Succ1);
-
- // Update PHI nodes in OldSucc to know that FromBB no longer branches to it.
- OldSucc->removePredecessor(FromBB);
-
- // Delete the old branch.
- FromBr->eraseFromParent();
- }
-
- MadeChange = true;
- return true;
-}
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