memcopy! and memset! intrinsics

LANGUAGE.md

@@ -180,6 +180,25 @@ infinity/NaN behavior.
 Only these six division bang calls select integer-division behavior. Bare calls such as
 `divfloor(a, b)` and qualified calls such as `math.divfloor(a, b)` resolve to ordinary functions.
 
+#### typed memory operations
+
+`memcopy!(destination, source)` and `memset!(destination, value)` are available at runtime and
+comptime. A destination must be a mutable slice or mutable pointer-to-array. A `memcopy!` source
+may be a slice or pointer-to-array; many-item pointers must first be sliced. Array pointers are
+treated as regions containing their explicit logical elements, including a sentinel only when it
+is part of that array region.
+
+`memcopy!` requires the same element type after alias resolution and the same element count. Its
+non-empty regions must not overlap. Comptime calls diagnose unequal lengths and overlap; runtime
+calls trap for either condition or if the element count cannot be converted to a byte count.
+Zero-sized elements still require equal counts. Empty copies are no-ops and may name the same
+region.
+
+`memset!` coerces `value` to the destination element type. Use `memset!(destination, 0)` to zero a
+region; there is no separate `memzero!`, and `memset!` does not promise secure zeroing. Copying or
+filling with `undefined` transfers undefined state without reading it. Each operand is evaluated
+exactly once. Bare functions named `memcopy` or `memset` remain ordinary user functions.
+
 ### functions, C interop, and linking
 
 - demand-monomorphized Brolang and C-ABI functions

README.md

@@ -244,6 +244,7 @@ Current prototype features:
 - Ordered linking of additional C sources, objects, archives, and libraries
 - Checked signed addition and unary negation
 - Float-only `/` plus explicit `divtrunc!`, `divfloor!`, `divexact!`, `divceil!`, `rem!`, and `mod!` scalar intrinsics
+- Runtime/comptime typed `memcopy!` and `memset!` over slices and pointers-to-arrays, with checked lengths and overlap
 - Static, eager runtime, mutable runtime, and deferred problematic globals
 - Runtime diagnostics followed by `llvm.trap`
 

TODO.md

@@ -934,6 +934,20 @@
   - fields without defaults remain required; C-layout records, unions, tuples, and anonymous
     generated structs do not accept defaults
 
+45. typed memory intrinsics (implemented)
+  - `memcopy!` copies equal-length, non-overlapping slices or pointers-to-arrays with identical
+    element types; comptime diagnoses invalid regions and runtime guards length, size, and overlap
+  - `memset!` fills a mutable region with a value coerced to its element type; bytes lower to LLVM
+    memset and wider values use typed stores
+  - both operations evaluate operands once, preserve undefined state without observing it, and work
+    identically during comptime evaluation; zeroing is `memset!(destination, 0)`
+  - `std/mem` aligned reallocation uses `memcopy!`
+
+46. fix `EnumFieldStruct` in `std/meta`
+  - currently, the `|info|` `.enum` payload capture doesn't preserve the comptime-ness in the match statement
+    this results in having to type other values in the scope like `[field!(typeinfo!(E), "enum").fields.len]mut []u8`
+    which is obviously absurd
+
 ## A word on unchecked casts
 
 For casts that bypass safety checks, Honey provides builtin functions:

compiler/checker/checker.odin

@@ -811,6 +811,68 @@ Division_Builtin :: enum u8 {
 	Mod,
 }
 
+Memory_Builtin :: enum u8 {
+	None,
+	Copy,
+	Set,
+}
+
+memory_builtin_call :: proc(checker: ^Checker, expr: ast.Expr) -> Memory_Builtin {
+	if !expr.intrinsic || expr.kind != .Call || expr.left != ast.INVALID_EXPR || symbol.is_valid(expr.qualifier) {
+		return .None
+	}
+	switch symbol_text(checker, expr.name) {
+	case "memcopy": return .Copy
+	case "memset":  return .Set
+	}
+	return .None
+}
+
+memory_region_type :: proc(checker: ^Checker, value: types.Type) -> (child: types.Type, mutable: bool, ok: bool) {
+	store := &checker.module.types
+	resolved := types.resolve_alias(value, store)
+	if item, item_ok := types.node(store, resolved); item_ok && item.kind == .Slice {
+		return item.child, item.mutable, true
+	}
+	pointer, pointer_ok := types.node(store, resolved)
+	if pointer_ok && pointer.kind == .Pointer && !pointer.many {
+		array, array_ok := types.node(store, types.resolve_alias(pointer.child, store))
+		if array_ok && array.kind == .Array {
+			return array.child, pointer.mutable && array.mutable, true
+		}
+	}
+	return types.INVALID, false, false
+}
+
+infer_memory_builtin :: proc(
+	checker: ^Checker,
+	expr: ast.Expr,
+	kind: Memory_Builtin,
+	locals: []Infer_Local,
+	pkg: ast.Package_Id,
+	file: ast.File_Id,
+	demanded: ^[dynamic]Spec_Id,
+	local_types: []types.Type,
+) -> types.Type {
+	if len(expr.args) != 2 {
+		return types.INVALID
+	}
+	destination := infer_nested_expr(checker, expr.args[0], locals, pkg, file, demanded, local_types)
+	child, _, ok := memory_region_type(checker, destination)
+	if !ok {
+		_ = infer_nested_expr(checker, expr.args[1], locals, pkg, file, demanded, local_types)
+		return types.INVALID
+	}
+	if kind == .Set {
+		if !is_undefined_expr(checker, expr.args[1]) {
+			_ = infer_nested_expr(checker, expr.args[1], locals, pkg, file, demanded, local_types, child)
+		}
+	} else {
+		_ = infer_nested_expr(checker, expr.args[1], locals, pkg, file, demanded, local_types)
+	}
+	return types.VOID
+}
+
 division_builtin_call :: proc(checker: ^Checker, expr: ast.Expr) -> Division_Builtin {
 	if !expr.intrinsic || expr.kind != .Call || expr.left != ast.INVALID_EXPR || symbol.is_valid(expr.qualifier) {
 		return .None
@@ -5036,6 +5098,11 @@ infer_expr :: proc(
 					_ = pop(&stack)
 					continue
 				}
+				if builtin := memory_builtin_call(checker, expr); builtin != .None {
+					last = infer_memory_builtin(checker, expr, builtin, locals, pkg, file, demanded, local_types)
+					_ = pop(&stack)
+					continue
+				}
 				if is_intrinsic_call(checker, expr, "some") {
 					if len(expr.args) == 1 && types.is_optional(frame.expected, &checker.module.types) {
 						child := types.child_type(frame.expected, &checker.module.types)
@@ -7548,6 +7615,71 @@ build_division_builtin :: proc(
 	})
 }
 
+build_memory_builtin :: proc(
+	checker: ^Checker,
+	expr: ast.Expr,
+	kind: Memory_Builtin,
+	locals: []Build_Local,
+	global_reads: ^[dynamic]hir.Global_Id,
+	calls: ^[dynamic]hir.Function_Id,
+	pkg: ast.Package_Id,
+	file: ast.File_Id,
+) -> hir.Expr_Id {
+	name := symbol_text(checker, expr.name)
+	if len(expr.args) != 2 {
+		id := source.addf(checker.diagnostics, expr.span, "%s! expects 2 arguments, got %d", name, len(expr.args))
+		return invalid_hir_expr(checker, expr.span, id, types.VOID)
+	}
+	destination := build_nested_expr(checker, expr.args[0], locals, global_reads, calls, types.INVALID, pkg, file)
+	destination_type := checker.module.exprs[destination].type
+	destination_child, destination_mutable, destination_ok := memory_region_type(checker, destination_type)
+	if !destination_ok || !destination_mutable {
+		id := source.addf(
+			checker.diagnostics, checker.ast_module.exprs[expr.args[0]].span,
+			"%s! destination must be a mutable slice or mutable pointer-to-array", name,
+		)
+		return invalid_hir_expr(checker, expr.span, id, types.VOID)
+	}
+	right := hir.INVALID_EXPR
+	result_kind := hir.Expr_Kind.Mem_Copy
+	if kind == .Set {
+		if is_undefined_expr(checker, expr.args[1]) {
+			right = add_hir_expr(checker, hir.Expr{
+				kind=.Undefined, span=checker.ast_module.exprs[expr.args[1]].span, type=destination_child,
+				target=hir.INVALID_REF, left=hir.INVALID_EXPR, right=hir.INVALID_EXPR,
+				diagnostic=source.INVALID_DIAGNOSTIC,
+			})
+		} else {
+			right = build_nested_expr(checker, expr.args[1], locals, global_reads, calls, destination_child, pkg, file)
+			right = coerce_expr(checker, right, destination_child, checker.ast_module.exprs[expr.args[1]].span)
+		}
+		result_kind = .Mem_Set
+	} else {
+		source_expr := build_nested_expr(checker, expr.args[1], locals, global_reads, calls, types.INVALID, pkg, file)
+		source_type := checker.module.exprs[source_expr].type
+		source_child, _, source_ok := memory_region_type(checker, source_type)
+		if !source_ok {
+			id := source.add(
+				checker.diagnostics, checker.ast_module.exprs[expr.args[1]].span,
+				"memcopy! source must be a slice or pointer-to-array",
+			)
+			return invalid_hir_expr(checker, expr.span, id, types.VOID)
+		}
+		if !types.equal(
+			types.resolve_alias(destination_child, &checker.module.types),
+			types.resolve_alias(source_child, &checker.module.types),
+		) {
+			id := source.add(checker.diagnostics, expr.span, "memcopy! source and destination element types must match")
+			return invalid_hir_expr(checker, expr.span, id, types.VOID)
+		}
+		right = source_expr
+	}
+	return add_hir_expr(checker, hir.Expr{
+		kind=result_kind, span=expr.span, type=types.VOID, left=destination, right=right,
+		target=hir.INVALID_REF, diagnostic=source.INVALID_DIAGNOSTIC,
+	})
+}
+
 fallible_aggregate :: proc(
 	checker: ^Checker,
 	span: source.Span,
@@ -8793,6 +8925,11 @@ build_expr :: proc(
 					_ = pop(&stack)
 					continue
 				}
+				if builtin := memory_builtin_call(checker, expr); builtin != .None {
+					last = build_memory_builtin(checker, expr, builtin, locals, global_reads, calls, pkg, file)
+					_ = pop(&stack)
+					continue
+				}
 				if is_intrinsic_call(checker, expr, "some") {
 					if len(expr.args) != 1 {
 						id := source.addf(checker.diagnostics, expr.span, "some! expects 1 argument, got %d", len(expr.args))

compiler/checker/comptime.odin

@@ -2421,6 +2421,166 @@ ct_eval_division_call :: proc(
 	return ct_eval_division_builtin(state, kind, left, right, expr.span)
 }
 
+ct_memory_region_info :: proc(state: ^Ct_State, value: Ct_Value) -> (child: types.Type, count: int, mutable: bool, ok: bool) {
+	store := &state.checker.module.types
+	if value.kind == .Slice {
+		item, item_ok := types.node(store, types.resolve_alias(value.type, store))
+		if item_ok && item.kind == .Slice {
+			return item.child, int(value.count), item.mutable, true
+		}
+	}
+	if value.kind == .Pointer {
+		pointer, pointer_ok := types.node(store, types.resolve_alias(value.type, store))
+		if pointer_ok && pointer.kind == .Pointer && !pointer.many {
+			array, array_ok := types.node(store, types.resolve_alias(pointer.child, store))
+			if array_ok && array.kind == .Array {
+				return array.child, int(array.count), pointer.mutable && array.mutable, true
+			}
+		}
+	}
+	if value.kind == .String && value.index < u64(len(state.checker.ast_module.strings)) {
+		return types.U8, len(state.checker.ast_module.strings[value.index]), false, true
+	}
+	return types.INVALID, 0, false, false
+}
+
+ct_memory_element_place :: proc(state: ^Ct_State, value: Ct_Value, index: int) -> Ct_Place_Id {
+	if value.kind == .Slice {
+		place, _, _ := ct_slice_element_place(state, value, index)
+		return place
+	}
+	if value.kind == .Pointer {
+		base, array_type, writable := ct_pointer_place(state, value)
+		array, ok := types.node(&state.checker.module.types, types.resolve_alias(array_type, &state.checker.module.types))
+		if base != INVALID_CT_PLACE && ok && array.kind == .Array && index >= 0 && index < int(array.count) {
+			return ct_extend_place(
+				state, base, Ct_Path_Elem{kind=.Index, index=u32(index)}, array.child, writable && array.mutable,
+			)
+		}
+	}
+	return INVALID_CT_PLACE
+}
+
+ct_places_equal :: proc(state: ^Ct_State, left_id, right_id: Ct_Place_Id) -> bool {
+	if left_id == INVALID_CT_PLACE || right_id == INVALID_CT_PLACE ||
+	   int(left_id) >= len(state.places) || int(right_id) >= len(state.places) {
+		return false
+	}
+	left, right := state.places[left_id], state.places[right_id]
+	if left.cell != right.cell || left.count != right.count {
+		return false
+	}
+	left_path, right_path := ct_place_path(state, left), ct_place_path(state, right)
+	for elem, index in left_path {
+		if elem != right_path[index] {
+			return false
+		}
+	}
+	return true
+}
+
+ct_eval_memory_call :: proc(
+	state: ^Ct_State,
+	expr: ast.Expr,
+	kind: Memory_Builtin,
+	depth: int,
+) -> (Ct_Value_Id, Ct_Flow, bool) {
+	name := symbol_text(state.checker, expr.name)
+	if len(expr.args) != 2 {
+		return INVALID_CT_VALUE, ct_flow(.Normal), ct_failf(state, .Not_Comptime, expr.span, "%s! expects 2 arguments, got %d", name, len(expr.args))
+	}
+	destination_id, destination_flow, destination_ok := ct_eval_expr(state, expr.args[0], types.INVALID, depth+1)
+	if !destination_ok || destination_flow.kind != .Normal || destination_id == INVALID_CT_VALUE || int(destination_id) >= len(state.values) {
+		return INVALID_CT_VALUE, destination_flow, destination_ok
+	}
+	destination := state.values[destination_id]
+	destination_child, destination_count, destination_mutable, region_ok := ct_memory_region_info(state, destination)
+	if !region_ok || !destination_mutable {
+		return INVALID_CT_VALUE, ct_flow(.Normal), ct_failf(
+			state, .Not_Comptime, state.checker.ast_module.exprs[expr.args[0]].span,
+			"%s! destination must be a mutable slice or mutable pointer-to-array", name,
+		)
+	}
+	destination_places := make([]Ct_Place_Id, destination_count, state.checker.allocator)
+	defer delete(destination_places, state.checker.allocator)
+	for &place, index in destination_places {
+		place = ct_memory_element_place(state, destination, index)
+		if place == INVALID_CT_PLACE || !state.places[place].writable {
+			return INVALID_CT_VALUE, ct_flow(.Normal), ct_fail(state, .Not_Comptime, expr.span, "comptime memory destination no longer points to writable storage")
+		}
+	}
+
+	if kind == .Set {
+		value, value_flow, value_ok := ct_eval_expr(state, expr.args[1], destination_child, depth+1)
+		if !value_ok || value_flow.kind != .Normal {
+			return INVALID_CT_VALUE, value_flow, value_ok
+		}
+		value, value_ok = ct_coerce_value(state, value, destination_child, state.checker.ast_module.exprs[expr.args[1]].span)
+		if !value_ok {
+			return INVALID_CT_VALUE, ct_flow(.Normal), false
+		}
+		for place in destination_places {
+			if !ct_place_set(state, place, value) {
+				return INVALID_CT_VALUE, ct_flow(.Normal), false
+			}
+		}
+		return ct_add_value(state, Ct_Value{kind=.Void, type=types.VOID}), ct_flow(.Normal), true
+	}
+
+	source_id, source_flow, source_ok := ct_eval_expr(state, expr.args[1], types.INVALID, depth+1)
+	if !source_ok || source_flow.kind != .Normal || source_id == INVALID_CT_VALUE || int(source_id) >= len(state.values) {
+		return INVALID_CT_VALUE, source_flow, source_ok
+	}
+	source := state.values[source_id]
+	source_child, source_count, _, source_region_ok := ct_memory_region_info(state, source)
+	if !source_region_ok {
+		return INVALID_CT_VALUE, ct_flow(.Normal), ct_fail(state, .Not_Comptime, state.checker.ast_module.exprs[expr.args[1]].span, "memcopy! source must be a slice or pointer-to-array")
+	}
+	if !types.equal(
+		types.resolve_alias(destination_child, &state.checker.module.types),
+		types.resolve_alias(source_child, &state.checker.module.types),
+	) {
+		return INVALID_CT_VALUE, ct_flow(.Normal), ct_fail(state, .Not_Comptime, expr.span, "memcopy! source and destination element types must match")
+	}
+	if destination_count != source_count {
+		return INVALID_CT_VALUE, ct_flow(.Normal), ct_fail(state, .Not_Comptime, expr.span, "memcopy! source and destination lengths differ")
+	}
+
+	source_places := make([]Ct_Place_Id, source_count, state.checker.allocator)
+	values := make([]Ct_Value_Id, source_count, state.checker.allocator)
+	defer delete(source_places, state.checker.allocator)
+	defer delete(values, state.checker.allocator)
+	for index in 0..<source_count {
+		if source.kind == .String {
+			values[index] = ct_add_value(state, Ct_Value{
+				kind=.Integer, type=types.U8, integer=i128(state.checker.ast_module.strings[source.index][index]),
+			})
+			continue
+		}
+		source_places[index] = ct_memory_element_place(state, source, index)
+		if source_places[index] == INVALID_CT_PLACE {
+			return INVALID_CT_VALUE, ct_flow(.Normal), ct_fail(state, .Not_Comptime, expr.span, "comptime memory source no longer points to live storage")
+		}
+		// ponytail: O(n^2) is simplest here; use canonical intervals if large comptime copies become common.
+		for destination_place in destination_places {
+			if ct_places_equal(state, source_places[index], destination_place) {
+				return INVALID_CT_VALUE, ct_flow(.Normal), ct_fail(state, .Not_Comptime, expr.span, "memcopy! source and destination overlap")
+			}
+		}
+		value, value_ok := ct_place_get(state, source_places[index])
+		if !value_ok {
+			return INVALID_CT_VALUE, ct_flow(.Normal), false
+		}
+		values[index] = value
+	}
+	for place, index in destination_places {
+		if !ct_place_set(state, place, values[index]) {
+			return INVALID_CT_VALUE, ct_flow(.Normal), false
+		}
+	}
+	return ct_add_value(state, Ct_Value{kind=.Void, type=types.VOID}), ct_flow(.Normal), true
+}
+
 ct_scalar_cast :: proc(state: ^Ct_State, id: Ct_Value_Id, target: types.Type, span: source.Span) -> (Ct_Value_Id, Ct_Flow, bool) {
 	if id == INVALID_CT_VALUE || int(id) >= len(state.values) {
 		return INVALID_CT_VALUE, ct_flow(.Normal), false
@@ -3075,6 +3235,9 @@ ct_eval_call_expr :: proc(state: ^Ct_State, expr: ast.Expr, expected: types.Type
 	if builtin := division_builtin_call(checker, expr); builtin != .None {
 		return ct_eval_division_call(state, expr, builtin, expected, depth+1)
 	}
+	if builtin := memory_builtin_call(checker, expr); builtin != .None {
+		return ct_eval_memory_call(state, expr, builtin, depth+1)
+	}
 	if expr.intrinsic {
 		if symbol.is_valid(expr.qualifier) {
 			return INVALID_CT_VALUE, ct_flow(.Normal), ct_fail(state, .Not_Comptime, expr.span, "intrinsic calls must be unqualified")

compiler/hir/hir.odin

@@ -79,6 +79,7 @@ Expr_Kind :: enum u8 {
 	Float,
 	String,
 	Bool,
+	Undefined,
 	Array,
 	Struct,
 	None,
@@ -137,6 +138,8 @@ Expr_Kind :: enum u8 {
 	And,
 	Or,
 	Range,
+	Mem_Copy,
+	Mem_Set,
 	Call,
 }
 

compiler/ir/ir.odin

@@ -68,6 +68,7 @@ Linkage :: enum u8 {
 Opcode :: enum u8 {
 	Param,
 	Const,
+	Poison,
 	String,
 	Aggregate,
 	None,
@@ -125,6 +126,8 @@ Opcode :: enum u8 {
 	Shift_Right,
 	Shift_Left_Saturating,
 	Compare,
+	Mem_Copy,
+	Mem_Set,
 	Label,
 	Br,
 	Cond_Br,

compiler/llvm/llvm.odin

@@ -240,6 +240,29 @@ valid_instruction :: proc(instructions: []ir.Instruction, instruction_id: ir.Ins
 	return instruction_id != ir.INVALID_INSTRUCTION && int(instruction_id) < len(instructions)
 }
 
+memory_region :: proc(value: types.Type, store: ^types.Store) -> (
+	child, array_type: types.Type,
+	count: u64,
+	mutable, is_slice, ok: bool,
+) {
+	resolved := types.resolve_alias(value, store)
+	item, item_ok := types.node(store, resolved)
+	if !item_ok {
+		return types.INVALID, types.INVALID, 0, false, false, false
+	}
+	if item.kind == .Slice {
+		return item.child, types.INVALID, 0, item.mutable, true, true
+	}
+	if item.kind == .Pointer && !item.many {
+		array_type = types.resolve_alias(item.child, store)
+		array, array_ok := types.node(store, array_type)
+		if array_ok && array.kind == .Array {
+			return array.child, array_type, array.count, item.mutable && array.mutable, false, true
+		}
+	}
+	return types.INVALID, types.INVALID, 0, false, false, false
+}
+
 valid_value :: proc(
 	instructions: []ir.Instruction,
 	value_id: ir.Instruction_Id,
@@ -252,7 +275,7 @@ valid_value :: proc(
 		return false
 	}
 	switch instructions[value_id].op {
-	case .Param, .Const, .String, .Aggregate, .None, .Optional_Some,
+	case .Param, .Const, .Poison, .String, .Aggregate, .None, .Optional_Some,
 	     .Load_Global, .Function_Address, .Address_Of, .Load, .Union_Tag, .Slice, .Length, .Slice_Ptr,
 	     .Fallible_Error, .Extract, .Select, .Unwrap,
 	     .Optional_Is_Some, .Optional_Value, .Orelse,
@@ -264,7 +287,7 @@ valid_value :: proc(
 	     .Shift_Left, .Shift_Right, .Shift_Left_Saturating, .Compare, .Call:
 		return true
 	case .Address_Global, .Alloca, .Index_Address, .Field_Address, .Orelse_Begin,
-	     .Store, .Fill, .Trap, .Label, .Br, .Cond_Br, .Return, .Return_Void:
+	     .Store, .Fill, .Mem_Copy, .Mem_Set, .Trap, .Label, .Br, .Cond_Br, .Return, .Return_Void:
 		return false
 	}
 	return false
@@ -333,6 +356,8 @@ write_operand :: proc(
 	value := instructions[value_id]
 	if value.op == .Const {
 		write_constant(builder, value.integer, expected, store)
+	} else if value.op == .Poison {
+		strings.write_string(builder, "poison")
 	} else {
 		fmt.sbprintf(builder, "%%v%d", value_id)
 	}
@@ -925,7 +950,7 @@ emit_instruction_stream :: proc(
 			after_terminator = false
 		}
 		switch instruction.op {
-		case .Param, .Const:
+		case .Param, .Const, .Poison:
 		case .String:
 			string_id := int(instruction.integer)
 			_, array, pointer_ok := types.array_pointer(instruction.type, &emitter.module.types)
@@ -1368,6 +1393,109 @@ emit_instruction_stream :: proc(
 				instruction.a,
 				types.size(instruction.type, &emitter.module.types, emitter.module.target),
 			)
+		case .Mem_Copy:
+			if !valid_instruction(instructions, instruction.a) || !valid_instruction(instructions, instruction.b) {
+				emit_recovery_value(emitter, instruction_index, instruction, "invalid memcopy operands")
+				continue
+			}
+			destination_type := instructions[instruction.a].type
+			source_type := instructions[instruction.b].type
+			destination_child, destination_array, destination_count, destination_mutable, destination_is_slice, destination_ok := memory_region(destination_type, &emitter.module.types)
+			source_child, source_array, source_count, _, source_is_slice, source_ok := memory_region(source_type, &emitter.module.types)
+			if !destination_ok || !destination_mutable || !source_ok ||
+			   !types.equal(types.resolve_alias(destination_child, &emitter.module.types), types.resolve_alias(source_child, &emitter.module.types)) ||
+			   !types.equal(types.resolve_alias(destination_child, &emitter.module.types), types.resolve_alias(instruction.type, &emitter.module.types)) {
+				emit_recovery_value(emitter, instruction_index, instruction, "invalid memcopy region types")
+				continue
+			}
+			if destination_is_slice {
+				fmt.sbprintf(&emitter.builder, "  %%memcopy_dst%d = extractvalue %s %%v%d, 0\n", instruction_index, llvm_type(destination_type, &emitter.module.types), instruction.a)
+				fmt.sbprintf(&emitter.builder, "  %%memcopy_dst_len%d = extractvalue %s %%v%d, 1\n", instruction_index, llvm_type(destination_type, &emitter.module.types), instruction.a)
+			} else {
+				fmt.sbprintf(&emitter.builder, "  %%memcopy_dst%d = getelementptr %s, ptr %%v%d, i64 0, i64 0\n", instruction_index, llvm_type(destination_array, &emitter.module.types), instruction.a)
+				fmt.sbprintf(&emitter.builder, "  %%memcopy_dst_len%d = add i64 0, %d\n", instruction_index, destination_count)
+			}
+			if source_is_slice {
+				fmt.sbprintf(&emitter.builder, "  %%memcopy_src%d = extractvalue %s %%v%d, 0\n", instruction_index, llvm_type(source_type, &emitter.module.types), instruction.b)
+				fmt.sbprintf(&emitter.builder, "  %%memcopy_src_len%d = extractvalue %s %%v%d, 1\n", instruction_index, llvm_type(source_type, &emitter.module.types), instruction.b)
+			} else {
+				fmt.sbprintf(&emitter.builder, "  %%memcopy_src%d = getelementptr %s, ptr %%v%d, i64 0, i64 0\n", instruction_index, llvm_type(source_array, &emitter.module.types), instruction.b)
+				fmt.sbprintf(&emitter.builder, "  %%memcopy_src_len%d = add i64 0, %d\n", instruction_index, source_count)
+			}
+			fmt.sbprintf(&emitter.builder, "  %%memcopy_len_ok%d = icmp eq i64 %%memcopy_dst_len%d, %%memcopy_src_len%d\n", instruction_index, instruction_index, instruction_index)
+			fmt.sbprintf(&emitter.builder, "  br i1 %%memcopy_len_ok%d, label %%memcopy_size_check%d, label %%memcopy_len_trap%d\nmemcopy_len_trap%d:\n", instruction_index, instruction_index, instruction_index, instruction_index)
+			message := diagnostic_message(emitter, source.INVALID_DIAGNOSTIC, instruction.span, "memcopy! source and destination lengths differ")
+			emit_trap_call(emitter, message)
+			fmt.sbprintf(&emitter.builder, "  unreachable\nmemcopy_size_check%d:\n", instruction_index)
+			element_size := types.size(instruction.type, &emitter.module.types, emitter.module.target)
+			if element_size == 0 {
+				continue
+			}
+			max_count := u64(0xffff_ffff_ffff_ffff)/element_size
+			fmt.sbprintf(&emitter.builder, "  %%memcopy_size_ok%d = icmp ule i64 %%memcopy_dst_len%d, %d\n", instruction_index, instruction_index, max_count)
+			fmt.sbprintf(&emitter.builder, "  br i1 %%memcopy_size_ok%d, label %%memcopy_overlap_check%d, label %%memcopy_size_trap%d\nmemcopy_size_trap%d:\n", instruction_index, instruction_index, instruction_index, instruction_index)
+			message = diagnostic_message(emitter, source.INVALID_DIAGNOSTIC, instruction.span, "memory operation size overflow")
+			emit_trap_call(emitter, message)
+			fmt.sbprintf(&emitter.builder, "  unreachable\nmemcopy_overlap_check%d:\n", instruction_index)
+			fmt.sbprintf(&emitter.builder, "  %%memcopy_bytes%d = mul i64 %%memcopy_dst_len%d, %d\n", instruction_index, instruction_index, element_size)
+			fmt.sbprintf(&emitter.builder, "  %%memcopy_dst_end%d = getelementptr i8, ptr %%memcopy_dst%d, i64 %%memcopy_bytes%d\n", instruction_index, instruction_index, instruction_index)
+			fmt.sbprintf(&emitter.builder, "  %%memcopy_src_end%d = getelementptr i8, ptr %%memcopy_src%d, i64 %%memcopy_bytes%d\n", instruction_index, instruction_index, instruction_index)
+			fmt.sbprintf(&emitter.builder, "  %%memcopy_before%d = icmp ule ptr %%memcopy_dst_end%d, %%memcopy_src%d\n", instruction_index, instruction_index, instruction_index)
+			fmt.sbprintf(&emitter.builder, "  %%memcopy_after%d = icmp ule ptr %%memcopy_src_end%d, %%memcopy_dst%d\n", instruction_index, instruction_index, instruction_index)
+			fmt.sbprintf(&emitter.builder, "  %%memcopy_disjoint%d = or i1 %%memcopy_before%d, %%memcopy_after%d\n", instruction_index, instruction_index, instruction_index)
+			fmt.sbprintf(&emitter.builder, "  %%memcopy_empty%d = icmp eq i64 %%memcopy_bytes%d, 0\n", instruction_index, instruction_index)
+			fmt.sbprintf(&emitter.builder, "  %%memcopy_ok%d = or i1 %%memcopy_empty%d, %%memcopy_disjoint%d\n", instruction_index, instruction_index, instruction_index)
+			fmt.sbprintf(&emitter.builder, "  br i1 %%memcopy_ok%d, label %%memcopy_continue%d, label %%memcopy_overlap_trap%d\nmemcopy_overlap_trap%d:\n", instruction_index, instruction_index, instruction_index, instruction_index)
+			message = diagnostic_message(emitter, source.INVALID_DIAGNOSTIC, instruction.span, "memcopy! source and destination overlap")
+			emit_trap_call(emitter, message)
+			fmt.sbprintf(&emitter.builder, "  unreachable\nmemcopy_continue%d:\n", instruction_index)
+			fmt.sbprintf(&emitter.builder, "  call void @llvm.memcpy.p0.p0.i64(ptr %%memcopy_dst%d, ptr %%memcopy_src%d, i64 %%memcopy_bytes%d, i1 false)\n", instruction_index, instruction_index, instruction_index)
+		case .Mem_Set:
+			if !valid_instruction(instructions, instruction.a) || !valid_value(instructions, instruction.b, instruction.type, &emitter.module.types) {
+				emit_recovery_value(emitter, instruction_index, instruction, "invalid memset operands")
+				continue
+			}
+			destination_type := instructions[instruction.a].type
+			destination_child, destination_array, destination_count, destination_mutable, destination_is_slice, destination_ok := memory_region(destination_type, &emitter.module.types)
+			if !destination_ok || !destination_mutable ||
+			   !types.equal(types.resolve_alias(destination_child, &emitter.module.types), types.resolve_alias(instruction.type, &emitter.module.types)) {
+				emit_recovery_value(emitter, instruction_index, instruction, "invalid memset destination")
+				continue
+			}
+			if destination_is_slice {
+				fmt.sbprintf(&emitter.builder, "  %%memset_dst%d = extractvalue %s %%v%d, 0\n", instruction_index, llvm_type(destination_type, &emitter.module.types), instruction.a)
+				fmt.sbprintf(&emitter.builder, "  %%memset_len%d = extractvalue %s %%v%d, 1\n", instruction_index, llvm_type(destination_type, &emitter.module.types), instruction.a)
+			} else {
+				fmt.sbprintf(&emitter.builder, "  %%memset_dst%d = getelementptr %s, ptr %%v%d, i64 0, i64 0\n", instruction_index, llvm_type(destination_array, &emitter.module.types), instruction.a)
+				fmt.sbprintf(&emitter.builder, "  %%memset_len%d = add i64 0, %d\n", instruction_index, destination_count)
+			}
+			element_size := types.size(instruction.type, &emitter.module.types, emitter.module.target)
+			if element_size == 0 {
+				continue
+			}
+			max_count := u64(0xffff_ffff_ffff_ffff)/element_size
+			fmt.sbprintf(&emitter.builder, "  %%memset_size_ok%d = icmp ule i64 %%memset_len%d, %d\n", instruction_index, instruction_index, max_count)
+			fmt.sbprintf(&emitter.builder, "  br i1 %%memset_size_ok%d, label %%memset_start%d, label %%memset_size_trap%d\nmemset_size_trap%d:\n", instruction_index, instruction_index, instruction_index, instruction_index)
+			message := diagnostic_message(emitter, source.INVALID_DIAGNOSTIC, instruction.span, "memory operation size overflow")
+			emit_trap_call(emitter, message)
+			fmt.sbprintf(&emitter.builder, "  unreachable\nmemset_start%d:\n", instruction_index)
+			representation := types.runtime_representation(instruction.type, &emitter.module.types)
+			if types.is_concrete_integer(representation) && types.bits(representation, emitter.module.target) == 8 {
+				fmt.sbprintf(&emitter.builder, "  %%memset_bytes%d = mul i64 %%memset_len%d, %d\n", instruction_index, instruction_index, element_size)
+				fmt.sbprintf(&emitter.builder, "  call void @llvm.memset.p0.i64(ptr %%memset_dst%d, i8 ", instruction_index)
+				write_operand(&emitter.builder, instructions, instruction.b, instruction.type, &emitter.module.types)
+				fmt.sbprintf(&emitter.builder, ", i64 %%memset_bytes%d, i1 false)\n", instruction_index)
+				continue
+			}
+			fmt.sbprintf(&emitter.builder, "  %%memset_index_slot%d = alloca i64\n  store i64 0, ptr %%memset_index_slot%d\n  br label %%memset_loop%d\nmemset_loop%d:\n", instruction_index, instruction_index, instruction_index, instruction_index)
+			fmt.sbprintf(&emitter.builder, "  %%memset_index%d = load i64, ptr %%memset_index_slot%d\n", instruction_index, instruction_index)
+			fmt.sbprintf(&emitter.builder, "  %%memset_more%d = icmp ult i64 %%memset_index%d, %%memset_len%d\n", instruction_index, instruction_index, instruction_index)
+			fmt.sbprintf(&emitter.builder, "  br i1 %%memset_more%d, label %%memset_body%d, label %%memset_done%d\nmemset_body%d:\n", instruction_index, instruction_index, instruction_index, instruction_index)
+			fmt.sbprintf(&emitter.builder, "  %%memset_element%d = getelementptr %s, ptr %%memset_dst%d, i64 %%memset_index%d\n", instruction_index, llvm_type(instruction.type, &emitter.module.types), instruction_index, instruction_index)
+			fmt.sbprintf(&emitter.builder, "  store %s ", llvm_type(instruction.type, &emitter.module.types))
+			write_operand(&emitter.builder, instructions, instruction.b, instruction.type, &emitter.module.types)
+			fmt.sbprintf(&emitter.builder, ", ptr %%memset_element%d\n", instruction_index)
+			fmt.sbprintf(&emitter.builder, "  %%memset_next%d = add i64 %%memset_index%d, 1\n  store i64 %%memset_next%d, ptr %%memset_index_slot%d\n  br label %%memset_loop%d\nmemset_done%d:\n", instruction_index, instruction_index, instruction_index, instruction_index, instruction_index, instruction_index)
 		case .Slice:
 			if !valid_instruction(instructions, instruction.a) {
 				emit_recovery_value(emitter, instruction_index, instruction, "invalid slice container")

compiler/lower/lower.odin

@@ -647,6 +647,24 @@ lower_compound_expr :: proc(state: ^State, expr_id: hir.Expr_Id) -> ir.Instructi
 	return append_recovery_value(state, expr.span, expr.type, expr.diagnostic)
 }
 
+memory_region_element_type :: proc(value: types.Type, store: ^types.Store) -> types.Type {
+	resolved := types.resolve_alias(value, store)
+	item, ok := types.node(store, resolved)
+	if !ok {
+		return types.INVALID
+	}
+	if item.kind == .Slice {
+		return item.child
+	}
+	if item.kind == .Pointer && !item.many {
+		array, array_ok := types.node(store, types.resolve_alias(item.child, store))
+		if array_ok && array.kind == .Array {
+			return array.child
+		}
+	}
+	return types.INVALID
+}
+
 lower_expr :: proc(state: ^State, expr_id: hir.Expr_Id) -> ir.Instruction_Id {
 	stack := state.expr_stack
 	state.expr_stack = nil
@@ -691,6 +709,13 @@ lower_expr :: proc(state: ^State, expr_id: hir.Expr_Id) -> ir.Instruction_Id {
 					target=ir.INVALID_REF, a=ir.INVALID_INSTRUCTION, b=ir.INVALID_INSTRUCTION, diagnostic=source.INVALID_DIAGNOSTIC,
 				})
 				_ = pop(&stack)
+			case .Undefined:
+				last = append_instruction(state, ir.Instruction{
+					op=.Poison, span=expr.span, type=expr.type,
+					target=ir.INVALID_REF, a=ir.INVALID_INSTRUCTION, b=ir.INVALID_INSTRUCTION,
+					diagnostic=source.INVALID_DIAGNOSTIC,
+				})
+				_ = pop(&stack)
 			case .String, .Array, .Struct, .Range, .None, .Optional_Some, .Address, .Deref,
 			     .Index, .Slice, .Field, .Union_Tag, .Length, .Slice_Ptr, .Unwrap, .Orelse,
 			     .Try, .Catch, .Not, .Eq, .Ne, .Lt, .Le, .Gt, .Ge, .And, .Or:
@@ -744,7 +769,7 @@ lower_expr :: proc(state: ^State, expr_id: hir.Expr_Id) -> ir.Instruction_Id {
 				append(&stack, Lower_Expr_Frame{expr=expr.left})
 			case .Add, .Sub, .Mul, .Div, .Div_Trunc, .Div_Floor, .Div_Exact, .Div_Ceil,
 			     .Rem, .Mod, .Pointer_Add, .Bit_And, .Bit_Or, .Bit_Xor, .Shift_Left,
-			     .Shift_Right, .Shift_Left_Saturating:
+			     .Shift_Right, .Shift_Left_Saturating, .Mem_Copy, .Mem_Set:
 				stack[frame_index].stage = 2
 				append(&stack, Lower_Expr_Frame{expr=expr.left})
 			case .Call:
@@ -823,6 +848,7 @@ lower_expr :: proc(state: ^State, expr_id: hir.Expr_Id) -> ir.Instruction_Id {
 		}
 		if frame.stage == 3 {
 			op := ir.Opcode.Add_Checked
+			result_type := expr.type
 			#partial switch expr.kind {
 			case .Sub:         op = .Sub_Checked
 			case .Mul:         op = .Mul_Checked
@@ -840,10 +866,16 @@ lower_expr :: proc(state: ^State, expr_id: hir.Expr_Id) -> ir.Instruction_Id {
 			case .Shift_Left:  op = .Shift_Left
 			case .Shift_Right: op = .Shift_Right
 			case .Shift_Left_Saturating: op = .Shift_Left_Saturating
+			case .Mem_Copy:
+				op = .Mem_Copy
+				result_type = memory_region_element_type(state.hir_module.exprs[expr.left].type, &state.hir_module.types)
+			case .Mem_Set:
+				op = .Mem_Set
+				result_type = memory_region_element_type(state.hir_module.exprs[expr.left].type, &state.hir_module.types)
 			}
 			last = append_instruction(state, ir.Instruction{
 				op=op,
-				span=expr.span, type=expr.type, target=ir.INVALID_REF,
+				span=expr.span, type=result_type, target=ir.INVALID_REF,
 				a=frame.left, b=last, diagnostic=source.INVALID_DIAGNOSTIC,
 			})
 			_ = pop(&stack)

compiler_tests.odin

@@ -2230,7 +2230,9 @@ old_intrinsic_spellings_are_not_recognized :: proc(t: ^testing.T) {
 
 @(test)
 bare_intrinsic_names_are_available_to_user_functions :: proc(t: ^testing.T) {
-	text := `ptrcast func() i32 { return 1 }
+	text := `memory :: import "./memory"
+
+ptrcast func() i32 { return 1 }
 sizeof func() i32 { return 2 }
 alignof func() i32 { return 3 }
 minval func() i32 { return 4 }
@@ -2241,19 +2243,29 @@ divexact func() i32 { return 8 }
 divceil func() i32 { return 9 }
 rem func() i32 { return 10 }
 mod func() i32 { return 11 }
+memcopy func() i32 { return 12 }
+memset func() i32 { return 13 }
 main func() i32 {
 	return ptrcast() + sizeof() + alignof() + minval() + maxval() +
-		divtrunc() + divfloor() + divexact() + divceil() + rem() + mod() - 66
+		divtrunc() + divfloor() + divexact() + divceil() + rem() + mod() +
+		memcopy() + memset() + memory.memcopy() + memory.memset() - 120
 }
 `
 	directory := "/tmp/brolang-test-user-intrinsic-names"
 	main_path := "/tmp/brolang-test-user-intrinsic-names/main.bro"
+	memory_directory := "/tmp/brolang-test-user-intrinsic-names/memory"
+	memory_path := "/tmp/brolang-test-user-intrinsic-names/memory/memory.bro"
 	output := "/tmp/brolang-test-user-intrinsic-names-output"
 	_ = os2.remove_all(directory)
 	defer _ = os2.remove_all(directory)
 	defer _ = os.remove(output)
 	testing.expect(t, os.make_directory(directory) == nil)
+	testing.expect(t, os.make_directory(memory_directory) == nil)
 	testing.expect(t, os.write_entire_file(main_path, transmute([]byte)text))
+	memory_text := `memcopy func() i32 { return 14 }
+memset func() i32 { return 15 }
+`
+	testing.expect(t, os.write_entire_file(memory_path, transmute([]byte)memory_text))
 	testing.expect_value(t, compiler_core.compile_package(directory, output), 0)
 }
 
@@ -2286,6 +2298,215 @@ intrinsic_call_diagnostics_are_precise :: proc(t: ^testing.T) {
 	testing.expect(t, found_qualified)
 }
 
+@(test)
+memory_intrinsics_compile_run_and_lower :: proc(t: ^testing.T) {
+	text := `Pair :: struct { x i32, y i32 }
+
+calls i32 = 0
+
+destination_view func(value []mut u8) []mut u8 {
+	calls += 1
+	return value
+}
+
+source_view func(value []u8) []u8 {
+	calls += 1
+	return value
+}
+
+compile_value func() [4]mut u8 {
+	source [4]mut u8 = [1, 2, 3, 4]
+	destination [4]mut u8 = undefined
+	memset!(&destination, undefined)
+	memcopy!(&destination, &source)
+	memset!(destination[1..3], 9)
+	memcopy!(destination[..0], destination[..0])
+	return destination
+}
+
+known :: $compile_value()
+
+main func() i32 {
+	if known[0] != 1 or known[1] != 9 or known[2] != 9 or known[3] != 4 { return 1 }
+
+	bytes [4]mut u8 = undefined
+	source [4]mut u8 = [4, 3, 2, 1]
+	memset!(&bytes, undefined)
+	memcopy!(destination_view(bytes[..]), source_view(source[..]))
+	if calls != 2 or bytes[0] != 4 or bytes[3] != 1 { return 2 }
+	memset!(bytes[1..3], 7)
+	if bytes[1] != 7 or bytes[2] != 7 { return 3 }
+
+	wide [2]mut i32 = undefined
+	memset!(&wide, 42)
+	if wide[0] != 42 or wide[1] != 42 { return 4 }
+
+	pairs [2]mut Pair = undefined
+	pair_source [2]mut Pair = [Pair{x = 1, y = 2}, Pair{x = 3, y = 4}]
+	memcopy!(&pairs, &pair_source)
+	memset!(pairs[1..], Pair{x = 7, y = 8})
+	if pairs[0].x != 1 or pairs[1].y != 8 { return 5 }
+
+	memcopy!(bytes[..0], bytes[..0])
+	return 0
+}
+`
+	source_file := source.Source{path="test.bro", text=text}
+	diagnostics := source.init_diagnostics(&source_file)
+	defer source.destroy_diagnostics(&diagnostics)
+	symbols := symbol.init_table()
+	defer symbol.destroy_table(&symbols)
+	stream := lexer.lex(&source_file, &diagnostics, &symbols)
+	defer delete(stream.items)
+	ast_module := parser.parse(&stream, &source_file, &diagnostics)
+	defer ast.destroy_module(&ast_module)
+	hir_module := checker.check(&ast_module, &diagnostics, &symbols)
+	defer hir.destroy_module(&hir_module)
+	ir_module := lower.lower(&hir_module)
+	defer ir.destroy_module(&ir_module)
+	llvm_text := llvm.emit(&ir_module, &diagnostics, &symbols)
+	defer delete(llvm_text)
+
+	copy_count, set_count := 0, 0
+	for function in ir_module.functions {
+		for instruction in function.instructions {
+			copy_count += 1 if instruction.op == .Mem_Copy else 0
+			set_count += 1 if instruction.op == .Mem_Set else 0
+		}
+	}
+	testing.expect_value(t, len(diagnostics.items), 0)
+	testing.expect(t, copy_count >= 3)
+	testing.expect(t, set_count >= 3)
+	testing.expect(t, strings.contains(llvm_text, "memcopy_len_ok"))
+	testing.expect(t, strings.contains(llvm_text, "memcopy_size_ok"))
+	testing.expect(t, strings.contains(llvm_text, "memcopy_disjoint"))
+	testing.expect(t, strings.contains(llvm_text, "call void @llvm.memcpy.p0.p0.i64"))
+	testing.expect(t, strings.contains(llvm_text, "call void @llvm.memset.p0.i64"))
+	testing.expect(t, strings.contains(llvm_text, "memset_loop"))
+
+	directory := "/tmp/brolang-test-memory-intrinsics"
+	main_path := "/tmp/brolang-test-memory-intrinsics/main.bro"
+	output := "/tmp/brolang-test-memory-intrinsics-output"
+	_ = os2.remove_all(directory)
+	defer _ = os2.remove_all(directory)
+	defer _ = os.remove(output)
+	testing.expect(t, os.make_directory(directory) == nil)
+	testing.expect(t, os.write_entire_file(main_path, transmute([]byte)text))
+	testing.expect_value(t, compiler_core.compile_package(directory, output), 0)
+	state := run_executable(output)
+	testing.expect_value(t, state.exit_code, 0)
+}
+
+@(test)
+memory_intrinsic_diagnostics_are_precise :: proc(t: ^testing.T) {
+	text := `bad_length func() [1]mut u8 {
+	destination [1]mut u8 = undefined
+	source [2]mut u8 = [1, 2]
+	memcopy!(&destination, &source)
+	return destination
+}
+
+bad_overlap func() [3]mut u8 {
+	items [3]mut u8 = [1, 2, 3]
+	memcopy!(items[..2], items[1..])
+	return items
+}
+
+bad_undefined func() u8 {
+	items [1]mut u8 = [1]
+	memset!(&items, undefined)
+	return items[0]
+}
+
+length_value :: $bad_length()
+overlap_value :: $bad_overlap()
+undefined_value :: $bad_undefined()
+
+main func() void {
+	immutable [2]u8 = [1, 2]
+	mutable [2]mut u8 = undefined
+	wide [2]mut u16 = undefined
+	memcopy!(&immutable, &mutable)
+	memcopy!(&mutable, &wide)
+	memcopy!(1, 2)
+	memset!(1, 0)
+	memcopy!()
+	memset!(&mutable)
+}
+`
+	source_file := source.Source{path="test.bro", text=text}
+	diagnostics := source.init_diagnostics(&source_file)
+	defer source.destroy_diagnostics(&diagnostics)
+	symbols := symbol.init_table()
+	defer symbol.destroy_table(&symbols)
+	stream := lexer.lex(&source_file, &diagnostics, &symbols)
+	defer delete(stream.items)
+	ast_module := parser.parse(&stream, &source_file, &diagnostics)
+	defer ast.destroy_module(&ast_module)
+	hir_module := checker.check(&ast_module, &diagnostics, &symbols)
+	defer hir.destroy_module(&hir_module)
+
+	expected := [?]string{
+		"memcopy! source and destination lengths differ",
+		"memcopy! source and destination overlap",
+		"cannot read an undefined value at comptime",
+		"memcopy! destination must be a mutable slice or mutable pointer-to-array",
+		"memcopy! source and destination element types must match",
+		"memset! destination must be a mutable slice or mutable pointer-to-array",
+		"memcopy! expects 2 arguments, got 0",
+		"memset! expects 2 arguments, got 1",
+	}
+	found: [len(expected)]bool
+	for diagnostic in diagnostics.items {
+		for message, index in expected {
+			found[index] = found[index] || strings.contains(diagnostic.message, message)
+		}
+	}
+	for present in found {
+		testing.expect(t, present)
+	}
+}
+
+@(test)
+memory_intrinsic_runtime_guards_trap :: proc(t: ^testing.T) {
+	cases := [?]struct {
+		directory, output, text: string,
+	}{
+		{
+			"/tmp/brolang-test-memcopy-length-trap",
+			"/tmp/brolang-test-memcopy-length-trap-output",
+			`copy func(destination []mut u8, source []u8) void { memcopy!(destination, source) }
+main func() void {
+	destination [2]mut u8 = undefined
+	source [3]mut u8 = [1, 2, 3]
+	copy(destination[..], source[..])
+}
+`,
+		},
+		{
+			"/tmp/brolang-test-memcopy-overlap-trap",
+			"/tmp/brolang-test-memcopy-overlap-trap-output",
+			`copy func(destination []mut u8, source []u8) void { memcopy!(destination, source) }
+main func() void {
+	items [4]mut u8 = [1, 2, 3, 4]
+	copy(items[1..], items[..3])
+}
+`,
+		},
+	}
+	for test_case in cases {
+		main_path := fmt.tprintf("%s/main.bro", test_case.directory)
+		_ = os2.remove_all(test_case.directory)
+		defer _ = os2.remove_all(test_case.directory)
+		defer _ = os.remove(test_case.output)
+		testing.expect(t, os.make_directory(test_case.directory) == nil)
+		testing.expect(t, os.write_entire_file(main_path, transmute([]byte)test_case.text))
+		testing.expect_value(t, compiler_core.compile_package(test_case.directory, test_case.output), 0)
+		state := run_executable(test_case.output)
+		testing.expect(t, !state.success)
+	}
+}
+
 @(test)
 malformed_intrinsic_calls_have_targeted_parse_diagnostics :: proc(t: ^testing.T) {
 	cases := [?]struct {

std/mem/mem.bro

@@ -174,10 +174,7 @@ hide c_realloc func(_ ?@mut anyopaque, memory ?*mut u8, old_size usize, new_size
 			if new_size < copy_size {
 				copy_size = new_size
 			}
-			i usize = 0
+			memcopy!(new_bytes[..copy_size], old_memory[..copy_size])
-			while i < copy_size : i += 1 {
-				new_bytes[i] = old_memory[i]
-			}
 			c.free(old_memory)
 		}
 		return new_memory