Auto merge of #77975 - bjorn3:cg_clif_subtree3, r=Mark-Simulacrum

Add cg_clif as optional codegen backend

Rustc_codegen_cranelift is an alternative codegen backend for rustc based on Cranelift. It has the potential to improve compilation times in debug mode. In my experience the compile time improvements over debug mode LLVM for a clean build are about 20-30% in most cases.

This PR adds cg_clif as optional codegen backend. By default it is only enabled for `./x.py check`. It can be enabled for `./x.py build` too by adding `cranelift` to the `rust.codegen-backends` array in `config.toml`.

MCP: rust-lang/compiler-team#270

r? `@Mark-Simulacrum`

Cargo.toml

@@ -31,6 +31,7 @@ members = [
 ]
 exclude = [
   "build",
+  "compiler/rustc_codegen_cranelift",
   # HACK(eddyb) This hardcodes the fact that our CI uses `/checkout/obj`.
   "obj",
 ]

compiler/rustc_codegen_cranelift/.gitattributes

@@ -0,0 +1 @@
+* text=auto eol=lf

compiler/rustc_codegen_cranelift/.github/workflows/main.yml

@@ -0,0 +1,54 @@
+name: CI
+
+on:
+  - push
+  - pull_request
+
+jobs:
+  build:
+    runs-on: ${{ matrix.os }}
+
+    strategy:
+      fail-fast: false
+      matrix:
+        os: [ubuntu-latest, macos-latest]
+
+    steps:
+    - uses: actions/checkout@v2
+
+    - name: Cache cargo installed crates
+      uses: actions/cache@v2
+      with:
+        path: ~/.cargo/bin
+        key: ${{ runner.os }}-cargo-installed-crates
+
+    - name: Cache cargo registry and index
+      uses: actions/cache@v2
+      with:
+        path: |
+            ~/.cargo/registry
+            ~/.cargo/git
+        key: ${{ runner.os }}-cargo-registry-and-index-${{ hashFiles('**/Cargo.lock') }}
+
+    - name: Cache cargo target dir
+      uses: actions/cache@v2
+      with:
+        path: target
+        key: ${{ runner.os }}-cargo-build-target-${{ hashFiles('rust-toolchain', '**/Cargo.lock') }}
+
+    - name: Prepare dependencies
+      run: |
+        git config --global user.email "user@example.com"
+        git config --global user.name "User"
+        ./prepare.sh
+
+    - name: Test
+      run: |
+        # Enable backtraces for easier debugging
+        export RUST_BACKTRACE=1
+
+        # Reduce amount of benchmark runs as they are slow
+        export COMPILE_RUNS=2
+        export RUN_RUNS=2
+
+        ./test.sh --release

compiler/rustc_codegen_cranelift/.gitignore

@@ -0,0 +1,14 @@
+target
+**/*.rs.bk
+*.rlib
+*.o
+perf.data
+perf.data.old
+*.events
+*.string*
+/build_sysroot/sysroot
+/build_sysroot/sysroot_src
+/rust
+/rand
+/regex
+/simple-raytracer

compiler/rustc_codegen_cranelift/.vscode/settings.json

@@ -0,0 +1,53 @@
+{
+    // source for rustc_* is not included in the rust-src component; disable the errors about this
+    "rust-analyzer.diagnostics.disabled": ["unresolved-extern-crate"],
+    "rust-analyzer.cargo.loadOutDirsFromCheck": true,
+    "rust-analyzer.linkedProjects": [
+        "./Cargo.toml",
+        //"./build_sysroot/sysroot_src/src/libstd/Cargo.toml",
+        {
+            "roots": [
+                "./example/mini_core.rs",
+                "./example/mini_core_hello_world.rs",
+                "./example/mod_bench.rs"
+            ],
+            "crates": [
+                {
+                    "root_module": "./example/mini_core.rs",
+                    "edition": "2018",
+                    "deps": [],
+                    "cfg": [],
+                },
+                {
+                    "root_module": "./example/mini_core_hello_world.rs",
+                    "edition": "2018",
+                    "deps": [{ "crate": 0, "name": "mini_core" }],
+                    "cfg": [],
+                },
+                {
+                    "root_module": "./example/mod_bench.rs",
+                    "edition": "2018",
+                    "deps": [],
+                    "cfg": [],
+                },
+            ]
+        },
+        {
+            "roots": ["./scripts/filter_profile.rs"],
+            "crates": [
+                {
+                    "root_module": "./scripts/filter_profile.rs",
+                    "edition": "2018",
+                    "deps": [{ "crate": 1, "name": "std" }],
+                    "cfg": [],
+                },
+                {
+                    "root_module": "./build_sysroot/sysroot_src/library/std/src/lib.rs",
+                    "edition": "2018",
+                    "deps": [],
+                    "cfg": [],
+                },
+            ]
+        }
+    ]
+}