Add YosysHQ/abc as a submodule located in abc.

[RCoeurjoly]

Add YosysHQ/abc as a submodule located in abc. Apart from cloning with submodules, no other modifications are made to github actions.

This would enable building yosys with abc fetched as tar.gz, as pointed out by @mmicko in #4238 (comment)

Before starting the compilation of abc, we check four cases:

1. abc directory does not exist. The compilation is stopped with the following error.

Error: The 'abc' directory does not exist.
Initialize the submodule: Run 'git submodule update --init' to set up 'abc' as a submodule.

2. abc is a clone of abc (abc/.gitcommit content is Format). The compilation is stopped with the following error.

Error: 'abc' is not configured as a git submodule.
To resolve this:

1. Back up your changes: Save any modifications from the 'abc' directory to another location.
2. Remove the existing 'abc' directory: Delete the 'abc' directory and all its contents.
3. Initialize the submodule: Run 'git submodule update --init' to set up 'abc' as a submodule.
4. Reapply your changes: Move your saved changes back to the 'abc' directory, if necessary.

3. abc comes from a tarball (abc/.gitcommit content is different than $Format:%h$). The compilation can continue.

'abc' comes from a tarball. Continuing.

4. abc is a git submodule (checked with git submodule status). The compilation can continue.

'abc' is a git submodule. Continuing.

[mmicko]

@RCoeurjoly please note that WASI is intentionally built in build directory since that exercise out of tree build that is used in YoWASP distribution. That is then very useful since it points out if changes done in Makefiles affect out of tree builds.

[RCoeurjoly]

@RCoeurjoly please note that WASI is intentionally built in build directory since that exercise out of tree build that is used in YoWASP distribution. That is then very useful since it points out if changes done in Makefiles affect out of tree builds.

Oh I see.

[mmicko]

Also abc.tar.gz that is used is one from https://github.com/YosysHQ/yosys/releases This is more for situations where people are downloading specific Yosys version and corresponding abc.tar.gz file and building them on isolated environments.

[whitequark]

$(ABCREV) was used to make sure abc actually gets rebuilt when you change the ABC checkout. Is this still the case? If not you'll need some other way to rebuild ABC when that happens.

[whitequark]

An out-of-tree build of Yosys should also do an out-of-tree build of abc.

[RCoeurjoly]

Should the abc executable be located in build in that case?

[whitequark]

Yep, along with all other files generated during the build. Running git clean -dxf in the Yosys or abc checkout should do nothing. (Modulo the odd case of abc being not actually a checked-out submodule, where generated files should live in the same place but my illustration does not work.)

[whitequark]

Should this not be /build? This would ignore every file or directory called build in the entire tree, which might unpleasantly surprise someone.

[whitequark]

This seems a bit of a confusing comment, as it appears to imply there's no support for out-of-tree builds.

[whitequark]

Finally!!! Great job!

[RCoeurjoly]

Finally!!! Great job!

Thanks! It was a team effort.
Also note that since you approved of the changes, I made a change to address @povik proposal here #4243 (comment).

You may want to review that also.

[whitequark]

This broke the YoWASP build after all: https://github.com/YoWASP/yosys/actions/runs/9010585766/job/24756882140#step:7:657

'abc' comes from a tarball. Continuing.
mkdir -p abc && make -C abc -f "" ABCSRC="/home/runner/work/yosys/yosys/yosys-src/abc"  CC="ccache clang" CXX="ccache clang" ABC_USE_LIBSTDCXX=1 ABC_USE_NAMESPACE=abc VERBOSE= AR="llvm-ar" RANLIB="llvm-ranlib" ARCHFLAGS="-target wasm32-wasi --sysroot /home/runner/work/yosys/yosys/wasi-sdk-19.0/share/wasi-sysroot  -D_WASI_EMULATED_PROCESS_CLOCKS -DABC_USE_STDINT_H -DABC_NO_DYNAMIC_LINKING -DABC_NO_RLIMIT" OPTFLAGS="-Os" "ABC_USE_NO_READLINE=1" "ABC_USE_NO_PTHREADS=1" PROG="abc" MSG_PREFIX="-> ABC: " libabc.a
make: the '-f' option requires a non-empty string argument
make: Entering an unknown directory
Usage: make [options] [target] ...

[whitequark]

So it turns out the YoWASP build was broken because I didn't check out submodules recursively, and the really confusing error message comes from the combination of an improper check for the presence of the submodule combined with the use of realpath.