[llvm] [clang] [clang][CoverageMapping] Refactor when setting MC/DC True/False (PR #78202)

[NAKAMURA Takumi via cfe-commits]

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@@ -663,54 +668,40 @@ struct MCDCCoverageBuilder {
 private:
   CodeGenModule &CGM;
 
-  llvm::SmallVector<MCDCConditionID> AndRHS;
-  llvm::SmallVector<MCDCConditionID> OrRHS;
-  llvm::SmallVector<const BinaryOperator *> NestLevel;
+  llvm::SmallVector<DecisionIDPair, 6> DecisionStack;
   llvm::DenseMap<const Stmt *, MCDCConditionID> &CondIDs;
   llvm::DenseMap<const Stmt *, unsigned> &MCDCBitmapMap;
   MCDCConditionID NextID = 1;
   bool NotMapped = false;
 
+  /// Represent a sentinel value of [0,0] for the bottom of DecisionStack.
+  static constexpr DecisionIDPair DecisionIDPairSentinel{0, 0};
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chapuni wrote:

Is "`DecisionStackSentinel`" better?

I think it would be more descriptive to move it onto the definition of `DecisionStack`.

https://github.com/llvm/llvm-project/pull/78202