From 19c234cd39f6cd8792758ff13fe37e773d30295d Mon Sep 17 00:00:00 2001 From: Jake Fecher Date: Tue, 3 Dec 2024 14:54:05 -0600 Subject: [PATCH] Revert "fix: Don't remove necessary RC instructions in DIE pass (#6585)" This reverts commit 440d94d8149ede5f211437e9405f65b460cfcbf8. --- compiler/noirc_evaluator/src/ssa/opt/die.rs | 91 +++++++++++-------- .../reference_counts/src/main.nr | 6 +- 2 files changed, 54 insertions(+), 43 deletions(-) diff --git a/compiler/noirc_evaluator/src/ssa/opt/die.rs b/compiler/noirc_evaluator/src/ssa/opt/die.rs index 9817d0a6738..8d3fa9cc615 100644 --- a/compiler/noirc_evaluator/src/ssa/opt/die.rs +++ b/compiler/noirc_evaluator/src/ssa/opt/die.rs @@ -127,9 +127,8 @@ impl Context { .push(instructions_len - instruction_index - 1); } } else { - // We can't remove rc instructions if they're loaded from a reference - // since we'd have no way of knowing whether the reference is still used. - if Self::is_inc_dec_instruction_on_known_array(instruction, &function.dfg) { + use Instruction::*; + if matches!(instruction, IncrementRc { .. } | DecrementRc { .. }) { self.rc_instructions.push((*instruction_id, block_id)); } else { instruction.for_each_value(|value| { @@ -141,6 +140,7 @@ impl Context { rc_tracker.track_inc_rcs_to_remove(*instruction_id, function); } + self.instructions_to_remove.extend(rc_tracker.get_non_mutated_arrays()); self.instructions_to_remove.extend(rc_tracker.rc_pairs_to_remove); // If there are some instructions that might trigger an out of bounds error, @@ -337,28 +337,6 @@ impl Context { inserted_check } - - /// True if this is a `Instruction::IncrementRc` or `Instruction::DecrementRc` - /// operating on an array directly from a `Instruction::MakeArray` or an - /// intrinsic known to return a fresh array. - fn is_inc_dec_instruction_on_known_array( - instruction: &Instruction, - dfg: &DataFlowGraph, - ) -> bool { - use Instruction::*; - if let IncrementRc { value } | DecrementRc { value } = instruction { - if let Value::Instruction { instruction, .. } = &dfg[*value] { - return match &dfg[*instruction] { - MakeArray { .. } => true, - Call { func, .. } => { - matches!(&dfg[*func], Value::Intrinsic(_) | Value::ForeignFunction(_)) - } - _ => false, - }; - } - } - false - } } fn instruction_might_result_in_out_of_bounds( @@ -532,11 +510,10 @@ struct RcTracker { // If we see an inc/dec RC pair within a block we can safely remove both instructions. rcs_with_possible_pairs: HashMap>, rc_pairs_to_remove: HashSet, - // 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>, - + mut_borrowed_arrays: HashSet, // 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. @@ -589,10 +566,35 @@ impl RcTracker { dec_rc.possibly_mutated = true; } } + + self.mut_borrowed_arrays.insert(*array); + } + Instruction::Store { value, .. } => { + // We are very conservative and say that any store of an array value means it has the potential + // to be mutated. This is done due to the tracking of mutable borrows still being per block. + let typ = function.dfg.type_of_value(*value); + if matches!(&typ, Type::Array(..) | Type::Slice(..)) { + self.mut_borrowed_arrays.insert(*value); + } } _ => {} } } + + fn get_non_mutated_arrays(&self) -> HashSet { + self.inc_rcs + .keys() + .filter_map(|value| { + if !self.mut_borrowed_arrays.contains(value) { + Some(&self.inc_rcs[value]) + } else { + None + } + }) + .flatten() + .copied() + .collect() + } } #[cfg(test)] mod test { @@ -828,23 +830,32 @@ mod test { } #[test] - fn does_not_remove_inc_or_dec_rc_of_if_they_are_loaded_from_a_reference() { + fn remove_inc_rcs_that_are_never_mutably_borrowed() { let src = " - brillig(inline) fn borrow_mut f0 { - b0(v0: &mut [Field; 3]): - v1 = load v0 -> [Field; 3] - inc_rc v1 // this one shouldn't be removed - v2 = load v0 -> [Field; 3] - inc_rc v2 // this one shouldn't be removed - v3 = load v0 -> [Field; 3] - v6 = array_set v3, index u32 0, value Field 5 - store v6 at v0 - dec_rc v6 - return + acir(inline) fn main f0 { + b0(v0: [Field; 2]): + inc_rc v0 + inc_rc v0 + inc_rc v0 + v2 = array_get v0, index u32 0 -> Field + inc_rc v0 + return v2 } "; let ssa = Ssa::from_str(src).unwrap(); + let main = ssa.main(); + + // The instruction count never includes the terminator instruction + assert_eq!(main.dfg[main.entry_block()].instructions().len(), 5); + + let expected = " + acir(inline) fn main f0 { + b0(v0: [Field; 2]): + v2 = array_get v0, index u32 0 -> Field + return v2 + } + "; let ssa = ssa.dead_instruction_elimination(); - assert_normalized_ssa_equals(ssa, src); + assert_normalized_ssa_equals(ssa, expected); } } diff --git a/test_programs/execution_success/reference_counts/src/main.nr b/test_programs/execution_success/reference_counts/src/main.nr index 86b5c812472..7ab7de893fa 100644 --- a/test_programs/execution_success/reference_counts/src/main.nr +++ b/test_programs/execution_success/reference_counts/src/main.nr @@ -1,6 +1,6 @@ fn main() { let mut array = [0, 1, 2]; - assert_refcount(array, 2); + assert_refcount(array, 1); borrow(array, std::mem::array_refcount(array)); borrow_mut(&mut array, std::mem::array_refcount(array)); @@ -13,13 +13,13 @@ fn borrow(array: [Field; 3], rc_before_call: u32) { } fn borrow_mut(array: &mut [Field; 3], rc_before_call: u32) { - assert_refcount(*array, rc_before_call + 1); + assert_refcount(*array, rc_before_call + 0); // Issue! This should be rc_before_call + 1 array[0] = 5; println(array[0]); } fn copy_mut(mut array: [Field; 3], rc_before_call: u32) { - assert_refcount(array, rc_before_call + 1); + assert_refcount(array, rc_before_call + 0); // Issue! This should be rc_before_call + 1 array[0] = 6; println(array[0]); }