1 files changed, 35 insertions, 4 deletions
diff --git a/compiler/rustc_codegen_cranelift/Readme.md b/compiler/rustc_codegen_cranelift/Readme.md
index c5222982a..9469feea0 100644
--- a/compiler/rustc_codegen_cranelift/Readme.md
+++ b/compiler/rustc_codegen_cranelift/Readme.md
@@ -10,8 +10,8 @@ If not please open an issue.
 ```bash
 $ git clone https://github.com/bjorn3/rustc_codegen_cranelift
 $ cd rustc_codegen_cranelift
-$ ./y.rs prepare
-$ ./y.rs build
+$ ./y.sh prepare
+$ ./y.sh build
 ```
 
 To run the test suite replace the last command with:
@@ -20,9 +20,14 @@ To run the test suite replace the last command with:
 $ ./test.sh
 ```
 
-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`.
+For more docs on how to build and test see [build_system/usage.txt](build_system/usage.txt) or the help message of `./y.sh`.
+
+## Precompiled builds
 
 Alternatively you can download a pre built version from the [releases] page.
+Extract the `dist` directory in the archive anywhere you want.
+If you want to use `cargo clif build` instead of having to specify the full path to the `cargo-clif` executable, you can add the `bin` subdirectory of the extracted `dist` directory to your `PATH`.
+(tutorial [for Windows](https://stackoverflow.com/a/44272417), and [for Linux/MacOS](https://unix.stackexchange.com/questions/26047/how-to-correctly-add-a-path-to-path/26059#26059)).
 
 [releases]: https://github.com/bjorn3/rustc_codegen_cranelift/releases/tag/dev
 
@@ -30,7 +35,7 @@ Alternatively you can download a pre built version from the [releases] page.
 
 rustc_codegen_cranelift can be used as a near-drop-in replacement for `cargo build` or `cargo run` for existing projects.
 
-Assuming `$cg_clif_dir` is the directory you cloned this repo into and you followed the instructions (`y.rs prepare` and `y.rs build` or `test.sh`).
+Assuming `$cg_clif_dir` is the directory you cloned this repo into and you followed the instructions (`y.sh prepare` and `y.sh build` or `test.sh`).
 
 In the directory with your project (where you can do the usual `cargo build`), run:
 
@@ -42,6 +47,32 @@ This will build your project with rustc_codegen_cranelift instead of the usual L
 
 For additional ways to use rustc_codegen_cranelift like the JIT mode see [usage.md](docs/usage.md).
 
+## Building and testing with changes in rustc code
+
+This is useful when changing code in `rustc_codegen_cranelift` as part of changing [main Rust repository](https://github.com/rust-lang/rust/).
+This can happen, for example, when you are implementing a new compiler intrinsic.
+
+Instruction below uses `$RustCheckoutDir` as substitute for any folder where you cloned Rust repository.
+
+You need to do this steps to successfully compile and use the cranelift backend with your changes in rustc code:
+
+1. `cd $RustCheckoutDir`
+2. Run `python x.py setup` and choose option for compiler (`b`).
+3. Build compiler and necessary tools: `python x.py build --stage=2 compiler library/std src/tools/rustdoc src/tools/rustfmt`
+   * (Optional) You can also build cargo by adding `src/tools/cargo` to previous command.
+4. Copy exectutable files from `./build/host/stage2-tools/<your hostname triple>/release`
+to `./build/host/stage2/bin/`. Note that you would need to do this every time you rebuilt `rust` repository.
+5. Copy cargo from another toolchain: `cp $(rustup which cargo) .build/<your hostname triple>/stage2/bin/cargo`
+   * Another option is to build it at step 3 and copy with other executables at step 4.
+6. Link your new `rustc` to toolchain: `rustup toolchain link stage2 ./build/host/stage2/`.
+7. (Windows only) compile y.rs: `rustc +stage2 -O y.rs`.
+8. You need to prefix every `./y.rs` (or `y` if you built `y.rs`) command by `rustup run stage2` to make cg_clif use your local changes in rustc.
+
+  * `rustup run stage2 ./y.rs prepare`
+  * `rustup run stage2 ./y.rs build`
+  * (Optional) run tests: `rustup run stage2 ./y.rs test`
+9. Now you can use your cg_clif build to compile other Rust programs, e.g. you can open any Rust crate and run commands like `$RustCheckoutDir/compiler/rustc_codegen_cranelift/dist/cargo-clif build --release`.
+
 ## Configuration
 
 See the documentation on the `BackendConfig` struct in [config.rs](src/config.rs) for all