[clang] [llvm] [Coverage][MC/DC] Show uncoverable and unreachable conditions (PR #94137)

[via cfe-commits]

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@@ -1128,15 +1132,22 @@ struct CounterCoverageMappingBuilder
         BranchParams = mcdc::BranchParameters{ID, Conds};
 
       // If a condition can fold to true or false, the corresponding branch
-      // will be removed.  Create a region with both counters hard-coded to
-      // zero. This allows us to visualize them in a special way.
+      // will be removed. Create a region with the relative counter hard-coded
+      // to zero. This allows us to visualize them in a special way.
       // Alternatively, we can prevent any optimization done via
       // constant-folding by ensuring that ConstantFoldsToSimpleInteger() in
       // CodeGenFunction.c always returns false, but that is very heavy-handed.
-      if (ConditionFoldsToBool(C))
-        popRegions(pushRegion(Counter::getZero(), getStart(C), getEnd(C),
-                              Counter::getZero(), BranchParams));
-      else
+      bool ConstantBool = false;
+      if (ConditionFoldsToBool(C, ConstantBool)) {
+        if (ConstantBool) {
+          popRegions(pushRegion(TrueCnt, getStart(C), getEnd(C),
+                                Counter::getZero(), BranchParams));
+        } else {
+          popRegions(pushRegion(Counter::getZero(), getStart(C), getEnd(C),
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Lambdaris wrote:

The only code where I found it may cause side effect seems never impact `BranchRegion` or `MCDCBranchRegion`: https://github.com/llvm/llvm-project/blob/327edbe07ab4370ceb20ea7c805f64950871d835/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp#L854 

https://github.com/llvm/llvm-project/pull/94137