[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, 1 insertions, 1 deletions

diff --git a/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp b/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp
index c713371..119e091 100644
--- a/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp
+++ b/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp
@@ -503,7 +503,7 @@ public:
       const auto &BranchParams = B->getBranchParams();
       PosToID[I] = BranchParams.ID;
       CondLoc[I] = B->startLoc();
-      Folded[I++] = (B->Count.isZero() && B->FalseCount.isZero());
+      Folded[I++] = (B->Count.isZero() || B->FalseCount.isZero());
     }
 
     // Using Profile Bitmap from runtime, mark the executed test vectors.