Add cache-based fast path for cfgs and check-cfgs

Author: Urgau

compiler/rustc_attr/src/builtin.rs

@@ -525,38 +525,40 @@ pub fn cfg_matches(
 ) -> bool {
     eval_condition(cfg, sess, features, &mut |cfg| {
         try_gate_cfg(cfg.name, cfg.span, sess, features);
-        match sess.psess.check_config.expecteds.get(&cfg.name) {
-            Some(ExpectedValues::Some(values)) if !values.contains(&cfg.value) => {
-                sess.psess.buffer_lint_with_diagnostic(
-                    UNEXPECTED_CFGS,
-                    cfg.span,
-                    lint_node_id,
-                    if let Some(value) = cfg.value {
-                        format!("unexpected `cfg` condition value: `{value}`")
-                    } else {
-                        format!("unexpected `cfg` condition value: (none)")
-                    },
-                    BuiltinLintDiag::UnexpectedCfgValue(
-                        (cfg.name, cfg.name_span),
-                        cfg.value.map(|v| (v, cfg.value_span.unwrap())),
-                    ),
-                );
-            }
-            None if sess.psess.check_config.exhaustive_names => {
-                sess.psess.buffer_lint_with_diagnostic(
-                    UNEXPECTED_CFGS,
-                    cfg.span,
-                    lint_node_id,
-                    format!("unexpected `cfg` condition name: `{}`", cfg.name),
-                    BuiltinLintDiag::UnexpectedCfgName(
-                        (cfg.name, cfg.name_span),
-                        cfg.value.map(|v| (v, cfg.value_span.unwrap())),
-                    ),
-                );
+        sess.psess.config_cache.contains(&(cfg.name, cfg.value)) || {
+            match sess.psess.check_config.expecteds.get(&cfg.name) {
+                Some(ExpectedValues::Some(values)) if !values.contains(&cfg.value) => {
+                    sess.psess.buffer_lint_with_diagnostic(
+                        UNEXPECTED_CFGS,
+                        cfg.span,
+                        lint_node_id,
+                        if let Some(value) = cfg.value {
+                            format!("unexpected `cfg` condition value: `{value}`")
+                        } else {
+                            format!("unexpected `cfg` condition value: (none)")
+                        },
+                        BuiltinLintDiag::UnexpectedCfgValue(
+                            (cfg.name, cfg.name_span),
+                            cfg.value.map(|v| (v, cfg.value_span.unwrap())),
+                        ),
+                    );
+                }
+                None if sess.psess.check_config.exhaustive_names => {
+                    sess.psess.buffer_lint_with_diagnostic(
+                        UNEXPECTED_CFGS,
+                        cfg.span,
+                        lint_node_id,
+                        format!("unexpected `cfg` condition name: `{}`", cfg.name),
+                        BuiltinLintDiag::UnexpectedCfgName(
+                            (cfg.name, cfg.name_span),
+                            cfg.value.map(|v| (v, cfg.value_span.unwrap())),
+                        ),
+                    );
+                }
+                _ => { /* not unexpected */ }
             }
-            _ => { /* not unexpected */ }
+            sess.psess.config.contains(&(cfg.name, cfg.value))
         }
-        sess.psess.config.contains(&(cfg.name, cfg.value))
     })
 }
 

compiler/rustc_interface/src/interface.rs

@@ -17,7 +17,7 @@ use rustc_query_impl::QueryCtxt;
 use rustc_query_system::query::print_query_stack;
 use rustc_session::config::{self, Cfg, CheckCfg, ExpectedValues, Input, OutFileName};
 use rustc_session::filesearch::sysroot_candidates;
-use rustc_session::parse::ParseSess;
+use rustc_session::parse::{CfgCache, ParseSess};
 use rustc_session::{lint, CompilerIO, EarlyDiagCtxt, Session};
 use rustc_span::source_map::FileLoader;
 use rustc_span::symbol::sym;
@@ -402,6 +402,23 @@ pub fn run_compiler<R: Send>(config: Config, f: impl FnOnce(&Compiler) -> R + Se
             check_cfg.fill_well_known(&sess.target);
             sess.psess.check_config = check_cfg;
 
+            let mut config_cache = CfgCache::default();
+            if sess.psess.check_config.expecteds.is_empty() {
+                config_cache.extend(sess.psess.config.iter().copied());
+            } else {
+                #[allow(rustc::potential_query_instability)]
+                for (n, v) in &sess.psess.check_config.expecteds {
+                    if let ExpectedValues::Some(v) = v {
+                        for v in v {
+                            if sess.psess.config.contains(&(*n, *v)) {
+                                config_cache.insert((*n, *v));
+                            }
+                        }
+                    }
+                }
+            }
+            sess.psess.config_cache = config_cache;
+
             if let Some(psess_created) = config.psess_created {
                 psess_created(&mut sess.psess);
             }

compiler/rustc_session/src/parse.rs

@@ -11,7 +11,7 @@ use crate::lint::{
 };
 use crate::Session;
 use rustc_ast::node_id::NodeId;
-use rustc_data_structures::fx::{FxHashMap, FxIndexMap, FxIndexSet};
+use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap, FxIndexSet};
 use rustc_data_structures::sync::{AppendOnlyVec, Lock, Lrc};
 use rustc_errors::emitter::{stderr_destination, HumanEmitter, SilentEmitter};
 use rustc_errors::{
@@ -196,12 +196,15 @@ pub fn add_feature_diagnostics_for_issue<G: EmissionGuarantee>(
     }
 }
 
+pub type CfgCache = FxHashSet<(Symbol, Option<Symbol>)>;
+
 /// Info about a parsing session.
 pub struct ParseSess {
     pub dcx: DiagCtxt,
     pub unstable_features: UnstableFeatures,
     pub config: Cfg,
     pub check_config: CheckCfg,
+    pub config_cache: CfgCache,
     pub edition: Edition,
     /// Places where raw identifiers were used. This is used to avoid complaining about idents
     /// clashing with keywords in new editions.
@@ -250,6 +253,7 @@ impl ParseSess {
             unstable_features: UnstableFeatures::from_environment(None),
             config: Cfg::default(),
             check_config: CheckCfg::default(),
+            config_cache: CfgCache::default(),
             edition: ExpnId::root().expn_data().edition,
             raw_identifier_spans: Default::default(),
             bad_unicode_identifiers: Lock::new(Default::default()),