//===- BreakCriticalEdges.cpp - Critical Edge Elimination Pass ------------===//
//
+// The LLVM Compiler Infrastructure
+//
+// This file is distributed under the University of Illinois Open Source
+// License. See LICENSE.TXT for details.
+//
+//===----------------------------------------------------------------------===//
+//
// BreakCriticalEdges pass - Break all of the critical edges in the CFG by
// inserting a dummy basic block. This pass may be "required" by passes that
// cannot deal with critical edges. For this usage, the structure type is
// forward declared. This pass obviously invalidates the CFG, but can update
-// forward dominator (set, immediate dominators, and tree) information.
+// forward dominator (set, immediate dominators, tree, and frontier)
+// information.
//
//===----------------------------------------------------------------------===//
+#define DEBUG_TYPE "break-crit-edges"
#include "llvm/Transforms/Scalar.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
#include "llvm/Analysis/Dominators.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/Analysis/ProfileInfo.h"
#include "llvm/Function.h"
-#include "llvm/iTerminators.h"
-#include "llvm/iPHINode.h"
+#include "llvm/Instructions.h"
+#include "llvm/Type.h"
#include "llvm/Support/CFG.h"
-#include "Support/StatisticReporter.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/Statistic.h"
+using namespace llvm;
-namespace {
- Statistic<> NumBroken("break-crit-edges\t- Number of blocks inserted");
+STATISTIC(NumBroken, "Number of blocks inserted");
+namespace {
struct BreakCriticalEdges : public FunctionPass {
+ static char ID; // Pass identification, replacement for typeid
+ BreakCriticalEdges() : FunctionPass(ID) {}
+
virtual bool runOnFunction(Function &F);
-
+
virtual void getAnalysisUsage(AnalysisUsage &AU) const {
- AU.addPreserved<DominatorSet>();
- AU.addPreserved<ImmediateDominators>();
AU.addPreserved<DominatorTree>();
+ AU.addPreserved<DominanceFrontier>();
+ AU.addPreserved<LoopInfo>();
+ AU.addPreserved<ProfileInfo>();
+
+ // No loop canonicalization guarantees are broken by this pass.
+ AU.addPreservedID(LoopSimplifyID);
}
};
-
- RegisterOpt<BreakCriticalEdges> X("break-crit-edges",
- "Break critical edges in CFG");
}
+char BreakCriticalEdges::ID = 0;
+static RegisterPass<BreakCriticalEdges>
+X("break-crit-edges", "Break critical edges in CFG");
+
// Publically exposed interface to pass...
-const PassInfo *BreakCriticalEdgesID = X.getPassInfo();
-Pass *createBreakCriticalEdgesPass() { return new BreakCriticalEdges(); }
+char &llvm::BreakCriticalEdgesID = BreakCriticalEdges::ID;
+FunctionPass *llvm::createBreakCriticalEdgesPass() {
+ return new BreakCriticalEdges();
+}
+
+// runOnFunction - Loop over all of the edges in the CFG, breaking critical
+// edges as they are found.
+//
+bool BreakCriticalEdges::runOnFunction(Function &F) {
+ bool Changed = false;
+ for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) {
+ TerminatorInst *TI = I->getTerminator();
+ if (TI->getNumSuccessors() > 1 && !isa<IndirectBrInst>(TI))
+ for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
+ if (SplitCriticalEdge(TI, i, this)) {
+ ++NumBroken;
+ Changed = true;
+ }
+ }
+ return Changed;
+}
+
+//===----------------------------------------------------------------------===//
+// Implementation of the external critical edge manipulation functions
+//===----------------------------------------------------------------------===//
// isCriticalEdge - Return true if the specified edge is a critical edge.
// Critical edges are edges from a block with multiple successors to a block
// with multiple predecessors.
//
-static bool isCriticalEdge(const TerminatorInst *TI, unsigned SuccNum) {
+bool llvm::isCriticalEdge(const TerminatorInst *TI, unsigned SuccNum,
+ bool AllowIdenticalEdges) {
assert(SuccNum < TI->getNumSuccessors() && "Illegal edge specification!");
- assert (TI->getNumSuccessors() > 1);
+ if (TI->getNumSuccessors() == 1) return false;
const BasicBlock *Dest = TI->getSuccessor(SuccNum);
- pred_const_iterator I = pred_begin(Dest), E = pred_end(Dest);
+ const_pred_iterator I = pred_begin(Dest), E = pred_end(Dest);
// If there is more than one predecessor, this is a critical edge...
assert(I != E && "No preds, but we have an edge to the block?");
+ const BasicBlock *FirstPred = *I;
++I; // Skip one edge due to the incoming arc from TI.
- return I != E;
+ if (!AllowIdenticalEdges)
+ return I != E;
+
+ // If AllowIdenticalEdges is true, then we allow this edge to be considered
+ // non-critical iff all preds come from TI's block.
+ while (I != E) {
+ const BasicBlock *P = *I;
+ if (P != FirstPred)
+ return true;
+ // Note: leave this as is until no one ever compiles with either gcc 4.0.1
+ // or Xcode 2. This seems to work around the pred_iterator assert in PR 2207
+ E = pred_end(P);
+ ++I;
+ }
+ return false;
}
-// SplitCriticalEdge - Insert a new node node to split the critical edge. This
-// will update DominatorSet, ImmediateDominator and DominatorTree information if
-// it is available, thus calling this pass will not invalidate either of them.
-//
-static void SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum, Pass *P) {
- assert(isCriticalEdge(TI, SuccNum) &&
- "Cannot break a critical edge, if it isn't a critical edge");
+/// CreatePHIsForSplitLoopExit - When a loop exit edge is split, LCSSA form
+/// may require new PHIs in the new exit block. This function inserts the
+/// new PHIs, as needed. Preds is a list of preds inside the loop, SplitBB
+/// is the new loop exit block, and DestBB is the old loop exit, now the
+/// successor of SplitBB.
+static void CreatePHIsForSplitLoopExit(SmallVectorImpl<BasicBlock *> &Preds,
+ BasicBlock *SplitBB,
+ BasicBlock *DestBB) {
+ // SplitBB shouldn't have anything non-trivial in it yet.
+ assert(SplitBB->getFirstNonPHI() == SplitBB->getTerminator() &&
+ "SplitBB has non-PHI nodes!");
+
+ // For each PHI in the destination block...
+ for (BasicBlock::iterator I = DestBB->begin();
+ PHINode *PN = dyn_cast<PHINode>(I); ++I) {
+ unsigned Idx = PN->getBasicBlockIndex(SplitBB);
+ Value *V = PN->getIncomingValue(Idx);
+ // If the input is a PHI which already satisfies LCSSA, don't create
+ // a new one.
+ if (const PHINode *VP = dyn_cast<PHINode>(V))
+ if (VP->getParent() == SplitBB)
+ continue;
+ // Otherwise a new PHI is needed. Create one and populate it.
+ PHINode *NewPN = PHINode::Create(PN->getType(), "split",
+ SplitBB->getTerminator());
+ for (unsigned i = 0, e = Preds.size(); i != e; ++i)
+ NewPN->addIncoming(V, Preds[i]);
+ // Update the original PHI.
+ PN->setIncomingValue(Idx, NewPN);
+ }
+}
+
+/// SplitCriticalEdge - If this edge is a critical edge, insert a new node to
+/// split the critical edge. This will update DominatorTree and
+/// DominatorFrontier information if it is available, thus calling this pass
+/// will not invalidate either of them. This returns the new block if the edge
+/// was split, null otherwise.
+///
+/// If MergeIdenticalEdges is true (not the default), *all* edges from TI to the
+/// specified successor will be merged into the same critical edge block.
+/// This is most commonly interesting with switch instructions, which may
+/// have many edges to any one destination. This ensures that all edges to that
+/// dest go to one block instead of each going to a different block, but isn't
+/// the standard definition of a "critical edge".
+///
+/// It is invalid to call this function on a critical edge that starts at an
+/// IndirectBrInst. Splitting these edges will almost always create an invalid
+/// program because the address of the new block won't be the one that is jumped
+/// to.
+///
+BasicBlock *llvm::SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum,
+ Pass *P, bool MergeIdenticalEdges) {
+ if (!isCriticalEdge(TI, SuccNum, MergeIdenticalEdges)) return 0;
+
+ assert(!isa<IndirectBrInst>(TI) &&
+ "Cannot split critical edge from IndirectBrInst");
+
BasicBlock *TIBB = TI->getParent();
+ BasicBlock *DestBB = TI->getSuccessor(SuccNum);
// Create a new basic block, linking it into the CFG.
- BasicBlock *NewBB = new BasicBlock(TIBB->getName()+"_crit_edge");
- BasicBlock *DestBB = TI->getSuccessor(SuccNum);
- // Create our unconditional branch...
- BranchInst *BI = new BranchInst(DestBB);
- NewBB->getInstList().push_back(BI);
-
- // Branch to the new block, breaking the edge...
+ BasicBlock *NewBB = BasicBlock::Create(TI->getContext(),
+ TIBB->getName() + "." + DestBB->getName() + "_crit_edge");
+ // Create our unconditional branch.
+ BranchInst::Create(DestBB, NewBB);
+
+ // Branch to the new block, breaking the edge.
TI->setSuccessor(SuccNum, NewBB);
// Insert the block into the function... right after the block TI lives in.
Function &F = *TIBB->getParent();
- F.getBasicBlockList().insert(TIBB->getNext(), NewBB);
-
+ Function::iterator FBBI = TIBB;
+ F.getBasicBlockList().insert(++FBBI, NewBB);
+
// If there are any PHI nodes in DestBB, we need to update them so that they
// merge incoming values from NewBB instead of from TIBB.
- //
- for (BasicBlock::iterator I = DestBB->begin();
- PHINode *PN = dyn_cast<PHINode>(&*I); ++I) {
- // We no longer enter through TIBB, now we come in through NewBB.
- PN->replaceUsesOfWith(TIBB, NewBB);
+ if (PHINode *APHI = dyn_cast<PHINode>(DestBB->begin())) {
+ // This conceptually does:
+ // foreach (PHINode *PN in DestBB)
+ // PN->setIncomingBlock(PN->getIncomingBlock(TIBB), NewBB);
+ // but is optimized for two cases.
+
+ if (APHI->getNumIncomingValues() <= 8) { // Small # preds case.
+ unsigned BBIdx = 0;
+ for (BasicBlock::iterator I = DestBB->begin(); isa<PHINode>(I); ++I) {
+ // We no longer enter through TIBB, now we come in through NewBB.
+ // Revector exactly one entry in the PHI node that used to come from
+ // TIBB to come from NewBB.
+ PHINode *PN = cast<PHINode>(I);
+
+ // Reuse the previous value of BBIdx if it lines up. In cases where we
+ // have multiple phi nodes with *lots* of predecessors, this is a speed
+ // win because we don't have to scan the PHI looking for TIBB. This
+ // happens because the BB list of PHI nodes are usually in the same
+ // order.
+ if (PN->getIncomingBlock(BBIdx) != TIBB)
+ BBIdx = PN->getBasicBlockIndex(TIBB);
+ PN->setIncomingBlock(BBIdx, NewBB);
+ }
+ } else {
+ // However, the foreach loop is slow for blocks with lots of predecessors
+ // because PHINode::getIncomingBlock is O(n) in # preds. Instead, walk
+ // the user list of TIBB to find the PHI nodes.
+ SmallPtrSet<PHINode*, 16> UpdatedPHIs;
+
+ for (Value::use_iterator UI = TIBB->use_begin(), E = TIBB->use_end();
+ UI != E; ) {
+ Value::use_iterator Use = UI++;
+ if (PHINode *PN = dyn_cast<PHINode>(*Use)) {
+ // Remove one entry from each PHI.
+ if (PN->getParent() == DestBB && UpdatedPHIs.insert(PN))
+ PN->setOperand(Use.getOperandNo(), NewBB);
+ }
+ }
+ }
}
-
- // Now if we have a pass object, update analysis information. Currently we
- // update DominatorSet and DominatorTree information if it's available.
- //
- if (P) {
- // Should we update DominatorSet information?
- if (DominatorSet *DS = P->getAnalysisToUpdate<DominatorSet>()) {
- // The blocks that dominate the new one are the blocks that dominate TIBB
- // plus the new block itself.
- DominatorSet::DomSetType DomSet = DS->getDominators(TIBB);
- DomSet.insert(NewBB); // A block always dominates itself.
- DS->addBasicBlock(NewBB, DomSet);
+
+ // If there are any other edges from TIBB to DestBB, update those to go
+ // through the split block, making those edges non-critical as well (and
+ // reducing the number of phi entries in the DestBB if relevant).
+ if (MergeIdenticalEdges) {
+ for (unsigned i = SuccNum+1, e = TI->getNumSuccessors(); i != e; ++i) {
+ if (TI->getSuccessor(i) != DestBB) continue;
+
+ // Remove an entry for TIBB from DestBB phi nodes.
+ DestBB->removePredecessor(TIBB);
+
+ // We found another edge to DestBB, go to NewBB instead.
+ TI->setSuccessor(i, NewBB);
}
+ }
+
+
+
+ // If we don't have a pass object, we can't update anything...
+ if (P == 0) return NewBB;
+
+ DominatorTree *DT = P->getAnalysisIfAvailable<DominatorTree>();
+ DominanceFrontier *DF = P->getAnalysisIfAvailable<DominanceFrontier>();
+ LoopInfo *LI = P->getAnalysisIfAvailable<LoopInfo>();
+ ProfileInfo *PI = P->getAnalysisIfAvailable<ProfileInfo>();
+
+ // If we have nothing to update, just return.
+ if (DT == 0 && DF == 0 && LI == 0 && PI == 0)
+ return NewBB;
+
+ // Now update analysis information. Since the only predecessor of NewBB is
+ // the TIBB, TIBB clearly dominates NewBB. TIBB usually doesn't dominate
+ // anything, as there are other successors of DestBB. However, if all other
+ // predecessors of DestBB are already dominated by DestBB (e.g. DestBB is a
+ // loop header) then NewBB dominates DestBB.
+ SmallVector<BasicBlock*, 8> OtherPreds;
- // Should we update ImmdediateDominator information?
- if (ImmediateDominators *ID =
- P->getAnalysisToUpdate<ImmediateDominators>()) {
- // TIBB is the new immediate dominator for NewBB. NewBB doesn't dominate
- // anything.
- ID->addNewBlock(NewBB, TIBB);
+ // If there is a PHI in the block, loop over predecessors with it, which is
+ // faster than iterating pred_begin/end.
+ if (PHINode *PN = dyn_cast<PHINode>(DestBB->begin())) {
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i)
+ if (PN->getIncomingBlock(i) != NewBB)
+ OtherPreds.push_back(PN->getIncomingBlock(i));
+ } else {
+ for (pred_iterator I = pred_begin(DestBB), E = pred_end(DestBB);
+ I != E; ++I) {
+ BasicBlock *P = *I;
+ if (P != NewBB)
+ OtherPreds.push_back(P);
}
+ }
- // Should we update DominatorTree information?
- if (DominatorTree *DT = P->getAnalysisToUpdate<DominatorTree>()) {
- DominatorTree::Node *TINode = DT->getNode(TIBB);
+ bool NewBBDominatesDestBB = true;
+
+ // Should we update DominatorTree information?
+ if (DT) {
+ DomTreeNode *TINode = DT->getNode(TIBB);
- // The new block is not the immediate dominator for any other nodes, but
- // TINode is the immediate dominator for the new node.
- //
- DT->createNewNode(NewBB, TINode);
+ // The new block is not the immediate dominator for any other nodes, but
+ // TINode is the immediate dominator for the new node.
+ //
+ if (TINode) { // Don't break unreachable code!
+ DomTreeNode *NewBBNode = DT->addNewBlock(NewBB, TIBB);
+ DomTreeNode *DestBBNode = 0;
+
+ // If NewBBDominatesDestBB hasn't been computed yet, do so with DT.
+ if (!OtherPreds.empty()) {
+ DestBBNode = DT->getNode(DestBB);
+ while (!OtherPreds.empty() && NewBBDominatesDestBB) {
+ if (DomTreeNode *OPNode = DT->getNode(OtherPreds.back()))
+ NewBBDominatesDestBB = DT->dominates(DestBBNode, OPNode);
+ OtherPreds.pop_back();
+ }
+ OtherPreds.clear();
+ }
+
+ // If NewBBDominatesDestBB, then NewBB dominates DestBB, otherwise it
+ // doesn't dominate anything.
+ if (NewBBDominatesDestBB) {
+ if (!DestBBNode) DestBBNode = DT->getNode(DestBB);
+ DT->changeImmediateDominator(DestBBNode, NewBBNode);
+ }
}
}
-}
-// runOnFunction - Loop over all of the edges in the CFG, breaking critical
-// edges as they are found.
-//
-bool BreakCriticalEdges::runOnFunction(Function &F) {
- bool Changed = false;
- for (Function::iterator I = F.begin(), E = F.end(); I != E; ++I) {
- TerminatorInst *TI = I->getTerminator();
- if (TI->getNumSuccessors() > 1)
- for (unsigned i = 0, e = TI->getNumSuccessors(); i != e; ++i)
- if (isCriticalEdge(TI, i)) {
- SplitCriticalEdge(TI, i, this);
- ++NumBroken;
- Changed = true;
+ // Should we update DominanceFrontier information?
+ if (DF) {
+ // If NewBBDominatesDestBB hasn't been computed yet, do so with DF.
+ if (!OtherPreds.empty()) {
+ // FIXME: IMPLEMENT THIS!
+ llvm_unreachable("Requiring domfrontiers but not idom/domtree/domset."
+ " not implemented yet!");
+ }
+
+ // Since the new block is dominated by its only predecessor TIBB,
+ // it cannot be in any block's dominance frontier. If NewBB dominates
+ // DestBB, its dominance frontier is the same as DestBB's, otherwise it is
+ // just {DestBB}.
+ DominanceFrontier::DomSetType NewDFSet;
+ if (NewBBDominatesDestBB) {
+ DominanceFrontier::iterator I = DF->find(DestBB);
+ if (I != DF->end()) {
+ DF->addBasicBlock(NewBB, I->second);
+
+ if (I->second.count(DestBB)) {
+ // However NewBB's frontier does not include DestBB.
+ DominanceFrontier::iterator NF = DF->find(NewBB);
+ DF->removeFromFrontier(NF, DestBB);
}
+ }
+ else
+ DF->addBasicBlock(NewBB, DominanceFrontier::DomSetType());
+ } else {
+ DominanceFrontier::DomSetType NewDFSet;
+ NewDFSet.insert(DestBB);
+ DF->addBasicBlock(NewBB, NewDFSet);
+ }
}
+
+ // Update LoopInfo if it is around.
+ if (LI) {
+ if (Loop *TIL = LI->getLoopFor(TIBB)) {
+ // If one or the other blocks were not in a loop, the new block is not
+ // either, and thus LI doesn't need to be updated.
+ if (Loop *DestLoop = LI->getLoopFor(DestBB)) {
+ if (TIL == DestLoop) {
+ // Both in the same loop, the NewBB joins loop.
+ DestLoop->addBasicBlockToLoop(NewBB, LI->getBase());
+ } else if (TIL->contains(DestLoop)) {
+ // Edge from an outer loop to an inner loop. Add to the outer loop.
+ TIL->addBasicBlockToLoop(NewBB, LI->getBase());
+ } else if (DestLoop->contains(TIL)) {
+ // Edge from an inner loop to an outer loop. Add to the outer loop.
+ DestLoop->addBasicBlockToLoop(NewBB, LI->getBase());
+ } else {
+ // Edge from two loops with no containment relation. Because these
+ // are natural loops, we know that the destination block must be the
+ // header of its loop (adding a branch into a loop elsewhere would
+ // create an irreducible loop).
+ assert(DestLoop->getHeader() == DestBB &&
+ "Should not create irreducible loops!");
+ if (Loop *P = DestLoop->getParentLoop())
+ P->addBasicBlockToLoop(NewBB, LI->getBase());
+ }
+ }
+ // If TIBB is in a loop and DestBB is outside of that loop, split the
+ // other exit blocks of the loop that also have predecessors outside
+ // the loop, to maintain a LoopSimplify guarantee.
+ if (!TIL->contains(DestBB) &&
+ P->mustPreserveAnalysisID(LoopSimplifyID)) {
+ assert(!TIL->contains(NewBB) &&
+ "Split point for loop exit is contained in loop!");
- return Changed;
+ // Update LCSSA form in the newly created exit block.
+ if (P->mustPreserveAnalysisID(LCSSAID)) {
+ SmallVector<BasicBlock *, 1> OrigPred;
+ OrigPred.push_back(TIBB);
+ CreatePHIsForSplitLoopExit(OrigPred, NewBB, DestBB);
+ }
+
+ // For each unique exit block...
+ SmallVector<BasicBlock *, 4> ExitBlocks;
+ TIL->getExitBlocks(ExitBlocks);
+ for (unsigned i = 0, e = ExitBlocks.size(); i != e; ++i) {
+ // Collect all the preds that are inside the loop, and note
+ // whether there are any preds outside the loop.
+ SmallVector<BasicBlock *, 4> Preds;
+ bool HasPredOutsideOfLoop = false;
+ BasicBlock *Exit = ExitBlocks[i];
+ for (pred_iterator I = pred_begin(Exit), E = pred_end(Exit);
+ I != E; ++I) {
+ BasicBlock *P = *I;
+ if (TIL->contains(P))
+ Preds.push_back(P);
+ else
+ HasPredOutsideOfLoop = true;
+ }
+ // If there are any preds not in the loop, we'll need to split
+ // the edges. The Preds.empty() check is needed because a block
+ // may appear multiple times in the list. We can't use
+ // getUniqueExitBlocks above because that depends on LoopSimplify
+ // form, which we're in the process of restoring!
+ if (!Preds.empty() && HasPredOutsideOfLoop) {
+ BasicBlock *NewExitBB =
+ SplitBlockPredecessors(Exit, Preds.data(), Preds.size(),
+ "split", P);
+ if (P->mustPreserveAnalysisID(LCSSAID))
+ CreatePHIsForSplitLoopExit(Preds, NewExitBB, Exit);
+ }
+ }
+ }
+ // LCSSA form was updated above for the case where LoopSimplify is
+ // available, which means that all predecessors of loop exit blocks
+ // are within the loop. Without LoopSimplify form, it would be
+ // necessary to insert a new phi.
+ assert((!P->mustPreserveAnalysisID(LCSSAID) ||
+ P->mustPreserveAnalysisID(LoopSimplifyID)) &&
+ "SplitCriticalEdge doesn't know how to update LCCSA form "
+ "without LoopSimplify!");
+ }
+ }
+
+ // Update ProfileInfo if it is around.
+ if (PI)
+ PI->splitEdge(TIBB, DestBB, NewBB, MergeIdenticalEdges);
+
+ return NewBB;
}
projects / oota-llvm.git / blobdiff