Profiling report with branch coverage for templates is misleading

[stma247]

The export mode of tool "llvm-cov" for format "lcov" does not combine the branch counts of C++ template functions instantiations.

A preceding discussion describes the issue in detail:
https://discourse.llvm.org/t/profiling-report-with-branch-coverage-for-templates-is-misleading/82323

[stma247]

I am already working on a solution. The PR will follow soon.

[chapuni]

Thanks for working on it.
Could it be applied to text and html as well?

[evodius96]

Thanks for working on it. Could it be applied to text and html as well?

This is only really for LCOV exporting. The text and html from llvm-cov show summaries show the right information.

[chapuni]

From llvm/test/tools/llvm-cov/branch-templates.cpp

   12|       |template<typename T>
   13|      3|int func(T x) {
   14|      3|  if(x)       // CHECK: |  Branch ([[@LINE]]:6): [True: 0, False: 1]
  ------------------
  |  Branch (14:6): [True: 0, False: 1]
  |  Branch (14:6): [True: 1, False: 0]
  |  Branch (14:6): [True: 0, False: 1]
  ------------------
   15|      1|    return 0; // CHECK: |  Branch ([[@LINE-1]]:6): [True: 1, False: 0]
   16|      2|  else        // CHECK: |  Branch ([[@LINE-2]]:6): [True: 0, False: 1]
   17|      2|    return 1;
   18|      0|  int j = 1;
   19|      0|}

I'll investigate further later.

[evodius96]

Hi @chapuni

Sorry, I didn't elaborate -- this is primarily an effect of the summary report. With llvm-cov show the summary report correctly merges the data across the corresponding instantiations showing the union of the data, whereas with llvm-cov export --format=lcov it was not correctly rendering the union with BRDA. As a result, LCOV was not displaying the summary correctly.

The source-level report that you show shows the individual branch coverage information across the instantiations, but the report summary for this should have merged this data and ought to show 100% coverage for the condition.