Remove print_vtable_sizes

Author: compiler-errors

compiler/rustc_interface/src/passes.rs

@@ -26,7 +26,6 @@ use rustc_parse::{
 };
 use rustc_passes::{abi_test, input_stats, layout_test};
 use rustc_resolve::Resolver;
-use rustc_session::code_stats::VTableSizeInfo;
 use rustc_session::config::{CrateType, Input, OutFileName, OutputFilenames, OutputType};
 use rustc_session::cstore::Untracked;
 use rustc_session::output::{collect_crate_types, filename_for_input, find_crate_name};
@@ -989,90 +988,6 @@ fn analysis(tcx: TyCtxt<'_>, (): ()) {
         // we will fail to emit overlap diagnostics. Thus we invoke it here unconditionally.
         let _ = tcx.all_diagnostic_items(());
     });
-
-    if sess.opts.unstable_opts.print_vtable_sizes {
-        let traits = tcx.traits(LOCAL_CRATE);
-
-        for &tr in traits {
-            if !tcx.is_dyn_compatible(tr) {
-                continue;
-            }
-
-            let name = ty::print::with_no_trimmed_paths!(tcx.def_path_str(tr));
-
-            let mut first_dsa = true;
-
-            // Number of vtable entries, if we didn't have upcasting
-            let mut entries_ignoring_upcasting = 0;
-            // Number of vtable entries needed solely for upcasting
-            let mut entries_for_upcasting = 0;
-
-            let trait_ref = ty::Binder::dummy(ty::TraitRef::identity(tcx, tr));
-
-            // A slightly edited version of the code in
-            // `rustc_trait_selection::traits::vtable::vtable_entries`, that works without self
-            // type and just counts number of entries.
-            //
-            // Note that this is technically wrong, for traits which have associated types in
-            // supertraits:
-            //
-            //   trait A: AsRef<Self::T> + AsRef<()> { type T; }
-            //
-            // Without self type we can't normalize `Self::T`, so we can't know if `AsRef<Self::T>`
-            // and `AsRef<()>` are the same trait, thus we assume that those are different, and
-            // potentially over-estimate how many vtable entries there are.
-            //
-            // Similarly this is wrong for traits that have methods with possibly-impossible bounds.
-            // For example:
-            //
-            //   trait B<T> { fn f(&self) where T: Copy; }
-            //
-            // Here `dyn B<u8>` will have 4 entries, while `dyn B<String>` will only have 3.
-            // However, since we don't know `T`, we can't know if `T: Copy` holds or not,
-            // thus we lean on the bigger side and say it has 4 entries.
-            traits::vtable::prepare_vtable_segments(tcx, trait_ref, |segment| {
-                match segment {
-                    traits::vtable::VtblSegment::MetadataDSA => {
-                        // If this is the first dsa, it would be included either way,
-                        // otherwise it's needed for upcasting
-                        if std::mem::take(&mut first_dsa) {
-                            entries_ignoring_upcasting += 3;
-                        } else {
-                            entries_for_upcasting += 3;
-                        }
-                    }
-
-                    traits::vtable::VtblSegment::TraitOwnEntries { trait_ref, emit_vptr } => {
-                        // Lookup the shape of vtable for the trait.
-                        let own_existential_entries =
-                            tcx.own_existential_vtable_entries(trait_ref.def_id());
-
-                        // The original code here ignores the method if its predicates are
-                        // impossible. We can't really do that as, for example, all not trivial
-                        // bounds on generic parameters are impossible (since we don't know the
-                        // parameters...), see the comment above.
-                        entries_ignoring_upcasting += own_existential_entries.len();
-
-                        if emit_vptr {
-                            entries_for_upcasting += 1;
-                        }
-                    }
-                }
-
-                std::ops::ControlFlow::Continue::<std::convert::Infallible>(())
-            });
-
-            sess.code_stats.record_vtable_size(tr, &name, VTableSizeInfo {
-                trait_name: name.clone(),
-                entries: entries_ignoring_upcasting + entries_for_upcasting,
-                entries_ignoring_upcasting,
-                entries_for_upcasting,
-                upcasting_cost_percent: entries_for_upcasting as f64
-                    / entries_ignoring_upcasting as f64
-                    * 100.,
-            })
-        }
-    }
 }
 
 /// Check for the `#[rustc_error]` annotation, which forces an error in codegen. This is used
@@ -1153,12 +1068,6 @@ pub(crate) fn start_codegen<'tcx>(
         tcx.sess.code_stats.print_type_sizes();
     }
 
-    if tcx.sess.opts.unstable_opts.print_vtable_sizes {
-        let crate_name = tcx.crate_name(LOCAL_CRATE);
-
-        tcx.sess.code_stats.print_vtable_sizes(crate_name);
-    }
-
     codegen
 }
 

compiler/rustc_session/src/code_stats.rs

@@ -1,10 +1,9 @@
 use std::cmp;
 
 use rustc_abi::{Align, Size};
-use rustc_data_structures::fx::{FxHashMap, FxHashSet};
+use rustc_data_structures::fx::FxHashSet;
 use rustc_data_structures::sync::Lock;
 use rustc_span::Symbol;
-use rustc_span::def_id::DefId;
 
 #[derive(Clone, PartialEq, Eq, Hash, Debug)]
 pub struct VariantInfo {
@@ -71,29 +70,9 @@ pub struct TypeSizeInfo {
     pub variants: Vec<VariantInfo>,
 }
 
-pub struct VTableSizeInfo {
-    pub trait_name: String,
-
-    /// Number of entries in a vtable with the current algorithm
-    /// (i.e. with upcasting).
-    pub entries: usize,
-
-    /// Number of entries in a vtable, as-if we did not have trait upcasting.
-    pub entries_ignoring_upcasting: usize,
-
-    /// Number of entries in a vtable needed solely for upcasting
-    /// (i.e. `entries - entries_ignoring_upcasting`).
-    pub entries_for_upcasting: usize,
-
-    /// Cost of having upcasting in % relative to the number of entries without
-    /// upcasting (i.e. `entries_for_upcasting / entries_ignoring_upcasting * 100%`).
-    pub upcasting_cost_percent: f64,
-}
-
 #[derive(Default)]
 pub struct CodeStats {
     type_sizes: Lock<FxHashSet<TypeSizeInfo>>,
-    vtable_sizes: Lock<FxHashMap<DefId, VTableSizeInfo>>,
 }
 
 impl CodeStats {
@@ -127,14 +106,6 @@ impl CodeStats {
         self.type_sizes.borrow_mut().insert(info);
     }
 
-    pub fn record_vtable_size(&self, trait_did: DefId, trait_name: &str, info: VTableSizeInfo) {
-        let prev = self.vtable_sizes.lock().insert(trait_did, info);
-        assert!(
-            prev.is_none(),
-            "size of vtable for `{trait_name}` ({trait_did:?}) is already recorded"
-        );
-    }
-
     pub fn print_type_sizes(&self) {
         let type_sizes = self.type_sizes.borrow();
         // We will soon sort, so the initial order does not matter.
@@ -238,33 +209,4 @@ impl CodeStats {
             }
         }
     }
-
-    pub fn print_vtable_sizes(&self, crate_name: Symbol) {
-        // We will soon sort, so the initial order does not matter.
-        #[allow(rustc::potential_query_instability)]
-        let mut infos =
-            std::mem::take(&mut *self.vtable_sizes.lock()).into_values().collect::<Vec<_>>();
-
-        // Primary sort: cost % in reverse order (from largest to smallest)
-        // Secondary sort: trait_name
-        infos.sort_by(|a, b| {
-            a.upcasting_cost_percent
-                .total_cmp(&b.upcasting_cost_percent)
-                .reverse()
-                .then_with(|| a.trait_name.cmp(&b.trait_name))
-        });
-
-        for VTableSizeInfo {
-            trait_name,
-            entries,
-            entries_ignoring_upcasting,
-            entries_for_upcasting,
-            upcasting_cost_percent,
-        } in infos
-        {
-            println!(
-                r#"print-vtable-sizes {{ "crate_name": "{crate_name}", "trait_name": "{trait_name}", "entries": "{entries}", "entries_ignoring_upcasting": "{entries_ignoring_upcasting}", "entries_for_upcasting": "{entries_for_upcasting}", "upcasting_cost_percent": "{upcasting_cost_percent}" }}"#
-            );
-        }
-    }
 }

compiler/rustc_session/src/options.rs

@@ -2033,8 +2033,6 @@ options! {
          Note that this overwrites the effect `-Clink-dead-code` has on collection!"),
     print_type_sizes: bool = (false, parse_bool, [UNTRACKED],
         "print layout information for each type encountered (default: no)"),
-    print_vtable_sizes: bool = (false, parse_bool, [UNTRACKED],
-        "print size comparison between old and new vtable layouts (default: no)"),
     proc_macro_backtrace: bool = (false, parse_bool, [UNTRACKED],
          "show backtraces for panics during proc-macro execution (default: no)"),
     proc_macro_execution_strategy: ProcMacroExecutionStrategy = (ProcMacroExecutionStrategy::SameThread,