Re: [RFC PATCH 2/2] gitlab-ci: Add a job building TCI with Clang

[Stefan Weil]

Am 23.01.21 um 09:59 schrieb Wataru Ashihara:

> Actually I use TCI also on macOS. Like the use case quoted by Philippe,
> there're even other reasons to use TCI:
>
> 1. Learning TCG ops.
> 2. Debugging QEMU with gdb. e.g. diagnose codegen or stepping into
>     helper functions from tci.c:tcg_qemu_tb_exec().
> 3. Guest instruction tracing. TCI is faster than TCG or KVM when tracing
>     the guest ops [1]. I guess qira is using TCI for this reason [2].
>
> [1]: https://twitter.com/wata_ash/status/1352899988032942080
> [2]: https://github.com/geohot/qira/blob/v1.3/tracers/qemu_build.sh#L55


Yes, TCI can help a lot for debugging, especially also when porting TCG 
to a new host architecture.

If we had binaries which can switch from native to interpreted TCG, it 
could also be a reference implementation used for unit tests, comparing 
the results for each TCG opcode.

Using TCI with profiling like gprof is useful to count the frequency of 
the different TCG opcodes in practical scenarios and can be used to 
detect bottlenecks (and less frequent or unused opcodes) for native TCG, 
too.

Stefan