[MC/DC] Refactor: Let MCDCConditionID int16_t with zero-origin (#81257)

Also, Let `NumConditions` `uint16_t`.

It is smarter to handle the ID as signed.
Narrowing to `int16_t` will reduce costs of handling byvalue. (See also
#81221 and #81227)

External behavior doesn't change. They below handle values as internal
values plus 1.
* `-dump-coverage-mapping`
* `CoverageMappingReader.cpp`
* `CoverageMappingWriter.cpp`

1 files changed, 12 insertions, 9 deletions

diff --git a/llvm/lib/ProfileData/Coverage/CoverageMappingReader.cpp b/llvm/lib/ProfileData/Coverage/CoverageMappingReader.cpp
index de7be52..d328460 100644
--- a/llvm/lib/ProfileData/Coverage/CoverageMappingReader.cpp
+++ b/llvm/lib/ProfileData/Coverage/CoverageMappingReader.cpp
@@ -244,7 +244,9 @@ Error RawCoverageMappingReader::readMappingRegionsSubArray(
   unsigned LineStart = 0;
   for (size_t I = 0; I < NumRegions; ++I) {
     Counter C, C2;
-    uint64_t BIDX, NC, ID, TID, FID;
+    uint64_t BIDX, NC;
+    // They are stored as internal values plus 1 (min is -1)
+    uint64_t ID1, TID1, FID1;
     mcdc::Parameters Params;
     CounterMappingRegion::RegionKind Kind = CounterMappingRegion::CodeRegion;
 
@@ -303,28 +305,29 @@ Error RawCoverageMappingReader::readMappingRegionsSubArray(
             return Err;
           if (auto Err = readCounter(C2))
             return Err;
-          if (auto Err = readIntMax(ID, std::numeric_limits<unsigned>::max()))
+          if (auto Err = readIntMax(ID1, std::numeric_limits<int16_t>::max()))
             return Err;
-          if (auto Err = readIntMax(TID, std::numeric_limits<unsigned>::max()))
+          if (auto Err = readIntMax(TID1, std::numeric_limits<int16_t>::max()))
             return Err;
-          if (auto Err = readIntMax(FID, std::numeric_limits<unsigned>::max()))
+          if (auto Err = readIntMax(FID1, std::numeric_limits<int16_t>::max()))
             return Err;
-          if (ID == 0)
+          if (ID1 == 0)
             return make_error<CoverageMapError>(
                 coveragemap_error::malformed,
                 "MCDCConditionID shouldn't be zero");
           Params = mcdc::BranchParameters{
-              static_cast<unsigned>(ID),
-              {static_cast<unsigned>(FID), static_cast<unsigned>(TID)}};
+              static_cast<int16_t>(static_cast<int16_t>(ID1) - 1),
+              {static_cast<int16_t>(static_cast<int16_t>(FID1) - 1),
+               static_cast<int16_t>(static_cast<int16_t>(TID1) - 1)}};
           break;
         case CounterMappingRegion::MCDCDecisionRegion:
           Kind = CounterMappingRegion::MCDCDecisionRegion;
           if (auto Err = readIntMax(BIDX, std::numeric_limits<unsigned>::max()))
             return Err;
-          if (auto Err = readIntMax(NC, std::numeric_limits<unsigned>::max()))
+          if (auto Err = readIntMax(NC, std::numeric_limits<int16_t>::max()))
             return Err;
           Params = mcdc::DecisionParameters{static_cast<unsigned>(BIDX),
-                                            static_cast<unsigned>(NC)};
+                                            static_cast<uint16_t>(NC)};
           break;
         default:
           return make_error<CoverageMapError>(coveragemap_error::malformed,