LoopAnnotationImporter.cpp

Go to the documentation of this file.

//===- LoopAnnotationImporter.cpp - Loop annotation import ----------------===//
//
// 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
//
//===----------------------------------------------------------------------===//
 
#include "LoopAnnotationImporter.h"
#include "llvm/ADT/ScopeExit.h"
#include "llvm/ADT/SmallPtrSet.h"
#include "llvm/IR/Constants.h"
 
using namespace mlir;
using namespace mlir::LLVM;
using namespace mlir::LLVM::detail;
 
namespace {
/// Helper class that keeps the state of one metadata to attribute conversion.
struct LoopMetadataConversion {
  /// Converts a loop ID, owning the recursion state for its follow-ups.
  static LoopAnnotationAttr convert(const llvm::MDNode *node, Location loc,
                                    LoopAnnotationImporter &importer);
 
private:
  LoopMetadataConversion(
      const llvm::MDNode *node, Location loc, DistinctAttr id,
      LoopAnnotationImporter &loopAnnotationImporter,
      llvm::SmallPtrSetImpl<const llvm::MDNode *> &activeNodes)
      : node(node), loc(loc), id(id),
        loopAnnotationImporter(loopAnnotationImporter), ctx(loc->getContext()),
        activeNodes(activeNodes) {}
 
  /// Converts a follow-up using the current recursion state.
  LoopAnnotationAttr convertFollowup(const llvm::MDNode *followup);
 
  /// Converts the properties after the validated loop ID or follow-up header.
  LoopAnnotationAttr convertProperties();
 
  /// Initializes the shared state for the conversion member functions.
  LogicalResult initConversionState();
 
  /// Helper function to get and erase a property.
  const llvm::MDNode *lookupAndEraseProperty(StringRef name);
 
  /// Helper functions to lookup and convert MDNodes into a specifc attribute
  /// kind. These functions return null-attributes if there is no node with the
  /// specified name, or failure, if the node is ill-formatted.
  FailureOr<BoolAttr> lookupUnitNode(StringRef name);
  FailureOr<BoolAttr> lookupBoolNode(StringRef name, bool negated = false);
  FailureOr<BoolAttr> lookupIntNodeAsBoolAttr(StringRef name);
  FailureOr<IntegerAttr> lookupIntNode(StringRef name);
  FailureOr<uint32_t> lookupUInt32Node(StringRef name);
  FailureOr<SmallVector<llvm::MDNode *>> lookupMDNodes(StringRef name);
  FailureOr<LoopAnnotationAttr> lookupFollowupNode(StringRef name);
  FailureOr<BoolAttr> lookupBooleanUnitNode(StringRef enableName,
                                            StringRef disableName,
                                            bool negated = false);
 
  /// Conversion functions for sub-attributes.
  FailureOr<LoopVectorizeAttr> convertVectorizeAttr();
  FailureOr<LoopInterleaveAttr> convertInterleaveAttr();
  FailureOr<LoopUnrollAttr> convertUnrollAttr();
  FailureOr<LoopUnrollAndJamAttr> convertUnrollAndJamAttr();
  FailureOr<LoopLICMAttr> convertLICMAttr();
  FailureOr<LoopDistributeAttr> convertDistributeAttr();
  FailureOr<LoopPipelineAttr> convertPipelineAttr();
  FailureOr<LoopPeeledAttr> convertPeeledAttr();
  FailureOr<LoopUnswitchAttr> convertUnswitchAttr();
  FailureOr<SmallVector<AccessGroupAttr>> convertParallelAccesses();
  FusedLoc convertStartLoc();
  FailureOr<FusedLoc> convertEndLoc();
 
  llvm::SmallVector<llvm::DILocation *, 2> locations;
  llvm::StringMap<const llvm::MDNode *> propertyMap;
  const llvm::MDNode *node;
  Location loc;
  DistinctAttr id;
  LoopAnnotationImporter &loopAnnotationImporter;
  MLIRContext *ctx;
  llvm::SmallPtrSetImpl<const llvm::MDNode *> &activeNodes;
};
} // namespace
 
LogicalResult LoopMetadataConversion::initConversionState() {
  for (const llvm::MDOperand &operand : llvm::drop_begin(node->operands())) {
    if (auto *diLoc = dyn_cast<llvm::DILocation>(operand)) {
      locations.push_back(diLoc);
      continue;
    }
 
    auto *property = dyn_cast<llvm::MDNode>(operand);
    if (!property)
      return emitWarning(loc) << "expected all loop properties to be either "
                                 "debug locations or metadata nodes";
 
    if (property->getNumOperands() == 0)
      return emitWarning(loc) << "cannot import empty loop property";
 
    auto *nameNode = dyn_cast<llvm::MDString>(property->getOperand(0));
    if (!nameNode)
      return emitWarning(loc) << "cannot import loop property without a name";
    StringRef name = nameNode->getString();
 
    bool succ = propertyMap.try_emplace(name, property).second;
    if (!succ)
      return emitWarning(loc)
             << "cannot import loop properties with duplicated names " << name;
  }
 
  return success();
}
 
const llvm::MDNode *
LoopMetadataConversion::lookupAndEraseProperty(StringRef name) {
  auto it = propertyMap.find(name);
  if (it == propertyMap.end())
    return nullptr;
  const llvm::MDNode *property = it->getValue();
  propertyMap.erase(it);
  return property;
}
 
FailureOr<BoolAttr> LoopMetadataConversion::lookupUnitNode(StringRef name) {
  const llvm::MDNode *property = lookupAndEraseProperty(name);
  if (!property)
    return BoolAttr(nullptr);
 
  if (property->getNumOperands() != 1)
    return emitWarning(loc)
           << "expected metadata node " << name << " to hold no value";
 
  return BoolAttr::get(ctx, true);
}
 
FailureOr<BoolAttr> LoopMetadataConversion::lookupBooleanUnitNode(
    StringRef enableName, StringRef disableName, bool negated) {
  auto enable = lookupUnitNode(enableName);
  auto disable = lookupUnitNode(disableName);
  if (failed(enable) || failed(disable))
    return failure();
 
  if (*enable && *disable)
    return emitWarning(loc)
           << "expected metadata nodes " << enableName << " and " << disableName
           << " to be mutually exclusive.";
 
  if (*enable)
    return BoolAttr::get(ctx, !negated);
 
  if (*disable)
    return BoolAttr::get(ctx, negated);
  return BoolAttr(nullptr);
}
 
FailureOr<BoolAttr> LoopMetadataConversion::lookupBoolNode(StringRef name,
                                                           bool negated) {
  const llvm::MDNode *property = lookupAndEraseProperty(name);
  if (!property)
    return BoolAttr(nullptr);
 
  auto emitNodeWarning = [&]() {
    return emitWarning(loc)
           << "expected metadata node " << name << " to hold a boolean value";
  };
 
  if (property->getNumOperands() != 2)
    return emitNodeWarning();
  llvm::ConstantInt *val =
      llvm::mdconst::dyn_extract<llvm::ConstantInt>(property->getOperand(1));
  if (!val || val->getBitWidth() != 1)
    return emitNodeWarning();
 
  return BoolAttr::get(ctx, val->getValue().getLimitedValue(1) ^ negated);
}
 
FailureOr<BoolAttr>
LoopMetadataConversion::lookupIntNodeAsBoolAttr(StringRef name) {
  const llvm::MDNode *property = lookupAndEraseProperty(name);
  if (!property)
    return BoolAttr(nullptr);
 
  auto emitNodeWarning = [&]() {
    return emitWarning(loc)
           << "expected metadata node " << name << " to hold an integer value";
  };
 
  if (property->getNumOperands() != 2)
    return emitNodeWarning();
  llvm::ConstantInt *val =
      llvm::mdconst::dyn_extract<llvm::ConstantInt>(property->getOperand(1));
  if (!val || val->getBitWidth() != 32)
    return emitNodeWarning();
 
  return BoolAttr::get(ctx, val->getValue().getLimitedValue(1));
}
 
/// Like lookupIntNode, but yields the value itself, with 0 for a missing node.
FailureOr<uint32_t> LoopMetadataConversion::lookupUInt32Node(StringRef name) {
  FailureOr<IntegerAttr> attr = lookupIntNode(name);
  if (failed(attr))
    return failure();
  return *attr ? uint32_t(attr->getValue().getZExtValue()) : uint32_t(0);
}
 
FailureOr<IntegerAttr> LoopMetadataConversion::lookupIntNode(StringRef name) {
  const llvm::MDNode *property = lookupAndEraseProperty(name);
  if (!property)
    return IntegerAttr(nullptr);
 
  auto emitNodeWarning = [&]() {
    return emitWarning(loc)
           << "expected metadata node " << name << " to hold an i32 value";
  };
 
  if (property->getNumOperands() != 2)
    return emitNodeWarning();
 
  llvm::ConstantInt *val =
      llvm::mdconst::dyn_extract<llvm::ConstantInt>(property->getOperand(1));
  if (!val || val->getBitWidth() != 32)
    return emitNodeWarning();
 
  return IntegerAttr::get(IntegerType::get(ctx, 32),
                          val->getValue().getLimitedValue());
}
 
FailureOr<SmallVector<llvm::MDNode *>>
LoopMetadataConversion::lookupMDNodes(StringRef name) {
  const llvm::MDNode *property = lookupAndEraseProperty(name);
  SmallVector<llvm::MDNode *> res;
  if (!property)
    return res;
 
  auto emitNodeWarning = [&]() {
    return emitWarning(loc) << "expected metadata node " << name
                            << " to hold one or multiple MDNodes";
  };
 
  if (property->getNumOperands() < 2)
    return emitNodeWarning();
 
  for (unsigned i = 1, e = property->getNumOperands(); i < e; ++i) {
    auto *node = dyn_cast<llvm::MDNode>(property->getOperand(i));
    if (!node)
      return emitNodeWarning();
    res.push_back(node);
  }
 
  return res;
}
 
FailureOr<LoopAnnotationAttr>
LoopMetadataConversion::lookupFollowupNode(StringRef name) {
  const llvm::MDNode *followup = lookupAndEraseProperty(name);
  if (!followup)
    return LoopAnnotationAttr(nullptr);
 
  LoopAnnotationAttr attr = convertFollowup(followup);
  if (!attr)
    return failure();
  return attr;
}
 
static bool isEmptyOrNull(const Attribute attr) { return !attr; }
 
static bool isEmptyOrNull(uint32_t value) { return !value; }
 
template <typename T>
static bool isEmptyOrNull(const SmallVectorImpl<T> &vec) {
  return vec.empty();
}
 
/// Helper function that returns true if any of the argument conversions failed
/// or if all of them are null or empty.
template <typename... P>
static bool anyFailedOrAllEmpty(const P &...args) {
  bool anyFailed = (failed(args) || ...);
  if (anyFailed)
    return true;
 
  return (isEmptyOrNull(*args) && ...);
}
 
/// Helper function that only creates and attribute of type T if all argument
/// conversion were successfull and at least one of them holds a non-null value.
template <typename T, typename... P>
static T createIfNonNull(MLIRContext *ctx, const P &...args) {
  if (anyFailedOrAllEmpty(args...))
    return {};
 
  return T::get(ctx, *args...);
}
 
FailureOr<LoopVectorizeAttr> LoopMetadataConversion::convertVectorizeAttr() {
  FailureOr<BoolAttr> enable = lookupBooleanUnitNode(
      "llvm.loop.vectorize.enable", "llvm.loop.vectorize.disable",
      /*negated=*/true);
  FailureOr<BoolAttr> predicateEnable =
      lookupBooleanUnitNode("llvm.loop.vectorize.predicate.enable",
                            "llvm.loop.vectorize.predicate.disable");
  FailureOr<BoolAttr> scalableEnable =
      lookupBooleanUnitNode("llvm.loop.vectorize.scalable.enable",
                            "llvm.loop.vectorize.scalable.disable");
  FailureOr<IntegerAttr> width = lookupIntNode("llvm.loop.vectorize.width");
  FailureOr<LoopAnnotationAttr> followupVec =
      lookupFollowupNode("llvm.loop.vectorize.followup_vectorized");
  FailureOr<LoopAnnotationAttr> followupEpi =
      lookupFollowupNode("llvm.loop.vectorize.followup_epilogue");
  FailureOr<LoopAnnotationAttr> followupAll =
      lookupFollowupNode("llvm.loop.vectorize.followup_all");
 
  return createIfNonNull<LoopVectorizeAttr>(ctx, enable, predicateEnable,
                                            scalableEnable, width, followupVec,
                                            followupEpi, followupAll);
}
 
FailureOr<LoopInterleaveAttr> LoopMetadataConversion::convertInterleaveAttr() {
  FailureOr<IntegerAttr> count = lookupIntNode("llvm.loop.interleave.count");
  return createIfNonNull<LoopInterleaveAttr>(ctx, count);
}
 
FailureOr<LoopUnrollAttr> LoopMetadataConversion::convertUnrollAttr() {
  FailureOr<BoolAttr> disable = lookupBooleanUnitNode(
      "llvm.loop.unroll.enable", "llvm.loop.unroll.disable", /*negated=*/true);
  FailureOr<IntegerAttr> count = lookupIntNode("llvm.loop.unroll.count");
  FailureOr<BoolAttr> runtimeDisable =
      lookupUnitNode("llvm.loop.unroll.runtime.disable");
  FailureOr<BoolAttr> full = lookupUnitNode("llvm.loop.unroll.full");
  FailureOr<LoopAnnotationAttr> followupUnrolled =
      lookupFollowupNode("llvm.loop.unroll.followup_unrolled");
  FailureOr<LoopAnnotationAttr> followupRemainder =
      lookupFollowupNode("llvm.loop.unroll.followup_remainder");
  FailureOr<LoopAnnotationAttr> followupAll =
      lookupFollowupNode("llvm.loop.unroll.followup_all");
 
  return createIfNonNull<LoopUnrollAttr>(ctx, disable, count, runtimeDisable,
                                         full, followupUnrolled,
                                         followupRemainder, followupAll);
}
 
FailureOr<LoopUnrollAndJamAttr>
LoopMetadataConversion::convertUnrollAndJamAttr() {
  FailureOr<BoolAttr> disable = lookupBooleanUnitNode(
      "llvm.loop.unroll_and_jam.enable", "llvm.loop.unroll_and_jam.disable",
      /*negated=*/true);
  FailureOr<IntegerAttr> count =
      lookupIntNode("llvm.loop.unroll_and_jam.count");
  FailureOr<LoopAnnotationAttr> followupOuter =
      lookupFollowupNode("llvm.loop.unroll_and_jam.followup_outer");
  FailureOr<LoopAnnotationAttr> followupInner =
      lookupFollowupNode("llvm.loop.unroll_and_jam.followup_inner");
  FailureOr<LoopAnnotationAttr> followupRemainderOuter =
      lookupFollowupNode("llvm.loop.unroll_and_jam.followup_remainder_outer");
  FailureOr<LoopAnnotationAttr> followupRemainderInner =
      lookupFollowupNode("llvm.loop.unroll_and_jam.followup_remainder_inner");
  FailureOr<LoopAnnotationAttr> followupAll =
      lookupFollowupNode("llvm.loop.unroll_and_jam.followup_all");
  return createIfNonNull<LoopUnrollAndJamAttr>(
      ctx, disable, count, followupOuter, followupInner, followupRemainderOuter,
      followupRemainderInner, followupAll);
}
 
FailureOr<LoopLICMAttr> LoopMetadataConversion::convertLICMAttr() {
  FailureOr<BoolAttr> disable = lookupUnitNode("llvm.licm.disable");
  FailureOr<BoolAttr> versioningDisable =
      lookupUnitNode("llvm.loop.licm_versioning.disable");
  return createIfNonNull<LoopLICMAttr>(ctx, disable, versioningDisable);
}
 
FailureOr<LoopDistributeAttr> LoopMetadataConversion::convertDistributeAttr() {
  FailureOr<BoolAttr> disable = lookupBooleanUnitNode(
      "llvm.loop.distribute.enable", "llvm.loop.distribute.disable",
      /*negated=*/true);
  FailureOr<LoopAnnotationAttr> followupCoincident =
      lookupFollowupNode("llvm.loop.distribute.followup_coincident");
  FailureOr<LoopAnnotationAttr> followupSequential =
      lookupFollowupNode("llvm.loop.distribute.followup_sequential");
  FailureOr<LoopAnnotationAttr> followupFallback =
      lookupFollowupNode("llvm.loop.distribute.followup_fallback");
  FailureOr<LoopAnnotationAttr> followupAll =
      lookupFollowupNode("llvm.loop.distribute.followup_all");
  return createIfNonNull<LoopDistributeAttr>(ctx, disable, followupCoincident,
                                             followupSequential,
                                             followupFallback, followupAll);
}
 
FailureOr<LoopPipelineAttr> LoopMetadataConversion::convertPipelineAttr() {
  FailureOr<BoolAttr> disable = lookupBoolNode("llvm.loop.pipeline.disable");
  FailureOr<IntegerAttr> initiationinterval =
      lookupIntNode("llvm.loop.pipeline.initiationinterval");
  return createIfNonNull<LoopPipelineAttr>(ctx, disable, initiationinterval);
}
 
FailureOr<LoopPeeledAttr> LoopMetadataConversion::convertPeeledAttr() {
  FailureOr<IntegerAttr> count = lookupIntNode("llvm.loop.peeled.count");
  return createIfNonNull<LoopPeeledAttr>(ctx, count);
}
 
FailureOr<LoopUnswitchAttr> LoopMetadataConversion::convertUnswitchAttr() {
  FailureOr<BoolAttr> partialDisable =
      lookupUnitNode("llvm.loop.unswitch.partial.disable");
  return createIfNonNull<LoopUnswitchAttr>(ctx, partialDisable);
}
 
FailureOr<SmallVector<AccessGroupAttr>>
LoopMetadataConversion::convertParallelAccesses() {
  FailureOr<SmallVector<llvm::MDNode *>> nodes =
      lookupMDNodes("llvm.loop.parallel_accesses");
  if (failed(nodes))
    return failure();
  SmallVector<AccessGroupAttr> refs;
  for (llvm::MDNode *node : *nodes) {
    FailureOr<SmallVector<AccessGroupAttr>> accessGroups =
        loopAnnotationImporter.lookupAccessGroupAttrs(node);
    if (failed(accessGroups)) {
      emitWarning(loc) << "could not lookup access group";
      continue;
    }
    llvm::append_range(refs, *accessGroups);
  }
  return refs;
}
 
FusedLoc LoopMetadataConversion::convertStartLoc() {
  if (locations.empty())
    return {};
  return dyn_cast<FusedLoc>(
      loopAnnotationImporter.moduleImport.translateLoc(locations[0]));
}
 
FailureOr<FusedLoc> LoopMetadataConversion::convertEndLoc() {
  if (locations.size() < 2)
    return FusedLoc();
  if (locations.size() > 2)
    return emitError(loc)
           << "expected loop metadata to have at most two DILocations";
  return dyn_cast<FusedLoc>(
      loopAnnotationImporter.moduleImport.translateLoc(locations[1]));
}
 
LoopAnnotationAttr
LoopMetadataConversion::convert(const llvm::MDNode *node, Location loc,
                                LoopAnnotationImporter &importer) {
  if (node->getNumOperands() == 0 ||
      dyn_cast<llvm::MDNode>(node->getOperand(0)) != node) {
    emitWarning(loc) << "invalid loop node";
    return {};
  }
 
  llvm::SmallPtrSet<const llvm::MDNode *, 4> activeNodes;
  DistinctAttr id = DistinctAttr::create(UnitAttr::get(loc->getContext()));
  return LoopMetadataConversion(node, loc, id, importer, activeNodes)
      .convertProperties();
}
 
LoopAnnotationAttr
LoopMetadataConversion::convertFollowup(const llvm::MDNode *followup) {
  if (followup->getNumOperands() == 0 ||
      !isa<llvm::MDString>(followup->getOperand(0))) {
    emitWarning(loc) << "invalid loop followup node";
    return {};
  }
 
  // An explicit empty follow-up is different from an absent follow-up.
  if (followup->getNumOperands() == 1)
    return LoopAnnotationAttr::get(ctx, {}, {}, {}, {}, {}, {}, {}, {}, {}, {},
                                   {}, {}, {}, {}, {}, {}, {});
 
  return LoopMetadataConversion(followup, loc, /*id=*/{},
                                loopAnnotationImporter, activeNodes)
      .convertProperties();
}
 
LoopAnnotationAttr LoopMetadataConversion::convertProperties() {
  if (!activeNodes.insert(node).second) {
    emitWarning(loc) << "cannot import cyclic loop annotation";
    return {};
  }
  llvm::scope_exit guard([&] { activeNodes.erase(node); });
 
  if (failed(initConversionState()))
    return {};
 
  FailureOr<BoolAttr> disableNonForced =
      lookupUnitNode("llvm.loop.disable_nonforced");
  FailureOr<LoopVectorizeAttr> vecAttr = convertVectorizeAttr();
  FailureOr<LoopInterleaveAttr> interleaveAttr = convertInterleaveAttr();
  FailureOr<LoopUnrollAttr> unrollAttr = convertUnrollAttr();
  FailureOr<LoopUnrollAndJamAttr> unrollAndJamAttr = convertUnrollAndJamAttr();
  FailureOr<LoopLICMAttr> licmAttr = convertLICMAttr();
  FailureOr<LoopDistributeAttr> distributeAttr = convertDistributeAttr();
  FailureOr<LoopPipelineAttr> pipelineAttr = convertPipelineAttr();
  FailureOr<LoopPeeledAttr> peeledAttr = convertPeeledAttr();
  FailureOr<LoopUnswitchAttr> unswitchAttr = convertUnswitchAttr();
  FailureOr<BoolAttr> mustProgress = lookupUnitNode("llvm.loop.mustprogress");
  FailureOr<BoolAttr> isVectorized =
      lookupIntNodeAsBoolAttr("llvm.loop.isvectorized");
  FailureOr<uint32_t> align = lookupUInt32Node("llvm.loop.align");
  FailureOr<SmallVector<AccessGroupAttr>> parallelAccesses =
      convertParallelAccesses();
 
  // Drop the metadata if there are parts that cannot be imported.
  if (!propertyMap.empty()) {
    for (auto name : propertyMap.keys())
      emitWarning(loc) << "unknown loop annotation " << name;
    return {};
  }
 
  FailureOr<FusedLoc> startLoc = convertStartLoc();
  FailureOr<FusedLoc> endLoc = convertEndLoc();
 
  // LoopID doesn't participate in 'failure', so check everything except it.
  if (anyFailedOrAllEmpty(disableNonForced, vecAttr, interleaveAttr, unrollAttr,
                          unrollAndJamAttr, licmAttr, distributeAttr,
                          pipelineAttr, peeledAttr, unswitchAttr, mustProgress,
                          isVectorized, align, startLoc, endLoc,
                          parallelAccesses))
    return {};
 
  return LoopAnnotationAttr::get(
      ctx, id, *disableNonForced, *vecAttr, *interleaveAttr, *unrollAttr,
      *unrollAndJamAttr, *licmAttr, *distributeAttr, *pipelineAttr, *peeledAttr,
      *unswitchAttr, *mustProgress, *isVectorized, *align, *startLoc, *endLoc,
      *parallelAccesses);
}
 
LoopAnnotationAttr
LoopAnnotationImporter::translateLoopAnnotation(const llvm::MDNode *node,
                                                Location loc) {
  if (!node)
    return {};
 
  // Note: This check is necessary to distinguish between failed translations
  // and not yet attempted translations.
  auto it = loopMetadataMapping.find(node);
  if (it != loopMetadataMapping.end())
    return it->getSecond();
 
  LoopAnnotationAttr attr = LoopMetadataConversion::convert(node, loc, *this);
 
  mapLoopMetadata(node, attr);
  return attr;
}
 
LogicalResult
LoopAnnotationImporter::translateAccessGroup(const llvm::MDNode *node,
                                             Location loc) {
  SmallVector<const llvm::MDNode *> accessGroups;
  if (!node->getNumOperands())
    accessGroups.push_back(node);
  for (const llvm::MDOperand &operand : node->operands()) {
    auto *childNode = dyn_cast<llvm::MDNode>(operand);
    if (!childNode)
      return failure();
    accessGroups.push_back(cast<llvm::MDNode>(operand.get()));
  }
 
  // Convert all entries of the access group list to access group operations.
  for (const llvm::MDNode *accessGroup : accessGroups) {
    if (accessGroupMapping.count(accessGroup))
      continue;
    // Verify the access group node is distinct and empty.
    if (accessGroup->getNumOperands() != 0 || !accessGroup->isDistinct())
      return emitWarning(loc)
             << "expected an access group node to be empty and distinct";
 
    // Add a mapping from the access group node to the newly created attribute.
    accessGroupMapping[accessGroup] = builder.getAttr<AccessGroupAttr>();
  }
  return success();
}
 
FailureOr<SmallVector<AccessGroupAttr>>
LoopAnnotationImporter::lookupAccessGroupAttrs(const llvm::MDNode *node) const {
  // An access group node is either a single access group or an access group
  // list.
  SmallVector<AccessGroupAttr> accessGroups;
  if (!node->getNumOperands())
    accessGroups.push_back(accessGroupMapping.lookup(node));
  for (const llvm::MDOperand &operand : node->operands()) {
    auto *node = cast<llvm::MDNode>(operand.get());
    accessGroups.push_back(accessGroupMapping.lookup(node));
  }
  // Exit if one of the access group node lookups failed.
  if (llvm::is_contained(accessGroups, nullptr))
    return failure();
  return accessGroups;
}