let it be so

.bazelrc

@@ -0,0 +1,2 @@
+build --incompatible_enable_cc_toolchain_resolution
+build --action_env BAZEL_DO_NOT_DETECT_CPP_TOOLCHAIN=1

.envrc

@@ -0,0 +1,45 @@
+set -eu
+
+BIN_DIR="$(git rev-parse --show-toplevel)/bin"
+export PATH="$BIN_DIR:$PATH"
+
+_u_bzl=https://github.com/bazelbuild/bazelisk/releases/download/v1.12.0/bazelisk-
+_u_bldf=https://github.com/bazelbuild/buildtools/releases/download/5.1.0/buildifier-
+
+if [[ "${PRINT_TOOL_HASHES:-no}" = "yes" ]]; then
+    for os in linux darwin; do
+        for arch in amd64 arm64; do
+            hash_bzl=$(direnv fetchurl "${_u_bzl}$os-$arch")
+            hash_bldf=$(direnv fetchurl "${_u_bldf}$os-$arch")
+            echo -e "bzl:  $os-$arch\t$hash_bzl"
+            echo -e "bldf: $os-$arch\t$hash_bldf"
+        done
+    done
+fi
+
+# to fetch the hashes, run:
+# $ PRINT_TOOL_HASHES=yes bash .envrc
+case "$(uname | tr A-Z a-z)-$(uname -m)" in
+    linux-x86_64)
+        bzl=$(direnv fetchurl "${_u_bzl}linux-amd64" sha256-awvLLqFbyhb/+r5v2nWANEA3U1TAhUgP42HSy/MlAds=)
+        bldf=$(direnv fetchurl "${_u_bldf}linux-amd64" sha256-Ur9rECy0+IRk4ZfKrAbWl5P6KwX1rVCn579vvWVmSKM=)
+        ;;
+    linux-aarch64)
+        bzl=$(direnv fetchurl "${_u_bzl}linux-arm64" sha256-KdhhykjfJKPo3sV/sAUIumZKMZIQR7JobDjPmiDUY58=)
+        bldf=$(direnv fetchurl "${_u_bldf}linux-arm64" sha256-kX1ZnbsEDmOuen4a23ENIFeBGQL9yeNczpJev9lm7rg=)
+        ;;
+    darwin-x86_64)
+        bzl=$(direnv fetchurl "${_u_bzl}darwin-amd64" sha256-cM9/50gI0WQY03H+uMzU58RCFdsD0sT/x1t2e3ZUCfs=)
+        bldf=$(direnv fetchurl "${_u_bldf}darwin-amd64" sha256-yTeNn0KT/DjsVKCPvHTnqdKJFNrmiRM0QB5Z849uZdw=)
+        ;;
+    darwin-arm64)
+        bzl=$(direnv fetchurl "${_u_bzl}darwin-arm64" sha256-NFu4uQDWue90I06enkE67Tj7Ke8lXkrhisYb9KYQLYQ=)
+        bldf=$(direnv fetchurl "${_u_bldf}darwin-arm64" sha256-dF/rXqlstv85p2soIcV1kf1wtSgyVWJIbUe10IkA4uQ=)
+        ;;
+    *)
+        >&2 echo "unsupported architecture tuple $(uname | tr A-Z a-z)-$(uname -m)"
+        exit 1;;
+esac
+
+ln -sf "${bzl}" "$BIN_DIR/bazel"
+ln -sf "${bldf}" "$BIN_DIR/buildifier"

.gitignore

@@ -0,0 +1,12 @@
+*~
+*.sw[op]
+
+/bin/bazel
+/bin/buildifier
+/bin/bazelisk-*
+
+/bazel-test-zigcc
+/bazel-bin
+/bazel-out
+/bazel-testlogs
+/bazel-x

BUILD

@@ -0,0 +1,9 @@
+NTESTS=96
+
+[
+    cc_binary(
+        name = "zigzag-{}".format(i),
+        srcs = ["main.c"],
+        copts = ["-DZIGZAG={}".format(i)],
+    ) for i in range(NTESTS)
+]

README.md

@@ -0,0 +1,35 @@
+bazel-zig-cc and llvm
+---------------------
+
+bazel-zig-cc has a performance issue when compiling many files. This repository
+reproduces that.
+
+Steps to reproduce
+------------------
+
+llvm14: 10-11 seconds to compile 96 binaries on an 8-core machine:
+
+```
+$ bazel clean; bazel shutdown; bazel build --extra_toolchains=@llvm_toolchain//:cc-toolchain-x86_64-linux ...
+INFO: Starting clean (this may take a while). Consider using --async if the clean takes more than several minutes.
+Starting local Bazel server and connecting to it...
+INFO: Analyzed 96 targets (41 packages loaded, 1458 targets configured).
+INFO: Found 96 targets...
+INFO: Elapsed time: 10.725s, Critical Path: 0.66s
+INFO: 481 processes: 289 internal, 192 linux-sandbox.
+INFO: Build completed successfully, 481 total actions
+```
+
+zig cc: 3.5 minutes. Anecdotally when looking at `htop` looks like it does not
+parallelize at all:
+
+```
+$ bazel clean; bazel shutdown; bazel build  --platforms=@zig_sdk//libc_aware/platform:linux_amd64_gnu.2.28 ...
+INFO: Starting clean (this may take a while). Consider using --async if the clean takes more than several minutes.
+Starting local Bazel server and connecting to it...
+INFO: Analyzed 96 targets (41 packages loaded, 14394 targets configured).
+INFO: Found 96 targets...
+INFO: Elapsed time: 214.333s, Critical Path: 18.31s
+INFO: 385 processes: 193 internal, 192 linux-sandbox.
+INFO: Build completed successfully, 385 total actions
+```

WORKSPACE

@@ -0,0 +1,57 @@
+load("@bazel_tools//tools/build_defs/repo:http.bzl", "http_archive")
+
+## LLVM-14
+
+BAZEL_TOOLCHAIN_TAG = "0.7.2"
+BAZEL_TOOLCHAIN_SHA = "f7aa8e59c9d3cafde6edb372d9bd25fb4ee7293ab20b916d867cd0baaa642529"
+
+http_archive(
+    name = "com_grail_bazel_toolchain",
+    sha256 = BAZEL_TOOLCHAIN_SHA,
+    strip_prefix = "bazel-toolchain-{tag}".format(tag = BAZEL_TOOLCHAIN_TAG),
+    canonical_id = BAZEL_TOOLCHAIN_TAG,
+    url = "https://github.com/grailbio/bazel-toolchain/archive/{tag}.tar.gz".format(tag = BAZEL_TOOLCHAIN_TAG),
+)
+
+load("@com_grail_bazel_toolchain//toolchain:deps.bzl", "bazel_toolchain_dependencies")
+
+bazel_toolchain_dependencies()
+
+load("@com_grail_bazel_toolchain//toolchain:rules.bzl", "llvm_toolchain")
+
+llvm_toolchain(
+    name = "llvm_toolchain",
+    llvm_version = "14.0.0",
+)
+
+load("@llvm_toolchain//:toolchains.bzl", "llvm_register_toolchains")
+
+#llvm_register_toolchains()
+
+### ZIG
+
+BAZEL_ZIG_CC_VERSION = "ae2746ebebc4e8d5c9d9638f0d1f858708002681"
+
+http_archive(
+    name = "bazel-zig-cc",
+    sha256 = "0f50bb8e130429ccae3017ba3274dd276ac744474b426f72df86a4a4a8c66ca0",
+    strip_prefix = "bazel-zig-cc-{}".format(BAZEL_ZIG_CC_VERSION),
+    urls = [
+        "https://git.sr.ht/~motiejus/bazel-zig-cc/archive/{}.tar.gz".format(BAZEL_ZIG_CC_VERSION),
+    ],
+)
+
+load("@bazel-zig-cc//toolchain:defs.bzl", zig_toolchains = "toolchains")
+
+zig_toolchains()
+
+register_toolchains(
+    # amd64 toolchains for libc-aware platforms:
+    "@zig_sdk//libc_aware/toolchain:linux_amd64_gnu.2.19",
+    "@zig_sdk//libc_aware/toolchain:linux_amd64_gnu.2.28",
+    "@zig_sdk//libc_aware/toolchain:linux_amd64_gnu.2.31",
+    "@zig_sdk//libc_aware/toolchain:linux_amd64_musl",
+    # arm64 toolchains for libc-aware platforms:
+    "@zig_sdk//libc_aware/toolchain:linux_arm64_gnu.2.28",
+    "@zig_sdk//libc_aware/toolchain:linux_arm64_musl",
+)

main.c

@@ -0,0 +1,11 @@
+#include <stdio.h>
+#include <features.h>
+
+int main() {
+    #ifdef __GLIBC__
+    printf("glibc_%d.%d\n", __GLIBC__, __GLIBC_MINOR__);
+    #else
+    printf("non-glibc\n");
+    #endif
+    return 0;
+}