feat(ssa): Hoist add and mul binary ops using known induction variables

compiler/noirc_evaluator/src/ssa/ir/instruction.rs

@@ -22,7 +22,7 @@
     value::{Value, ValueId},
 };
 
-mod binary;
+pub(crate) mod binary;
 mod call;
 mod cast;
 mod constrain;
@@ -407,7 +407,7 @@
             // These can fail.
             Constrain(..) | RangeCheck { .. } => true,
 
             // This should never be side-effectful
             MakeArray { .. } | Noop => false,
 
             // Some binary math can overflow or underflow

compiler/noirc_evaluator/src/ssa/ir/instruction/binary.rs

@@ -39,9 +39,9 @@
     Or,
     /// Bitwise xor (^)
     Xor,
     /// Bitshift left (<<)
     Shl,
     /// Bitshift right (>>)
     Shr,
 }
 
@@ -294,7 +294,7 @@
 }
 
 /// Evaluate a binary operation with constant arguments.
-fn eval_constant_binary_op(
+pub(crate) fn eval_constant_binary_op(
     lhs: FieldElement,
     rhs: FieldElement,
     operator: BinaryOp,

compiler/noirc_evaluator/src/ssa/opt/loop_invariant.rs

@@ -15,7 +15,7 @@ use crate::ssa::{
         basic_block::BasicBlockId,
         function::Function,
         function_inserter::FunctionInserter,
-        instruction::{Instruction, InstructionId},
+        instruction::{binary::eval_constant_binary_op, BinaryOp, Instruction, InstructionId},
         types::Type,
         value::ValueId,
     },
@@ -207,6 +207,7 @@ impl<'f> LoopInvariantContext<'f> {
 
         let can_be_deduplicated = instruction.can_be_deduplicated(self.inserter.function, false)
             || matches!(instruction, Instruction::MakeArray { .. })
+            || matches!(instruction, Instruction::Binary(_))
             || self.can_be_deduplicated_from_upper_bound(&instruction);
 
         is_loop_invariant && can_be_deduplicated
@@ -231,6 +232,31 @@ impl<'f> LoopInvariantContext<'f> {
                     false
                 }
             }
+            Instruction::Binary(binary) => {
+                if !matches!(binary.operator, BinaryOp::Add | BinaryOp::Mul) {
+                    return false;
+                }
+
+                let operand_type =
+                    self.inserter.function.dfg.type_of_value(binary.lhs).unwrap_numeric();
+
+                let lhs_const =
+                    self.inserter.function.dfg.get_numeric_constant_with_type(binary.lhs);
+                let rhs_const =
+                    self.inserter.function.dfg.get_numeric_constant_with_type(binary.rhs);
+                let (lhs, rhs) = match (
+                    lhs_const,
+                    rhs_const,
+                    self.outer_induction_variables.get(&binary.lhs),
+                    self.outer_induction_variables.get(&binary.rhs),
+                ) {
+                    (Some((lhs, _)), None, None, Some(upper_bound)) => (lhs, *upper_bound),
+                    (None, Some((rhs, _)), Some(upper_bound), None) => (*upper_bound, rhs),
+                    _ => return false,
+                };
+
+                eval_constant_binary_op(lhs, rhs, binary.operator, operand_type).is_some()
+            }
             _ => false,
         }
     }