#include "llvm/Support/raw_ostream.h"
#include "llvm/Analysis/ConstantFolding.h"
#include "llvm/Transforms/Utils/BasicBlockUtils.h"
+#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallVector.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/ADT/Statistic.h"
PN->addIncoming(PN->getIncomingValueForBlock(ExistPred), NewPred);
}
-/// CanPropagatePredecessorsForPHIs - Return true if we can fold BB, an
-/// almost-empty BB ending in an unconditional branch to Succ, into succ.
-///
-/// Assumption: Succ is the single successor for BB.
-///
-static bool CanPropagatePredecessorsForPHIs(BasicBlock *BB, BasicBlock *Succ) {
- assert(*succ_begin(BB) == Succ && "Succ is not successor of BB!");
-
- DEBUG(errs() << "Looking to fold " << BB->getName() << " into "
- << Succ->getName() << "\n");
- // Shortcut, if there is only a single predecessor it must be BB and merging
- // is always safe
- if (Succ->getSinglePredecessor()) return true;
-
- // Make a list of the predecessors of BB
- typedef SmallPtrSet<BasicBlock*, 16> BlockSet;
- BlockSet BBPreds(pred_begin(BB), pred_end(BB));
-
- // Use that list to make another list of common predecessors of BB and Succ
- BlockSet CommonPreds;
- for (pred_iterator PI = pred_begin(Succ), PE = pred_end(Succ);
- PI != PE; ++PI)
- if (BBPreds.count(*PI))
- CommonPreds.insert(*PI);
-
- // Shortcut, if there are no common predecessors, merging is always safe
- if (CommonPreds.empty())
- return true;
-
- // Look at all the phi nodes in Succ, to see if they present a conflict when
- // merging these blocks
- for (BasicBlock::iterator I = Succ->begin(); isa<PHINode>(I); ++I) {
- PHINode *PN = cast<PHINode>(I);
-
- // If the incoming value from BB is again a PHINode in
- // BB which has the same incoming value for *PI as PN does, we can
- // merge the phi nodes and then the blocks can still be merged
- PHINode *BBPN = dyn_cast<PHINode>(PN->getIncomingValueForBlock(BB));
- if (BBPN && BBPN->getParent() == BB) {
- for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
- PI != PE; PI++) {
- if (BBPN->getIncomingValueForBlock(*PI)
- != PN->getIncomingValueForBlock(*PI)) {
- DEBUG(errs() << "Can't fold, phi node " << PN->getName() << " in "
- << Succ->getName() << " is conflicting with "
- << BBPN->getName() << " with regard to common predecessor "
- << (*PI)->getName() << "\n");
- return false;
- }
- }
- } else {
- Value* Val = PN->getIncomingValueForBlock(BB);
- for (BlockSet::iterator PI = CommonPreds.begin(), PE = CommonPreds.end();
- PI != PE; PI++) {
- // See if the incoming value for the common predecessor is equal to the
- // one for BB, in which case this phi node will not prevent the merging
- // of the block.
- if (Val != PN->getIncomingValueForBlock(*PI)) {
- DEBUG(errs() << "Can't fold, phi node " << PN->getName() << " in "
- << Succ->getName() << " is conflicting with regard to common "
- << "predecessor " << (*PI)->getName() << "\n");
- return false;
- }
- }
- }
- }
-
- return true;
-}
-
-/// TryToSimplifyUncondBranchFromEmptyBlock - BB contains an unconditional
-/// branch to Succ, and contains no instructions other than PHI nodes and the
-/// branch. If possible, eliminate BB.
-static bool TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB,
- BasicBlock *Succ) {
- // Check to see if merging these blocks would cause conflicts for any of the
- // phi nodes in BB or Succ. If not, we can safely merge.
- if (!CanPropagatePredecessorsForPHIs(BB, Succ)) return false;
-
- // Check for cases where Succ has multiple predecessors and a PHI node in BB
- // has uses which will not disappear when the PHI nodes are merged. It is
- // possible to handle such cases, but difficult: it requires checking whether
- // BB dominates Succ, which is non-trivial to calculate in the case where
- // Succ has multiple predecessors. Also, it requires checking whether
- // constructing the necessary self-referential PHI node doesn't intoduce any
- // conflicts; this isn't too difficult, but the previous code for doing this
- // was incorrect.
- //
- // Note that if this check finds a live use, BB dominates Succ, so BB is
- // something like a loop pre-header (or rarely, a part of an irreducible CFG);
- // folding the branch isn't profitable in that case anyway.
- if (!Succ->getSinglePredecessor()) {
- BasicBlock::iterator BBI = BB->begin();
- while (isa<PHINode>(*BBI)) {
- for (Value::use_iterator UI = BBI->use_begin(), E = BBI->use_end();
- UI != E; ++UI) {
- if (PHINode* PN = dyn_cast<PHINode>(*UI)) {
- if (PN->getIncomingBlock(UI) != BB)
- return false;
- } else {
- return false;
- }
- }
- ++BBI;
- }
- }
-
- DEBUG(errs() << "Killing Trivial BB: \n" << *BB);
-
- if (isa<PHINode>(Succ->begin())) {
- // 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));
-
- // 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]);
- }
- }
- }
-
- while (PHINode *PN = dyn_cast<PHINode>(&BB->front())) {
- if (Succ->getSinglePredecessor()) {
- // BB is the only predecessor of Succ, so Succ will end up with exactly
- // the same predecessors BB had.
- Succ->getInstList().splice(Succ->begin(),
- BB->getInstList(), BB->begin());
- } else {
- // We explicitly check for such uses in CanPropagatePredecessorsForPHIs.
- assert(PN->use_empty() && "There shouldn't be any uses here!");
- PN->eraseFromParent();
- }
- }
-
- // Everything that jumped to BB now goes to Succ.
- BB->replaceAllUsesWith(Succ);
- if (!Succ->hasName()) Succ->takeName(BB);
- BB->eraseFromParent(); // Delete the old basic block.
- return true;
-}
/// GetIfCondition - Given a basic block (BB) with two predecessors (and
/// presumably PHI nodes in it), check to see if the merge at this block is due
}
// Check for trivial simplification.
- if (Constant *C = ConstantFoldInstruction(N, BB->getContext())) {
+ if (Constant *C = ConstantFoldInstruction(N)) {
TranslateMap[BBI] = C;
delete N; // Constant folded away, don't need actual inst
} else {
return true;
}
-
/// SimplifyCFG - This function is used to do simplification of a CFG. For
/// example, it adjusts branches to branches to eliminate the extra hop, it
/// eliminates unreachable basic blocks, and does other "peephole" optimization
// away...
Changed |= ConstantFoldTerminator(BB);
+ // Check for and eliminate duplicate PHI nodes in this block.
+ Changed |= EliminateDuplicatePHINodes(BB);
+
// If there is a trivial two-entry PHI node in this basic block, and we can
// eliminate it, do so now.
if (PHINode *PN = dyn_cast<PHINode>(BB->begin()))
if (BI->isUnconditional()) {
BasicBlock::iterator BBI = BB->getFirstNonPHI();
- BasicBlock *Succ = BI->getSuccessor(0);
// Ignore dbg intrinsics.
while (isa<DbgInfoIntrinsic>(BBI))
++BBI;
- if (BBI->isTerminator() && // Terminator is the only non-phi instruction!
- Succ != BB) // Don't hurt infinite loops!
- if (TryToSimplifyUncondBranchFromEmptyBlock(BB, Succ))
+ if (BBI->isTerminator()) // Terminator is the only non-phi instruction!
+ if (TryToSimplifyUncondBranchFromEmptyBlock(BB))
return true;
} else { // Conditional branch
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