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-rw-r--r--lib/Transforms/Utils/Local.cpp170
1 files changed, 147 insertions, 23 deletions
diff --git a/lib/Transforms/Utils/Local.cpp b/lib/Transforms/Utils/Local.cpp
index e470e14..ca9f2b1 100644
--- a/lib/Transforms/Utils/Local.cpp
+++ b/lib/Transforms/Utils/Local.cpp
@@ -525,6 +525,13 @@ void llvm::MergeBasicBlockIntoOnlyPred(BasicBlock *DestBB, Pass *P) {
PredBB->eraseFromParent();
}
+/// CanMergeValues - Return true if we can choose one of these values to use
+/// in place of the other. Note that we will always choose the non-undef
+/// value to keep.
+static bool CanMergeValues(Value *First, Value *Second) {
+ return First == Second || isa<UndefValue>(First) || isa<UndefValue>(Second);
+}
+
/// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
/// almost-empty BB ending in an unconditional branch to Succ, into succ.
///
@@ -555,7 +562,8 @@ static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
for (unsigned PI = 0, PE = PN->getNumIncomingValues(); PI != PE; ++PI) {
BasicBlock *IBB = PN->getIncomingBlock(PI);
if (BBPreds.count(IBB) &&
- BBPN->getIncomingValueForBlock(IBB) != PN->getIncomingValue(PI)) {
+ !CanMergeValues(BBPN->getIncomingValueForBlock(IBB),
+ PN->getIncomingValue(PI))) {
DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
<< Succ->getName() << " is conflicting with "
<< BBPN->getName() << " with regard to common predecessor "
@@ -570,7 +578,8 @@ static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
// one for BB, in which case this phi node will not prevent the merging
// of the block.
BasicBlock *IBB = PN->getIncomingBlock(PI);
- if (BBPreds.count(IBB) && Val != PN->getIncomingValue(PI)) {
+ if (BBPreds.count(IBB) &&
+ !CanMergeValues(Val, PN->getIncomingValue(PI))) {
DEBUG(dbgs() << "Can't fold, phi node " << PN->getName() << " in "
<< Succ->getName() << " is conflicting with regard to common "
<< "predecessor " << IBB->getName() << "\n");
@@ -583,6 +592,139 @@ static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
return true;
}
+typedef SmallVector<BasicBlock *, 16> PredBlockVector;
+typedef DenseMap<BasicBlock *, Value *> IncomingValueMap;
+
+/// \brief Determines the value to use as the phi node input for a block.
+///
+/// Select between \p OldVal any value that we know flows from \p BB
+/// to a particular phi on the basis of which one (if either) is not
+/// undef. Update IncomingValues based on the selected value.
+///
+/// \param OldVal The value we are considering selecting.
+/// \param BB The block that the value flows in from.
+/// \param IncomingValues A map from block-to-value for other phi inputs
+/// that we have examined.
+///
+/// \returns the selected value.
+static Value *selectIncomingValueForBlock(Value *OldVal, BasicBlock *BB,
+ IncomingValueMap &IncomingValues) {
+ if (!isa<UndefValue>(OldVal)) {
+ assert((!IncomingValues.count(BB) ||
+ IncomingValues.find(BB)->second == OldVal) &&
+ "Expected OldVal to match incoming value from BB!");
+
+ IncomingValues.insert(std::make_pair(BB, OldVal));
+ return OldVal;
+ }
+
+ IncomingValueMap::const_iterator It = IncomingValues.find(BB);
+ if (It != IncomingValues.end()) return It->second;
+
+ return OldVal;
+}
+
+/// \brief Create a map from block to value for the operands of a
+/// given phi.
+///
+/// Create a map from block to value for each non-undef value flowing
+/// into \p PN.
+///
+/// \param PN The phi we are collecting the map for.
+/// \param IncomingValues [out] The map from block to value for this phi.
+static void gatherIncomingValuesToPhi(PHINode *PN,
+ IncomingValueMap &IncomingValues) {
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
+ BasicBlock *BB = PN->getIncomingBlock(i);
+ Value *V = PN->getIncomingValue(i);
+
+ if (!isa<UndefValue>(V))
+ IncomingValues.insert(std::make_pair(BB, V));
+ }
+}
+
+/// \brief Replace the incoming undef values to a phi with the values
+/// from a block-to-value map.
+///
+/// \param PN The phi we are replacing the undefs in.
+/// \param IncomingValues A map from block to value.
+static void replaceUndefValuesInPhi(PHINode *PN,
+ const IncomingValueMap &IncomingValues) {
+ for (unsigned i = 0, e = PN->getNumIncomingValues(); i != e; ++i) {
+ Value *V = PN->getIncomingValue(i);
+
+ if (!isa<UndefValue>(V)) continue;
+
+ BasicBlock *BB = PN->getIncomingBlock(i);
+ IncomingValueMap::const_iterator It = IncomingValues.find(BB);
+ if (It == IncomingValues.end()) continue;
+
+ PN->setIncomingValue(i, It->second);
+ }
+}
+
+/// \brief Replace a value flowing from a block to a phi with
+/// potentially multiple instances of that value flowing from the
+/// block's predecessors to the phi.
+///
+/// \param BB The block with the value flowing into the phi.
+/// \param BBPreds The predecessors of BB.
+/// \param PN The phi that we are updating.
+static void redirectValuesFromPredecessorsToPhi(BasicBlock *BB,
+ const PredBlockVector &BBPreds,
+ PHINode *PN) {
+ Value *OldVal = PN->removeIncomingValue(BB, false);
+ assert(OldVal && "No entry in PHI for Pred BB!");
+
+ IncomingValueMap IncomingValues;
+
+ // We are merging two blocks - BB, and the block containing PN - and
+ // as a result we need to redirect edges from the predecessors of BB
+ // to go to the block containing PN, and update PN
+ // accordingly. Since we allow merging blocks in the case where the
+ // predecessor and successor blocks both share some predecessors,
+ // and where some of those common predecessors might have undef
+ // values flowing into PN, we want to rewrite those values to be
+ // consistent with the non-undef values.
+
+ gatherIncomingValuesToPhi(PN, IncomingValues);
+
+ // If this incoming value is one of the PHI nodes in BB, the new entries
+ // in the PHI node are the entries from the old PHI.
+ if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
+ PHINode *OldValPN = cast<PHINode>(OldVal);
+ for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i) {
+ // Note that, since we are merging phi nodes and BB and Succ might
+ // have common predecessors, we could end up with a phi node with
+ // identical incoming branches. This will be cleaned up later (and
+ // will trigger asserts if we try to clean it up now, without also
+ // simplifying the corresponding conditional branch).
+ BasicBlock *PredBB = OldValPN->getIncomingBlock(i);
+ Value *PredVal = OldValPN->getIncomingValue(i);
+ Value *Selected = selectIncomingValueForBlock(PredVal, PredBB,
+ IncomingValues);
+
+ // And add a new incoming value for this predecessor for the
+ // newly retargeted branch.
+ PN->addIncoming(Selected, PredBB);
+ }
+ } else {
+ for (unsigned i = 0, e = BBPreds.size(); i != e; ++i) {
+ // Update existing incoming values in PN for this
+ // predecessor of BB.
+ BasicBlock *PredBB = BBPreds[i];
+ Value *Selected = selectIncomingValueForBlock(OldVal, PredBB,
+ IncomingValues);
+
+ // And add a new incoming value for this predecessor for the
+ // newly retargeted branch.
+ PN->addIncoming(Selected, PredBB);
+ }
+ }
+
+ replaceUndefValuesInPhi(PN, IncomingValues);
+}
+
/// TryToSimplifyUncondBranchFromEmptyBlock - BB is known to contain an
/// unconditional branch, and contains no instructions other than PHI nodes,
/// potential side-effect free intrinsics and the branch. If possible,
@@ -634,31 +776,13 @@ bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) {
// If there is more than one pred of succ, and there are PHI nodes in
// the successor, then we need to add incoming edges for the PHI nodes
//
- const SmallVector<BasicBlock*, 16> BBPreds(pred_begin(BB), pred_end(BB));
+ const PredBlockVector BBPreds(pred_begin(BB), pred_end(BB));
// Loop over all of the PHI nodes in the successor of BB.
for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
PHINode *PN = cast<PHINode>(I);
- Value *OldVal = PN->removeIncomingValue(BB, false);
- assert(OldVal && "No entry in PHI for Pred BB!");
-
- // If this incoming value is one of the PHI nodes in BB, the new entries
- // in the PHI node are the entries from the old PHI.
- if (isa<PHINode>(OldVal) && cast<PHINode>(OldVal)->getParent() == BB) {
- PHINode *OldValPN = cast<PHINode>(OldVal);
- for (unsigned i = 0, e = OldValPN->getNumIncomingValues(); i != e; ++i)
- // Note that, since we are merging phi nodes and BB and Succ might
- // have common predecessors, we could end up with a phi node with
- // identical incoming branches. This will be cleaned up later (and
- // will trigger asserts if we try to clean it up now, without also
- // simplifying the corresponding conditional branch).
- PN->addIncoming(OldValPN->getIncomingValue(i),
- OldValPN->getIncomingBlock(i));
- } else {
- // Add an incoming value for each of the new incoming values.
- for (unsigned i = 0, e = BBPreds.size(); i != e; ++i)
- PN->addIncoming(OldVal, BBPreds[i]);
- }
+
+ redirectValuesFromPredecessorsToPhi(BB, BBPreds, PN);
}
}
generated by cgit v1.1 at 2025-07-03 12:54:51 +0000