Rust doesn't use the Bitcode loader, so don't build it

[ZuseZ4]

Rust recently updated to llvm 21: rust-lang/rust#143684
This caused build failures in the BCLoader.

[6/8] Building CXX object BCLoad/CMakeFiles/EnzymeBCLoad-21.dir/BCLoader.cpp.o
FAILED: BCLoad/CMakeFiles/EnzymeBCLoad-21.dir/BCLoader.cpp.o
/usr/bin/c++ -DENZYME_VERSION_MAJOR=0 -DENZYME_VERSION_MINOR=0 -DENZYME_VERSION_PATCH=79 -DEnzymeBCLoad_21_EXPORTS -I/home/gh-Sa4dUs/rust/build/aarch64-unknown-linux-gnu/llvm/include -I/home/gh-Sa4dUs/rust/build/aarch64-unknown-linux-gnu/enzyme/build/include -I/home/gh-Sa4dUs/rust/build/aarch64-unknown-linux-gnu/enzyme/build/BCLoad/gsl -Wall -fno-rtti -ffunction-sections -fdata-sections -fPIC -Werror=unused-variable -Werror=dangling-else -Werror=unused-but-set-variable -Werror=return-type -Werror=nonnull -Werror=unused-result -Werror=reorder -Werror=switch -O2 -std=gnu++17 -fPIC   -D_GNU_SOURCE -D_DEBUG -D_GLIBCXX_ASSERTIONS -DEXPERIMENTAL_KEY_INSTRUCTIONS -D__STDC_CONSTANT_MACROS -D__STDC_FORMAT_MACROS -D__STDC_LIMIT_MACROS -MD -MT BCLoad/CMakeFiles/EnzymeBCLoad-21.dir/BCLoader.cpp.o -MF BCLoad/CMakeFiles/EnzymeBCLoad-21.dir/BCLoader.cpp.o.d -o BCLoad/CMakeFiles/EnzymeBCLoad-21.dir/BCLoader.cpp.o -c /home/gh-Sa4dUs/rust/src/tools/enzyme/enzyme/BCLoad/BCLoader.cpp
/home/gh-Sa4dUs/rust/src/tools/enzyme/enzyme/BCLoad/BCLoader.cpp: In function 'bool provideDefinitions(llvm::Module&, std::set<std::__cxx11::basic_string<char> >, std::vector<std::__cxx11::basic_string<char> >&)':
/home/gh-Sa4dUs/rust/src/tools/enzyme/enzyme/BCLoad/BCLoader.cpp:135:25: error: cannot convert 'const char [1]' to 'llvm::Triple'
  135 |     BC->setTargetTriple("");
      |                         ^~
      |                         |
      |                         const char [1]
In file included from /home/gh-Sa4dUs/rust/src/tools/enzyme/enzyme/BCLoad/BCLoader.cpp:2:
/home/gh-Sa4dUs/rust/build/aarch64-unknown-linux-gnu/llvm/include/llvm/IR/Module.h:324:31: note:   initializing argument 1 of 'void llvm::Module::setTargetTriple(llvm::Triple)'
  324 |   void setTargetTriple(Triple T) { TargetTriple = std::move(T); }
      |                        ~~~~~~~^
ninja: build stopped: subcommand failed.

The failure should be fixed independently, but afaik on the Rust side we don't use the BCloader, so I think there is no reason to build it in the first place. With this patch, rust bootstrap works again, so I merged rust-lang#29 for now, but would like to upstream it.

Relatedly, I should probably disable the following:

[116/144] Performing download step (git clone) for 'fblas'
Cloning into 'fblas'...
HEAD is now at 94f7c31 fix
[125/144] Performing download step (git clone) for 'gsl64'
Cloning into 'gsl64'...
HEAD is now at 5805b83 Remove short circuit
Submodule 'ampl/thirdparty/asl' (https://github.com/ampl/asl.git) registered for path 'ampl/thirdparty/asl'
Cloning into '/prog/rust/build/x86_64-unknown-linux-gnu/enzyme/build/BCLoad/gsl64/src/gsl64/ampl/thirdparty/asl'...
Submodule path 'ampl/thirdparty/asl': checked out 'dd1c4c4e5647ead51169caad280c36a88d0f0237'
[128/144] Performing download step (git clone) for 'gsl'
Cloning into 'gsl'...
HEAD is now at 5805b83 Remove short circuit
Submodule 'ampl/thirdparty/asl' (https://github.com/ampl/asl.git) registered for path 'ampl/thirdparty/asl'
Cloning into 'prog/rust/build/x86_64-unknown-linux-gnu/enzyme/build/BCLoad/gsl/src/gsl/ampl/thirdparty/asl'...
Submodule path 'ampl/thirdparty/asl': checked out 'dd1c4c4e5647ead51169caad280c36a88d0f0237'

(The toolchain size increase of ~9 MiB through Enzyme currently is the only reason why std::autodiff isn't enabled in nightly by default, so that's somewhat relevant.)

[wsmoses]

this is fine, but also could you add the fix for the bcloader on llvm21 (presumably BC->setTargetTriple(""); becomes BC->setTargetTriple(llvm::Triple("")); )

[wsmoses]

also probably add LLVM 21 integration test CI, so then this will be caught in the future?

[ZuseZ4]

I've added your fix, it works locally from LLVM15 onwards, but somehow Julia seems unhappy. So I just limited the fix to 21+.

[wsmoses]

can you also add the LLVM21 test to confirm this builds as expected?

[ZuseZ4]

We don't have LLVM-21 CI, and touching enzyme CI is a bit beyond the time I have atm.

[wsmoses]

it should just be adding it to the relevant yml file

[ZuseZ4]

ping @wsmoses this keeps comming up

[ZuseZ4]

thx