Merge from rustc

Author: The rustc-dev-guide Cronjob Bot

src/autodiff/flags.md

@@ -6,6 +6,7 @@ To support you while debugging or profiling, we have added support for an experi
 
 ```text
 PrintTA // Print TypeAnalysis information
+PrintTAFn // Print TypeAnalysis information for a specific function
 PrintAA // Print ActivityAnalysis information
 Print // Print differentiated functions while they are being generated and optimized
 PrintPerf // Print AD related Performance warnings

src/tests/ui.md

@@ -13,6 +13,11 @@ used for many other purposes. For example, tests can also be configured to [run
 the resulting program](#controlling-passfail-expectations) to verify its
 behavior.
 
+For a survey of each subdirectory's purpose under `tests/ui`, consult the
+[SUMMARY.md](https://github.com/rust-lang/rust/tree/master/tests/ui/SUMMARY.md).
+This is useful if you write a new test, and are looking for a category to
+place it in.
+
 If you need to work with `#![no_std]` cross-compiling tests, consult the
 [`minicore` test auxiliary](./minicore.md) chapter.
 
@@ -54,6 +59,11 @@ The output is normalized to ignore unwanted differences, see the
 [Normalization](#normalization) section. If the file is missing, then
 compiletest expects the corresponding output to be empty.
 
+A common reason to use normalization, revisions, and most of the other following tools,
+is to account for platform differences. Consider alternatives to these tools, like
+e.g. using the `extern "rust-invalid"` ABI that is invalid on every platform
+instead of fixing the test to use cross-compilation and testing every possibly-invalid ABI.
+
 There can be multiple stdout/stderr files. The general form is:
 
 ```text