diff --git a/clang/lib/CodeGen/CoverageMappingGen.cpp b/clang/lib/CodeGen/CoverageMappingGen.cpp
index 0c43317642bca4..da5d43cda91209 100644
--- a/clang/lib/CodeGen/CoverageMappingGen.cpp
+++ b/clang/lib/CodeGen/CoverageMappingGen.cpp
@@ -97,6 +97,8 @@ void CoverageSourceInfo::updateNextTokLoc(SourceLocation Loc) {
 namespace {
 using MCDCConditionID = CounterMappingRegion::MCDCConditionID;
 using MCDCParameters = CounterMappingRegion::MCDCParameters;
+using MCDCBranchParameters = CounterMappingRegion::MCDCBranchParameters;
+using MCDCDecisionParameters = CounterMappingRegion::MCDCDecisionParameters;
 
 /// A region of source code that can be mapped to a counter.
 class SourceMappingRegion {
@@ -185,7 +187,17 @@ class SourceMappingRegion {
 
   bool isBranch() const { return FalseCount.has_value(); }
 
-  bool isMCDCDecision() const { return MCDCParams.NumConditions != 0; }
+  bool isMCDCDecision() const {
+    const auto *DecisionParams =
+        std::get_if<MCDCDecisionParameters>(&MCDCParams);
+    assert(!DecisionParams || DecisionParams->NumConditions > 0);
+    return DecisionParams;
+  }
+
+  const auto &getMCDCDecisionParams() const {
+    return CounterMappingRegion::getParams<const MCDCDecisionParameters>(
+        MCDCParams);
+  }
 
   const MCDCParameters &getMCDCParams() const { return MCDCParams; }
 };
@@ -483,13 +495,13 @@ class CoverageMappingBuilder {
             SR.ColumnEnd));
       } else if (Region.isBranch()) {
         MappingRegions.push_back(CounterMappingRegion::makeBranchRegion(
-            Region.getCounter(), Region.getFalseCounter(),
-            Region.getMCDCParams(), *CovFileID, SR.LineStart, SR.ColumnStart,
-            SR.LineEnd, SR.ColumnEnd));
+            Region.getCounter(), Region.getFalseCounter(), *CovFileID,
+            SR.LineStart, SR.ColumnStart, SR.LineEnd, SR.ColumnEnd,
+            Region.getMCDCParams()));
       } else if (Region.isMCDCDecision()) {
         MappingRegions.push_back(CounterMappingRegion::makeDecisionRegion(
-            Region.getMCDCParams(), *CovFileID, SR.LineStart, SR.ColumnStart,
-            SR.LineEnd, SR.ColumnEnd));
+            Region.getMCDCDecisionParams(), *CovFileID, SR.LineStart,
+            SR.ColumnStart, SR.LineEnd, SR.ColumnEnd));
       } else {
         MappingRegions.push_back(CounterMappingRegion::makeRegion(
             Region.getCounter(), *CovFileID, SR.LineStart, SR.ColumnStart,
@@ -865,8 +877,7 @@ struct CounterCoverageMappingBuilder
                     std::optional<SourceLocation> StartLoc = std::nullopt,
                     std::optional<SourceLocation> EndLoc = std::nullopt,
                     std::optional<Counter> FalseCount = std::nullopt,
-                    MCDCConditionID ID = 0, MCDCConditionID TrueID = 0,
-                    MCDCConditionID FalseID = 0) {
+                    const MCDCParameters &BranchParams = std::monostate()) {
 
     if (StartLoc && !FalseCount) {
       MostRecentLocation = *StartLoc;
@@ -885,9 +896,7 @@ struct CounterCoverageMappingBuilder
       StartLoc = std::nullopt;
     if (EndLoc && EndLoc->isInvalid())
       EndLoc = std::nullopt;
-    RegionStack.emplace_back(Count, FalseCount,
-                             MCDCParameters{0, 0, ID, TrueID, FalseID},
-                             StartLoc, EndLoc);
+    RegionStack.emplace_back(Count, FalseCount, BranchParams, StartLoc, EndLoc);
 
     return RegionStack.size() - 1;
   }
@@ -896,8 +905,8 @@ struct CounterCoverageMappingBuilder
                     std::optional<SourceLocation> StartLoc = std::nullopt,
                     std::optional<SourceLocation> EndLoc = std::nullopt) {
 
-    RegionStack.emplace_back(MCDCParameters{BitmapIdx, Conditions}, StartLoc,
-                             EndLoc);
+    RegionStack.emplace_back(MCDCDecisionParameters{BitmapIdx, Conditions},
+                             StartLoc, EndLoc);
 
     return RegionStack.size() - 1;
   }
@@ -1042,9 +1051,10 @@ struct CounterCoverageMappingBuilder
     // function's SourceRegions) because it doesn't apply to any other source
     // code other than the Condition.
     if (CodeGenFunction::isInstrumentedCondition(C)) {
+      MCDCParameters BranchParams;
       MCDCConditionID ID = MCDCBuilder.getCondID(C);
-      MCDCConditionID TrueID = IDPair.TrueID;
-      MCDCConditionID FalseID = IDPair.FalseID;
+      if (ID > 0)
+        BranchParams = MCDCBranchParameters{ID, IDPair.TrueID, IDPair.FalseID};
 
       // If a condition can fold to true or false, the corresponding branch
       // will be removed.  Create a region with both counters hard-coded to
@@ -1054,11 +1064,11 @@ struct CounterCoverageMappingBuilder
       // CodeGenFunction.c always returns false, but that is very heavy-handed.
       if (ConditionFoldsToBool(C))
         popRegions(pushRegion(Counter::getZero(), getStart(C), getEnd(C),
-                              Counter::getZero(), ID, TrueID, FalseID));
+                              Counter::getZero(), BranchParams));
       else
         // Otherwise, create a region with the True counter and False counter.
-        popRegions(pushRegion(TrueCnt, getStart(C), getEnd(C), FalseCnt, ID,
-                              TrueID, FalseID));
+        popRegions(pushRegion(TrueCnt, getStart(C), getEnd(C), FalseCnt,
+                              BranchParams));
     }
   }
 
@@ -1149,12 +1159,9 @@ struct CounterCoverageMappingBuilder
         // we've seen this region.
         if (StartLocs.insert(Loc).second) {
           if (I.isBranch())
-            SourceRegions.emplace_back(
-                I.getCounter(), I.getFalseCounter(),
-                MCDCParameters{0, 0, I.getMCDCParams().ID,
-                               I.getMCDCParams().TrueID,
-                               I.getMCDCParams().FalseID},
-                Loc, getEndOfFileOrMacro(Loc), I.isBranch());
+            SourceRegions.emplace_back(I.getCounter(), I.getFalseCounter(),
+                                       I.getMCDCParams(), Loc,
+                                       getEndOfFileOrMacro(Loc), I.isBranch());
           else
             SourceRegions.emplace_back(I.getCounter(), Loc,
                                        getEndOfFileOrMacro(Loc));
@@ -2120,9 +2127,10 @@ static void dump(llvm::raw_ostream &OS, StringRef FunctionName,
     OS << "File " << R.FileID << ", " << R.LineStart << ":" << R.ColumnStart
        << " -> " << R.LineEnd << ":" << R.ColumnEnd << " = ";
 
-    if (R.Kind == CounterMappingRegion::MCDCDecisionRegion) {
-      OS << "M:" << R.MCDCParams.BitmapIdx;
-      OS << ", C:" << R.MCDCParams.NumConditions;
+    if (const auto *DecisionParams =
+            std::get_if<MCDCDecisionParameters>(&R.MCDCParams)) {
+      OS << "M:" << DecisionParams->BitmapIdx;
+      OS << ", C:" << DecisionParams->NumConditions;
     } else {
       Ctx.dump(R.Count, OS);
 
@@ -2133,9 +2141,10 @@ static void dump(llvm::raw_ostream &OS, StringRef FunctionName,
       }
     }
 
-    if (R.Kind == CounterMappingRegion::MCDCBranchRegion) {
-      OS << " [" << R.MCDCParams.ID << "," << R.MCDCParams.TrueID;
-      OS << "," << R.MCDCParams.FalseID << "] ";
+    if (const auto *BranchParams =
+            std::get_if<MCDCBranchParameters>(&R.MCDCParams)) {
+      OS << " [" << BranchParams->ID << "," << BranchParams->TrueID;
+      OS << "," << BranchParams->FalseID << "] ";
     }
 
     if (R.Kind == CounterMappingRegion::ExpansionRegion)
diff --git a/llvm/include/llvm/ProfileData/Coverage/CoverageMapping.h b/llvm/include/llvm/ProfileData/Coverage/CoverageMapping.h
index 88ec60c7aa33c6..0ad6d48a0eb798 100644
--- a/llvm/include/llvm/ProfileData/Coverage/CoverageMapping.h
+++ b/llvm/include/llvm/ProfileData/Coverage/CoverageMapping.h
@@ -39,6 +39,7 @@
 #include <system_error>
 #include <tuple>
 #include <utility>
+#include <variant>
 #include <vector>
 
 namespace llvm {
@@ -250,18 +251,27 @@ struct CounterMappingRegion {
   };
 
   using MCDCConditionID = unsigned int;
-  struct MCDCParameters {
+  struct MCDCDecisionParameters {
     /// Byte Index of Bitmap Coverage Object for a Decision Region.
-    unsigned BitmapIdx = 0;
+    unsigned BitmapIdx;
 
     /// Number of Conditions used for a Decision Region.
-    unsigned NumConditions = 0;
+    unsigned NumConditions;
 
+    MCDCDecisionParameters() = delete;
+  };
+
+  struct MCDCBranchParameters {
     /// IDs used to represent a branch region and other branch regions
     /// evaluated based on True and False branches.
-    MCDCConditionID ID = 0, TrueID = 0, FalseID = 0;
+    MCDCConditionID ID, TrueID, FalseID;
+
+    MCDCBranchParameters() = delete;
   };
 
+  using MCDCParameters = std::variant<std::monostate, MCDCDecisionParameters,
+                                      MCDCBranchParameters>;
+
   /// Primary Counter that is also used for Branch Regions (TrueCount).
   Counter Count;
 
@@ -271,6 +281,24 @@ struct CounterMappingRegion {
   /// Parameters used for Modified Condition/Decision Coverage
   MCDCParameters MCDCParams;
 
+  template <class MaybeConstInnerParameters, class MaybeConstMCDCParameters>
+  static auto &getParams(MaybeConstMCDCParameters &MCDCParams) {
+    using InnerParameters =
+        typename std::remove_const<MaybeConstInnerParameters>::type;
+    MaybeConstInnerParameters *Params =
+        std::get_if<InnerParameters>(&MCDCParams);
+    assert(Params && "InnerParameters unavailable");
+    return *Params;
+  }
+
+  const auto &getDecisionParams() const {
+    return getParams<const MCDCDecisionParameters>(MCDCParams);
+  }
+
+  const auto &getBranchParams() const {
+    return getParams<const MCDCBranchParameters>(MCDCParams);
+  }
+
   unsigned FileID = 0;
   unsigned ExpandedFileID = 0;
   unsigned LineStart, ColumnStart, LineEnd, ColumnEnd;
@@ -284,19 +312,20 @@ struct CounterMappingRegion {
         LineStart(LineStart), ColumnStart(ColumnStart), LineEnd(LineEnd),
         ColumnEnd(ColumnEnd), Kind(Kind) {}
 
-  CounterMappingRegion(Counter Count, Counter FalseCount,
-                       MCDCParameters MCDCParams, unsigned FileID,
+  CounterMappingRegion(Counter Count, Counter FalseCount, unsigned FileID,
                        unsigned ExpandedFileID, unsigned LineStart,
                        unsigned ColumnStart, unsigned LineEnd,
-                       unsigned ColumnEnd, RegionKind Kind)
+                       unsigned ColumnEnd, RegionKind Kind,
+                       const MCDCParameters &MCDCParams = std::monostate())
       : Count(Count), FalseCount(FalseCount), MCDCParams(MCDCParams),
         FileID(FileID), ExpandedFileID(ExpandedFileID), LineStart(LineStart),
         ColumnStart(ColumnStart), LineEnd(LineEnd), ColumnEnd(ColumnEnd),
         Kind(Kind) {}
 
-  CounterMappingRegion(MCDCParameters MCDCParams, unsigned FileID,
-                       unsigned LineStart, unsigned ColumnStart,
-                       unsigned LineEnd, unsigned ColumnEnd, RegionKind Kind)
+  CounterMappingRegion(const MCDCDecisionParameters &MCDCParams,
+                       unsigned FileID, unsigned LineStart,
+                       unsigned ColumnStart, unsigned LineEnd,
+                       unsigned ColumnEnd, RegionKind Kind)
       : MCDCParams(MCDCParams), FileID(FileID), LineStart(LineStart),
         ColumnStart(ColumnStart), LineEnd(LineEnd), ColumnEnd(ColumnEnd),
         Kind(Kind) {}
@@ -333,24 +362,18 @@ struct CounterMappingRegion {
   static CounterMappingRegion
   makeBranchRegion(Counter Count, Counter FalseCount, unsigned FileID,
                    unsigned LineStart, unsigned ColumnStart, unsigned LineEnd,
-                   unsigned ColumnEnd) {
-    return CounterMappingRegion(Count, FalseCount, MCDCParameters(), FileID, 0,
-                                LineStart, ColumnStart, LineEnd, ColumnEnd,
-                                BranchRegion);
-  }
-
-  static CounterMappingRegion
-  makeBranchRegion(Counter Count, Counter FalseCount, MCDCParameters MCDCParams,
-                   unsigned FileID, unsigned LineStart, unsigned ColumnStart,
-                   unsigned LineEnd, unsigned ColumnEnd) {
-    return CounterMappingRegion(Count, FalseCount, MCDCParams, FileID, 0,
-                                LineStart, ColumnStart, LineEnd, ColumnEnd,
-                                MCDCParams.ID == 0 ? BranchRegion
-                                                   : MCDCBranchRegion);
+                   unsigned ColumnEnd,
+                   const MCDCParameters &MCDCParams = std::monostate()) {
+    return CounterMappingRegion(Count, FalseCount, FileID, 0, LineStart,
+                                ColumnStart, LineEnd, ColumnEnd,
+                                (std::get_if<MCDCBranchParameters>(&MCDCParams)
+                                     ? MCDCBranchRegion
+                                     : BranchRegion),
+                                MCDCParams);
   }
 
   static CounterMappingRegion
-  makeDecisionRegion(MCDCParameters MCDCParams, unsigned FileID,
+  makeDecisionRegion(const MCDCDecisionParameters &MCDCParams, unsigned FileID,
                      unsigned LineStart, unsigned ColumnStart, unsigned LineEnd,
                      unsigned ColumnEnd) {
     return CounterMappingRegion(MCDCParams, FileID, LineStart, ColumnStart,
@@ -415,9 +438,7 @@ struct MCDCRecord {
 
   CounterMappingRegion getDecisionRegion() const { return Region; }
   unsigned getNumConditions() const {
-    assert(Region.MCDCParams.NumConditions != 0 &&
-           "In MC/DC, NumConditions should never be zero!");
-    return Region.MCDCParams.NumConditions;
+    return Region.getDecisionParams().NumConditions;
   }
   unsigned getNumTestVectors() const { return TV.size(); }
   bool isCondFolded(unsigned Condition) const { return Folded[Condition]; }
diff --git a/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp b/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp
index 6b189c31463283..646b9fb077ef07 100644
--- a/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp
+++ b/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp
@@ -234,6 +234,7 @@ class MCDCRecordProcessor {
 
   /// Decision Region to which the ExecutedTestVectorBitmap applies.
   const CounterMappingRegion &Region;
+  const CounterMappingRegion::MCDCDecisionParameters &DecisionParams;
 
   /// Array of branch regions corresponding each conditions in the boolean
   /// expression.
@@ -244,8 +245,9 @@ class MCDCRecordProcessor {
 
   unsigned BitmapIdx;
 
-  /// Mapping of a condition ID to its corresponding branch region.
-  llvm::DenseMap<unsigned, const CounterMappingRegion *> Map;
+  /// Mapping of a condition ID to its corresponding branch params.
+  llvm::DenseMap<unsigned, const CounterMappingRegion::MCDCBranchParameters *>
+      BranchParamsMap;
 
   /// Vector used to track whether a condition is constant folded.
   MCDCRecord::BoolVector Folded;
@@ -264,9 +266,10 @@ class MCDCRecordProcessor {
   MCDCRecordProcessor(const BitVector &Bitmap,
                       const CounterMappingRegion &Region,
                       ArrayRef<const CounterMappingRegion *> Branches)
-      : Bitmap(Bitmap), Region(Region), Branches(Branches),
-        NumConditions(Region.MCDCParams.NumConditions),
-        BitmapIdx(Region.MCDCParams.BitmapIdx * CHAR_BIT),
+      : Bitmap(Bitmap), Region(Region),
+        DecisionParams(Region.getDecisionParams()), Branches(Branches),
+        NumConditions(DecisionParams.NumConditions),
+        BitmapIdx(DecisionParams.BitmapIdx * CHAR_BIT),
         Folded(NumConditions, false), IndependencePairs(NumConditions),
         TestVectors((size_t)1 << NumConditions) {}
 
@@ -286,18 +289,18 @@ class MCDCRecordProcessor {
   // the truth table.
   void buildTestVector(MCDCRecord::TestVector &TV, unsigned ID,
                        unsigned Index) {
-    const CounterMappingRegion *Branch = Map[ID];
+    auto [UnusedID, TrueID, FalseID] = *BranchParamsMap[ID];
 
     TV[ID - 1] = MCDCRecord::MCDC_False;
-    if (Branch->MCDCParams.FalseID > 0)
-      buildTestVector(TV, Branch->MCDCParams.FalseID, Index);
+    if (FalseID > 0)
+      buildTestVector(TV, FalseID, Index);
     else
       recordTestVector(TV, Index, MCDCRecord::MCDC_False);
 
     Index |= 1 << (ID - 1);
     TV[ID - 1] = MCDCRecord::MCDC_True;
-    if (Branch->MCDCParams.TrueID > 0)
-      buildTestVector(TV, Branch->MCDCParams.TrueID, Index);
+    if (TrueID > 0)
+      buildTestVector(TV, TrueID, Index);
     else
       recordTestVector(TV, Index, MCDCRecord::MCDC_True);
 
@@ -374,8 +377,9 @@ class MCDCRecordProcessor {
     // - Record whether the condition is constant folded so that we exclude it
     //   from being measured.
     for (const auto *B : Branches) {
-      Map[B->MCDCParams.ID] = B;
-      PosToID[I] = B->MCDCParams.ID - 1;
+      const auto &BranchParams = B->getBranchParams();
+      BranchParamsMap[BranchParams.ID] = &BranchParams;
+      PosToID[I] = BranchParams.ID - 1;
       CondLoc[I] = B->startLoc();
       Folded[I++] = (B->Count.isZero() && B->FalseCount.isZero());
     }
@@ -501,10 +505,12 @@ static unsigned getMaxBitmapSize(const CounterMappingContext &Ctx,
   // Note that `<=` is used insted of `<`, because `BitmapIdx == 0` is valid
   // and `MaxBitmapIdx is `unsigned`. `BitmapIdx` is unique in the record.
   for (const auto &Region : reverse(Record.MappingRegions)) {
-    if (Region.Kind == CounterMappingRegion::MCDCDecisionRegion &&
-        MaxBitmapIdx <= Region.MCDCParams.BitmapIdx) {
-      MaxBitmapIdx = Region.MCDCParams.BitmapIdx;
-      NumConditions = Region.MCDCParams.NumConditions;
+    if (Region.Kind != CounterMappingRegion::MCDCDecisionRegion)
+      continue;
+    const auto &DecisionParams = Region.getDecisionParams();
+    if (MaxBitmapIdx <= DecisionParams.BitmapIdx) {
+      MaxBitmapIdx = DecisionParams.BitmapIdx;
+      NumConditions = DecisionParams.NumConditions;
     }
   }
   unsigned SizeInBits = llvm::alignTo(uint64_t(1) << NumConditions, CHAR_BIT);
@@ -526,6 +532,7 @@ class MCDCDecisionRecorder {
     /// They are reflected from DecisionRegion for convenience.
     LineColPair DecisionStartLoc;
     LineColPair DecisionEndLoc;
+    CounterMappingRegion::MCDCDecisionParameters DecisionParams;
 
     /// This is passed to `MCDCRecordProcessor`, so this should be compatible
     /// to`ArrayRef<const CounterMappingRegion *>`.
@@ -543,7 +550,8 @@ class MCDCDecisionRecorder {
 
     DecisionRecord(const CounterMappingRegion &Decision)
         : DecisionRegion(&Decision), DecisionStartLoc(Decision.startLoc()),
-          DecisionEndLoc(Decision.endLoc()) {
+          DecisionEndLoc(Decision.endLoc()),
+          DecisionParams(Decision.getDecisionParams()) {
       assert(Decision.Kind == CounterMappingRegion::MCDCDecisionRegion);
     }
 
@@ -570,17 +578,17 @@ class MCDCDecisionRecorder {
     Result addBranch(const CounterMappingRegion &Branch) {
       assert(Branch.Kind == CounterMappingRegion::MCDCBranchRegion);
 
-      auto ConditionID = Branch.MCDCParams.ID;
+      auto ConditionID = Branch.getBranchParams().ID;
       assert(ConditionID > 0 && "ConditionID should begin with 1");
 
       if (ConditionIDs.contains(ConditionID) ||
-          ConditionID > DecisionRegion->MCDCParams.NumConditions)
+          ConditionID > DecisionParams.NumConditions)
         return NotProcessed;
 
       if (!this->dominates(Branch))
         return NotProcessed;
 
-      assert(MCDCBranches.size() < DecisionRegion->MCDCParams.NumConditions);
+      assert(MCDCBranches.size() < DecisionParams.NumConditions);
 
       // Put `ID=1` in front of `MCDCBranches` for convenience
       // even if `MCDCBranches` is not topological.
@@ -593,9 +601,8 @@ class MCDCDecisionRecorder {
       ConditionIDs.insert(ConditionID);
 
       // `Completed` when `MCDCBranches` is full
-      return (MCDCBranches.size() == DecisionRegion->MCDCParams.NumConditions
-                  ? Completed
-                  : Processed);
+      return (MCDCBranches.size() == DecisionParams.NumConditions ? Completed
+                                                                  : Processed);
     }
 
     /// Record Expansion if it is relevant to this Decision.
diff --git a/llvm/lib/ProfileData/Coverage/CoverageMappingReader.cpp b/llvm/lib/ProfileData/Coverage/CoverageMappingReader.cpp
index ac8e6b56379f21..bd2ca2afe31d6a 100644
--- a/llvm/lib/ProfileData/Coverage/CoverageMappingReader.cpp
+++ b/llvm/lib/ProfileData/Coverage/CoverageM...
[truncated]