Auto merge of rust-lang#118336 - saethlin:const-to-op-cache, r=<try>

Add a cache for const_val_to_op

r? `@ghost`

Author: bors

Diff for: compiler/rustc_const_eval/src/interpret/eval_context.rs

@@ -4,6 +4,8 @@ use std::{fmt, mem};
 use either::{Either, Left, Right};
 
 use hir::CRATE_HIR_ID;
+use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::sync::Lock;
 use rustc_hir::{self as hir, def_id::DefId, definitions::DefPathData};
 use rustc_index::IndexVec;
 use rustc_middle::mir;
@@ -20,9 +22,9 @@ use rustc_span::Span;
 use rustc_target::abi::{call::FnAbi, Align, HasDataLayout, Size, TargetDataLayout};
 
 use super::{
-    AllocId, GlobalId, Immediate, InterpErrorInfo, InterpResult, MPlaceTy, Machine, MemPlace,
-    MemPlaceMeta, Memory, MemoryKind, OpTy, Operand, Place, PlaceTy, Pointer, PointerArithmetic,
-    Projectable, Provenance, Scalar, StackPopJump,
+    AllocId, ConstAllocation, GlobalId, Immediate, InterpErrorInfo, InterpResult, MPlaceTy,
+    Machine, MemPlace, MemPlaceMeta, Memory, MemoryKind, OpTy, Operand, Place, PlaceTy, Pointer,
+    PointerArithmetic, Projectable, Provenance, Scalar, StackPopJump,
 };
 use crate::errors;
 use crate::util;
@@ -47,6 +49,8 @@ pub struct InterpCx<'mir, 'tcx, M: Machine<'mir, 'tcx>> {
 
     /// The recursion limit (cached from `tcx.recursion_limit(())`)
     pub recursion_limit: Limit,
+
+    pub const_cache: Lock<FxHashMap<(ConstAllocation<'tcx>, u64, Span), Immediate<M::Provenance>>>,
 }
 
 // The Phantomdata exists to prevent this type from being `Send`. If it were sent across a thread
@@ -440,6 +444,7 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             param_env,
             memory: Memory::new(),
             recursion_limit: tcx.recursion_limit(),
+            const_cache: Lock::new(FxHashMap::default()),
         }
     }
 

Diff for: compiler/rustc_const_eval/src/interpret/operand.rs

@@ -2,6 +2,7 @@
 //! All high-level functions to read from memory work on operands as sources.
 
 use std::assert_matches::assert_matches;
+use std::collections::hash_map::Entry;
 
 use either::{Either, Left, Right};
 
@@ -13,9 +14,9 @@ use rustc_middle::{mir, ty};
 use rustc_target::abi::{self, Abi, HasDataLayout, Size};
 
 use super::{
-    alloc_range, from_known_layout, mir_assign_valid_types, AllocId, Frame, InterpCx, InterpResult,
-    MPlaceTy, Machine, MemPlace, MemPlaceMeta, OffsetMode, PlaceTy, Pointer, Projectable,
-    Provenance, Scalar,
+    alloc_range, from_known_layout, mir_assign_valid_types, AllocId, ConstAllocation, Frame,
+    InterpCx, InterpResult, MPlaceTy, Machine, MemPlace, MemPlaceMeta, OffsetMode, PlaceTy,
+    Pointer, Projectable, Provenance, Scalar,
 };
 
 /// An `Immediate` represents a single immediate self-contained Rust value.
@@ -757,14 +758,29 @@ impl<'mir, 'tcx: 'mir, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             }
             mir::ConstValue::Scalar(x) => adjust_scalar(x)?.into(),
             mir::ConstValue::ZeroSized => Immediate::Uninit,
-            mir::ConstValue::Slice { data, meta } => {
+            mir::ConstValue::Slice { data, meta } => self.const_slice_to_op(data, meta)?,
+        };
+        Ok(OpTy { op: Operand::Immediate(imm), layout })
+    }
+
+    fn const_slice_to_op(
+        &self,
+        data: ConstAllocation<'tcx>,
+        meta: u64,
+    ) -> InterpResult<'tcx, Immediate<M::Provenance>> {
+        let span = self.cur_span();
+        let imm = match self.const_cache.lock().entry((data, meta, span)) {
+            Entry::Occupied(e) => e.get().clone(),
+            Entry::Vacant(e) => {
                 // We rely on mutability being set correctly in `data` to prevent writes
                 // where none should happen.
                 let ptr = Pointer::new(self.tcx.reserve_and_set_memory_alloc(data), Size::ZERO);
-                Immediate::new_slice(self.global_base_pointer(ptr)?.into(), meta, self)
+                let imm = Immediate::new_slice(self.global_base_pointer(ptr)?.into(), meta, self);
+                e.insert(imm.clone());
+                imm
             }
         };
-        Ok(OpTy { op: Operand::Immediate(imm), layout })
+        Ok(imm)
     }
 }