[llvm-cov gcov] Fix calculating coverage of template functions

Template functions share the same lines in source files, so the common
container of lines' properties cannot be used to calculate the coverage
statistics of individual functions.

> cat tmpl.cpp
template <int N> int test() { return N; }
int main() { return test<1>() + test<2>(); }
> clang++ --coverage tmpl.cpp -o tmpl
> ./tmpl
> llvm-cov gcov tmpl.cpp -f
...
Function '_Z4testILi1EEiv'
Lines executed:100.00% of 1

Function '_Z4testILi2EEiv'
Lines executed:-nan% of 0
...
> llvm-cov-patched gcov tmpl.cpp -f
...
Function '_Z4testILi1EEiv'
Lines executed:100.00% of 1

Function '_Z4testILi2EEiv'
Lines executed:100.00% of 1
...

Differential Revision: https://reviews.llvm.org/D121390

Author: igorkudrin

llvm/lib/ProfileData/GCOV.cpp

@@ -13,6 +13,7 @@
 
 #include "llvm/ProfileData/GCOV.h"
 #include "llvm/ADT/STLExtras.h"
+#include "llvm/ADT/SmallSet.h"
 #include "llvm/Config/llvm-config.h"
 #include "llvm/Demangle/Demangle.h"
 #include "llvm/Support/Debug.h"
@@ -662,6 +663,8 @@ void Context::collectFunction(GCOVFunction &f, Summary &summary) {
   if (f.startLine >= si.startLineToFunctions.size())
     si.startLineToFunctions.resize(f.startLine + 1);
   si.startLineToFunctions[f.startLine].push_back(&f);
+  SmallSet<uint32_t, 16> lines;
+  SmallSet<uint32_t, 16> linesExec;
   for (const GCOVBlock &b : f.blocksRange()) {
     if (b.lines.empty())
       continue;
@@ -670,9 +673,9 @@ void Context::collectFunction(GCOVFunction &f, Summary &summary) {
       si.lines.resize(maxLineNum + 1);
     for (uint32_t lineNum : b.lines) {
       LineInfo &line = si.lines[lineNum];
-      if (!line.exists)
+      if (lines.insert(lineNum).second)
         ++summary.lines;
-      if (line.count == 0 && b.count)
+      if (b.count && linesExec.insert(lineNum).second)
         ++summary.linesExec;
       line.exists = true;
       line.count += b.count;

llvm/test/tools/llvm-cov/gcov/Inputs/tmpl.cpp

@@ -0,0 +1,4 @@
+template <int N>
+int test() { return N; }
+
+int main() { return test<1>() + test<2>(); }

llvm/test/tools/llvm-cov/gcov/Inputs/tmpl.gcda

@@ -0,0 +1,19 @@
+# Check that the coverage statistics for template functions are calculated as expected.
+
+RUN: rm -rf %t
+RUN: mkdir %t
+RUN: cd %t
+RUN: cp %p/Inputs/tmpl* .
+
+RUN: llvm-cov gcov tmpl.cpp -f | FileCheck %s --check-prefix=F
+RUN: llvm-cov gcov tmpl.cpp -t | FileCheck %s --check-prefix=T
+
+F:      Function '_Z4testILi1EEiv'
+F-NEXT: Lines executed:100.00% of 1
+F:      Function '_Z4testILi2EEiv'
+F-NEXT: Lines executed:100.00% of 1
+
+T:      -: 1:template <int N>
+T-NEXT: 2: 2:int test() { return N; }
+T-NEXT: -: 3:
+T-NEXT: 1: 4:int main() { return test<1>() + test<2>(); }