Rollup merge of #136201 - davidv1992:eliminate-field-offset-alt, r=Mark-Simulacrum

Removed dependency on the field-offset crate, alternate approach

This is an alternate approach to reach the same goals as #136003. As it touches the core of the query system, this too probably should be evaluated for performance.

r? ``@Mark-Simulacrum``

compiler/rustc_middle/Cargo.toml

@@ -7,7 +7,6 @@ edition = "2021"
 # tidy-alphabetical-start
 bitflags = "2.4.1"
 either = "1.5.0"
-field-offset = "0.3.5"
 gsgdt = "0.1.2"
 polonius-engine = "0.13.0"
 rustc-rayon-core = { version = "0.5.0" }

compiler/rustc_middle/src/query/plumbing.rs

@@ -1,6 +1,5 @@
 use std::ops::Deref;
 
-use field_offset::FieldOffset;
 use rustc_data_structures::sync::{AtomicU64, WorkerLocal};
 use rustc_hir::def_id::{DefId, LocalDefId};
 use rustc_hir::hir_id::OwnerId;
@@ -24,8 +23,10 @@ pub struct DynamicQuery<'tcx, C: QueryCache> {
     pub eval_always: bool,
     pub dep_kind: DepKind,
     pub handle_cycle_error: HandleCycleError,
-    pub query_state: FieldOffset<QueryStates<'tcx>, QueryState<C::Key>>,
-    pub query_cache: FieldOffset<QueryCaches<'tcx>, C>,
+    // Offset of this query's state field in the QueryStates struct
+    pub query_state: usize,
+    // Offset of this query's cache field in the QueryCaches struct
+    pub query_cache: usize,
     pub cache_on_disk: fn(tcx: TyCtxt<'tcx>, key: &C::Key) -> bool,
     pub execute_query: fn(tcx: TyCtxt<'tcx>, k: C::Key) -> C::Value,
     pub compute: fn(tcx: TyCtxt<'tcx>, key: C::Key) -> C::Value,

compiler/rustc_query_impl/Cargo.toml

@@ -5,7 +5,6 @@ edition = "2021"
 
 [dependencies]
 # tidy-alphabetical-start
-field-offset = "0.3.5"
 measureme = "11"
 rustc_data_structures = { path = "../rustc_data_structures" }
 rustc_errors = { path = "../rustc_errors" }

compiler/rustc_query_impl/src/lib.rs

@@ -11,7 +11,6 @@
 #![warn(unreachable_pub)]
 // tidy-alphabetical-end
 
-use field_offset::offset_of;
 use rustc_data_structures::stable_hasher::HashStable;
 use rustc_data_structures::sync::AtomicU64;
 use rustc_middle::arena::Arena;
@@ -89,7 +88,13 @@ where
     where
         QueryCtxt<'tcx>: 'a,
     {
-        self.dynamic.query_state.apply(&qcx.tcx.query_system.states)
+        // Safety:
+        // This is just manually doing the subfield referencing through pointer math.
+        unsafe {
+            &*(&qcx.tcx.query_system.states as *const QueryStates<'tcx>)
+                .byte_add(self.dynamic.query_state)
+                .cast::<QueryState<Self::Key>>()
+        }
     }
 
     #[inline(always)]
@@ -97,7 +102,13 @@ where
     where
         'tcx: 'a,
     {
-        self.dynamic.query_cache.apply(&qcx.tcx.query_system.caches)
+        // Safety:
+        // This is just manually doing the subfield referencing through pointer math.
+        unsafe {
+            &*(&qcx.tcx.query_system.caches as *const QueryCaches<'tcx>)
+                .byte_add(self.dynamic.query_cache)
+                .cast::<Self::Cache>()
+        }
     }
 
     #[inline(always)]

compiler/rustc_query_impl/src/plumbing.rs

@@ -605,8 +605,8 @@ macro_rules! define_queries {
                     eval_always: is_eval_always!([$($modifiers)*]),
                     dep_kind: dep_graph::dep_kinds::$name,
                     handle_cycle_error: handle_cycle_error!([$($modifiers)*]),
-                    query_state: offset_of!(QueryStates<'tcx> => $name),
-                    query_cache: offset_of!(QueryCaches<'tcx> => $name),
+                    query_state: std::mem::offset_of!(QueryStates<'tcx>, $name),
+                    query_cache: std::mem::offset_of!(QueryCaches<'tcx>, $name),
                     cache_on_disk: |tcx, key| ::rustc_middle::query::cached::$name(tcx, key),
                     execute_query: |tcx, key| erase(tcx.$name(key)),
                     compute: |tcx, key| {