[llvm] Restore #125407, Make covmap tolerant of nested Decisions (PR #183073)

[NAKAMURA Takumi via llvm-commits]

================
@@ -907,56 +919,14 @@ Error CoverageMapping::loadFunctionRecord(
       Record.MappingRegions[0].Count.isZero() && Counts[0] > 0)
     return Error::success();
 
-  MCDCDecisionRecorder MCDCDecisions;
   FunctionRecord Function(OrigFuncName, Record.Filenames);
-  for (const auto &Region : Record.MappingRegions) {
-    // MCDCDecisionRegion should be handled first since it overlaps with
-    // others inside.
-    if (Region.Kind == CounterMappingRegion::MCDCDecisionRegion) {
-      MCDCDecisions.registerDecision(Region);
-      continue;
-    }
-    Expected<int64_t> ExecutionCount = Ctx.evaluate(Region.Count);
-    if (auto E = ExecutionCount.takeError()) {
-      consumeError(std::move(E));
-      return Error::success();
-    }
-    Expected<int64_t> AltExecutionCount = Ctx.evaluate(Region.FalseCount);
-    if (auto E = AltExecutionCount.takeError()) {
-      consumeError(std::move(E));
-      return Error::success();
-    }
-    Function.pushRegion(Region, *ExecutionCount, *AltExecutionCount);
-
-    // Record ExpansionRegion.
-    if (Region.Kind == CounterMappingRegion::ExpansionRegion) {
-      MCDCDecisions.recordExpansion(Region);
-      continue;
-    }
-
-    // Do nothing unless MCDCBranchRegion.
-    if (Region.Kind != CounterMappingRegion::MCDCBranchRegion)
-      continue;
 
-    auto Result = MCDCDecisions.processBranch(Region);
-    if (!Result) // Any Decision doesn't complete.
-      continue;
-
-    auto MCDCDecision = Result->first;
-    auto &MCDCBranches = Result->second;
-
-    // Since the bitmap identifies the executed test vectors for an MC/DC
-    // DecisionRegion, all of the information is now available to process.
-    // This is where the bulk of the MC/DC progressing takes place.
-    Expected<MCDCRecord> Record =
-        Ctx.evaluateMCDCRegion(*MCDCDecision, MCDCBranches, IsVersion11);
-    if (auto E = Record.takeError()) {
-      consumeError(std::move(E));
-      return Error::success();
-    }
-
-    // Save the MC/DC Record so that it can be visualized later.
-    Function.pushMCDCRecord(std::move(*Record));
+  // Emit CountedRegions into FunctionRecord.
+  if (auto E = CountedRegionEmitter(Record, Ctx, Function, IsVersion11)
+                   .emitCountedRegions()) {
+    errs() << "warning: " << Record.FunctionName << ": ";
+    logAllUnhandledErrors(std::move(E), errs());
+    return Error::success();
----------------
chapuni wrote:

I have not been able to identify any issues caused by my changes so far.

I guess the root cause would be possibly in the correlation resolution in `llvm-profdata merge`.
I was trying to reproduce issues with `check-llvm` by seeing the commad line introduced in #180277.

In my attempts, incorrect correlation sometimes select  improper `prf_cnts` as if it were right, to lead warnings. I don't know how `llvm-profdata merge` would be handled in you environment.

Eventually, I succeeded `llvm-cov` with the binary correlation without any "noisy" warnings.

1. Give `-profile-correlate=binary --build-id`
2. Write and run the script that pick up corresponding elf and profraw(s) by build-id and merge them to *-correlate-resolved.profdata
3. Run `llvm-profdata merge *-correlate-resolved.profdata` (not `profraw`) as the final stage

Note, I was not able to validate or repair the provided profdata. I guess it would be broken with reasons above.

https://github.com/llvm/llvm-project/pull/183073