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

[Fangrui Song via llvm-commits]

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@@ -638,20 +810,13 @@ Error CoverageMapping::loadFunctionRecord(
       Record.MappingRegions[0].Count.isZero() && Counts[0] > 0)
     return Error::success();
 
-  unsigned NumConds = 0;
-  const CounterMappingRegion *MCDCDecision;
-  std::vector<const CounterMappingRegion *> MCDCBranches;
-
+  MCDCDecisionRecorder MCDCDecisions;
   FunctionRecord Function(OrigFuncName, Record.Filenames);
   for (const auto &Region : Record.MappingRegions) {
-    // If an MCDCDecisionRegion is seen, track the BranchRegions that follow
-    // it according to Region.NumConditions.
-    if (Region.Kind == CounterMappingRegion::MCDCDecisionRegion) {
-      assert(NumConds == 0);
-      MCDCDecision = &Region;
-      NumConds = Region.MCDCParams.NumConditions;
+    // MCDCDecisionRegion should be handled first since it overlaps with
+    // others inside.
+    if (MCDCDecisions.registerDecision(Region))
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MaskRay wrote:

I think it reads better if the `CounterMappingRegion::MCDCDecisionRegion` guard is moved here. The same applies to `MCDCDecisions.processRegion(Region);`

I.e. we check different types of `Region` here and dispatch actions to `MCDCDecisions`.

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