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

[NAKAMURA Takumi via llvm-commits]

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@@ -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`.
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chapuni wrote:

I haven't written doxygen comments for long time. Please point out any mistakes.

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