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

[NAKAMURA Takumi via llvm-commits]

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@@ -580,6 +583,72 @@ static unsigned getMaxBitmapSize(const CounterMappingContext &Ctx,
   return MaxBitmapID + (SizeInBits / CHAR_BIT);
 }
 
+struct DecisionRow {
+  const CounterMappingRegion *DecisionRegion;
+  LineColPair DecisionStartLoc;
+  LineColPair DecisionEndLoc;
+
+  SmallVector<const CounterMappingRegion *, 6> Branches;
+  DenseSet<CounterMappingRegion::MCDCConditionID> IDs;
+  SmallVector<const CounterMappingRegion *> Expansions;
+
+  DecisionRow(const CounterMappingRegion &Decision)
+      : DecisionRegion(&Decision), DecisionStartLoc(Decision.startLoc()),
+        DecisionEndLoc(Decision.endLoc()) {}
+
+  bool insert(const CounterMappingRegion &Branch) {
+    auto ID = Branch.MCDCParams.ID;
+    if (ID == 1)
+      Branches.insert(Branches.begin(), &Branch);
+    else
+      Branches.push_back(&Branch);
+    IDs.insert(ID);
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chapuni wrote:

Yes.

I had to introduce `DenseMap` to distinguish parallel sets of `Branch`(es).

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