InstrProf: Teach llvm-cov to show the max count instead of the last

When multiple regions start on the same line, llvm-cov was just
showing the count of the last one as the line count. This can be
confusing and misleading for things like one-liner loops, where the
count at the end isn't very interesting, or even "if" statements with
an opening brace at the end of the line.

Instead, use the maximum of all of the region start counts.

llvm-svn: 230263

llvm/test/tools/llvm-cov/showLineExecutionCounts.cpp

@@ -12,11 +12,11 @@ int main() {                             // CHECK:   1| [[@LINE]]|int main(
     x = 1;                               // CHECK:   1| [[@LINE]]|    x = 1
   }                                      // CHECK:   1| [[@LINE]]|  }
                                          // CHECK:   1| [[@LINE]]|
-  for (int i = 0; i < 100; ++i) {        // CHECK: 100| [[@LINE]]|  for (
+  for (int i = 0; i < 100; ++i) {        // CHECK: 101| [[@LINE]]|  for (
     x = 1;                               // CHECK: 100| [[@LINE]]|    x = 1
   }                                      // CHECK: 100| [[@LINE]]|  }
                                          // CHECK:   1| [[@LINE]]|
-  x = x < 10 ? x + 1 : x - 1;            // CHECK:   0| [[@LINE]]|  x =
+  x = x < 10 ? x + 1 : x - 1;            // CHECK:   1| [[@LINE]]|  x =
   x = x > 10 ?                           // CHECK:   1| [[@LINE]]|  x =
         x - 1:                           // CHECK:   0| [[@LINE]]|        x
         x + 1;                           // CHECK:   1| [[@LINE]]|        x

llvm/tools/llvm-cov/SourceCoverageView.h

@@ -90,15 +90,14 @@ private:
     bool hasMultipleRegions() const { return RegionCount > 1; }
 
     void addRegionStartCount(uint64_t Count) {
-      Mapped = true;
-      ExecutionCount = Count;
+      // The max of all region starts is the most interesting value.
+      addRegionCount(RegionCount ? std::max(ExecutionCount, Count) : Count);
       ++RegionCount;
     }
 
     void addRegionCount(uint64_t Count) {
       Mapped = true;
-      if (!RegionCount)
-        ExecutionCount = Count;
+      ExecutionCount = Count;
     }
   };