Inline and replace Statement::replace_nop.

It has a single call site, and doesn't seem worth having as an API
function.

Author: nnethercote

compiler/rustc_middle/src/mir/mod.rs

@@ -4,8 +4,8 @@
 
 use std::borrow::Cow;
 use std::fmt::{self, Debug, Formatter};
+use std::iter;
 use std::ops::{Index, IndexMut};
-use std::{iter, mem};
 
 pub use basic_blocks::BasicBlocks;
 use either::Either;

compiler/rustc_middle/src/mir/statement.rs

@@ -19,15 +19,6 @@ impl Statement<'_> {
     pub fn make_nop(&mut self) {
         self.kind = StatementKind::Nop
     }
-
-    /// Changes a statement to a nop and returns the original statement.
-    #[must_use = "If you don't need the statement, use `make_nop` instead"]
-    pub fn replace_nop(&mut self) -> Self {
-        Statement {
-            source_info: self.source_info,
-            kind: mem::replace(&mut self.kind, StatementKind::Nop),
-        }
-    }
 }
 
 impl<'tcx> StatementKind<'tcx> {

compiler/rustc_mir_transform/src/single_use_consts.rs

@@ -48,9 +48,11 @@ impl<'tcx> crate::MirPass<'tcx> for SingleUseConsts {
 
             // We're only changing an operand, not the terminator kinds or successors
             let basic_blocks = body.basic_blocks.as_mut_preserves_cfg();
-            let init_statement =
-                basic_blocks[init_loc.block].statements[init_loc.statement_index].replace_nop();
-            let StatementKind::Assign(place_and_rvalue) = init_statement.kind else {
+            let init_statement_kind = std::mem::replace(
+                &mut basic_blocks[init_loc.block].statements[init_loc.statement_index].kind,
+                StatementKind::Nop,
+            );
+            let StatementKind::Assign(place_and_rvalue) = init_statement_kind else {
                 bug!("No longer an assign?");
             };
             let (place, rvalue) = *place_and_rvalue;