[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, 30 insertions, 21 deletions

diff --git a/llvm/tools/llvm-cov/SourceCoverageViewHTML.cpp b/llvm/tools/llvm-cov/SourceCoverageViewHTML.cpp
index 6f4d327..7421763 100644
--- a/llvm/tools/llvm-cov/SourceCoverageViewHTML.cpp
+++ b/llvm/tools/llvm-cov/SourceCoverageViewHTML.cpp
@@ -1128,36 +1128,45 @@ void SourceCoverageViewHTML::renderBranchView(raw_ostream &OS, BranchView &BRV,
               "line-number") +
               "): [";
 
-    if (R.Folded) {
+    if (R.TrueFolded && R.FalseFolded) {
       OS << "Folded - Ignored]\n";
       continue;
     }
 
     // Display TrueCount or TruePercent.
-    std::string TrueColor = R.ExecutionCount ? "None" : "red branch";
+    std::string TrueColor =
+        (R.TrueFolded || R.ExecutionCount ? "None" : "red branch");
     std::string TrueCovClass =
-        (R.ExecutionCount > 0) ? "covered-line" : "uncovered-line";
-
-    OS << tag("span", "True", TrueColor);
-    OS << ": ";
-    if (getOptions().ShowBranchCounts)
-      OS << tag("span", formatCount(R.ExecutionCount), TrueCovClass) << ", ";
-    else
-      OS << format("%0.2f", TruePercent) << "%, ";
+        (R.TrueFolded || R.ExecutionCount > 0 ? "covered-line"
+                                              : "uncovered-line");
+
+    if (R.TrueFolded)
+      OS << "Folded, ";
+    else {
+      OS << tag("span", "True", TrueColor) << ": ";
+      if (getOptions().ShowBranchCounts)
+        OS << tag("span", formatCount(R.ExecutionCount), TrueCovClass) << ", ";
+      else
+        OS << format("%0.2f", TruePercent) << "%, ";
+    }
 
     // Display FalseCount or FalsePercent.
-    std::string FalseColor = R.FalseExecutionCount ? "None" : "red branch";
+    std::string FalseColor =
+        (R.FalseFolded || R.FalseExecutionCount ? "None" : "red branch");
     std::string FalseCovClass =
-        (R.FalseExecutionCount > 0) ? "covered-line" : "uncovered-line";
-
-    OS << tag("span", "False", FalseColor);
-    OS << ": ";
-    if (getOptions().ShowBranchCounts)
-      OS << tag("span", formatCount(R.FalseExecutionCount), FalseCovClass);
-    else
-      OS << format("%0.2f", FalsePercent) << "%";
-
-    OS << "]\n";
+        (R.FalseFolded || R.FalseExecutionCount > 0 ? "covered-line"
+                                                    : "uncovered-line");
+
+    if (R.FalseFolded)
+      OS << "Folded]\n";
+    else {
+      OS << tag("span", "False", FalseColor) << ": ";
+      if (getOptions().ShowBranchCounts)
+        OS << tag("span", formatCount(R.FalseExecutionCount), FalseCovClass)
+           << "]\n";
+      else
+        OS << format("%0.2f", FalsePercent) << "%]\n";
+    }
   }
   OS << EndPre;
   OS << EndExpansionDiv;