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rustc: Split Emscripten to a separate codegen backend

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This commit introduces a separately compiled backend for Emscripten, avoiding
compiling the `JSBackend` target in the main LLVM codegen backend. This builds
on the foundation provided by #47671 to create a new codegen backend dedicated
solely to Emscripten, removing the `JSBackend` of the main codegen backend in
the process.

A new field was added to each target for this commit which specifies the backend
to use for translation, the default being `llvm` which is the main backend that
we use. The Emscripten targets specify an `emscripten` backend instead of the
main `llvm` one.

There's a whole bunch of consequences of this change, but I'll try to enumerate
them here:

* A *second* LLVM submodule was added in this commit. The main LLVM submodule
  will soon start to drift from the Emscripten submodule, but currently they're
  both at the same revision.
* Logic was added to rustbuild to *not* build the Emscripten backend by default.
  This is gated behind a `--enable-emscripten` flag to the configure script. By
  default users should neither check out the emscripten submodule nor compile
  it.
* The `init_repo.sh` script was updated to fetch the Emscripten submodule from
  GitHub the same way we do the main LLVM submodule (a tarball fetch).
* The Emscripten backend, turned off by default, is still turned on for a number
  of targets on CI. We'll only be shipping an Emscripten backend with Tier 1
  platforms, though. All cross-compiled platforms will not be receiving an
  Emscripten backend yet.

This commit means that when you download the `rustc` package in Rustup for Tier
1 platforms you'll be receiving two trans backends, one for Emscripten and one
that's the general LLVM backend. If you never compile for Emscripten you'll
never use the Emscripten backend, so we may update this one day to only download
the Emscripten backend when you add the Emscripten target. For now though it's
just an extra 10MB gzip'd.

Closes #46819
This commit is contained in:
Alex Crichton
2018-01-24 08:22:34 -08:00
parent 385ef1514c
commit c6daea7c9a
23 changed files with 272 additions and 129 deletions
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75
src/bootstrap/native.rs
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@@ -22,7 +22,7 @@ use std::env;
use std::ffi::OsString;
use std::fs::{self, File};
use std::io::{Read, Write};
use std::path::Path;
use std::path::{Path, PathBuf};
use std::process::Command;
use build_helper::output;
@@ -30,7 +30,7 @@ use cmake;
use cc;
use Build;
use util;
use util::{self, exe};
use build_helper::up_to_date;
use builder::{Builder, RunConfig, ShouldRun, Step};
use cache::Interned;
@@ -38,30 +38,42 @@ use cache::Interned;
#[derive(Debug, Copy, Clone, Hash, PartialEq, Eq)]
pub struct Llvm {
pub target: Interned<String>,
pub emscripten: bool,
}
impl Step for Llvm {
type Output = ();
type Output = PathBuf; // path to llvm-config
const ONLY_HOSTS: bool = true;
fn should_run(run: ShouldRun) -> ShouldRun {
run.path("src/llvm")
run.path("src/llvm").path("src/llvm-emscripten")
}
fn make_run(run: RunConfig) {
run.builder.ensure(Llvm { target: run.target })
let emscripten = run.path.map(|p| {
p.ends_with("llvm-emscripten")
}).unwrap_or(false);
run.builder.ensure(Llvm {
target: run.target,
emscripten,
});
}
/// Compile LLVM for `target`.
fn run(self, builder: &Builder) {
fn run(self, builder: &Builder) -> PathBuf {
let build = builder.build;
let target = self.target;
let emscripten = self.emscripten;
// If we're using a custom LLVM bail out here, but we can only use a
// custom LLVM for the build triple.
if let Some(config) = build.config.target_config.get(&target) {
if let Some(ref s) = config.llvm_config {
return check_llvm_version(build, s);
if !self.emscripten {
if let Some(config) = build.config.target_config.get(&target) {
if let Some(ref s) = config.llvm_config {
check_llvm_version(build, s);
return s.to_path_buf()
}
}
}
@@ -69,8 +81,17 @@ impl Step for Llvm {
let mut rebuild_trigger_contents = String::new();
t!(t!(File::open(&rebuild_trigger)).read_to_string(&mut rebuild_trigger_contents));
let out_dir = build.llvm_out(target);
let (out_dir, llvm_config_ret_dir) = if emscripten {
let dir = build.emscripten_llvm_out(target);
let config_dir = dir.join("bin");
(dir, config_dir)
} else {
(build.llvm_out(target),
build.llvm_out(build.config.build).join("bin"))
};
let done_stamp = out_dir.join("llvm-finished-building");
let build_llvm_config = llvm_config_ret_dir
.join(exe("llvm-config", &*build.config.build));
if done_stamp.exists() {
let mut done_contents = String::new();
t!(t!(File::open(&done_stamp)).read_to_string(&mut done_contents));
@@ -78,17 +99,19 @@ impl Step for Llvm {
// If LLVM was already built previously and contents of the rebuild-trigger file
// didn't change from the previous build, then no action is required.
if done_contents == rebuild_trigger_contents {
return
return build_llvm_config
}
}
let _folder = build.fold_output(|| "llvm");
println!("Building LLVM for {}", target);
let descriptor = if emscripten { "Emscripten " } else { "" };
println!("Building {}LLVM for {}", descriptor, target);
let _time = util::timeit();
t!(fs::create_dir_all(&out_dir));
// http://llvm.org/docs/CMake.html
let mut cfg = cmake::Config::new(build.src.join("src/llvm"));
let root = if self.emscripten { "src/llvm-emscripten" } else { "src/llvm" };
let mut cfg = cmake::Config::new(build.src.join(root));
if build.config.ninja {
cfg.generator("Ninja");
}
@@ -99,13 +122,22 @@ impl Step for Llvm {
(true, true) => "RelWithDebInfo",
};
// NOTE: remember to also update `config.toml.example` when changing the defaults!
let llvm_targets = match build.config.llvm_targets {
Some(ref s) => s,
None => "X86;ARM;AArch64;Mips;PowerPC;SystemZ;JSBackend;MSP430;Sparc;NVPTX;Hexagon",
// NOTE: remember to also update `config.toml.example` when changing the
// defaults!
let llvm_targets = if self.emscripten {
"JSBackend"
} else {
match build.config.llvm_targets {
Some(ref s) => s,
None => "X86;ARM;AArch64;Mips;PowerPC;SystemZ;MSP430;Sparc;NVPTX;Hexagon",
}
};
let llvm_exp_targets = &build.config.llvm_experimental_targets;
let llvm_exp_targets = if self.emscripten {
""
} else {
&build.config.llvm_experimental_targets[..]
};
let assertions = if build.config.llvm_assertions {"ON"} else {"OFF"};
@@ -155,7 +187,10 @@ impl Step for Llvm {
// http://llvm.org/docs/HowToCrossCompileLLVM.html
if target != build.build {
builder.ensure(Llvm { target: build.build });
builder.ensure(Llvm {
target: build.build,
emscripten: false,
});
// FIXME: if the llvm root for the build triple is overridden then we
// should use llvm-tblgen from there, also should verify that it
// actually exists most of the time in normal installs of LLVM.
@@ -241,6 +276,8 @@ impl Step for Llvm {
cfg.build();
t!(t!(File::create(&done_stamp)).write_all(rebuild_trigger_contents.as_bytes()));
build_llvm_config
}
}