NewGVN: Fix PR 33119, PR 33129, due to regressed undef handling
Fix PR33120 and others by eliminating self-cycles a different way. llvm-svn: 303875
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@ -858,7 +858,14 @@ PHIExpression *NewGVN::createPHIExpression(Instruction *I, bool &HasBackedge,
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// Filter out unreachable phi operands.
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auto Filtered = make_filter_range(PHIOperands, [&](const Use *U) {
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return ReachableEdges.count({PN->getIncomingBlock(*U), PHIBlock});
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if (*U == PN)
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return false;
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if (!ReachableEdges.count({PN->getIncomingBlock(*U), PHIBlock}))
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return false;
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// Things in TOPClass are equivalent to everything.
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if (ValueToClass.lookup(*U) == TOPClass)
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return false;
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return true;
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});
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std::transform(Filtered.begin(), Filtered.end(), op_inserter(E),
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[&](const Use *U) -> Value * {
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@ -866,14 +873,6 @@ PHIExpression *NewGVN::createPHIExpression(Instruction *I, bool &HasBackedge,
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HasBackedge = HasBackedge || isBackedge(BB, PHIBlock);
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OriginalOpsConstant =
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OriginalOpsConstant && isa<Constant>(*U);
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// Use nullptr to distinguish between things that were
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// originally self-defined and those that have an operand
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// leader that is self-defined.
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if (*U == PN)
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return nullptr;
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// Things in TOPClass are equivalent to everything.
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if (ValueToClass.lookup(*U) == TOPClass)
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return nullptr;
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return lookupOperandLeader(*U);
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});
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return E;
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@ -1585,6 +1584,30 @@ bool NewGVN::isCycleFree(const Instruction *I) const {
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// Evaluate PHI nodes symbolically, and create an expression result.
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const Expression *NewGVN::performSymbolicPHIEvaluation(Instruction *I) const {
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// Resolve irreducible and reducible phi cycles.
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// FIXME: This is hopefully a temporary solution while we resolve the issues
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// with fixpointing self-cycles. It currently should be "guaranteed" to be
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// correct, but non-optimal. The SCCFinder does not, for example, take
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// reachability of arguments into account, etc.
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SCCFinder.Start(I);
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bool CanOptimize = true;
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SmallPtrSet<Value *, 8> OuterOps;
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auto &Component = SCCFinder.getComponentFor(I);
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for (auto *Member : Component) {
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if (!isa<PHINode>(Member)) {
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CanOptimize = false;
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break;
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}
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for (auto &PHIOp : cast<PHINode>(Member)->operands())
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if (!isa<PHINode>(PHIOp) || !Component.count(cast<PHINode>(PHIOp)))
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OuterOps.insert(PHIOp);
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}
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if (CanOptimize && OuterOps.size() == 1) {
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DEBUG(dbgs() << "Resolving cyclic phi to value " << *(*OuterOps.begin())
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<< "\n");
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return createVariableOrConstant(*OuterOps.begin());
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}
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// True if one of the incoming phi edges is a backedge.
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bool HasBackedge = false;
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// All constant tracks the state of whether all the *original* phi operands
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@ -1598,17 +1621,7 @@ const Expression *NewGVN::performSymbolicPHIEvaluation(Instruction *I) const {
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// See if all arguments are the same.
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// We track if any were undef because they need special handling.
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bool HasUndef = false;
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bool CycleFree = isCycleFree(I);
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auto Filtered = make_filter_range(E->operands(), [&](Value *Arg) {
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if (Arg == nullptr)
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return false;
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// Original self-operands are already eliminated during expression creation.
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// We can only eliminate value-wise self-operands if it's cycle
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// free. Otherwise, eliminating the operand can cause our value to change,
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// which can cause us to not eliminate the operand, which changes the value
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// back to what it was before, cycling forever.
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if (CycleFree && Arg == I)
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return false;
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if (isa<UndefValue>(Arg)) {
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HasUndef = true;
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return false;
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@ -1617,6 +1630,14 @@ const Expression *NewGVN::performSymbolicPHIEvaluation(Instruction *I) const {
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});
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// If we are left with no operands, it's dead.
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if (Filtered.begin() == Filtered.end()) {
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// If it has undef at this point, it means there are no-non-undef arguments,
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// and thus, the value of the phi node must be undef.
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if (HasUndef) {
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DEBUG(dbgs() << "PHI Node " << *I
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<< " has no non-undef arguments, valuing it as undef\n");
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return createConstantExpression(UndefValue::get(I->getType()));
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}
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DEBUG(dbgs() << "No arguments of PHI node " << *I << " are live\n");
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deleteExpression(E);
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return createDeadExpression();
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@ -1646,7 +1667,7 @@ const Expression *NewGVN::performSymbolicPHIEvaluation(Instruction *I) const {
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// constants, or all operands are ignored but the undef, it also must be
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// cycle free.
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if (!AllConstant && HasBackedge && NumOps > 0 &&
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!isa<UndefValue>(AllSameValue) && !CycleFree)
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!isa<UndefValue>(AllSameValue) && !isCycleFree(I))
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return E;
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// Only have to check for instructions
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@ -3560,6 +3581,7 @@ bool NewGVN::eliminateInstructions(Function &F) {
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// Map to store the use counts
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DenseMap<const Value *, unsigned int> UseCounts;
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for (auto *CC : reverse(CongruenceClasses)) {
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DEBUG(dbgs() << "Eliminating in congruence class " << CC->getID() << "\n");
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// Track the equivalent store info so we can decide whether to try
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// dead store elimination.
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SmallVector<ValueDFS, 8> PossibleDeadStores;
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@ -3606,8 +3628,6 @@ bool NewGVN::eliminateInstructions(Function &F) {
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}
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CC->swap(MembersLeft);
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} else {
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DEBUG(dbgs() << "Eliminating in congruence class " << CC->getID()
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<< "\n");
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// If this is a singleton, we can skip it.
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if (CC->size() != 1 || RealToTemp.lookup(Leader)) {
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// This is a stack because equality replacement/etc may place
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@ -17,7 +17,8 @@ define void @reorder_ref_pic_list() local_unnamed_addr {
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; CHECK-NEXT: [[INC_I:%.*]] = add nsw i32 [[REFIDXLX_0]], 1
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; CHECK-NEXT: br label [[FOR_BODY8_I:%.*]]
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; CHECK: for.body8.i:
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; CHECK-NEXT: br i1 undef, label [[FOR_INC24_I:%.*]], label [[IF_THEN17_I:%.*]]
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; CHECK-NEXT: [[NIDX_052_I:%.*]] = phi i32 [ [[INC_I]], [[IF_THEN13]] ], [ [[NIDX_052_I]], [[FOR_INC24_I:%.*]] ]
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; CHECK-NEXT: br i1 undef, label [[FOR_INC24_I]], label [[IF_THEN17_I:%.*]]
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; CHECK: if.then17.i:
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; CHECK-NEXT: br label [[FOR_INC24_I]]
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; CHECK: for.inc24.i:
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