#include "llvm/Instructions.h"
#include "llvm/Intrinsics.h"
#include "llvm/IntrinsicInst.h"
-#include "llvm/LLVMContext.h"
+#include "llvm/ADT/DenseMap.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/Analysis/ConstantFolding.h"
-#include "llvm/Analysis/DebugInfo.h"
-#include "llvm/Analysis/MemoryBuiltins.h"
+#include "llvm/Analysis/InstructionSimplify.h"
#include "llvm/Analysis/ProfileInfo.h"
#include "llvm/Target/TargetData.h"
+#include "llvm/Support/CFG.h"
+#include "llvm/Support/Debug.h"
#include "llvm/Support/GetElementPtrTypeIterator.h"
#include "llvm/Support/MathExtras.h"
+#include "llvm/Support/ValueHandle.h"
+#include "llvm/Support/raw_ostream.h"
using namespace llvm;
-//===----------------------------------------------------------------------===//
-// Local analysis.
-//
-
-/// isSafeToLoadUnconditionally - Return true if we know that executing a load
-/// from this value cannot trap. If it is not obviously safe to load from the
-/// specified pointer, we do a quick local scan of the basic block containing
-/// ScanFrom, to determine if the address is already accessed.
-bool llvm::isSafeToLoadUnconditionally(Value *V, Instruction *ScanFrom) {
- // If it is an alloca it is always safe to load from.
- if (isa<AllocaInst>(V)) return true;
-
- // If it is a global variable it is mostly safe to load from.
- if (const GlobalValue *GV = dyn_cast<GlobalVariable>(V))
- // Don't try to evaluate aliases. External weak GV can be null.
- return !isa<GlobalAlias>(GV) && !GV->hasExternalWeakLinkage();
-
- // Otherwise, be a little bit agressive by scanning the local block where we
- // want to check to see if the pointer is already being loaded or stored
- // from/to. If so, the previous load or store would have already trapped,
- // so there is no harm doing an extra load (also, CSE will later eliminate
- // the load entirely).
- BasicBlock::iterator BBI = ScanFrom, E = ScanFrom->getParent()->begin();
-
- while (BBI != E) {
- --BBI;
-
- // If we see a free or a call which may write to memory (i.e. which might do
- // a free) the pointer could be marked invalid.
- if (isFreeCall(BBI) || (isa<CallInst>(BBI) && BBI->mayWriteToMemory() &&
- !isa<DbgInfoIntrinsic>(BBI)))
- return false;
-
- if (LoadInst *LI = dyn_cast<LoadInst>(BBI)) {
- if (LI->getOperand(0) == V) return true;
- } else if (StoreInst *SI = dyn_cast<StoreInst>(BBI)) {
- if (SI->getOperand(1) == V) return true;
- }
- }
- return false;
-}
-
-
//===----------------------------------------------------------------------===//
// Local constant propagation.
//
// unconditional branch.
BI->setUnconditionalDest(Destination);
return true;
- } else if (Dest2 == Dest1) { // Conditional branch to same location?
+ }
+
+ if (Dest2 == Dest1) { // Conditional branch to same location?
// This branch matches something like this:
// br bool %cond, label %Dest, label %Dest
// and changes it into: br label %Dest
BI->setUnconditionalDest(Dest1);
return true;
}
- } else if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) {
+ return false;
+ }
+
+ if (SwitchInst *SI = dyn_cast<SwitchInst>(T)) {
// If we are switching on a constant, we can convert the switch into a
// single branch instruction!
ConstantInt *CI = dyn_cast<ConstantInt>(SI->getCondition());
assert(TheOnlyDest == SI->getDefaultDest() &&
"Default destination is not successor #0?");
- // Figure out which case it goes to...
+ // Figure out which case it goes to.
for (unsigned i = 1, e = SI->getNumSuccessors(); i != e; ++i) {
// Found case matching a constant operand?
if (SI->getSuccessorValue(i) == CI) {
// Check to see if this branch is going to the same place as the default
// dest. If so, eliminate it as an explicit compare.
if (SI->getSuccessor(i) == DefaultDest) {
- // Remove this entry...
+ // Remove this entry.
DefaultDest->removePredecessor(SI->getParent());
SI->removeCase(i);
--i; --e; // Don't skip an entry...
// If we found a single destination that we can fold the switch into, do so
// now.
if (TheOnlyDest) {
- // Insert the new branch..
+ // Insert the new branch.
BranchInst::Create(TheOnlyDest, SI);
BasicBlock *BB = SI->getParent();
Succ->removePredecessor(BB);
}
- // Delete the old switch...
+ // Delete the old switch.
BB->getInstList().erase(SI);
return true;
- } else if (SI->getNumSuccessors() == 2) {
+ }
+
+ if (SI->getNumSuccessors() == 2) {
// Otherwise, we can fold this switch into a conditional branch
// instruction if it has only one non-default destination.
Value *Cond = new ICmpInst(SI, ICmpInst::ICMP_EQ, SI->getCondition(),
SI->getSuccessorValue(1), "cond");
- // Insert the new branch...
+ // Insert the new branch.
BranchInst::Create(SI->getSuccessor(1), SI->getSuccessor(0), Cond, SI);
- // Delete the old switch...
+ // Delete the old switch.
SI->eraseFromParent();
return true;
}
+ return false;
+ }
+
+ if (IndirectBrInst *IBI = dyn_cast<IndirectBrInst>(T)) {
+ // indirectbr blockaddress(@F, @BB) -> br label @BB
+ if (BlockAddress *BA =
+ dyn_cast<BlockAddress>(IBI->getAddress()->stripPointerCasts())) {
+ BasicBlock *TheOnlyDest = BA->getBasicBlock();
+ // Insert the new branch.
+ BranchInst::Create(TheOnlyDest, IBI);
+
+ for (unsigned i = 0, e = IBI->getNumDestinations(); i != e; ++i) {
+ if (IBI->getDestination(i) == TheOnlyDest)
+ TheOnlyDest = 0;
+ else
+ IBI->getDestination(i)->removePredecessor(IBI->getParent());
+ }
+ IBI->eraseFromParent();
+
+ // If we didn't find our destination in the IBI successor list, then we
+ // have undefined behavior. Replace the unconditional branch with an
+ // 'unreachable' instruction.
+ if (TheOnlyDest) {
+ BB->getTerminator()->eraseFromParent();
+ new UnreachableInst(BB->getContext(), BB);
+ }
+
+ return true;
+ }
}
+
return false;
}
//===----------------------------------------------------------------------===//
-// Local dead code elimination...
+// Local dead code elimination.
//
/// isInstructionTriviallyDead - Return true if the result produced by the
// We don't want debug info removed by anything this general.
if (isa<DbgInfoIntrinsic>(I)) return false;
+ // Likewise for memory use markers.
+ if (isa<MemoryUseIntrinsic>(I)) return false;
+
if (!I->mayHaveSideEffects()) return true;
// Special case intrinsics that "may have side effects" but can be deleted
/// RecursivelyDeleteTriviallyDeadInstructions - If the specified value is a
/// trivially dead instruction, delete it. If that makes any of its operands
-/// trivially dead, delete them too, recursively.
-void llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V) {
+/// trivially dead, delete them too, recursively. Return true if any
+/// instructions were deleted.
+bool llvm::RecursivelyDeleteTriviallyDeadInstructions(Value *V) {
Instruction *I = dyn_cast<Instruction>(V);
if (!I || !I->use_empty() || !isInstructionTriviallyDead(I))
- return;
+ return false;
SmallVector<Instruction*, 16> DeadInsts;
DeadInsts.push_back(I);
- while (!DeadInsts.empty()) {
+ do {
I = DeadInsts.pop_back_val();
// Null out all of the instruction's operands to see if any operand becomes
}
I->eraseFromParent();
- }
+ } while (!DeadInsts.empty());
+
+ return true;
}
/// RecursivelyDeleteDeadPHINode - If the specified value is an effectively
/// dead PHI node, due to being a def-use chain of single-use nodes that
/// either forms a cycle or is terminated by a trivially dead instruction,
/// delete it. If that makes any of its operands trivially dead, delete them
-/// too, recursively.
-void
+/// too, recursively. Return true if the PHI node is actually deleted.
+bool
llvm::RecursivelyDeleteDeadPHINode(PHINode *PN) {
// We can remove a PHI if it is on a cycle in the def-use graph
// where each node in the cycle has degree one, i.e. only one use,
// and is an instruction with no side effects.
if (!PN->hasOneUse())
- return;
+ return false;
+ bool Changed = false;
SmallPtrSet<PHINode *, 4> PHIs;
PHIs.insert(PN);
for (Instruction *J = cast<Instruction>(*PN->use_begin());
if (!PHIs.insert(cast<PHINode>(JP))) {
// Break the cycle and delete the PHI and its operands.
JP->replaceAllUsesWith(UndefValue::get(JP->getType()));
- RecursivelyDeleteTriviallyDeadInstructions(JP);
+ (void)RecursivelyDeleteTriviallyDeadInstructions(JP);
+ Changed = true;
break;
}
+ return Changed;
+}
+
+/// SimplifyInstructionsInBlock - Scan the specified basic block and try to
+/// simplify any instructions in it and recursively delete dead instructions.
+///
+/// This returns true if it changed the code, note that it can delete
+/// instructions in other blocks as well in this block.
+bool llvm::SimplifyInstructionsInBlock(BasicBlock *BB, const TargetData *TD) {
+ bool MadeChange = false;
+ for (BasicBlock::iterator BI = BB->begin(), E = BB->end(); BI != E; ) {
+ Instruction *Inst = BI++;
+
+ if (Value *V = SimplifyInstruction(Inst, TD)) {
+ WeakVH BIHandle(BI);
+ ReplaceAndSimplifyAllUses(Inst, V, TD);
+ MadeChange = true;
+ if (BIHandle != BI)
+ BI = BB->begin();
+ continue;
+ }
+
+ MadeChange |= RecursivelyDeleteTriviallyDeadInstructions(Inst);
+ }
+ return MadeChange;
}
//===----------------------------------------------------------------------===//
-// Control Flow Graph Restructuring...
+// Control Flow Graph Restructuring.
//
+
+/// RemovePredecessorAndSimplify - Like BasicBlock::removePredecessor, this
+/// method is called when we're about to delete Pred as a predecessor of BB. If
+/// BB contains any PHI nodes, this drops the entries in the PHI nodes for Pred.
+///
+/// Unlike the removePredecessor method, this attempts to simplify uses of PHI
+/// nodes that collapse into identity values. For example, if we have:
+/// x = phi(1, 0, 0, 0)
+/// y = and x, z
+///
+/// .. and delete the predecessor corresponding to the '1', this will attempt to
+/// recursively fold the and to 0.
+void llvm::RemovePredecessorAndSimplify(BasicBlock *BB, BasicBlock *Pred,
+ TargetData *TD) {
+ // This only adjusts blocks with PHI nodes.
+ if (!isa<PHINode>(BB->begin()))
+ return;
+
+ // Remove the entries for Pred from the PHI nodes in BB, but do not simplify
+ // them down. This will leave us with single entry phi nodes and other phis
+ // that can be removed.
+ BB->removePredecessor(Pred, true);
+
+ WeakVH PhiIt = &BB->front();
+ while (PHINode *PN = dyn_cast<PHINode>(PhiIt)) {
+ PhiIt = &*++BasicBlock::iterator(cast<Instruction>(PhiIt));
+
+ Value *PNV = PN->hasConstantValue();
+ if (PNV == 0) continue;
+
+ // If we're able to simplify the phi to a single value, substitute the new
+ // value into all of its uses.
+ assert(PNV != PN && "hasConstantValue broken");
+
+ Value *OldPhiIt = PhiIt;
+ ReplaceAndSimplifyAllUses(PN, PNV, TD);
+
+ // If recursive simplification ended up deleting the next PHI node we would
+ // iterate to, then our iterator is invalid, restart scanning from the top
+ // of the block.
+ if (PhiIt != OldPhiIt) PhiIt = &BB->front();
+ }
+}
+
+
/// MergeBasicBlockIntoOnlyPred - DestBB is a block with one predecessor and its
/// predecessor is known to have one successor (DestBB!). Eliminate the edge
/// between them, moving the instructions in the predecessor into DestBB and
// Splice all the instructions from PredBB to DestBB.
PredBB->getTerminator()->eraseFromParent();
DestBB->getInstList().splice(DestBB->begin(), PredBB->getInstList());
+
+ // Zap anything that took the address of DestBB. Not doing this will give the
+ // address an invalid value.
+ if (DestBB->hasAddressTaken()) {
+ BlockAddress *BA = BlockAddress::get(DestBB);
+ Constant *Replacement =
+ ConstantInt::get(llvm::Type::getInt32Ty(BA->getContext()), 1);
+ BA->replaceAllUsesWith(ConstantExpr::getIntToPtr(Replacement,
+ BA->getType()));
+ BA->destroyConstant();
+ }
// Anything that branched to PredBB now branches to DestBB.
PredBB->replaceAllUsesWith(DestBB);
PredBB->eraseFromParent();
}
-/// OnlyUsedByDbgIntrinsics - Return true if the instruction I is only used
-/// by DbgIntrinsics. If DbgInUses is specified then the vector is filled
-/// with the DbgInfoIntrinsic that use the instruction I.
-bool llvm::OnlyUsedByDbgInfoIntrinsics(Instruction *I,
- SmallVectorImpl<DbgInfoIntrinsic *> *DbgInUses) {
- if (DbgInUses)
- DbgInUses->clear();
-
- for (Value::use_iterator UI = I->use_begin(), UE = I->use_end(); UI != UE;
- ++UI) {
- if (DbgInfoIntrinsic *DI = dyn_cast<DbgInfoIntrinsic>(*UI)) {
- if (DbgInUses)
- DbgInUses->push_back(DI);
+/// 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(dbgs() << "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) {
+ BasicBlock *P = *PI;
+ if (BBPreds.count(P))
+ CommonPreds.insert(P);
+ }
+
+ // 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(dbgs() << "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(dbgs() << "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 is known to contain an
+/// unconditional branch, and contains no instructions other than PHI nodes,
+/// potential debug intrinsics and the branch. If possible, eliminate BB by
+/// rewriting all the predecessors to branch to the successor block and return
+/// true. If we can't transform, return false.
+bool llvm::TryToSimplifyUncondBranchFromEmptyBlock(BasicBlock *BB) {
+ // We can't eliminate infinite loops.
+ BasicBlock *Succ = cast<BranchInst>(BB->getTerminator())->getSuccessor(0);
+ if (BB == Succ) return false;
+
+ // 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(dbgs() << "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 {
- if (DbgInUses)
- DbgInUses->clear();
- return false;
+ // 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;
}
+/// EliminateDuplicatePHINodes - Check for and eliminate duplicate PHI
+/// nodes in this block. This doesn't try to be clever about PHI nodes
+/// which differ only in the order of the incoming values, but instcombine
+/// orders them so it usually won't matter.
+///
+bool llvm::EliminateDuplicatePHINodes(BasicBlock *BB) {
+ bool Changed = false;
+
+ // This implementation doesn't currently consider undef operands
+ // specially. Theroetically, two phis which are identical except for
+ // one having an undef where the other doesn't could be collapsed.
+
+ // Map from PHI hash values to PHI nodes. If multiple PHIs have
+ // the same hash value, the element is the first PHI in the
+ // linked list in CollisionMap.
+ DenseMap<uintptr_t, PHINode *> HashMap;
+
+ // Maintain linked lists of PHI nodes with common hash values.
+ DenseMap<PHINode *, PHINode *> CollisionMap;
+
+ // Examine each PHI.
+ for (BasicBlock::iterator I = BB->begin();
+ PHINode *PN = dyn_cast<PHINode>(I++); ) {
+ // Compute a hash value on the operands. Instcombine will likely have sorted
+ // them, which helps expose duplicates, but we have to check all the
+ // operands to be safe in case instcombine hasn't run.
+ uintptr_t Hash = 0;
+ for (User::op_iterator I = PN->op_begin(), E = PN->op_end(); I != E; ++I) {
+ // This hash algorithm is quite weak as hash functions go, but it seems
+ // to do a good enough job for this particular purpose, and is very quick.
+ Hash ^= reinterpret_cast<uintptr_t>(static_cast<Value *>(*I));
+ Hash = (Hash << 7) | (Hash >> (sizeof(uintptr_t) * CHAR_BIT - 7));
+ }
+ // If we've never seen this hash value before, it's a unique PHI.
+ std::pair<DenseMap<uintptr_t, PHINode *>::iterator, bool> Pair =
+ HashMap.insert(std::make_pair(Hash, PN));
+ if (Pair.second) continue;
+ // Otherwise it's either a duplicate or a hash collision.
+ for (PHINode *OtherPN = Pair.first->second; ; ) {
+ if (OtherPN->isIdenticalTo(PN)) {
+ // A duplicate. Replace this PHI with its duplicate.
+ PN->replaceAllUsesWith(OtherPN);
+ PN->eraseFromParent();
+ Changed = true;
+ break;
+ }
+ // A non-duplicate hash collision.
+ DenseMap<PHINode *, PHINode *>::iterator I = CollisionMap.find(OtherPN);
+ if (I == CollisionMap.end()) {
+ // Set this PHI to be the head of the linked list of colliding PHIs.
+ PHINode *Old = Pair.first->second;
+ Pair.first->second = PN;
+ CollisionMap[PN] = Old;
+ break;
+ }
+ // Procede to the next PHI in the list.
+ OtherPN = I->second;
+ }
+ }
+
+ return Changed;
+}
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