From 7087c8d7e7419210dfca9fb6e7ec2718725416a9 Mon Sep 17 00:00:00 2001
From: Tom French <tom@tomfren.ch>
Date: Mon, 13 Jan 2025 13:44:54 +0000
Subject: [PATCH] feat: add more lazy removal of instructions with
 `Instruction::noop`

---
 compiler/noirc_evaluator/src/ssa/opt/mem2reg.rs |  7 ++-----
 compiler/noirc_evaluator/src/ssa/opt/rc.rs      | 14 +++-----------
 2 files changed, 5 insertions(+), 16 deletions(-)

diff --git a/compiler/noirc_evaluator/src/ssa/opt/mem2reg.rs b/compiler/noirc_evaluator/src/ssa/opt/mem2reg.rs
index 96a24583837..4bf01844b56 100644
--- a/compiler/noirc_evaluator/src/ssa/opt/mem2reg.rs
+++ b/compiler/noirc_evaluator/src/ssa/opt/mem2reg.rs
@@ -592,11 +592,8 @@ impl<'f> PerFunctionContext<'f> {
     /// This is expected to contain any loads which were replaced and any stores which are
     /// no longer needed.
     fn remove_instructions(&mut self) {
-        // The order we iterate blocks in is not important
-        for block in self.post_order.as_slice() {
-            self.inserter.function.dfg[*block]
-                .instructions_mut()
-                .retain(|instruction| !self.instructions_to_remove.contains(instruction));
+        for instruction in &self.instructions_to_remove {
+            self.inserter.function.dfg.remove_instruction(*instruction);
         }
     }
 
diff --git a/compiler/noirc_evaluator/src/ssa/opt/rc.rs b/compiler/noirc_evaluator/src/ssa/opt/rc.rs
index e25ad350145..86aa9840542 100644
--- a/compiler/noirc_evaluator/src/ssa/opt/rc.rs
+++ b/compiler/noirc_evaluator/src/ssa/opt/rc.rs
@@ -64,7 +64,9 @@ impl Function {
         context.find_rcs_in_entry_block(self);
         context.scan_for_array_sets(self);
         let to_remove = context.find_rcs_to_remove(self);
-        remove_instructions(to_remove, self);
+        for instruction in to_remove {
+            self.dfg.remove_instruction(instruction);
+        }
     }
 }
 
@@ -141,16 +143,6 @@ pub(crate) fn pop_rc_for(
     Some(rcs.remove(position))
 }
 
-fn remove_instructions(to_remove: HashSet<InstructionId>, function: &mut Function) {
-    if !to_remove.is_empty() {
-        for block in function.reachable_blocks() {
-            function.dfg[block]
-                .instructions_mut()
-                .retain(|instruction| !to_remove.contains(instruction));
-        }
-    }
-}
-
 #[cfg(test)]
 mod test {
     use std::sync::Arc;