Auto merge of #100810 - matthiaskrgr:rollup-xep778s, r=matthiaskrgr

Rollup of 9 pull requests

Successful merges:

 - #97963 (net listen backlog set to negative on Linux.)
 - #99935 (Reenable disabled early syntax gates as future-incompatibility lints)
 - #100129 (add miri-test-libstd support to libstd)
 - #100500 (Ban references to `Self` in trait object substs for projection predicates too.)
 - #100636 (Revert "Revert "Allow dynamic linking for iOS/tvOS targets."")
 - #100718 ([rustdoc] Fix item info display)
 - #100769 (Suggest adding a reference to a trait assoc item)
 - #100777 (elaborate how revisions work with FileCheck stuff in src/test/codegen)
 - #100796 (Refactor: remove unnecessary string searchings)

Failed merges:

r? `@ghost`
`@rustbot` modify labels: rollup

1 files changed, 22 insertions, 0 deletions

diff --git a/src/test/codegen/README.md b/src/test/codegen/README.md
index 00de55eeab1..8f2daaafcc7 100644
--- a/src/test/codegen/README.md
+++ b/src/test/codegen/README.md
@@ -1,2 +1,24 @@
 The files here use the LLVM FileCheck framework, documented at
 <https://llvm.org/docs/CommandGuide/FileCheck.html>.
+
+One extension worth noting is the use of revisions as custom prefixes for
+FileCheck. If your codegen test has different behavior based on the chosen
+target or different compiler flags that you want to exercise, you can use a
+revisions annotation, like so:
+
+```rust
+// revisions: aaa bbb
+// [bbb] compile-flags: --flags-for-bbb
+```
+
+After specifying those variations, you can write different expected, or
+explicitly *unexpected* output by using `<prefix>-SAME:` and `<prefix>-NOT:`,
+like so:
+
+```rust
+// CHECK: expected code
+// aaa-SAME: emitted-only-for-aaa
+// aaa-NOT:                        emitted-only-for-bbb
+// bbb-NOT:  emitted-only-for-aaa
+// bbb-SAME:                       emitted-only-for-bbb
+```