[coverage] Make smaller regions for the first case of a switch.

We never overwrite the end location of a region, so we would end up with
an overly large region when we reused the switch's region.

It's possible this code will be substantially rewritten in the near
future to deal with fallthrough more accurately, but this seems like
an improvement on its own for now.

Differential Revision: https://reviews.llvm.org/D34801

llvm-svn: 309901

1 files changed, 13 insertions, 6 deletions

diff --git a/clang/lib/CodeGen/CoverageMappingGen.cpp b/clang/lib/CodeGen/CoverageMappingGen.cpp
index 51f5902b91a..1484ec78b88 100644
--- a/clang/lib/CodeGen/CoverageMappingGen.cpp
+++ b/clang/lib/CodeGen/CoverageMappingGen.cpp
@@ -704,6 +704,8 @@ struct CounterCoverageMappingBuilder
     assert(!BreakContinueStack.empty() && "break not in a loop or switch!");
     BreakContinueStack.back().BreakCount = addCounters(
         BreakContinueStack.back().BreakCount, getRegion().getCounter());
+    // FIXME: a break in a switch should terminate regions for all preceding
+    // case statements, not just the most recent one.
     terminateRegion(S);
   }
 
@@ -845,15 +847,20 @@ struct CounterCoverageMappingBuilder
     extendRegion(Body);
     if (const auto *CS = dyn_cast<CompoundStmt>(Body)) {
       if (!CS->body_empty()) {
-        // The body of the switch needs a zero region so that fallthrough counts
-        // behave correctly, but it would be misleading to include the braces of
-        // the compound statement in the zeroed area, so we need to handle this
-        // specially.
+        // Make a region for the body of the switch.  If the body starts with
+        // a case, that case will reuse this region; otherwise, this covers
+        // the unreachable code at the beginning of the switch body.
         size_t Index =
-            pushRegion(Counter::getZero(), getStart(CS->body_front()),
-                       getEnd(CS->body_back()));
+            pushRegion(Counter::getZero(), getStart(CS->body_front()));
         for (const auto *Child : CS->children())
           Visit(Child);
+
+        // Set the end for the body of the switch, if it isn't already set.
+        for (size_t i = RegionStack.size(); i != Index; --i) {
+          if (!RegionStack[i - 1].hasEndLoc())
+            RegionStack[i - 1].setEndLoc(getEnd(CS->body_back()));
+        }
+
         popRegions(Index);
       }
     } else