llvm-project/llvm/tools/llvm-reduce/deltas/ReduceDistinctMetadata.cpp

//===- ReduceDistinctMetadata.cpp - Specialized Delta Pass ----------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//
//
// This file implements two functions used by the Generic Delta Debugging
// Algorithm, which are used to reduce unnamed distinct metadata nodes.
//
//===----------------------------------------------------------------------===//

#include "ReduceDistinctMetadata.h"
#include "llvm/ADT/SetVector.h"
#include "llvm/ADT/SmallVector.h"
#include <queue>

using namespace llvm;

// Traverse the graph breadth-first and try to remove unnamed metadata nodes
static void
reduceNodes(MDNode *Root,
            SetVector<std::pair<unsigned int, MDNode *>> &NodesToDelete,
            MDNode *TemporaryNode, Oracle &O, Module &Program) {
  std::queue<MDNode *> NodesToTraverse{};
  // Keep track of visited nodes not to get into loops
  SetVector<MDNode *> VisitedNodes{};
  NodesToTraverse.push(Root);

  while (!NodesToTraverse.empty()) {
    MDNode *CurrentNode = NodesToTraverse.front();
    NodesToTraverse.pop();

    // Mark the nodes for removal
    for (unsigned int I = 0; I < CurrentNode->getNumOperands(); ++I) {
      if (MDNode *Operand =
              dyn_cast_or_null<MDNode>(CurrentNode->getOperand(I).get())) {
        // Check whether node has been visited
        if (VisitedNodes.insert(Operand))
          NodesToTraverse.push(Operand);
        // Delete the node only if it is distinct
        if (Operand->isDistinct()) {
          // Add to removal list
          NodesToDelete.insert(std::make_pair(I, CurrentNode));
        }
      }
    }

    // Remove the nodes
    for (auto [PositionToReplace, Node] : NodesToDelete) {
      if (!O.shouldKeep())
        Node->replaceOperandWith(PositionToReplace, TemporaryNode);
    }
    NodesToDelete.clear();
  }
}

// After reducing metadata, we need to remove references to the temporary node,
// this is also done with BFS
static void cleanUpTemporaries(NamedMDNode &NamedNode, MDTuple *TemporaryTuple,
                               Module &Program) {
  std::queue<MDTuple *> NodesToTraverse{};
  SetVector<MDTuple *> VisitedNodes{};

  // Push all first level operands of the named node to the queue
  for (auto I = NamedNode.op_begin(); I != NamedNode.op_end(); ++I) {
    // If the node hasn't been traversed yet, add it to the queue of nodes to
    // traverse.
    if (MDTuple *TupleI = dyn_cast_or_null<MDTuple>((*I))) {
      if (VisitedNodes.insert(TupleI))
        NodesToTraverse.push(TupleI);
    }
  }

  while (!NodesToTraverse.empty()) {
    MDTuple *CurrentTuple = NodesToTraverse.front();
    NodesToTraverse.pop();

    // Shift all of the interesting elements to the left, pop remaining
    // afterwards
    if (CurrentTuple->isDistinct()) {
      // Do resizing and cleaning operations only if the node is distinct,
      // as resizing is not supported for unique nodes and is redundant.
      unsigned int NotToRemove = 0;
      for (unsigned int I = 0; I < CurrentTuple->getNumOperands(); ++I) {
        Metadata *Operand = CurrentTuple->getOperand(I).get();
        // If current operand is not the temporary node, move it to the front
        // and increase notToRemove so that it will be saved
        if (Operand != TemporaryTuple) {
          Metadata *TemporaryMetadata =
              CurrentTuple->getOperand(NotToRemove).get();
          CurrentTuple->replaceOperandWith(NotToRemove, Operand);
          CurrentTuple->replaceOperandWith(I, TemporaryMetadata);
          ++NotToRemove;
        }
      }

      // Remove all the uninteresting elements
      unsigned int OriginalOperands = CurrentTuple->getNumOperands();
      for (unsigned int I = 0; I < OriginalOperands - NotToRemove; ++I)
        CurrentTuple->pop_back();
    }

    // Push the remaining nodes into the queue
    for (unsigned int I = 0; I < CurrentTuple->getNumOperands(); ++I) {
      MDTuple *Operand =
          dyn_cast_or_null<MDTuple>(CurrentTuple->getOperand(I).get());
      if (Operand && VisitedNodes.insert(Operand))
        // If the node hasn't been traversed yet, add it to the queue of nodes
        // to traverse.
        NodesToTraverse.push(Operand);
    }
  }
}

void llvm::reduceDistinctMetadataDeltaPass(Oracle &O,
                                           ReducerWorkItem &WorkItem) {
  Module &Program = WorkItem.getModule();
  MDTuple *TemporaryTuple =
      MDTuple::getDistinct(Program.getContext(), SmallVector<Metadata *, 1>{});
  SetVector<std::pair<unsigned int, MDNode *>> NodesToDelete{};
  for (NamedMDNode &NamedNode :
       Program.named_metadata()) { // Iterate over the named nodes
    for (unsigned int I = 0; I < NamedNode.getNumOperands();
         ++I) { // Iterate over first level unnamed nodes..
      if (MDTuple *Operand = dyn_cast_or_null<MDTuple>(NamedNode.getOperand(I)))
        reduceNodes(Operand, NodesToDelete, TemporaryTuple, O, Program);
    }
  }
  for (NamedMDNode &NamedNode : Program.named_metadata())
    cleanUpTemporaries(NamedNode, TemporaryTuple, Program);
}