Stub out codegen backend test pages

Author: jieyouxu

src/doc/rustc-dev-guide/src/SUMMARY.md

@@ -30,6 +30,9 @@
         - [Crater](./tests/crater.md)
         - [Fuchsia](./tests/ecosystem-test-jobs/fuchsia.md)
         - [Rust for Linux](./tests/ecosystem-test-jobs/rust-for-linux.md)
+    - [Codegen backend testing](./tests/codegen-backend-tests/intro.md)
+        - [Cranelift codegen backend](./tests/codegen-backend-tests/cg_clif.md)
+        - [GCC codegen backend](./tests/codegen-backend-tests/cg_gcc.md)
     - [Performance testing](./tests/perf.md)
     - [Suggest tests tool](./tests/suggest-tests.md)
     - [Misc info](./tests/misc.md)

src/doc/rustc-dev-guide/src/tests/codegen-backend-tests/cg_clif.md

@@ -0,0 +1,3 @@
+# Cranelift codegen backend tests
+
+TODO: please add some more information to this page.

src/doc/rustc-dev-guide/src/tests/codegen-backend-tests/cg_gcc.md

@@ -0,0 +1,3 @@
+# GCC codegen backend tests
+
+TODO: please add some more information to this page.

src/doc/rustc-dev-guide/src/tests/codegen-backend-tests/intro.md

@@ -0,0 +1,13 @@
+# Codegen backend testing
+
+See also the [Code generation](../../../src/backend/codegen.md) chapter.
+
+In addition to the primary LLVM codegen backend, the rust-lang/rust CI also runs tests of the [cranelift][cg_clif] and [GCC][cg_gcc] codegen backends in certain test jobs.
+
+For more details on the tests involved, see:
+
+- [Cranelift codegen backend tests](./cg_clif.md)
+- [GCC codegen backend tests](./cg_gcc.md)
+
+[cg_clif]: https://github.com/rust-lang/rustc_codegen_cranelift
+[cg_gcc]: https://github.com/rust-lang/rustc_codegen_gcc

src/doc/rustc-dev-guide/src/tests/intro.md

@@ -38,7 +38,7 @@ directory, and `x` will essentially run `cargo test` on that package.
 Examples:
 
 | Command                                   | Description                           |
-| ----------------------------------------- | ------------------------------------- |
+|-------------------------------------------|---------------------------------------|
 | `./x test library/std`                    | Runs tests on `std` only              |
 | `./x test library/core`                   | Runs tests on `core` only             |
 | `./x test compiler/rustc_data_structures` | Runs tests on `rustc_data_structures` |
@@ -86,7 +86,7 @@ above.
 Examples:
 
 | Command                 | Description                                                        |
-| ----------------------- | ------------------------------------------------------------------ |
+|-------------------------|--------------------------------------------------------------------|
 | `./x fmt --check`       | Checks formatting and exits with an error if formatting is needed. |
 | `./x fmt`               | Runs rustfmt across the entire codebase.                           |
 | `./x test tidy --bless` | First runs rustfmt to format the codebase, then runs tidy checks.  |
@@ -155,6 +155,10 @@ chapter](ecosystem.md) for more details.
 A separate infrastructure is used for testing and tracking performance of the
 compiler. See the [Performance testing chapter](perf.md) for more details.
 
+### Codegen backend testing
+
+See [Codegen backend testing](./codegen-backend-tests/intro.md).
+
 ## Miscellaneous information
 
 There are some other useful testing-related info at [Misc info](misc.md).