[Coverage] Introduce "partial fold" on BranchRegion (#112694)

Currently both True/False counts were folded. It lost the information,
"It is True or False before folding." It prevented recalling branch
counts in merging template instantiations.

In `llvm-cov`, a folded branch is shown as:

- `[True: n, Folded]`
- `[Folded, False n]`

In the case If `n` is zero, a branch is reported as "uncovered". This is
distinguished from "folded" branch. When folded branches are merged,
`Folded` may be dissolved.

In the coverage map, either `Counter` is `Zero`. Currently both were
`Zero`.

Since "partial fold" has been introduced, either case in `switch` is
omitted as `Folded`.

Each `case:` in `switch` is reported as `[True: n, Folded]`, since
`False` count doesn't show meaningful value.

When `switch` doesn't have `default:`, `switch (Cond)` is reported as
`[Folded, False: n]`, since `True` count was just the sum of `case`(s).
`switch` with `default` can be considered as "the statement that doesn't
have any `False`(s)".

1 files changed, 27 insertions, 20 deletions

diff --git a/llvm/tools/llvm-cov/SourceCoverageViewText.cpp b/llvm/tools/llvm-cov/SourceCoverageViewText.cpp
index 8b93b59..444f33d 100644
--- a/llvm/tools/llvm-cov/SourceCoverageViewText.cpp
+++ b/llvm/tools/llvm-cov/SourceCoverageViewText.cpp
@@ -309,31 +309,38 @@ void SourceCoverageViewText::renderBranchView(raw_ostream &OS, BranchView &BRV,
     renderLinePrefix(OS, ViewDepth);
     OS << "  Branch (" << R.LineStart << ":" << R.ColumnStart << "): [";
 
-    if (R.Folded) {
+    if (R.TrueFolded && R.FalseFolded) {
       OS << "Folded - Ignored]\n";
       continue;
     }
 
-    colored_ostream(OS, raw_ostream::RED,
-                    getOptions().Colors && !R.ExecutionCount,
-                    /*Bold=*/false, /*BG=*/true)
-        << "True";
-
-    if (getOptions().ShowBranchCounts)
-      OS << ": " << formatCount(R.ExecutionCount) << ", ";
-    else
-      OS << ": " << format("%0.2f", TruePercent) << "%, ";
-
-    colored_ostream(OS, raw_ostream::RED,
-                    getOptions().Colors && !R.FalseExecutionCount,
-                    /*Bold=*/false, /*BG=*/true)
-        << "False";
+    if (R.TrueFolded)
+      OS << "Folded, ";
+    else {
+      colored_ostream(OS, raw_ostream::RED,
+                      getOptions().Colors && !R.ExecutionCount,
+                      /*Bold=*/false, /*BG=*/true)
+          << "True";
+
+      if (getOptions().ShowBranchCounts)
+        OS << ": " << formatCount(R.ExecutionCount) << ", ";
+      else
+        OS << ": " << format("%0.2f", TruePercent) << "%, ";
+    }
 
-    if (getOptions().ShowBranchCounts)
-      OS << ": " << formatCount(R.FalseExecutionCount);
-    else
-      OS << ": " << format("%0.2f", FalsePercent) << "%";
-    OS << "]\n";
+    if (R.FalseFolded)
+      OS << "Folded]\n";
+    else {
+      colored_ostream(OS, raw_ostream::RED,
+                      getOptions().Colors && !R.FalseExecutionCount,
+                      /*Bold=*/false, /*BG=*/true)
+          << "False";
+
+      if (getOptions().ShowBranchCounts)
+        OS << ": " << formatCount(R.FalseExecutionCount) << "]\n";
+      else
+        OS << ": " << format("%0.2f", FalsePercent) << "%]\n";
+    }
   }
 }