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

[Jessica Paquette via llvm-commits]

================
@@ -582,6 +583,87 @@ static unsigned getMaxBitmapSize(const CounterMappingContext &Ctx,
   return MaxBitmapID + (SizeInBits / CHAR_BIT);
 }
 
+/// This holds the DecisionRegion and MCDCBranch(es) under it.
+/// Also traverses Expansion(s).
+struct DecisionRow {
+  /// The subject
+  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 *, 6> Branches;
+
+  /// Each `ID` in `Branches` should be unique.
+  DenseSet<CounterMappingRegion::MCDCConditionID> IDs;
+
+  /// Relevant `Expansion`(s) should be caught to find expanded Branches.
+  SmallVector<const CounterMappingRegion *> Expansions;
+
+  DecisionRow(const CounterMappingRegion &Decision)
+      : DecisionRegion(&Decision), DecisionStartLoc(Decision.startLoc()),
+        DecisionEndLoc(Decision.endLoc()) {}
+
+  /// Determine whether `R` is included in `DecisionRegion`.
+  bool inDecisionRegion(const CounterMappingRegion &R) {
+    return (R.FileID == DecisionRegion->FileID &&
+            R.startLoc() >= DecisionStartLoc && R.endLoc() <= DecisionEndLoc);
+  }
+
+  /// Determin whether `R` is pointed by any of Expansions.
+  bool inExpansions(const CounterMappingRegion &R) {
+    return any_of(Expansions, [&](const auto &Expansion) {
+      return (Expansion->ExpandedFileID == R.FileID);
+    });
+  }
+
+  enum class UpdateResult {
----------------
ornata wrote:

This should be documented

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