[llvm] [MC/DC] Introduce `class TestVector` with a pair of `BitVector` (PR #82174)

[NAKAMURA Takumi via llvm-commits]

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@@ -323,22 +318,15 @@ class MCDCRecordProcessor {
       for (unsigned J = 0; J < I; ++J) {
         const MCDCRecord::TestVector &B = ExecVectors[J];
         // Enumerate two execution vectors whose outcomes are different.
-        if (A[NumConditions] == B[NumConditions])
+        if (!A.isDifferentOutcome(B))
           continue;
-        unsigned Flip = NumConditions, Idx;
-        for (Idx = 0; Idx < NumConditions; ++Idx) {
-          MCDCRecord::CondState ACond = A[Idx], BCond = B[Idx];
-          if (ACond == BCond || ACond == MCDCRecord::MCDC_DontCare ||
-              BCond == MCDCRecord::MCDC_DontCare)
-            continue;
-          if (Flip != NumConditions)
-            break;
-          Flip = Idx;
-        }
         // If the two vectors differ in exactly one condition, ignoring DontCare
         // conditions, we have found an independence pair.
-        if (Idx == NumConditions && Flip != NumConditions)
-          IndependencePairs.insert({Flip, std::make_pair(J + 1, I + 1)});
+        auto AB = A.getDifferences(B);
+        assert(AB[NumConditions] && "The last element should be different");
+        if (AB.count() == 2) // The single condition and the last element
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chapuni wrote:

This could be `== 1` aka `has_single_bit`.

https://github.com/llvm/llvm-project/pull/82174