Fix performance issue with record_operands_moved

Large arrays/tuples can have enough operands that removing items one at a time is significantly slower than creating a hash set first.

Author: matthewjasper

compiler/rustc_mir_build/src/build/scope.rs

@@ -84,7 +84,7 @@ that contains only loops and breakable blocks. It tracks where a `break`,
 use std::mem;
 
 use crate::build::{BlockAnd, BlockAndExtension, BlockFrame, Builder, CFG};
-use rustc_data_structures::fx::FxHashMap;
+use rustc_data_structures::fx::{FxHashMap, FxHashSet};
 use rustc_hir::HirId;
 use rustc_index::{IndexSlice, IndexVec};
 use rustc_middle::middle::region;
@@ -1110,15 +1110,18 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
  assert_eq!(scope.region_scope, local_scope, "local scope is not the topmost scope!",);
 
  // look for moves of a local variable, like `MOVE(_X)`
- let locals_moved = operands.iter().flat_map(|operand| match operand {
- Operand::Copy(_) | Operand::Constant(_) => None,
- Operand::Move(place) => place.as_local(),
- });
+ let locals_moved: FxHashSet<Local> = operands
+ .iter()
+ .flat_map(|operand| match operand {
+ Operand::Copy(_) | Operand::Constant(_) => None,
+ Operand::Move(place) => place.as_local(),
+ })
+ .collect();
 
- for local in locals_moved {
-  // Unschedule drops from the scope.
- scope.drops.retain(|drop| drop.local != local || drop.kind != DropKind::Value);
- }
+ // Unschedule drops from the scope.
+ scope
+ .drops
+  .retain(|drop| drop.kind != DropKind::Value || !locals_moved.contains(&drop.local));
  scope.invalidate_cache();
  }