LLVM Embedded Toolchains Working Group sync up

[smithp35]

I recommend posting a separate thread to the list just in case it gets buried at the end of the thread

The most recent threads I can find on code coverage are:

Code coverage metrics for LLVM Compiler Infrastructure

Code coverage is the percentage of code that is executed by automated tests. Code coverage tells us which lines of a project have been executed and which have not. The LLVM Compiler Infrastructure has upwards of 100,000 tests (unit, regression, and test suite) that can be executed with a single make check-all command, and a very large codebase consisting of millions of lines and multiple subprojects such as Clang, MLIR, OpenMP, Polly etc. It is therefore natural that some parts of the compiler …

Proposal: add instrumentation for PGO and code coverage

Background: PGO: LLVM already has support for branch weight metadata and can use that to compute block frequencies and generate better code. Those branch weights can come from __builtin_expect or from real profile data. We currently have some support for IR-level instrumentation to insert CFG edge counts and then read those counts back into the IR as branch weights. That support is not very well integrated into clang and does not work well if the IR changes at all after the profile data is …

These may be a good source for some authoratitive reviewers.

I’m willing to help for general comments, but I’ve personally no prior experience in the code-coverage parts of LLVM so I fall into the category of someone that might help but won’t be able to approve.