Auto merge of #121232 - RalfJung:miri, r=RalfJung

Miri subtree update

r? `@ghost`

Author: bors

Cargo.lock

@@ -2524,14 +2524,12 @@ dependencies = [
  "aes",
  "colored",
  "ctrlc",
- "env_logger 0.10.2",
  "getrandom",
  "jemalloc-sys",
  "lazy_static",
  "libc",
  "libffi",
  "libloading",
- "log",
  "measureme",
  "rand",
  "regex",

src/tools/miri/CONTRIBUTING.md

@@ -78,6 +78,8 @@ custom target file, you might have to set `MIRI_NO_STD=1`.
 base directory, e.g. `./miri test fail` will run all compile-fail tests). These filters are passed
 to `cargo test`, so for multiple filers you need to use `./miri test -- FILTER1 FILTER2`.
 
+#### Fine grained logging
+
 You can get a trace of which MIR statements are being executed by setting the
 `MIRI_LOG` environment variable.  For example:
 
@@ -94,9 +96,16 @@ stacked borrows implementation:
 MIRI_LOG=rustc_mir::interpret=info,miri::stacked_borrows ./miri run tests/pass/vec.rs
 ```
 
-In addition, you can set `MIRI_BACKTRACE=1` to get a backtrace of where an
+Note that you will only get `info`, `warn` or `error` messages if you use a prebuilt compiler.
+In order to get `debug` and `trace` level messages, you need to build miri with a locally built
+compiler that has `debug=true` set in `config.toml`.
+
+#### Debugging error messages
+
+You can set `MIRI_BACKTRACE=1` to get a backtrace of where an
 evaluation error was originally raised.
 
+
 ### UI testing
 
 We use ui-testing in Miri, meaning we generate `.stderr` and `.stdout` files for the output