Auto merge of rust-lang#129761 - saethlin:cacher-location, r=<try>

Rub come caching on caller_location

Inspired by the huge perf wins from making track_caller a no-op: rust-lang#129704, I started poking around and it looks like we have no deduplication of identical `panic::Location` allocations.

Nora says I can use a query here, but I'm scared of query overhead so I'm going to perf something very crude first.

r? `@ghost`

Author: bors

compiler/rustc_const_eval/src/util/caller_location.rs

@@ -1,3 +1,5 @@
+use std::collections::hash_map::Entry;
+
 use rustc_hir::LangItem;
 use rustc_middle::query::TyCtxtAt;
 use rustc_middle::ty::layout::LayoutOf;
@@ -57,6 +59,11 @@ pub(crate) fn const_caller_location_provider(
     col: u32,
 ) -> mir::ConstValue<'_> {
     trace!("const_caller_location: {}:{}:{}", file, line, col);
+    let mut cache = tcx.caller_location_cache.lock();
+    let entry = match cache.entry((file, line, col)) {
+        Entry::Occupied(oe) => return *oe.get(),
+        Entry::Vacant(ve) => ve,
+    };
     let mut ecx = mk_eval_cx_to_read_const_val(
         tcx.tcx,
         tcx.span,
@@ -68,5 +75,7 @@ pub(crate) fn const_caller_location_provider(
     if intern_const_alloc_recursive(&mut ecx, InternKind::Constant, &loc_place).is_err() {
         bug!("intern_const_alloc_recursive should not error in this case")
     }
-    mir::ConstValue::Scalar(Scalar::from_maybe_pointer(loc_place.ptr(), &tcx))
+    let val = mir::ConstValue::Scalar(Scalar::from_maybe_pointer(loc_place.ptr(), &tcx));
+    entry.insert(val);
+    val
 }

compiler/rustc_middle/src/ty/context.rs

@@ -66,7 +66,7 @@ use crate::metadata::ModChild;
 use crate::middle::codegen_fn_attrs::CodegenFnAttrs;
 use crate::middle::{resolve_bound_vars, stability};
 use crate::mir::interpret::{self, Allocation, ConstAllocation};
-use crate::mir::{Body, Local, Place, PlaceElem, ProjectionKind, Promoted};
+use crate::mir::{Body, ConstValue, Local, Place, PlaceElem, ProjectionKind, Promoted};
 use crate::query::plumbing::QuerySystem;
 use crate::query::{IntoQueryParam, LocalCrate, Providers, TyCtxtAt};
 use crate::thir::Thir;
@@ -1295,6 +1295,8 @@ pub struct GlobalCtxt<'tcx> {
     /// Stores memory for globals (statics/consts).
     pub(crate) alloc_map: Lock<interpret::AllocMap<'tcx>>,
 
+    pub caller_location_cache: Lock<FxHashMap<(Symbol, u32, u32), ConstValue<'tcx>>>,
+
     current_gcx: CurrentGcx,
 }
 
@@ -1525,6 +1527,7 @@ impl<'tcx> TyCtxt<'tcx> {
             canonical_param_env_cache: Default::default(),
             data_layout,
             alloc_map: Lock::new(interpret::AllocMap::new()),
+            caller_location_cache: Default::default(),
             current_gcx,
         }
     }