From 62f528929b13f8b27dde2a4694d335bc5341e759 Mon Sep 17 00:00:00 2001
From: Jake Fecher <jfecher11@gmail.com>
Date: Thu, 19 Dec 2024 11:59:01 -0600
Subject: [PATCH 1/2] Use smallvec for instruction results

---
 Cargo.lock                                 | 4 ++++
 compiler/noirc_evaluator/Cargo.toml        | 1 +
 compiler/noirc_evaluator/src/ssa/ir/dfg.rs | 7 ++++---
 3 files changed, 9 insertions(+), 3 deletions(-)

diff --git a/Cargo.lock b/Cargo.lock
index 4907de7ae62..f08467e0172 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -3184,6 +3184,7 @@ dependencies = [
  "serde_json",
  "serde_with",
  "similar-asserts",
+ "smallvec",
  "test-case",
  "thiserror",
  "tracing",
@@ -4487,6 +4488,9 @@ name = "smallvec"
 version = "1.13.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "3c5e1a9a646d36c3599cd173a41282daf47c44583ad367b8e6837255952e5c67"
+dependencies = [
+ "serde",
+]
 
 [[package]]
 name = "smawk"
diff --git a/compiler/noirc_evaluator/Cargo.toml b/compiler/noirc_evaluator/Cargo.toml
index 72fba8aadc2..15531fafff7 100644
--- a/compiler/noirc_evaluator/Cargo.toml
+++ b/compiler/noirc_evaluator/Cargo.toml
@@ -28,6 +28,7 @@ tracing.workspace = true
 chrono = "0.4.37"
 rayon.workspace = true
 cfg-if.workspace = true
+smallvec = { version = "1.13.2", features = ["serde"] }
 
 [dev-dependencies]
 proptest.workspace = true
diff --git a/compiler/noirc_evaluator/src/ssa/ir/dfg.rs b/compiler/noirc_evaluator/src/ssa/ir/dfg.rs
index 27eeaa0e15b..f5e1ecc57f7 100644
--- a/compiler/noirc_evaluator/src/ssa/ir/dfg.rs
+++ b/compiler/noirc_evaluator/src/ssa/ir/dfg.rs
@@ -42,7 +42,7 @@ pub(crate) struct DataFlowGraph {
     /// Call instructions require the func signature, but
     /// other instructions may need some more reading on my part
     #[serde_as(as = "HashMap<DisplayFromStr, _>")]
-    results: HashMap<InstructionId, Vec<ValueId>>,
+    results: HashMap<InstructionId, smallvec::SmallVec<[ValueId; 1]>>,
 
     /// Storage for all of the values defined in this
     /// function.
@@ -346,10 +346,11 @@ impl DataFlowGraph {
         ctrl_typevars: Option<Vec<Type>>,
     ) {
         let result_types = self.instruction_result_types(instruction_id, ctrl_typevars);
-        let results = vecmap(result_types.into_iter().enumerate(), |(position, typ)| {
+
+        let results = result_types.into_iter().enumerate().map(|(position, typ)| {
             let instruction = instruction_id;
             self.values.insert(Value::Instruction { typ, position, instruction })
-        });
+        }).collect();
 
         self.results.insert(instruction_id, results);
     }

From ad0bfc799eed9e3b1351e58bc3e91a1e0c9ef1c5 Mon Sep 17 00:00:00 2001
From: Jake Fecher <jfecher11@gmail.com>
Date: Thu, 19 Dec 2024 12:07:30 -0600
Subject: [PATCH 2/2] Avoid allocating in instruction_result_type

---
 compiler/noirc_evaluator/src/ssa/ir/dfg.rs | 34 ++++++++++++----------
 1 file changed, 19 insertions(+), 15 deletions(-)

diff --git a/compiler/noirc_evaluator/src/ssa/ir/dfg.rs b/compiler/noirc_evaluator/src/ssa/ir/dfg.rs
index f5e1ecc57f7..9ccf7f11512 100644
--- a/compiler/noirc_evaluator/src/ssa/ir/dfg.rs
+++ b/compiler/noirc_evaluator/src/ssa/ir/dfg.rs
@@ -342,17 +342,18 @@ impl DataFlowGraph {
     /// Returns the results of the instruction
     pub(crate) fn make_instruction_results(
         &mut self,
-        instruction_id: InstructionId,
+        instruction: InstructionId,
         ctrl_typevars: Option<Vec<Type>>,
     ) {
-        let result_types = self.instruction_result_types(instruction_id, ctrl_typevars);
-
-        let results = result_types.into_iter().enumerate().map(|(position, typ)| {
-            let instruction = instruction_id;
-            self.values.insert(Value::Instruction { typ, position, instruction })
-        }).collect();
+        let mut results = smallvec::SmallVec::new();
+        let mut position = 0;
+        self.for_each_instruction_result_type(instruction, ctrl_typevars, |this, typ| {
+            let result = this.values.insert(Value::Instruction { typ, position, instruction });
+            position += 1;
+            results.push(result);
+        });
 
-        self.results.insert(instruction_id, results);
+        self.results.insert(instruction, results);
     }
 
     /// Return the result types of this instruction.
@@ -363,18 +364,21 @@ impl DataFlowGraph {
     /// the type of an instruction that does not require them. Compared to passing an empty Vec,
     /// Option has the benefit of panicking if it is accidentally used for a Call instruction,
     /// rather than silently returning the empty Vec and continuing.
-    fn instruction_result_types(
-        &self,
+    fn for_each_instruction_result_type(
+        &mut self,
         instruction_id: InstructionId,
         ctrl_typevars: Option<Vec<Type>>,
-    ) -> Vec<Type> {
+        mut f: impl FnMut(&mut Self, Type),
+    ) {
         let instruction = &self.instructions[instruction_id];
         match instruction.result_type() {
-            InstructionResultType::Known(typ) => vec![typ],
-            InstructionResultType::Operand(value) => vec![self.type_of_value(value)],
-            InstructionResultType::None => vec![],
+            InstructionResultType::Known(typ) => f(self, typ),
+            InstructionResultType::Operand(value) => f(self, self.type_of_value(value)),
+            InstructionResultType::None => (),
             InstructionResultType::Unknown => {
-                ctrl_typevars.expect("Control typevars required but not given")
+                for typ in ctrl_typevars.expect("Control typevars required but not given") {
+                    f(self, typ);
+                }
             }
         }
     }