nullability/inference/merge.h

// Part of the Crubit project, under the Apache License v2.0 with LLVM
// Exceptions. See /LICENSE for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception

// Combines evidence of the nullability of a slot into inference conclusions.
//
// This evidence was gathered from local analysis across the codebase in a
// "map" phase, merging this evidence is conceptually the "reduce" phase.
//
// To allow this to be distributed efficiently for commonly-used slots,
// merging is performed incrementally by repeatedly combining partial results.

#ifndef CRUBIT_NULLABILITY_INFERENCE_MERGE_H_
#define CRUBIT_NULLABILITY_INFERENCE_MERGE_H_

#include "nullability/inference/inference.proto.h"
#include "llvm/ADT/ArrayRef.h"

namespace clang::tidy::nullability {

// Build a SlotPartial representing a single piece of evidence.
SlotPartial partialFromEvidence(const Evidence &);
// Update LHS to include the evidence from RHS.
// The merging of partials is commutative and associative.
void mergePartials(SlotPartial &LHS, const SlotPartial &RHS);
// Form a nullability conclusion from a set of evidence.
SlotInference finalize(const SlotPartial &, bool EnableSoftRules = true);

struct InferResult {
  Nullability Nullability;
  bool Conflict = false;
  bool Trivial = false;
};
// Final inference decision, based on event counts.
//
// If EnableSoftRules is true, this will use heuristics to infer nullability
// when the event counts do not strictly require a particular nullability for
// safety.
//
// TODO: once this interface sticks, move to a dedicated file.
InferResult infer(llvm::ArrayRef<unsigned> EventCounts,
                  bool EnableSoftRules = true);

// Combines local evidence about a slot's nullability to form a global
// conclusion. All evidence must for be the same slot, and there must be some.
//
// This signature fundamentally limits the scalability of merging: we must see
// all the evidence for a slot at once.
inline SlotInference mergeEvidence(llvm::ArrayRef<Evidence> Ev) {
  SlotPartial P = partialFromEvidence(Ev.front());
  for (const auto &E : Ev.drop_front())
    mergePartials(P, partialFromEvidence(E));
  return finalize(P);
}

}  // namespace clang::tidy::nullability

#endif