test-zig-cc/README.md

bazel-zig-cc and llvm
---------------------

bazel-zig-cc has a performance issue when compiling many files. This repository
reproduces that.

Steps to reproduce
------------------

llvm14: 12-13 seconds to compile 64 binaries on an 8-core machine:

```
$ bazel clean; bazel shutdown; bazel build --extra_toolchains=@llvm_toolchain//:cc-toolchain-x86_64-linux ...
INFO: Elapsed time: 12.454s, Critical Path: 1.11s
```

zig cc: 142 seconds:

```
$ bazel clean; bazel shutdown; bazel build  --platforms=@zig_sdk//libc_aware/platform:linux_amd64_gnu.2.28 ...
INFO: Elapsed time: 142.264s, Critical Path: 20.65s
```

zig cc with `--sandbox_base=/dev/shm`: 40 seconds:

```
bazel clean; bazel shutdown; bazel build --sandbox_base=/dev/shm  --platforms=@zig_sdk//libc_aware/platform:linux_amd64_gnu.2.28 ...
INFO: Elapsed time: 42.251s, Critical Path: 5.26s
```

zig cc without the sandbox (which means zig will treat its dependencies as the same file): 17 seconds:

```
bazel clean; bazel shutdown; bazel build --spawn_strategy=local  --platforms=@zig_sdk//libc_aware/platform:linux_amd64_gnu.2.28 ...
INFO: Elapsed time: 17.021s, Critical Path: 1.67s
```