Rollup merge of rust-lang#137671 - meithecatte:discoverable-dump-mir, r=Nadrieril

Make -Z unpretty=mir suggest -Z dump-mir as well for discoverability

While debugging something else, I got quite annoyed with `-Z unpretty=mir` showing me post-processed MIR instead of the one just after it is built. I ended up asking on Zulip and got pointed to `-Z dump-mir`. While this feature is documented in the rustc dev guide, I think it'd be good if the possibility of making use of it was staring you in the face while you need it.

Author: fmease

compiler/rustc_middle/src/mir/pretty.rs

@@ -319,6 +319,7 @@ pub fn write_mir_pretty<'tcx>(
 
     writeln!(w, "// WARNING: This output format is intended for human consumers only")?;
     writeln!(w, "// and is subject to change without notice. Knock yourself out.")?;
+    writeln!(w, "// HINT: See also -Z dump-mir for MIR at specific points during compilation.")?;
 
     let mut first = true;
     for def_id in dump_mir_def_ids(tcx, single) {

tests/run-make/const_fn_mir/dump.mir

@@ -1,5 +1,6 @@
 // WARNING: This output format is intended for human consumers only
 // and is subject to change without notice. Knock yourself out.
+// HINT: See also -Z dump-mir for MIR at specific points during compilation.
 fn foo() -> i32 {
     let mut _0: i32;
     let mut _1: (i32, bool);