[Coverage] Use gap regions to select better line exec counts

After clang started emitting deferred regions (r312818), llvm-cov has
had a hard time picking reasonable line execuction counts. There have
been one or two generic improvements in this area (e.g r310012), but
line counts can still report coverage for whitespace instead of code
(llvm.org/PR34612).

To fix the problem:

 * Introduce a new region kind so that frontends can explicitly label
   gap areas.

   This is done by changing the encoding of the columnEnd field of
   MappingRegion. This doesn't substantially increase binary size, and
   makes it easy to maintain backwards-compatibility.

 * Don't set the line count to a count from a gap area, unless the count
   comes from a wrapped segment.

 * Don't highlight gap areas as uncovered.

Fixes llvm.org/PR34612.

llvm-svn: 313597

1 files changed, 1 insertions, 1 deletions

diff --git a/llvm/tools/llvm-cov/SourceCoverageViewText.cpp b/llvm/tools/llvm-cov/SourceCoverageViewText.cpp
index a88558fceca..a78c0575cdc 100644
--- a/llvm/tools/llvm-cov/SourceCoverageViewText.cpp
+++ b/llvm/tools/llvm-cov/SourceCoverageViewText.cpp
@@ -120,7 +120,7 @@ void SourceCoverageViewText::renderLine(
     Col = End;
     if (Col == ExpansionCol)
       Highlight = raw_ostream::CYAN;
-    else if (S->HasCount && S->Count == 0)
+    else if (!S->IsGapRegion && S->HasCount && S->Count == 0)
       Highlight = raw_ostream::RED;
     else
       Highlight = None;