Finch/bootstrap/README.md
Claude 0bf66740df
Compiler and docs on every system: macOS Intel in CI, releases made by CI, docs for vectors and --cpu
- CI: macOS on Apple Silicon and Intel (macos-15, macos-15-intel); a tag v* attaches every package
  (Linux x64/ARM64, macOS ARM64/x64, Windows x64, the VS Code extension) to its release
- vectors: fma is llvm.fmuladd (llvm.fma was a libm call per lane without FMA hardware: 3.5x slower)
- examples/simd.fch: a dot product eight at a time, timed against the plain loop
- README and the English guides: installing on Linux, macOS and Windows; vectors (SIMD); --cpu;
  -g is DWARF on Windows too (lldb from llvm-mingw); no more mention of the C++ compiler
- comments left from the C++ compiler (src/target.cpp, src/codegen.cpp, "never frees") brought up to date

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Psc42moPLwP43Cmb9oZqSR
2026-11-01 13:57:28 +00:00

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# The seed
Finch's compiler is written in Finch. To build it you need something that already runs Finch: the **seed**, which is
the compiler's own LLVM IR, one file per system:
| File | System | Built and tested in CI on |
|---|---|---|
| `linux-x86_64.ll` | Linux x86-64 | ubuntu-24.04 |
| `linux-aarch64.ll` | Linux ARM64 | ubuntu-24.04-arm |
| `macos-arm64.ll` | macOS, Apple Silicon | macos-15 |
| `macos-x86_64.ll` | macOS, Intel | macos-15-intel |
| `windows-x86_64.ll` | Windows x86-64 (MinGW: llvm-mingw's clang + libclang.dll) | windows-2022 |
Each CI job builds the compiler from its seed, then from itself, runs every test, and packs the result; a tag `v*` attaches
the packages to the release.
`bootstrap/build.sh` compiles the seed with `clang` (and the runtime, and libclang) into `build/finch0`; `finch0` builds
`src/` into `finch1`; `finch1` builds `src/` again into `build/finch`; the two must make the same IR, or the script stops.
## Why one per system
The seed includes how this system's C compiler passes structs by value, because the compiler calls libclang with
`CXCursor`, `CXType` and `CXString` (the calling convention is different on x86-64, on ARM64 and on Windows). So a seed
made for one system doesn't run on another, and a seed needs the target system's C headers to be made.
## When to make a new one
When the compiler's own source starts to use a feature that the committed seed doesn't have, `build.sh` fails at the first
step. Make the seed from a working compiler:
```sh
bootstrap/build.sh seed # writes bootstrap/<this system>.ll
```
For another system, from a machine that has that system's headers and a cross compiler (what `tests/cross.sh` uses):
```sh
FINCH_CC=aarch64-linux-gnu-gcc build/finch ir src/main.fch --target arm64 > bootstrap/linux-aarch64.ll
```
## Windows and macOS
Windows: `windows-x86_64.ll` is made by `bootstrap/winseed.sh` on Linux (llvm-mingw's MinGW headers and the headers of an
official LLVM for Windows); `bootstrap/winbuild.sh` turns it into `finch.exe` for trying under Wine. On a Windows machine
`bootstrap/build.sh` does the same from Git Bash: put llvm-mingw's `bin` in PATH and set `FINCH_LIBCLANG` (the path of
`libclang.dll`), `FINCH_LLVM_INCLUDE` (its `include` folder) and `FINCH_LDFLAGS=-L<folder of libclang.dll>`.
macOS: the seeds were made with the macOS 11.3 SDK. `brew install llvm@21`
gives clang and libclang; set `FINCH_CLANG`, `FINCH_LIBCLANG` and `FINCH_LLVM_INCLUDE` as the CI job does (the
[technicians' guide](../docs/en/for-technicians.md#option-b-build-it-yourself) has the lines).