Rollup merge of #145306 - Stypox:tracing-misc, r=RalfJung

Add tracing to various miscellaneous functions

This PR adds tracing to:
- `ty.fn_sig()`. There is only one place where `fn_sig` is called for real within `rustc_const_eval`. There are three other places where it's called, but one is inside `ConstCx::fn_sig` (which does not seem to be used anywhere), another is under `if cfg!(debug_assertions)`, and the last is within `call_main` and thus gets called only once.
- the two possible things `find_mir_or_eval_fn` can do: "emulate_foreign_item" and "load_mir"
- all calls to `Const.eval()` within the Miri or the `rustc_const_eval` codebase.
- a separate commit also fixes the style of some tracing macros

Those are all quite long-lived operations, that in total make up for 6-7% of the total time spent in the program. I found out about them by looking for long periods of time that were previously not traced at all, using this SQL query in ui.perfetto.dev:

```sql
with ordered as (select s1.*, row_number() over (order by s1.ts) as rn from slices as s1 where s1.parent_id is null and s1.dur > 0 and s1.name != "frame" and s1.name != "step" and s1.name != "backtrace") select a.ts+a.dur as ts, b.ts-a.ts-a.dur as dur, a.id, a.track_id, a.category, a.depth, a.stack_id, a.parent_stack_id, a.parent_id, a.arg_set_id, a.thread_ts, a.thread_instruction_count, a.thread_instruction_delta, a.cat, a.slice_id, "empty" as name from ordered as a inner join ordered as b on a.rn=b.rn-1 /*where b.ts-a.ts-a.dur > 5000*/ order by b.ts-a.ts-a.dur desc
```

<details>
<summary>How the table was obtained</summary>

The above image was obtained in ui.perfetto.dev with the following SQL query after obtaining a trace file by running Miri on the following Rust code with `n=100`.

```sql
select "TOTAL PROGRAM DURATION" as name, count(*), max(ts + dur) as "sum(dur)", 100.0 as "%", null as "min(dur)", null as "max(dur)", null as "avg(dur)", null as "stddev(dur)" from slices union select "TOTAL OVER ALL SPANS (excluding events)" as name, count(*), sum(dur), cast(cast(sum(dur) as float) / (select max(ts + dur) from slices) * 1000 as int) / 10.0 as "%", min(dur), max(dur), cast(avg(dur) as int) as "avg(dur)", cast(sqrt(avg(dur*dur)-avg(dur)*avg(dur)) as int) as "stddev(dur)" from slices where parent_id is null and name != "frame" and name != "step" and dur > 0 union select name, count(*), sum(dur), cast(cast(sum(dur) as float) / (select max(ts + dur) from slices) * 1000 as int) / 10.0 as "%", min(dur), max(dur), cast(avg(dur) as int) as "avg(dur)", cast(sqrt(avg(dur*dur)-avg(dur)*avg(dur)) as int) as "stddev(dur)" from slices where parent_id is null and name != "frame" and name != "step" group by name order by sum(dur) desc, count(*) desc
```

```rust
fn main() {
    let n: usize = std::env::args().nth(1).unwrap().parse().unwrap();
    let mut v = (0..n).into_iter().collect::<Vec<_>>();
    for i in &mut v {
        *i += 1;
    }
}
```

</details>

<img width="1689" height="317" alt="image" src="https://github.com/user-attachments/assets/ee2c81f5-d74a-4da5-b4b6-ab2770175b14" />

4 files changed, 13 insertions, 5 deletions

diff --git a/compiler/rustc_const_eval/src/interpret/eval_context.rs b/compiler/rustc_const_eval/src/interpret/eval_context.rs
index a8a1ac1c980..9681d89ce35 100644
--- a/compiler/rustc_const_eval/src/interpret/eval_context.rs
+++ b/compiler/rustc_const_eval/src/interpret/eval_context.rs
@@ -325,8 +325,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         let _trace = enter_trace_span!(
             M,
             "instantiate_from_frame_and_normalize_erasing_regions",
-            "{}",
-            frame.instance
+            %frame.instance
         );
         frame
             .instance
@@ -583,6 +582,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         span: Span,
         layout: Option<TyAndLayout<'tcx>>,
     ) -> InterpResult<'tcx, OpTy<'tcx, M::Provenance>> {
+        let _trace = enter_trace_span!(M, const_eval::eval_mir_constant, ?val);
         let const_val = val.eval(*self.tcx, self.typing_env, span).map_err(|err| {
                 if M::ALL_CONSTS_ARE_PRECHECKED {
                     match err {
diff --git a/compiler/rustc_const_eval/src/interpret/stack.rs b/compiler/rustc_const_eval/src/interpret/stack.rs
index 73cc87508ef..7cabfd96121 100644
--- a/compiler/rustc_const_eval/src/interpret/stack.rs
+++ b/compiler/rustc_const_eval/src/interpret/stack.rs
@@ -20,7 +20,7 @@ use super::{
     MemoryKind, Operand, PlaceTy, Pointer, Provenance, ReturnAction, Scalar, from_known_layout,
     interp_ok, throw_ub, throw_unsup,
 };
-use crate::errors;
+use crate::{enter_trace_span, errors};
 
 // The Phantomdata exists to prevent this type from being `Send`. If it were sent across a thread
 // boundary and dropped in the other thread, it would exit the span in the other thread.
@@ -386,6 +386,9 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
 
         // Make sure all the constants required by this frame evaluate successfully (post-monomorphization check).
         for &const_ in body.required_consts() {
+            // We can't use `eval_mir_constant` here as that assumes that all required consts have
+            // already been checked, so we need a separate tracing call.
+            let _trace = enter_trace_span!(M, const_eval::required_consts, ?const_.const_);
             let c =
                 self.instantiate_from_current_frame_and_normalize_erasing_regions(const_.const_)?;
             c.eval(*self.tcx, self.typing_env, const_.span).map_err(|err| {
diff --git a/compiler/rustc_const_eval/src/interpret/step.rs b/compiler/rustc_const_eval/src/interpret/step.rs
index f1995b3f132..5143278e69a 100644
--- a/compiler/rustc_const_eval/src/interpret/step.rs
+++ b/compiler/rustc_const_eval/src/interpret/step.rs
@@ -436,7 +436,10 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
             .map(|arg| self.eval_fn_call_argument(&arg.node))
             .collect::<InterpResult<'tcx, Vec<_>>>()?;
 
-        let fn_sig_binder = func.layout.ty.fn_sig(*self.tcx);
+        let fn_sig_binder = {
+            let _trace = enter_trace_span!(M, "fn_sig", ty = ?func.layout.ty.kind());
+            func.layout.ty.fn_sig(*self.tcx)
+        };
         let fn_sig = self.tcx.normalize_erasing_late_bound_regions(self.typing_env, fn_sig_binder);
         let extra_args = &args[fn_sig.inputs().len()..];
         let extra_args =
diff --git a/compiler/rustc_const_eval/src/interpret/validity.rs b/compiler/rustc_const_eval/src/interpret/validity.rs
index 5e8bee65706..02e3d90f4af 100644
--- a/compiler/rustc_const_eval/src/interpret/validity.rs
+++ b/compiler/rustc_const_eval/src/interpret/validity.rs
@@ -1418,7 +1418,9 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         let _trace = enter_trace_span!(
             M,
             "validate_operand",
-            "recursive={recursive}, reset_provenance_and_padding={reset_provenance_and_padding}, val={val:?}"
+            recursive,
+            reset_provenance_and_padding,
+            ?val,
         );
 
         // Note that we *could* actually be in CTFE here with `-Zextra-const-ub-checks`, but it's