[Coverage] Use the most-recent completed region count (PR35437)

This is a fix for the coverage segment builder.

If multiple regions must be popped off the active stack at once, and
more than one of them end at the same location, emit a segment using the
count from the most-recent completed region.

Fixes PR35437, rdar://35760630

Testing: invoked llvm-cov on a stage2 build of clang, additional unit
tests, check-profile

llvm-svn: 319391

1 files changed, 6 insertions, 0 deletions

diff --git a/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp b/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp
index 6cde3863f18..0d52e48084f 100644
--- a/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp
+++ b/llvm/lib/ProfileData/Coverage/CoverageMapping.cpp
@@ -388,6 +388,12 @@ class SegmentBuilder {
       if (CompletedSegmentLoc == CompletedRegion->endLoc())
         continue;
 
+      // Use the count from the next completed region if it ends at the same
+      // location.
+      if (I + 1 < E &&
+          CompletedRegion->endLoc() == ActiveRegions[I + 1]->endLoc())
+        CompletedRegion = ActiveRegions[I + 1];
+
       startSegment(*CompletedRegion, CompletedSegmentLoc, false);
     }