[llvm] [Coverage] Rework Decision/Expansion/Branch (PR #78969)

[Fangrui Song via llvm-commits]

================
@@ -582,6 +583,177 @@ static unsigned getMaxBitmapSize(const CounterMappingContext &Ctx,
   return MaxBitmapID + (SizeInBits / CHAR_BIT);
 }
 
+namespace {
+
+/// Collect Decisions, Branchs, and Expansions and associate them.
+class MCDCDecisionRecorder {
+
+private:
+  /// This holds the DecisionRegion and MCDCBranches under it.
+  /// Also traverses Expansion(s).
+  /// The Decision has the number of MCDCBranches and will complete
+  /// when it is filled with unique ConditionID of MCDCBranches.
+  struct DecisionRecord {
+    const CounterMappingRegion *DecisionRegion;
+
+    /// They are reflected from DecisionRegion for convenience.
+    LineColPair DecisionStartLoc;
+    LineColPair DecisionEndLoc;
+
+    /// This is passed to `MCDCRecordProcessor`, so this should be compatible
+    /// to`ArrayRef<const CounterMappingRegion *>`.
+    SmallVector<const CounterMappingRegion *> MCDCBranches;
+
+    /// IDs that are stored in MCDCBranches
+    /// Complete when all IDs (1 to NumConditions) are met.
+    DenseSet<CounterMappingRegion::MCDCConditionID> ConditionIDs;
+
+    /// Set of IDs of Expansion(s) that are relevant to DecisionRegion
+    /// and its children (via expansions).
+    /// FileID  pointed by ExpandedFileID is dedicated to the expansion, so
+    /// the location in the expansion doesn't matter.
+    DenseSet<unsigned> ExpandedFileIDs;
+
+    DecisionRecord(const CounterMappingRegion &Decision)
+        : DecisionRegion(&Decision), DecisionStartLoc(Decision.startLoc()),
+          DecisionEndLoc(Decision.endLoc()) {
+      assert(Decision.Kind == CounterMappingRegion::MCDCDecisionRegion);
+    }
+
+    /// Determine whether DecisionRecord dominates `R`.
+    bool dominates(const CounterMappingRegion &R) {
+      // Determine whether `R` is included in `DecisionRegion`.
+      if (R.FileID == DecisionRegion->FileID &&
+          R.startLoc() >= DecisionStartLoc && R.endLoc() <= DecisionEndLoc)
+        return true;
+
+      // Determine whether `R` is pointed by any of Expansions.
+      return ExpandedFileIDs.contains(R.FileID);
+    }
+
+    enum Result {
+      NotProcessed = 0, /// Irrelevant to this Decision
+      Processed,        /// Added to this Decision
+      Completed,        /// Added and filled this Decision
+    };
+
+    /// Add Branch into the Decision
+    /// \param Branch expects MCDCBranchRegion
+    /// \returns NotProcessed/Processed/Completed
+    Result addBranch(const CounterMappingRegion &Branch) {
+      assert(Branch.Kind == CounterMappingRegion::MCDCBranchRegion);
+
+      auto ConditionID = Branch.MCDCParams.ID;
+      assert(ConditionID > 0 && "ConditionID should begin with 1");
+
+      if (ConditionIDs.contains(ConditionID) ||
+          ConditionID > DecisionRegion->MCDCParams.NumConditions)
+        return NotProcessed;
+
+      if (!this->dominates(Branch))
+        return NotProcessed;
+
+      assert(MCDCBranches.size() < DecisionRegion->MCDCParams.NumConditions);
+
+      // Put `ID=1` in front of `MCDCBranches` for convenience
+      // even if `MCDCBranches` is not topological.
+      if (ConditionID == 1)
+        MCDCBranches.insert(MCDCBranches.begin(), &Branch);
+      else
+        MCDCBranches.push_back(&Branch);
+
+      // Mark `ID` as `assigned`.
+      ConditionIDs.insert(ConditionID);
+
+      // `Completed` when `MCDCBranches` is full
+      return (MCDCBranches.size() == DecisionRegion->MCDCParams.NumConditions
+                  ? Completed
+                  : Processed);
+    }
+
+    /// Record Expansion if it is relevant to this Decision.
+    /// Each `Expansion` may nest.
+    /// \returns true if recorded.
+    bool recordExpansion(const CounterMappingRegion &Expansion) {
+      if (!this->dominates(Expansion))
+        return false;
+
+      ExpandedFileIDs.insert(Expansion.ExpandedFileID);
+      return true;
+    }
+  };
+
+private:
+  /// Decisions in progress
+  /// DecisionRecord is added for each MCDCDecisionRegion.
+  /// DecisionRecord is removed when Decision is completed.
+  SmallVector<DecisionRecord> Decisions;
+
+public:
+  ~MCDCDecisionRecorder() {
+    assert(Decisions.empty() && "All Decisions have not been resolved");
+  }
+
+  /// Register Region and start recording if it is MCDCDecisionRegion.
+  /// \param Region to be inspected
+  /// \returns true if recording started.
+  bool registerDecision(const CounterMappingRegion &Region) {
+    if (Region.Kind != CounterMappingRegion::MCDCDecisionRegion)
+      return false;
+
+    // Start recording Region to create DecisionRecord
+    Decisions.emplace_back(Region);
+    return true;
+  }
+
+  using DecisionAndBranches =
+      std::pair<const CounterMappingRegion *,             /// Decision
+                SmallVector<const CounterMappingRegion *> /// Branches
+                >;
+
+  /// If Region is ExpansionRegion, record it.
+  /// If Region is MCDCBranchRegion, add it to DecisionRecord.
+  /// \param Region to be inspected
+  /// \returns DecisionsAndBranches if DecisionRecord completed.
+  ///     Or returns nullopt.
+  std::optional<DecisionAndBranches>
+  processRegion(const CounterMappingRegion &Region) {
+
+    // Record ExpansionRegion.
+    if (Region.Kind == CounterMappingRegion::ExpansionRegion) {
----------------
MaskRay wrote:

I think it's clear to move `ExpansionRegion` handling to the caller.

https://github.com/llvm/llvm-project/pull/78969