[llvm-dev] Getting a combined llvm-cov report for a set of tests

[Chris Brown via llvm-dev]

I am working on a large software project with many thousands of tests. A
common workflow using gcov as a coverage tool is:

1) Build code with coverage instrumentation
2) Run *all* the tests. Gcov aggregates the line coverage counters together
into its .gcda files
3) Generate a report for some set of files using those combined gcda files.
4) Analyze the report to find files/sections of code that are not covered
by any test.

Using llvm's source-based code coverage, I don't believe I can accomplish
steps 3-4. Each binary produces a .profraw file which contains profile
counts, but the mapping of those profile counts to files is contained
inside the binary.  I can use llvm-profdata merge to merge multiple
.profraw files together, but the report can still only be generated for a
single binary, and so only the files contained in that binary's
__llvm_covmap section will be produced as part of the report.

Am I correct in this thinking? Is there a way to get a single coverage
report for a set of multiple binaries? I discovered the undocumented
'llvm-cov convert-for-testing' command which generates 'covmapping files',
which appear to be the contents of __llvm_covmap with an additional header.
Maybe it's possible to merge multiple of these covmapping files and
generate a report from that data (plus the merged profraw files)? Or
perhaps I could use 'llvm-cov export' on each binary individually and
manually merge the results somehow (although in that case, I would not be
able to 'import' the merge to create the usual report) ? Are there other
suggestions, or is this a planned feature in 4.0? I found some discussion
on this thread, but I am not sure if this is asking the same thing:
https://groups.google.com/forum/#!topic/llvm-dev/r4qOdN-y9hc

Thanks!
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