Rollup merge of rust-lang#144727 - Stypox:add-tracing-to-resolve, r=RalfJung

Add tracing to resolve-related functions

Resolve-related functions are not called often but still make up for ~3% of execution time for non-repetitive programs (as seen in the first table below, obtained from running the rust snippet at the bottom with `n=1`). On the other hand, for repetitive programs they become less relevant (I tested the same snippet but with `n=100` and got ~1.5%), and it appears that only `try_resolve` is called more often (see the last two tables).

The first table was obtained by opening the trace file in https://ui.perfetto.dev and running the following query:

```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
```

<img width="1687" height="242" alt="image" src="https://github.com/user-attachments/assets/4d4bd890-869b-40f3-a473-8e4c42b02da4" />

The following two tables show how many `resolve` spans there per subname/subcategory, and how much time is spent in each. The first is for `n=1` and the second for `n=100`. The query that was used is:

```sql
select args.string_value as name, count(*), max(dur), avg(dur), sum(dur) from slices inner join args USING (arg_set_id) where args.key = "args." || slices.name and name = "resolve" group by args.string_value
```

<img width="1688" height="159" alt="image" src="https://github.com/user-attachments/assets/a8749856-c099-492e-a86e-6d67b146af9c" />

<img width="1688" height="159" alt="image" src="https://github.com/user-attachments/assets/ce3ac1b5-5c06-47d9-85a6-9b921aea348e" />

The snippet I tested with Miri to obtain the above traces is:

```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;
    }
}
```

Author: GuillaumeGomez

compiler/rustc_const_eval/src/interpret/call.rs

@@ -736,13 +736,16 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         let existential_trait_ref = ty::ExistentialTraitRef::erase_self_ty(tcx, virtual_trait_ref);
         let concrete_trait_ref = existential_trait_ref.with_self_ty(tcx, dyn_ty);
 
-        let concrete_method = Instance::expect_resolve_for_vtable(
-            tcx,
-            self.typing_env,
-            def_id,
-            virtual_instance.args.rebase_onto(tcx, trait_def_id, concrete_trait_ref.args),
-            self.cur_span(),
-        );
+        let concrete_method = {
+            let _trace = enter_trace_span!(M, resolve::expect_resolve_for_vtable, ?def_id);
+            Instance::expect_resolve_for_vtable(
+                tcx,
+                self.typing_env,
+                def_id,
+                virtual_instance.args.rebase_onto(tcx, trait_def_id, concrete_trait_ref.args),
+                self.cur_span(),
+            )
+        };
         assert_eq!(concrete_instance, concrete_method);
     }
 
@@ -825,7 +828,11 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                 place
             }
         };
-        let instance = ty::Instance::resolve_drop_in_place(*self.tcx, place.layout.ty);
+        let instance = {
+            let _trace =
+                enter_trace_span!(M, resolve::resolve_drop_in_place, ty = ?place.layout.ty);
+            ty::Instance::resolve_drop_in_place(*self.tcx, place.layout.ty)
+        };
         let fn_abi = self.fn_abi_of_instance(instance, ty::List::empty())?;
 
         let arg = self.mplace_to_ref(&place)?;

compiler/rustc_const_eval/src/interpret/cast.rs

@@ -16,8 +16,8 @@ use super::{
     FnVal, ImmTy, Immediate, InterpCx, Machine, OpTy, PlaceTy, err_inval, interp_ok, throw_ub,
     throw_ub_custom,
 };
-use crate::fluent_generated as fluent;
 use crate::interpret::Writeable;
+use crate::{enter_trace_span, fluent_generated as fluent};
 
 impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
     pub fn cast(
@@ -81,13 +81,16 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                 // The src operand does not matter, just its type
                 match *src.layout.ty.kind() {
                     ty::FnDef(def_id, args) => {
-                        let instance = ty::Instance::resolve_for_fn_ptr(
-                            *self.tcx,
-                            self.typing_env,
-                            def_id,
-                            args,
-                        )
-                        .ok_or_else(|| err_inval!(TooGeneric))?;
+                        let instance = {
+                            let _trace = enter_trace_span!(M, resolve::resolve_for_fn_ptr, ?def_id);
+                            ty::Instance::resolve_for_fn_ptr(
+                                *self.tcx,
+                                self.typing_env,
+                                def_id,
+                                args,
+                            )
+                            .ok_or_else(|| err_inval!(TooGeneric))?
+                        };
 
                         let fn_ptr = self.fn_ptr(FnVal::Instance(instance));
                         self.write_pointer(fn_ptr, dest)?;
@@ -114,12 +117,15 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                 // The src operand does not matter, just its type
                 match *src.layout.ty.kind() {
                     ty::Closure(def_id, args) => {
-                        let instance = ty::Instance::resolve_closure(
-                            *self.tcx,
-                            def_id,
-                            args,
-                            ty::ClosureKind::FnOnce,
-                        );
+                        let instance = {
+                            let _trace = enter_trace_span!(M, resolve::resolve_closure, ?def_id);
+                            ty::Instance::resolve_closure(
+                                *self.tcx,
+                                def_id,
+                                args,
+                                ty::ClosureKind::FnOnce,
+                            )
+                        };
                         let fn_ptr = self.fn_ptr(FnVal::Instance(instance));
                         self.write_pointer(fn_ptr, dest)?;
                     }

compiler/rustc_const_eval/src/interpret/eval_context.rs

@@ -344,6 +344,7 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
         def: DefId,
         args: GenericArgsRef<'tcx>,
     ) -> InterpResult<'tcx, ty::Instance<'tcx>> {
+        let _trace = enter_trace_span!(M, resolve::try_resolve, def = ?def);
         trace!("resolve: {:?}, {:#?}", def, args);
         trace!("typing_env: {:#?}", self.typing_env);
         trace!("args: {:#?}", args);

compiler/rustc_const_eval/src/interpret/step.rs

@@ -560,7 +560,11 @@ impl<'tcx, M: Machine<'tcx>> InterpCx<'tcx, M> {
                     "Async Drop must be expanded or reset to sync in runtime MIR"
                 );
                 let place = self.eval_place(place)?;
-                let instance = Instance::resolve_drop_in_place(*self.tcx, place.layout.ty);
+                let instance = {
+                    let _trace =
+                        enter_trace_span!(M, resolve::resolve_drop_in_place, ty = ?place.layout.ty);
+                    Instance::resolve_drop_in_place(*self.tcx, place.layout.ty)
+                };
                 if let ty::InstanceKind::DropGlue(_, None) = instance.def {
                     // This is the branch we enter if and only if the dropped type has no drop glue
                     // whatsoever. This can happen as a result of monomorphizing a drop of a

src/tools/miri/src/helpers.rs

@@ -32,6 +32,8 @@ pub enum AccessKind {
 ///
 /// A `None` namespace indicates we are looking for a module.
 fn try_resolve_did(tcx: TyCtxt<'_>, path: &[&str], namespace: Option<Namespace>) -> Option<DefId> {
+    let _trace = enter_trace_span!("try_resolve_did", ?path);
+
     /// Yield all children of the given item, that have the given name.
     fn find_children<'tcx: 'a, 'a>(
         tcx: TyCtxt<'tcx>,