[llvm-dev] [EXTERNAL] How to get branch coverage by using 'source-based code coverage'

Phipps, Alan via llvm-dev llvm-dev at lists.llvm.org
Tue Apr 28 07:14:14 PDT 2020

Hi Ted,

Presently, branch coverage is not supported in clang source-based code coverage, but I am working on implementing branch condition coverage right now.  It will track True/False branches for each leaf-level condition, including within Boolean expressions comprised of logical operators (“&&”, “||”).  Technically, this condition-based coverage is more granular than how “branch coverage” is often defined (tracking on that control flow decisions allow for all regions to be hit), and is closer to the granularity that GCOV provides, but it’s anchored to the source code, won’t count “hidden branches”, and isn’t negatively impacted by optimization (although the reverse isn’t true: coverage instrumentation may impact optimization).

My work is a step closer to getting us toward Modified Condition/Decision Coverage (MC/DC).  I hope to upstream my work within the next few months, so unfortunately it won’t help you in the short-term.  Region coverage may be enough for what you need if you can ascertain based on the coverage that control-flow decisions have evaluated to both true and false, but I’ll let others comment here with suggestions.

-Alan Phipps

From: llvm-dev [mailto:llvm-dev-bounces at lists.llvm.org] On Behalf Of LoveZhi Xie via llvm-dev
Sent: Sunday, April 26, 2020 11:36 AM
To: llvm-dev at lists.llvm.org
Subject: [EXTERNAL] [llvm-dev] How to get branch coverage by using 'source-based code coverage'

Hi, llvm/clang experts

I need to get the branch coverage for some testing code. But i found gcov can't give a expected coverage which may
count some 'hidden branch' in (See stackoverflow answer<https://stackoverflow.com/questions/42003783/lcov-gcov-branch-coverage-with-c-producing-branches-all-over-the-place>). Instead, I turn to use clang and the 'source-based code coverage' feature
may be a right choice. But i can't find anything to describe branch coverage explicitly on the official site<https://clang.llvm.org/docs/SourceBasedCodeCoverage.html>.

So how to use clang to get branch coverage by utilizing 'source-based...' feature?  And is region coverage equivalent to branch coverage?
(I tested on a simple program and region coverage seems pretty close to branch coverage)

Any help is highly appreciated

Ted Xie

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