Improve readme and build system help message

Author: bjorn3

Readme.md

@@ -8,9 +8,9 @@ If not please open an issue.
 ## Building and testing
 
 ```bash
-$ git clone https://github.com/bjorn3/rustc_codegen_cranelift.git
+$ git clone https://github.com/bjorn3/rustc_codegen_cranelift
 $ cd rustc_codegen_cranelift
-$ ./y.rs prepare # download and patch sysroot src and install hyperfine for benchmarking
+$ ./y.rs prepare
 $ ./y.rs build
 ```
 
@@ -20,13 +20,12 @@ To run the test suite replace the last command with:
 $ ./test.sh
 ```
 
-This will implicitly build cg_clif too. Both `y.rs build` and `test.sh` accept a `--debug` argument to
-build in debug mode.
+For more docs on how to build and test see [build_system/usage.txt](build_system/usage.txt) or the help message of `./y.rs`.
 
-Alternatively you can download a pre built version from [GHA]. It is listed in the artifacts section
+Alternatively you can download a pre built version from [Github Actions]. It is listed in the artifacts section
 of workflow runs. Unfortunately due to GHA restrictions you need to be logged in to access it.
 
-[GHA]: https://github.com/bjorn3/rustc_codegen_cranelift/actions?query=branch%3Amaster+event%3Apush+is%3Asuccess
+[Github Actions]: https://github.com/bjorn3/rustc_codegen_cranelift/actions?query=branch%3Amaster+event%3Apush+is%3Asuccess
 
 ## Usage
 

build_system/mod.rs

@@ -15,32 +15,8 @@ mod rustc_info;
 mod tests;
 mod utils;
 
-const USAGE: &str = r#"The build system of cg_clif.
-
-USAGE:
-    ./y.rs prepare [--out-dir DIR]
-    ./y.rs build [--debug] [--sysroot none|clif|llvm] [--out-dir DIR] [--no-unstable-features]
-    ./y.rs test [--debug] [--sysroot none|clif|llvm] [--out-dir DIR] [--no-unstable-features]
-    ./y.rs bench [--debug] [--sysroot none|clif|llvm] [--out-dir DIR] [--no-unstable-features]
-
-OPTIONS:
-    --sysroot none|clif|llvm
-            Which sysroot libraries to use:
-            `none` will not include any standard library in the sysroot.
-            `clif` will build the standard library using Cranelift.
-            `llvm` will use the pre-compiled standard library of rustc which is compiled with LLVM.
-
-    --out-dir DIR
-            Specify the directory in which the download, build and dist directories are stored.
-            By default this is the working directory.
-
-    --no-unstable-features
-            fSome features are not yet ready for production usage. This option will disable these
-            features. This includes the JIT mode and inline assembly support.
-"#;
-
 fn usage() {
-    eprintln!("{USAGE}");
+    eprintln!("{}", include_str!("usage.txt"));
 }
 
 macro_rules! arg_error {

build_system/usage.txt

@@ -0,0 +1,34 @@
+The build system of cg_clif.
+
+USAGE:
+    ./y.rs prepare [--out-dir DIR]
+    ./y.rs build [--debug] [--sysroot none|clif|llvm] [--out-dir DIR] [--no-unstable-features]
+    ./y.rs test [--debug] [--sysroot none|clif|llvm] [--out-dir DIR] [--no-unstable-features]
+    ./y.rs bench [--debug] [--sysroot none|clif|llvm] [--out-dir DIR] [--no-unstable-features]
+
+OPTIONS:
+    --debug
+            Build cg_clif and the standard library in debug mode rather than release mode.
+            Warning: An unoptimized cg_clif is very slow.
+
+    --sysroot none|clif|llvm
+            Which sysroot libraries to use:
+            `none` will not include any standard library in the sysroot.
+            `clif` will build the standard library using Cranelift.
+            `llvm` will use the pre-compiled standard library of rustc which is compiled with LLVM.
+
+    --out-dir DIR
+            Specify the directory in which the download, build and dist directories are stored.
+            By default this is the working directory.
+
+    --no-unstable-features
+            Some features are not yet ready for production usage. This option will disable these
+            features. This includes the JIT mode and inline assembly support.
+
+REQUIREMENTS:
+    * Rustup: The build system has a hard coded dependency on rustup to install the right nightly
+      version and make sure it is used where necessary.
+    * Git: `./y.rs prepare` uses git for applying patches and on Windows for downloading test repos.
+    * Curl and tar (non-Windows only): Used by `./y.rs prepare` to download a single commit for
+      repos. Git will be used to clone the whole repo when using Windows.
+    * [Hyperfine](https://github.com/sharkdp/hyperfine/): Used for benchmarking with `./y.rs bench`.