Move find_self_call.

It's a function that does stuff with MIR and yet it weirdly has its own
module in `rustc_middle::util`. This commit moves it into
`rustc_middle::mir`, a more sensible home.

Author: nnethercote

Diff for: compiler/rustc_borrowck/src/diagnostics/conflict_errors.rs

@@ -3777,7 +3777,7 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
         let tcx = self.infcx.tcx;
         if let Some(Terminator { kind: TerminatorKind::Call { call_source, fn_span, .. }, .. }) =
             &self.body[loan.reserve_location.block].terminator
-            && let Some((method_did, method_args)) = rustc_middle::util::find_self_call(
+            && let Some((method_did, method_args)) = mir::find_self_call(
                 tcx,
                 self.body,
                 loan.assigned_place.local,

Diff for: compiler/rustc_borrowck/src/diagnostics/mod.rs

@@ -17,7 +17,7 @@ use rustc_middle::mir::tcx::PlaceTy;
 use rustc_middle::mir::{
     AggregateKind, CallSource, ConstOperand, ConstraintCategory, FakeReadCause, Local, LocalInfo,
     LocalKind, Location, Operand, Place, PlaceRef, ProjectionElem, Rvalue, Statement,
-    StatementKind, Terminator, TerminatorKind,
+    StatementKind, Terminator, TerminatorKind, find_self_call,
 };
 use rustc_middle::ty::print::Print;
 use rustc_middle::ty::{self, Ty, TyCtxt};
@@ -1016,12 +1016,9 @@ impl<'infcx, 'tcx> MirBorrowckCtxt<'_, 'infcx, 'tcx> {
             kind: TerminatorKind::Call { fn_span, call_source, .. }, ..
         }) = &self.body[location.block].terminator
         {
-            let Some((method_did, method_args)) = rustc_middle::util::find_self_call(
-                self.infcx.tcx,
-                self.body,
-                target_temp,
-                location.block,
-            ) else {
+            let Some((method_did, method_args)) =
+                find_self_call(self.infcx.tcx, self.body, target_temp, location.block)
+            else {
                 return normal_ret;
             };
 

Diff for: compiler/rustc_middle/src/mir/mod.rs

@@ -27,7 +27,7 @@ use rustc_macros::{HashStable, TyDecodable, TyEncodable, TypeFoldable, TypeVisit
 use rustc_serialize::{Decodable, Encodable};
 use rustc_span::source_map::Spanned;
 use rustc_span::{DUMMY_SP, Span, Symbol};
-use tracing::trace;
+use tracing::{debug, trace};
 
 pub use self::query::*;
 use self::visit::TyContext;
@@ -1796,6 +1796,47 @@ impl DefLocation {
     }
 }
 
+/// Checks if the specified `local` is used as the `self` parameter of a method call
+/// in the provided `BasicBlock`. If it is, then the `DefId` of the called method is
+/// returned.
+pub fn find_self_call<'tcx>(
+    tcx: TyCtxt<'tcx>,
+    body: &Body<'tcx>,
+    local: Local,
+    block: BasicBlock,
+) -> Option<(DefId, GenericArgsRef<'tcx>)> {
+    debug!("find_self_call(local={:?}): terminator={:?}", local, body[block].terminator);
+    if let Some(Terminator { kind: TerminatorKind::Call { func, args, .. }, .. }) =
+        &body[block].terminator
+        && let Operand::Constant(box ConstOperand { const_, .. }) = func
+        && let ty::FnDef(def_id, fn_args) = *const_.ty().kind()
+        && let Some(ty::AssocItem { fn_has_self_parameter: true, .. }) =
+            tcx.opt_associated_item(def_id)
+        && let [Spanned { node: Operand::Move(self_place) | Operand::Copy(self_place), .. }, ..] =
+            **args
+    {
+        if self_place.as_local() == Some(local) {
+            return Some((def_id, fn_args));
+        }
+
+        // Handle the case where `self_place` gets reborrowed.
+        // This happens when the receiver is `&T`.
+        for stmt in &body[block].statements {
+            if let StatementKind::Assign(box (place, rvalue)) = &stmt.kind
+                && let Some(reborrow_local) = place.as_local()
+                && self_place.as_local() == Some(reborrow_local)
+                && let Rvalue::Ref(_, _, deref_place) = rvalue
+                && let PlaceRef { local: deref_local, projection: [ProjectionElem::Deref] } =
+                    deref_place.as_ref()
+                && deref_local == local
+            {
+                return Some((def_id, fn_args));
+            }
+        }
+    }
+    None
+}
+
 // Some nodes are used a lot. Make sure they don't unintentionally get bigger.
 #[cfg(target_pointer_width = "64")]
 mod size_asserts {

Diff for: compiler/rustc_middle/src/util/find_self_call.rs

@@ -1,8 +1,5 @@
 pub mod bug;
 pub mod common;
-pub mod find_self_call;
-
-pub use find_self_call::find_self_call;
 
 #[derive(Default, Copy, Clone)]
 pub struct Providers {

Diff for: compiler/rustc_middle/src/util/mod.rs

@@ -133,7 +133,7 @@ impl<'tcx> Visitor<'tcx> for ConstMutationChecker<'_, 'tcx> {
                 // the `self` parameter of a method call (as the terminator of our current
                 // BasicBlock). If so, we emit a more specific lint.
                 let method_did = self.target_local.and_then(|target_local| {
-                    rustc_middle::util::find_self_call(self.tcx, self.body, target_local, loc.block)
+                    find_self_call(self.tcx, self.body, target_local, loc.block)
                 });
                 let lint_loc =
                     if method_did.is_some() { self.body.terminator_loc(loc.block) } else { loc };