//
//===----------------------------------------------------------------------===//
-#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/Instructions.h"
-#include "llvm/Type.h"
-#include "llvm/Support/CFG.h"
-#include "llvm/Support/ErrorHandling.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/Statistic.h"
+#include "llvm/Analysis/CFG.h"
+#include "llvm/Analysis/LoopInfo.h"
+#include "llvm/IR/CFG.h"
+#include "llvm/IR/Dominators.h"
+#include "llvm/IR/Function.h"
+#include "llvm/IR/Instructions.h"
+#include "llvm/IR/Type.h"
+#include "llvm/Support/ErrorHandling.h"
+#include "llvm/Transforms/Utils/BasicBlockUtils.h"
using namespace llvm;
+#define DEBUG_TYPE "break-crit-edges"
+
STATISTIC(NumBroken, "Number of blocks inserted");
namespace {
initializeBreakCriticalEdgesPass(*PassRegistry::getPassRegistry());
}
- virtual bool runOnFunction(Function &F);
+ bool runOnFunction(Function &F) override;
- virtual void getAnalysisUsage(AnalysisUsage &AU) const {
- AU.addPreserved<DominatorTree>();
+ void getAnalysisUsage(AnalysisUsage &AU) const override {
+ AU.addPreserved<DominatorTreeWrapperPass>();
AU.addPreserved<LoopInfo>();
- AU.addPreserved<ProfileInfo>();
// No loop canonicalization guarantees are broken by this pass.
AU.addPreservedID(LoopSimplifyID);
// 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.
-//
-bool llvm::isCriticalEdge(const TerminatorInst *TI, unsigned SuccNum,
- bool AllowIdenticalEdges) {
- assert(SuccNum < TI->getNumSuccessors() && "Illegal edge specification!");
- if (TI->getNumSuccessors() == 1) return false;
-
- const BasicBlock *Dest = TI->getSuccessor(SuccNum);
- 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.
- 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;
-}
-
-/// CreatePHIsForSplitLoopExit - When a loop exit edge is split, LCSSA form
+/// 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
+/// 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,
+static void createPHIsForSplitLoopExit(ArrayRef<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!");
+ assert((SplitBB->getFirstNonPHI() == SplitBB->getTerminator() ||
+ SplitBB->isLandingPad()) && "SplitBB has non-PHI nodes!");
- // For each PHI in the destination block...
+ // 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(), Preds.size(), "split",
- SplitBB->getTerminator());
+ PHINode *NewPN =
+ PHINode::Create(PN->getType(), Preds.size(), "split",
+ SplitBB->isLandingPad() ?
+ SplitBB->begin() : 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);
}
/// 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
+/// 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
+/// 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
/// to.
///
BasicBlock *llvm::SplitCriticalEdge(TerminatorInst *TI, unsigned SuccNum,
- Pass *P, bool MergeIdenticalEdges) {
- if (!isCriticalEdge(TI, SuccNum, MergeIdenticalEdges)) return 0;
-
+ Pass *P, bool MergeIdenticalEdges,
+ bool DontDeleteUselessPhis,
+ bool SplitLandingPads) {
+ if (!isCriticalEdge(TI, SuccNum, MergeIdenticalEdges)) return nullptr;
+
assert(!isa<IndirectBrInst>(TI) &&
"Cannot split critical edge from IndirectBrInst");
-
+
BasicBlock *TIBB = TI->getParent();
BasicBlock *DestBB = TI->getSuccessor(SuccNum);
+ // Splitting the critical edge to a landing pad block is non-trivial. Don't do
+ // it in this generic function.
+ if (DestBB->isLandingPad()) return nullptr;
+
// Create a new basic block, linking it into the CFG.
BasicBlock *NewBB = BasicBlock::Create(TI->getContext(),
TIBB->getName() + "." + DestBB->getName() + "_crit_edge");
Function &F = *TIBB->getParent();
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.
{
// happens because the BB list of PHI nodes are usually in the same
// order.
if (PN->getIncomingBlock(BBIdx) != TIBB)
- BBIdx = PN->getBasicBlockIndex(TIBB);
+ BBIdx = PN->getBasicBlockIndex(TIBB);
PN->setIncomingBlock(BBIdx, NewBB);
}
}
-
+
// 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);
-
+ DestBB->removePredecessor(TIBB, DontDeleteUselessPhis);
+
// 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>();
+ if (!P) return NewBB;
+
+ DominatorTreeWrapperPass *DTWP =
+ P->getAnalysisIfAvailable<DominatorTreeWrapperPass>();
+ DominatorTree *DT = DTWP ? &DTWP->getDomTree() : nullptr;
LoopInfo *LI = P->getAnalysisIfAvailable<LoopInfo>();
- ProfileInfo *PI = P->getAnalysisIfAvailable<ProfileInfo>();
-
+
// If we have nothing to update, just return.
- if (DT == 0 && LI == 0 && PI == 0)
+ if (!DT && !LI)
return NewBB;
// Now update analysis information. Since the only predecessor of NewBB is
}
bool NewBBDominatesDestBB = true;
-
+
// Should we update DominatorTree information?
if (DT) {
DomTreeNode *TINode = DT->getNode(TIBB);
//
if (TINode) { // Don't break unreachable code!
DomTreeNode *NewBBNode = DT->addNewBlock(NewBB, TIBB);
- DomTreeNode *DestBBNode = 0;
-
+ DomTreeNode *DestBBNode = nullptr;
+
// If NewBBDominatesDestBB hasn't been computed yet, do so with DT.
if (!OtherPreds.empty()) {
DestBBNode = DT->getNode(DestBB);
}
OtherPreds.clear();
}
-
+
// If NewBBDominatesDestBB, then NewBB dominates DestBB, otherwise it
// doesn't dominate anything.
if (NewBBDominatesDestBB) {
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 TIBB is in a loop and DestBB is outside of that loop, we may need
+ // to update LoopSimplify form and LCSSA form.
if (!TIL->contains(DestBB) &&
P->mustPreserveAnalysisID(LoopSimplifyID)) {
assert(!TIL->contains(NewBB) &&
"Split point for loop exit is contained in loop!");
// 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);
- }
+ if (P->mustPreserveAnalysisID(LCSSAID))
+ createPHIsForSplitLoopExit(TIBB, 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);
+ // The only that we can break LoopSimplify form by splitting a critical
+ // edge is if after the split there exists some edge from TIL to DestBB
+ // *and* the only edge into DestBB from outside of TIL is that of
+ // NewBB. If the first isn't true, then LoopSimplify still holds, NewBB
+ // is the new exit block and it has no non-loop predecessors. If the
+ // second isn't true, then DestBB was not in LoopSimplify form prior to
+ // the split as it had a non-loop predecessor. In both of these cases,
+ // the predecessor must be directly in TIL, not in a subloop, or again
+ // LoopSimplify doesn't hold.
+ SmallVector<BasicBlock *, 4> LoopPreds;
+ for (pred_iterator I = pred_begin(DestBB), E = pred_end(DestBB); I != E;
+ ++I) {
+ BasicBlock *P = *I;
+ if (P == NewBB)
+ continue; // The new block is known.
+ if (LI->getLoopFor(P) != TIL) {
+ // No need to re-simplify, it wasn't to start with.
+ LoopPreds.clear();
+ break;
}
+ LoopPreds.push_back(P);
+ }
+ if (!LoopPreds.empty()) {
+ assert(!DestBB->isLandingPad() &&
+ "We don't split edges to landing pads!");
+ BasicBlock *NewExitBB =
+ SplitBlockPredecessors(DestBB, LoopPreds, "split", P);
+ if (P->mustPreserveAnalysisID(LCSSAID))
+ createPHIsForSplitLoopExit(LoopPreds, NewExitBB, DestBB);
}
}
// LCSSA form was updated above for the case where LoopSimplify is
}
}
- // Update ProfileInfo if it is around.
- if (PI)
- PI->splitEdge(TIBB, DestBB, NewBB, MergeIdenticalEdges);
-
return NewBB;
}
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