chore: PR 6782 w/ PR 6783

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

@@ -10,12 +10,14 @@ use crate::ssa::{
         function::Function,
         instruction::{BinaryOp, Instruction, InstructionId, Intrinsic},
         post_order::PostOrder,
-        types::NumericType,
+        types::{NumericType, Type},
         value::{Value, ValueId},
     },
     ssa_gen::Ssa,
 };
 
+use super::rc::{pop_rc_for, RcInstruction};
+
 impl Ssa {
     /// Performs Dead Instruction Elimination (DIE) to remove any instructions with
     /// unused results.
@@ -104,6 +106,8 @@ impl Context {
 
         let instructions_len = block.instructions().len();
 
+        let mut rc_tracker = RcTracker::default();
+
         // Indexes of instructions that might be out of bounds.
         // We'll remove those, but before that we'll insert bounds checks for them.
         let mut possible_index_out_of_bounds_indexes = Vec::new();
@@ -131,8 +135,13 @@ impl Context {
                     });
                 }
             }
+
+            rc_tracker.track_inc_rcs_to_remove(*instruction_id, function);
         }
 
+        self.instructions_to_remove.extend(rc_tracker.get_non_mutated_arrays(&function.dfg));
+        self.instructions_to_remove.extend(rc_tracker.rc_pairs_to_remove);
+
         // If there are some instructions that might trigger an out of bounds error,
         // first add constrain checks. Then run the DIE pass again, which will remove those
         // but leave the constrains (any any value needed by those constrains)
@@ -517,6 +526,112 @@ fn apply_side_effects(
     (lhs, rhs)
 }
 
+#[derive(Default)]
+struct RcTracker {
+    // We can track IncrementRc instructions per block to determine whether they are useless.
+    // IncrementRc and DecrementRc instructions are normally side effectual instructions, but we remove
+    // them if their value is not used anywhere in the function. However, even when their value is used, their existence
+    // is pointless logic if there is no array set between the increment and the decrement of the reference counter.
+    // We track per block whether an IncrementRc instruction has a paired DecrementRc instruction
+    // with the same value but no array set in between.
+    // If we see an inc/dec RC pair within a block we can safely remove both instructions.
+    rcs_with_possible_pairs: HashMap<Type, Vec<RcInstruction>>,
+    rc_pairs_to_remove: HashSet<InstructionId>,
+    // We also separately track all IncrementRc instructions and all arrays which have been mutably borrowed.
+    // If an array has not been mutably borrowed we can then safely remove all IncrementRc instructions on that array.
+    inc_rcs: HashMap<ValueId, HashSet<InstructionId>>,
+    mutated_array_types: HashSet<Type>,
+    // The SSA often creates patterns where after simplifications we end up with repeat
+    // IncrementRc instructions on the same value. We track whether the previous instruction was an IncrementRc,
+    // and if the current instruction is also an IncrementRc on the same value we remove the current instruction.
+    // `None` if the previous instruction was anything other than an IncrementRc
+    previous_inc_rc: Option<ValueId>,
+}
+
+impl RcTracker {
+    fn track_inc_rcs_to_remove(&mut self, instruction_id: InstructionId, function: &Function) {
+        let instruction = &function.dfg[instruction_id];
+
+        if let Instruction::IncrementRc { value } = instruction {
+            if let Some(previous_value) = self.previous_inc_rc {
+                if previous_value == *value {
+                    self.rc_pairs_to_remove.insert(instruction_id);
+                }
+            }
+            self.previous_inc_rc = Some(*value);
+        } else {
+            self.previous_inc_rc = None;
+        }
+
+        // DIE loops over a block in reverse order, so we insert an RC instruction for possible removal
+        // when we see a DecrementRc and check whether it was possibly mutated when we see an IncrementRc.
+        match instruction {
+            Instruction::IncrementRc { value } => {
+                if let Some(inc_rc) =
+                    pop_rc_for(*value, function, &mut self.rcs_with_possible_pairs)
+                {
+                    if !inc_rc.possibly_mutated {
+                        self.rc_pairs_to_remove.insert(inc_rc.id);
+                        self.rc_pairs_to_remove.insert(instruction_id);
+                    }
+                }
+
+                self.inc_rcs.entry(*value).or_default().insert(instruction_id);
+            }
+            Instruction::DecrementRc { value } => {
+                let typ = function.dfg.type_of_value(*value);
+
+                // We assume arrays aren't mutated until we find an array_set
+                let dec_rc =
+                    RcInstruction { id: instruction_id, array: *value, possibly_mutated: false };
+                self.rcs_with_possible_pairs.entry(typ).or_default().push(dec_rc);
+            }
+            Instruction::ArraySet { array, .. } => {
+                let typ = function.dfg.type_of_value(*array);
+                if let Some(dec_rcs) = self.rcs_with_possible_pairs.get_mut(&typ) {
+                    for dec_rc in dec_rcs {
+                        dec_rc.possibly_mutated = true;
+                    }
+                }
+
+                self.mutated_array_types.insert(typ);
+            }
+            Instruction::Store { value, .. } => {
+                // We are very conservative and say that any store of an array type means it has the potential to be mutated.
+                let typ = function.dfg.type_of_value(*value);
+                if matches!(&typ, Type::Array(..) | Type::Slice(..)) {
+                    self.mutated_array_types.insert(typ);
+                }
+            }
+            Instruction::Call { arguments, .. } => {
+                for arg in arguments {
+                    let typ = function.dfg.type_of_value(*arg);
+                    if matches!(&typ, Type::Array(..) | Type::Slice(..)) {
+                        self.mutated_array_types.insert(typ);
+                    }
+                }
+            }
+            _ => {}
+        }
+    }
+
+    fn get_non_mutated_arrays(&self, dfg: &DataFlowGraph) -> HashSet<InstructionId> {
+        self.inc_rcs
+            .keys()
+            .filter_map(|value| {
+                let typ = dfg.type_of_value(*value);
+                if !self.mutated_array_types.contains(&typ) {
+                    Some(&self.inc_rcs[value])
+                } else {
+                    None
+                }
+            })
+            .flatten()
+            .copied()
+            .collect()
+    }
+}
+
 #[cfg(test)]
 mod test {
     use std::sync::Arc;

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

@@ -9,6 +9,7 @@
 //! We also check that we are not hoisting instructions with side effects.
 use acvm::{acir::AcirField, FieldElement};
 use fxhash::{FxHashMap as HashMap, FxHashSet as HashSet};
+use iter_extended::vecmap;
 
 use crate::ssa::{
     ir::{
@@ -109,6 +110,28 @@ impl<'f> LoopInvariantContext<'f> {
 
                 if hoist_invariant {
                     self.inserter.push_instruction(instruction_id, pre_header);
+
+                    // We track whether we may mutate MakeArray instructions before we deduplicate
+                    // them but we still need to issue an extra inc_rc in case they're mutated afterward.
+                    if matches!(
+                        self.inserter.function.dfg[instruction_id],
+                        Instruction::MakeArray { .. }
+                    ) {
+                        let results =
+                            self.inserter.function.dfg.instruction_results(instruction_id).to_vec();
+                        let results = vecmap(results, |value| self.inserter.resolve(value));
+                        assert_eq!(
+                            results.len(),
+                            1,
+                            "ICE: We expect only a single result from an `Instruction::MakeArray`"
+                        );
+                        let inc_rc = Instruction::IncrementRc { value: results[0] };
+                        let call_stack = self.inserter.function.dfg.get_call_stack(instruction_id);
+                        self.inserter
+                            .function
+                            .dfg
+                            .insert_instruction_and_results(inc_rc, *block, None, call_stack);
+                    }
                 } else {
                     self.inserter.push_instruction(instruction_id, *block);
                 }
@@ -186,6 +209,7 @@ impl<'f> LoopInvariantContext<'f> {
         });
 
         let can_be_deduplicated = instruction.can_be_deduplicated(self.inserter.function, false)
+            || matches!(instruction, Instruction::MakeArray { .. })
             || self.can_be_deduplicated_from_upper_bound(&instruction);
 
         is_loop_invariant && can_be_deduplicated
@@ -555,4 +579,94 @@ mod test {
         let ssa = ssa.loop_invariant_code_motion();
         assert_normalized_ssa_equals(ssa, expected);
     }
+
+    #[test]
+    fn insert_inc_rc_when_moving_make_array() {
+        // SSA for the following program:
+        //
+        // unconstrained fn main(x: u32, y: u32) {
+        //   let mut a1 = [1, 2, 3, 4, 5];
+        //   a1[x] = 64;
+        //   for i in 0 .. 5 {
+        //       let mut a2 = [1, 2, 3, 4, 5];
+        //       a2[y + i] = 128;
+        //       foo(a2);
+        //   }
+        //   foo(a1);
+        // }
+        //
+        // We want to make sure move a loop invariant make_array instruction,
+        // to account for whether that array has been marked as mutable.
+        // To do so, we increment the reference counter on the array we are moving.
+        // In the SSA below, we want to move `v42` out of the loop.
+        let src = "
+        brillig(inline) fn main f0 {
+          b0(v0: u32, v1: u32):
+            v8 = make_array [Field 1, Field 2, Field 3, Field 4, Field 5] : [Field; 5]
+            v9 = allocate -> &mut [Field; 5]
+            v11 = array_set v8, index v0, value Field 64
+            v13 = add v0, u32 1
+            store v11 at v9
+            jmp b1(u32 0)
+          b1(v2: u32):
+            v16 = lt v2, u32 5
+            jmpif v16 then: b3, else: b2
+          b2():
+            v17 = load v9 -> [Field; 5]
+            call f1(v17)
+            return
+          b3():
+            v19 = make_array [Field 1, Field 2, Field 3, Field 4, Field 5] : [Field; 5]
+            v20 = allocate -> &mut [Field; 5]
+            v21 = add v1, v2
+            v23 = array_set v19, index v21, value Field 128
+            call f1(v23)
+            v25 = add v2, u32 1
+            jmp b1(v25)
+        }
+        brillig(inline) fn foo f1 {
+          b0(v0: [Field; 5]):
+            return
+        }
+        ";
+
+        let ssa = Ssa::from_str(src).unwrap();
+
+        // We expect the `make_array` at the top of `b3` to be replaced with an `inc_rc`
+        // of the newly hoisted `make_array` at the end of `b0`.
+        let expected = "
+        brillig(inline) fn main f0 {
+          b0(v0: u32, v1: u32):
+            v8 = make_array [Field 1, Field 2, Field 3, Field 4, Field 5] : [Field; 5]
+            v9 = allocate -> &mut [Field; 5]
+            v11 = array_set v8, index v0, value Field 64
+            v13 = add v0, u32 1
+            store v11 at v9
+            v14 = make_array [Field 1, Field 2, Field 3, Field 4, Field 5] : [Field; 5]
+            jmp b1(u32 0)
+          b1(v2: u32):
+            v17 = lt v2, u32 5
+            jmpif v17 then: b3, else: b2
+          b2():
+            v18 = load v9 -> [Field; 5]
+            call f1(v18)
+            return
+          b3():
+            inc_rc v14
+            v20 = allocate -> &mut [Field; 5]
+            v21 = add v1, v2
+            v23 = array_set v14, index v21, value Field 128
+            call f1(v23)
+            v25 = add v2, u32 1
+            jmp b1(v25)
+        }
+        brillig(inline) fn foo f1 {
+          b0(v0: [Field; 5]):
+            return
+        }
+        ";
+
+        let ssa = ssa.loop_invariant_code_motion();
+        assert_normalized_ssa_equals(ssa, expected);
+    }
 }

test_programs/gates_report_brillig_execution.sh

@@ -8,8 +8,6 @@ excluded_dirs=(
   "double_verify_nested_proof" 
   "overlapping_dep_and_mod" 
   "comptime_println"
-  #  Takes a very long time to execute as large loops do not get simplified.
-  "regression_4709"
   #  bit sizes for bigint operation doesn't match up.
   "bigint"
   #  Expected to fail as test asserts on which runtime it is in.

tooling/nargo_cli/build.rs

@@ -42,9 +42,7 @@ fn main() {
 
 /// Some tests are explicitly ignored in brillig due to them failing.
 /// These should be fixed and removed from this list.
-const IGNORED_BRILLIG_TESTS: [&str; 11] = [
-    // Takes a very long time to execute as large loops do not get simplified.
-    "regression_4709",
+const IGNORED_BRILLIG_TESTS: [&str; 10] = [
     // bit sizes for bigint operation doesn't match up.
     "bigint",
     // ICE due to looking for function which doesn't exist.