Merge 26ec4fa into 8d7f1f9

noir-lang · Jan 8, 2025 · e0d9016 · e0d9016
2 parents 8d7f1f9 + 26ec4fa
commit e0d9016
Showing 1 changed file with 33 additions and 12 deletions.
diff --git a/compiler/noirc_evaluator/src/ssa/opt/flatten_cfg/value_merger.rs b/compiler/noirc_evaluator/src/ssa/opt/flatten_cfg/value_merger.rs
@@ -117,18 +117,39 @@ impl<'a> ValueMerger<'a> {
         let then_condition =
             dfg.insert_instruction_and_results(cast, block, None, call_stack).first();
 
-        let cast = Instruction::Cast(else_condition, else_type);
-        let else_condition =
-            dfg.insert_instruction_and_results(cast, block, None, call_stack).first();
-
-        let mul = Instruction::binary(BinaryOp::Mul, then_condition, then_value);
-        let then_value = dfg.insert_instruction_and_results(mul, block, None, call_stack).first();
-
-        let mul = Instruction::binary(BinaryOp::Mul, else_condition, else_value);
-        let else_value = dfg.insert_instruction_and_results(mul, block, None, call_stack).first();
-
-        let add = Instruction::binary(BinaryOp::Add, then_value, else_value);
-        dfg.insert_instruction_and_results(add, block, None, call_stack).first()
+        if then_type == NumericType::NativeField {
+            // We're merging two fields so we can do a more efficient value merger as by converting
+            // the expression `if c { a } else { b }` as `c * (a-b) + b`.
+            //
+            // This removes a multiplication compared to the standard `c*a + (!c)*b`.
+
+            let diff = Instruction::binary(BinaryOp::Sub, then_value, else_value);
+            let diff_value =
+                dfg.insert_instruction_and_results(diff, block, None, call_stack).first();
+
+            let conditional_diff = Instruction::binary(BinaryOp::Mul, then_condition, diff_value);
+            let conditional_diff_value = dfg
+                .insert_instruction_and_results(conditional_diff, block, None, call_stack)
+                .first();
+
+            let merged_field =
+                Instruction::binary(BinaryOp::Add, else_value, conditional_diff_value);
+            dfg.insert_instruction_and_results(merged_field, block, None, call_stack)
+                .first()
+        } else {
+            let cast = Instruction::Cast(else_condition, else_type);
+            let else_condition =
+                dfg.insert_instruction_and_results(cast, block, None, call_stack).first();
+
+            let mul = Instruction::binary(BinaryOp::Mul, then_condition, then_value);
+            let then_value = dfg.insert_instruction_and_results(mul, block, None, call_stack).first();
+
+            let mul = Instruction::binary(BinaryOp::Mul, else_condition, else_value);
+            let else_value = dfg.insert_instruction_and_results(mul, block, None, call_stack).first();
+
+            let add = Instruction::binary(BinaryOp::Add, then_value, else_value);
+            dfg.insert_instruction_and_results(add, block, None, call_stack).first()
+        }
     }
 
     /// Given an if expression that returns an array: `if c { array1 } else { array2 }`,