feat: Dynamic indexing of non-homogenous slices (noir-lang#2883)

compiler/noirc_evaluator/src/ssa/acir_gen/acir_ir/acir_variable.rs

@@ -913,7 +913,7 @@ impl AcirContext {
                     self.brillig_array_input(var_expressions, var)?;
                 }
             }
-            AcirValue::DynamicArray(AcirDynamicArray { block_id, len }) => {
+            AcirValue::DynamicArray(AcirDynamicArray { block_id, len, .. }) => {
                 for i in 0..len {
                     // We generate witnesses corresponding to the array values
                     let index_var = self.add_constant(FieldElement::from(i as u128));

compiler/noirc_evaluator/src/ssa/function_builder/mod.rs

@@ -275,9 +275,8 @@ impl FunctionBuilder {
         array: ValueId,
         index: ValueId,
         value: ValueId,
-        length: Option<ValueId>,
     ) -> ValueId {
-        self.insert_instruction(Instruction::ArraySet { array, index, value, length }, None).first()
+        self.insert_instruction(Instruction::ArraySet { array, index, value }, None).first()
     }
 
     /// Terminates the current block with the given terminator instruction

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

@@ -178,9 +178,7 @@ pub(crate) enum Instruction {
 
     /// Creates a new array with the new value at the given index. All other elements are identical
     /// to those in the given array. This will not modify the original array.
-    ///
-    /// An optional length can be provided to enable handling of dynamic slice indices.
-    ArraySet { array: ValueId, index: ValueId, value: ValueId, length: Option<ValueId> },
+    ArraySet { array: ValueId, index: ValueId, value: ValueId },
 }
 
 impl Instruction {
@@ -306,12 +304,9 @@ impl Instruction {
             Instruction::ArrayGet { array, index } => {
                 Instruction::ArrayGet { array: f(*array), index: f(*index) }
             }
-            Instruction::ArraySet { array, index, value, length } => Instruction::ArraySet {
-                array: f(*array),
-                index: f(*index),
-                value: f(*value),
-                length: length.map(f),
-            },
+            Instruction::ArraySet { array, index, value } => {
+                Instruction::ArraySet { array: f(*array), index: f(*index), value: f(*value) }
+            }
         }
     }
 
@@ -348,11 +343,10 @@ impl Instruction {
                 f(*array);
                 f(*index);
             }
-            Instruction::ArraySet { array, index, value, length } => {
+            Instruction::ArraySet { array, index, value } => {
                 f(*array);
                 f(*index);
                 f(*value);
-                length.map(&mut f);
             }
             Instruction::EnableSideEffects { condition } => {
                 f(*condition);

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

@@ -163,19 +163,14 @@ pub(crate) fn display_instruction(
         Instruction::ArrayGet { array, index } => {
             writeln!(f, "array_get {}, index {}", show(*array), show(*index))
         }
-        Instruction::ArraySet { array, index, value, length } => {
-            write!(
+        Instruction::ArraySet { array, index, value } => {
+            writeln!(
                 f,
                 "array_set {}, index {}, value {}",
                 show(*array),
                 show(*index),
                 show(*value)
-            )?;
-            if let Some(length) = length {
-                writeln!(f, ", length {}", show(*length))
-            } else {
-                writeln!(f)
-            }
+            )
         }
     }
 }

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

@@ -461,8 +461,7 @@ impl<'f> Context<'f> {
                     // The smaller slice is filled with placeholder data. Codegen for slice accesses must
                     // include checks against the dynamic slice length so that this placeholder data is not incorrectly accessed.
                     if len <= index_value.to_u128() as usize {
-                        let zero = FieldElement::zero();
-                        self.inserter.function.dfg.make_constant(zero, Type::field())
+                        self.make_slice_dummy_data(element_type)
                     } else {
                         let get = Instruction::ArrayGet { array, index };
                         self.insert_instruction_with_typevars(get, typevars).first()
@@ -484,6 +483,37 @@ impl<'f> Context<'f> {
         self.inserter.function.dfg.make_array(merged, typ)
     }
 
+    /// Construct a dummy value to be attached to the smaller of two slices being merged.
+    /// We need to make sure we follow the internal element type structure of the slice type
+    /// even for dummy data to ensure that we do not have errors later in the compiler,
+    /// such as with dynamic indexing of non-homogenous slices.
+    fn make_slice_dummy_data(&mut self, typ: &Type) -> ValueId {
+        match typ {
+            Type::Numeric(_) => {
+                let zero = FieldElement::zero();
+                self.inserter.function.dfg.make_constant(zero, Type::field())
+            }
+            Type::Array(element_types, len) => {
+                let mut array = im::Vector::new();
+                for _ in 0..*len {
+                    for typ in element_types.iter() {
+                        array.push_back(self.make_slice_dummy_data(typ));
+                    }
+                }
+                self.inserter.function.dfg.make_array(array, typ.clone())
+            }
+            Type::Slice(_) => {
+                unreachable!("ICE: Slices of slice is unsupported")
+            }
+            Type::Reference => {
+                unreachable!("ICE: Merging references is unsupported")
+            }
+            Type::Function => {
+                unreachable!("ICE: Merging functions is unsupported")
+            }
+        }
+    }
+
     fn get_slice_length(&mut self, value_id: ValueId) -> usize {
         let value = &self.inserter.function.dfg[value_id];
         match value {

compiler/noirc_evaluator/src/ssa/ssa_gen/context.rs

@@ -661,19 +661,14 @@ impl<'a> FunctionContext<'a> {
         match lvalue {
             LValue::Ident => unreachable!("Cannot assign to a variable without a reference"),
             LValue::Index { old_array: mut array, index, array_lvalue, location } => {
-                array = self.assign_lvalue_index(new_value, array, index, None, location);
+                array = self.assign_lvalue_index(new_value, array, index, location);
                 self.assign_new_value(*array_lvalue, array.into());
             }
             LValue::SliceIndex { old_slice: slice, index, slice_lvalue, location } => {
                 let mut slice_values = slice.into_value_list(self);
 
-                slice_values[1] = self.assign_lvalue_index(
-                    new_value,
-                    slice_values[1],
-                    index,
-                    Some(slice_values[0]),
-                    location,
-                );
+                slice_values[1] =
+                    self.assign_lvalue_index(new_value, slice_values[1], index, location);
 
                 // The size of the slice does not change in a slice index assignment so we can reuse the same length value
                 let new_slice = Tree::Branch(vec![slice_values[0].into(), slice_values[1].into()]);
@@ -694,7 +689,6 @@ impl<'a> FunctionContext<'a> {
         new_value: Values,
         mut array: ValueId,
         index: ValueId,
-        length: Option<ValueId>,
         location: Location,
     ) -> ValueId {
         let element_size = self.builder.field_constant(self.element_size(array));
@@ -706,7 +700,7 @@ impl<'a> FunctionContext<'a> {
 
         new_value.for_each(|value| {
             let value = value.eval(self);
-            array = self.builder.insert_array_set(array, index, value, length);
+            array = self.builder.insert_array_set(array, index, value);
             index = self.builder.insert_binary(index, BinaryOp::Add, one);
         });
         array

tooling/nargo_cli/tests/execution_success/nested_slice_dynamic/Nargo.toml

@@ -0,0 +1,7 @@
+[package]
+name = "nested_slice_dynamic"
+type = "bin"
+authors = [""]
+compiler_version = "0.13.0"
+
+[dependencies]

tooling/nargo_cli/tests/execution_success/nested_slice_dynamic/Prover.toml

@@ -0,0 +1 @@
+y = "3"

tooling/nargo_cli/tests/execution_success/nested_slice_dynamic/src/main.nr

@@ -0,0 +1,49 @@
+struct Bar {
+    inner: [Field; 3],
+}
+
+struct Foo {
+    a: Field,
+    b: [Field; 3],
+    bar: Bar,
+}
+
+fn main(y :  Field) {
+    let foo_one = Foo { a: 1, b: [2, 3, 20], bar: Bar { inner: [100, 101, 102] } };
+    let foo_two = Foo { a: 4, b: [5, 6, 21], bar: Bar { inner: [103, 104, 105] } };
+    let foo_three = Foo { a: 7, b: [8, 9, 22], bar: Bar { inner: [106, 107, 108] } };
+    let foo_four = Foo { a: 10, b: [11, 12, 23], bar: Bar { inner: [109, 110, 111] } };
+    let mut x = [foo_one];
+    x = x.push_back(foo_two);
+    x = x.push_back(foo_three);
+    x = x.push_back(foo_four);
+
+    assert(x[y - 3].a == 1);
+    assert(x[y - 3].b == [2, 3, 20]);
+    assert(x[y - 2].a == 4);
+    assert(x[y - 2].b == [5, 6, 21]);
+    assert(x[y - 1].a == 7);
+    assert(x[y - 1].b == [8, 9, 22]);
+    assert(x[y].a == 10);
+    assert(x[y].b == [11, 12, 23]);
+    assert(x[y].bar.inner == [109, 110, 111]);
+
+    if y != 2 {
+        x[y - 2].a = 50;
+    } else {
+        x[y - 2].a = 100;
+    }
+    assert(x[y - 2].a == 50);
+
+    if y == 2 {
+        x[y - 1].b = [50, 51, 52];
+    } else {
+        x[y - 1].b = [100, 101, 102];
+    }
+    assert(x[2].b == [100, 101, 102]);
+
+    assert(x[y - 3].bar.inner == [100, 101, 102]);
+    assert(x[y - 2].bar.inner == [103, 104, 105]);
+    assert(x[y - 1].bar.inner == [106, 107, 108]);
+    assert(x[y].bar.inner == [109, 110, 111]);
+}