Auto merge of #143333 - cjgillot:local-value-numbering, r=<try>

[TOY] Extend GVN to perform local value numbering.

Author: rust-bors[bot]

Cargo.lock

@@ -4292,6 +4292,7 @@ name = "rustc_mir_transform"
 version = "0.0.0"
 dependencies = [
  "either",
+ "hashbrown",
  "itertools",
  "rustc_abi",
  "rustc_arena",

compiler/rustc_middle/src/mir/visit.rs

@@ -1415,6 +1415,23 @@ impl PlaceContext {
         )
     }
 
+    /// Returns `true` if this place context may be used to know the address of the given place.
+    pub fn may_observe_address(self) -> bool {
+        matches!(
+            self,
+            PlaceContext::NonMutatingUse(
+                NonMutatingUseContext::SharedBorrow
+                    | NonMutatingUseContext::RawBorrow
+                    | NonMutatingUseContext::FakeBorrow
+            ) | PlaceContext::MutatingUse(
+                MutatingUseContext::Drop
+                    | MutatingUseContext::Borrow
+                    | MutatingUseContext::RawBorrow
+                    | MutatingUseContext::AsmOutput
+            )
+        )
+    }
+
     /// Returns `true` if this place context represents a storage live or storage dead marker.
     #[inline]
     pub fn is_storage_marker(self) -> bool {

compiler/rustc_mir_dataflow/src/value_analysis.rs

@@ -6,7 +6,7 @@ use rustc_data_structures::fx::{FxHashMap, FxIndexSet, StdEntry};
 use rustc_data_structures::stack::ensure_sufficient_stack;
 use rustc_index::IndexVec;
 use rustc_index::bit_set::DenseBitSet;
-use rustc_middle::mir::visit::{MutatingUseContext, PlaceContext, Visitor};
+use rustc_middle::mir::visit::{PlaceContext, Visitor};
 use rustc_middle::mir::*;
 use rustc_middle::ty::{self, Ty, TyCtxt};
 use tracing::debug;
@@ -917,12 +917,7 @@ pub fn excluded_locals(body: &Body<'_>) -> DenseBitSet<Local> {
 
     impl<'tcx> Visitor<'tcx> for Collector {
         fn visit_place(&mut self, place: &Place<'tcx>, context: PlaceContext, _location: Location) {
-            if (context.is_borrow()
-                || context.is_address_of()
-                || context.is_drop()
-                || context == PlaceContext::MutatingUse(MutatingUseContext::AsmOutput))
-                && !place.is_indirect()
-            {
+            if context.may_observe_address() && !place.is_indirect() {
                 // A pointer to a place could be used to access other places with the same local,
                 // hence we have to exclude the local completely.
                 self.result.insert(place.local);

compiler/rustc_mir_transform/Cargo.toml

@@ -6,6 +6,7 @@ edition = "2024"
 [dependencies]
 # tidy-alphabetical-start
 either = "1"
+hashbrown = "0.15"
 itertools = "0.12"
 rustc_abi = { path = "../rustc_abi" }
 rustc_arena = { path = "../rustc_arena" }