Add general support for `bit_field`s

10 files changed, 215 insertions, 15 deletions

diff --git a/src/check_expr.cpp b/src/check_expr.cpp
index 685bcdd6e..9b15ae3b2 100644
--- a/src/check_expr.cpp
+++ b/src/check_expr.cpp
@@ -100,7 +100,7 @@ gb_internal void     check_union_type               (CheckerContext *c, Type *un
 gb_internal Type *   check_init_variable            (CheckerContext *c, Entity *e, Operand *operand, String context_name);
 
 
-gb_internal void check_assignment_error_suggestion(CheckerContext *c, Operand *o, Type *type);
+gb_internal void check_assignment_error_suggestion(CheckerContext *c, Operand *o, Type *type, i64 max_bit_size=0);
 gb_internal void add_map_key_type_dependencies(CheckerContext *ctx, Type *key);
 
 gb_internal Type *make_soa_struct_slice(CheckerContext *ctx, Ast *array_typ_expr, Ast *elem_expr, Type *elem);
@@ -2071,11 +2071,17 @@ gb_internal bool check_representable_as_constant(CheckerContext *c, ExactValue i
 }
 
 
-gb_internal bool check_integer_exceed_suggestion(CheckerContext *c, Operand *o, Type *type) {
+gb_internal bool check_integer_exceed_suggestion(CheckerContext *c, Operand *o, Type *type, i64 max_bit_size=0) {
 	if (is_type_integer(type) && o->value.kind == ExactValue_Integer) {
 		gbString b = type_to_string(type);
 
 		i64 sz = type_size_of(type);
+		i64 bit_size = 8*sz;
+		bool size_changed = false;
+		if (max_bit_size > 0) {
+			size_changed = (bit_size != max_bit_size);
+			bit_size = gb_min(bit_size, max_bit_size);
+		}
 		BigInt *bi = &o->value.value_integer;
 		if (is_type_unsigned(type)) {
 			if (big_int_is_neg(bi)) {
@@ -2083,25 +2089,36 @@ gb_internal bool check_integer_exceed_suggestion(CheckerContext *c, Operand *o,
 			} else {
 				BigInt one = big_int_make_u64(1);
 				BigInt max_size = big_int_make_u64(1);
-				BigInt bits = big_int_make_i64(8*sz);
+				BigInt bits = big_int_make_i64(bit_size);
 				big_int_shl_eq(&max_size, &bits);
 				big_int_sub_eq(&max_size, &one);
 				String max_size_str = big_int_to_string(temporary_allocator(), &max_size);
-				error_line("\tThe maximum value that can be represented by '%s' is '%.*s'\n", b, LIT(max_size_str));
+
+				if (size_changed) {
+					error_line("\tThe maximum value that can be represented with that bit_field's field of '%s | %u' is '%.*s'\n", b, bit_size, LIT(max_size_str));
+				} else {
+					error_line("\tThe maximum value that can be represented by '%s' is '%.*s'\n", b, LIT(max_size_str));
+				}
 			}
 		} else {
 			BigInt zero = big_int_make_u64(0);
 			BigInt one = big_int_make_u64(1);
 			BigInt max_size = big_int_make_u64(1);
-			BigInt bits = big_int_make_i64(8*sz - 1);
+			BigInt bits = big_int_make_i64(bit_size - 1);
 			big_int_shl_eq(&max_size, &bits);
+
+			String max_size_str = {};
 			if (big_int_is_neg(bi)) {
 				big_int_neg(&max_size, &max_size);
-				String max_size_str = big_int_to_string(temporary_allocator(), &max_size);
-				error_line("\tThe minimum value that can be represented by '%s' is '%.*s'\n", b, LIT(max_size_str));
+				max_size_str = big_int_to_string(temporary_allocator(), &max_size);
 			} else {
 				big_int_sub_eq(&max_size, &one);
-				String max_size_str = big_int_to_string(temporary_allocator(), &max_size);
+				max_size_str = big_int_to_string(temporary_allocator(), &max_size);
+			}
+
+			if (size_changed) {
+				error_line("\tThe maximum value that can be represented with that bit_field's field of '%s | %u' is '%.*s'\n", b, bit_size, LIT(max_size_str));
+			} else {
 				error_line("\tThe maximum value that can be represented by '%s' is '%.*s'\n", b, LIT(max_size_str));
 			}
 		}
@@ -2112,7 +2129,7 @@ gb_internal bool check_integer_exceed_suggestion(CheckerContext *c, Operand *o,
 	}
 	return false;
 }
-gb_internal void check_assignment_error_suggestion(CheckerContext *c, Operand *o, Type *type) {
+gb_internal void check_assignment_error_suggestion(CheckerContext *c, Operand *o, Type *type, i64 max_bit_size) {
 	gbString a = expr_to_string(o->expr);
 	gbString b = type_to_string(type);
 	defer(
@@ -2143,7 +2160,7 @@ gb_internal void check_assignment_error_suggestion(CheckerContext *c, Operand *o
 		error_line("\t            whereas slices in general are assumed to be mutable.\n");
 	} else if (is_type_u8_slice(src) && are_types_identical(dst, t_string) && o->mode != Addressing_Constant) {
 		error_line("\tSuggestion: the expression may be casted to %s\n", b);
-	} else if (check_integer_exceed_suggestion(c, o, type)) {
+	} else if (check_integer_exceed_suggestion(c, o, type, max_bit_size)) {
 		return;
 	}
 }
@@ -2217,13 +2234,18 @@ gb_internal bool check_is_expressible(CheckerContext *ctx, Operand *o, Type *typ
 			if (!is_type_integer(o->type) && is_type_integer(type)) {
 				error(o->expr, "'%s' truncated to '%s', got %s", a, b, s);
 			} else {
+				i64 max_bit_size = 0;
+				if (ctx->bit_field_bit_size) {
+					max_bit_size = ctx->bit_field_bit_size;
+				}
+
 				if (are_types_identical(o->type, type)) {
 					error(o->expr, "Numeric value '%s' from '%s' cannot be represented by '%s'", s, a, b);
 				} else {
 					error(o->expr, "Cannot convert numeric value '%s' from '%s' to '%s' from '%s'", s, a, b, c);
 				}
 
-				check_assignment_error_suggestion(ctx, o, type);
+				check_assignment_error_suggestion(ctx, o, type, max_bit_size);
 			}
 		} else {
 			error(o->expr, "Cannot convert '%s' to '%s' from '%s', got %s", a, b, c, s);
@@ -2234,6 +2256,11 @@ gb_internal bool check_is_expressible(CheckerContext *ctx, Operand *o, Type *typ
 }
 
 gb_internal bool check_is_not_addressable(CheckerContext *c, Operand *o) {
+	if (o->expr && o->expr->kind == Ast_SelectorExpr) {
+		if (o->expr->SelectorExpr.is_bit_field) {
+			return true;
+		}
+	}
 	if (o->mode == Addressing_OptionalOk) {
 		Ast *expr = unselector_expr(o->expr);
 		if (expr->kind != Ast_TypeAssertion) {
@@ -2306,6 +2333,8 @@ gb_internal void check_unary_expr(CheckerContext *c, Operand *o, Token op, Ast *
 				Entity *e = entity_of_node(ue->expr);
 				if (e != nullptr && (e->flags & EntityFlag_Param) != 0) {
 					error(op, "Cannot take the pointer address of '%s' which is a procedure parameter", str);
+				} else if (e != nullptr && (e->flags & EntityFlag_BitFieldField) != 0) {
+					error(op, "Cannot take the pointer address of '%s' which is a bit_field's field", str);
 				} else {
 					switch (o->mode) {
 					case Addressing_Constant:
@@ -5067,6 +5096,11 @@ gb_internal Entity *check_selector(CheckerContext *c, Operand *operand, Ast *nod
 	operand->type = entity->type;
 	operand->expr = node;
 
+	if (entity->flags & EntityFlag_BitFieldField) {
+		add_package_dependency(c, "runtime", "__write_bits");
+		add_package_dependency(c, "runtime", "__read_bits");
+	}
+
 	switch (entity->kind) {
 	case Entity_Constant:
 	operand->value = entity->Constant.value;
@@ -5080,6 +5114,9 @@ gb_internal Entity *check_selector(CheckerContext *c, Operand *operand, Ast *nod
 		}
 		break;
 	case Entity_Variable:
+		if (sel.is_bit_field) {
+			se->is_bit_field = true;
+		}
 		if (sel.indirect) {
 			operand->mode = Addressing_Variable;
 		} else if (operand->mode == Addressing_Context) {
@@ -11115,6 +11152,33 @@ gb_internal gbString write_expr_to_string(gbString str, Ast *node, bool shorthan
 	case_end;
 
 
+	case_ast_node(f, BitFieldField, node);
+		str = write_expr_to_string(str, f->name, shorthand);
+		str = gb_string_appendc(str, ": ");
+		str = write_expr_to_string(str, f->type, shorthand);
+		str = gb_string_appendc(str, " | ");
+		str = write_expr_to_string(str, f->bit_size, shorthand);
+	case_end;
+	case_ast_node(bf, BitFieldType, node);
+		str = gb_string_appendc(str, "bit_field ");
+		if (!shorthand) {
+			str = write_expr_to_string(str, bf->backing_type, shorthand);
+		}
+		str = gb_string_appendc(str, " {");
+		if (shorthand) {
+			str = gb_string_appendc(str, "...");
+		} else {
+			for_array(i, bf->fields) {
+				if (i > 0) {
+					str = gb_string_appendc(str, ", ");
+				}
+				str = write_expr_to_string(str, bf->fields[i], false);
+			}
+			return str;
+		}
+		str = gb_string_appendc(str, "}");
+	case_end;
+
 	case_ast_node(ia, InlineAsmExpr, node);
 		str = gb_string_appendc(str, "asm(");
 		for_array(i, ia->param_types) {
diff --git a/src/check_stmt.cpp b/src/check_stmt.cpp
index 6897701d6..a7dd9743b 100644
--- a/src/check_stmt.cpp
+++ b/src/check_stmt.cpp
@@ -485,7 +485,17 @@ gb_internal Type *check_assignment_variable(CheckerContext *ctx, Operand *lhs, O
 	}
 	}
 
+	Entity *lhs_e = entity_of_node(lhs->expr);
+	u8 prev_bit_field_bit_size = ctx->bit_field_bit_size;
+	if (lhs_e && lhs_e->kind == Entity_Variable && lhs_e->Variable.bit_field_bit_size) {
+		// HACK NOTE(bill): This is a bit of a hack, but it will work fine for this use case
+		ctx->bit_field_bit_size = lhs_e->Variable.bit_field_bit_size;
+	}
+
 	check_assignment(ctx, rhs, assignment_type, str_lit("assignment"));
+
+	ctx->bit_field_bit_size = prev_bit_field_bit_size;
+
 	if (rhs->mode == Addressing_Invalid) {
 		return nullptr;
 	}
diff --git a/src/check_type.cpp b/src/check_type.cpp
index 8afac2fc5..8c746a2f7 100644
--- a/src/check_type.cpp
+++ b/src/check_type.cpp
@@ -1035,11 +1035,19 @@ gb_internal void check_bit_field_type(CheckerContext *ctx, Type *bit_field_type,
 				error(f->bit_size, "A bit_field's specified bit size cannot exceed 64 bits, got %lld", cast(long long)bit_size_i64);
 				bit_size_i64 = 64;
 			}
+			i64 sz = 8*type_size_of(type);
+			if (bit_size_i64 > sz) {
+				error(f->bit_size, "A bit_field's specified bit size cannot exceed its type, got %lld, expect <=%lld", cast(long long)bit_size_i64, cast(long long)sz);
+				bit_size_i64 = sz;
+			}
+
 			bit_size_u8 = cast(u8)bit_size_i64;
 
 			Entity *e = alloc_entity_field(ctx->scope, f->name->Ident.token, type, false, field_src_index);
 			e->Variable.docs    = docs;
 			e->Variable.comment = comment;
+			e->Variable.bit_field_bit_size = bit_size_u8;
+			e->flags |= EntityFlag_BitFieldField;
 
 			add_entity(ctx, ctx->scope, nullptr, e);
 			array_add(&fields, e);
@@ -1050,6 +1058,14 @@ gb_internal void check_bit_field_type(CheckerContext *ctx, Type *bit_field_type,
 
 	GB_ASSERT(fields.count <= bf->fields.count);
 
+	auto bit_offsets = slice_make<i64>(permanent_allocator(), fields.count);
+	i64 curr_offset = 0;
+	for_array(i, bit_sizes) {
+		bit_offsets[i] = curr_offset;
+		curr_offset += cast(i64)bit_sizes[i];
+	}
+
+
 	if (total_bit_size > maximum_bit_size) {
 		gbString s = type_to_string(backing_type);
 		error(node, "The numbers required %llu exceeds the backing type's (%s) bit size %llu",
@@ -1059,8 +1075,9 @@ gb_internal void check_bit_field_type(CheckerContext *ctx, Type *bit_field_type,
 		gb_string_free(s);
 	}
 
-	bit_field_type->BitField.fields    = slice_from_array(fields);
-	bit_field_type->BitField.bit_sizes = slice_from_array(bit_sizes);
+	bit_field_type->BitField.fields      = slice_from_array(fields);
+	bit_field_type->BitField.bit_sizes   = slice_from_array(bit_sizes);
+	bit_field_type->BitField.bit_offsets = bit_offsets;
 }
 
 gb_internal bool is_type_valid_bit_set_range(Type *t) {
diff --git a/src/checker.hpp b/src/checker.hpp
index 9aee82257..066d6bb4a 100644
--- a/src/checker.hpp
+++ b/src/checker.hpp
@@ -475,6 +475,7 @@ struct CheckerContext {
 	bool       hide_polymorphic_errors;
 	bool       in_polymorphic_specialization;
 	bool       allow_arrow_right_selector_expr;
+	u8         bit_field_bit_size;
 	Scope *    polymorphic_scope;
 
 	Ast *assignment_lhs_hint;
diff --git a/src/entity.cpp b/src/entity.cpp
index e6c46d37e..916c2b2bd 100644
--- a/src/entity.cpp
+++ b/src/entity.cpp
@@ -43,6 +43,7 @@ enum EntityFlag : u64 {
 	EntityFlag_NoAlias       = 1ull<<9,
 	EntityFlag_TypeField     = 1ull<<10,
 	EntityFlag_Value         = 1ull<<11,
+	EntityFlag_BitFieldField = 1ull<<12,
 
 
 
@@ -212,6 +213,7 @@ struct Entity {
 			Ast *init_expr; // only used for some variables within procedure bodies
 			i32  field_index;
 			i32  field_group_index;
+			u8   bit_field_bit_size;
 
 			ParameterValue param_value;
 
diff --git a/src/llvm_backend.hpp b/src/llvm_backend.hpp
index 026454c81..00d1b7a21 100644
--- a/src/llvm_backend.hpp
+++ b/src/llvm_backend.hpp
@@ -84,6 +84,8 @@ enum lbAddrKind {
 
 	lbAddr_Swizzle,
 	lbAddr_SwizzleLarge,
+
+	lbAddr_BitField,
 };
 
 struct lbAddr {
@@ -118,6 +120,12 @@ struct lbAddr {
 			Type *type;
 			Slice<i32> indices;
 		} swizzle_large;
+		struct {
+			Type *type;
+			i64 index;
+			i64 bit_offset;
+			i64 bit_size;
+		} bitfield;
 	};
 };
 
diff --git a/src/llvm_backend_expr.cpp b/src/llvm_backend_expr.cpp
index 0c06c8c1b..6bef21822 100644
--- a/src/llvm_backend_expr.cpp
+++ b/src/llvm_backend_expr.cpp
@@ -4627,6 +4627,22 @@ gb_internal lbAddr lb_build_addr_internal(lbProcedure *p, Ast *expr) {
 
 			Selection sel = lookup_field(type, selector, false);
 			GB_ASSERT(sel.entity != nullptr);
+			if (sel.is_bit_field) {
+				lbAddr addr = lb_build_addr(p, se->expr);
+				Type *bf_type = base_type(type_deref(lb_addr_type(addr)));
+				GB_ASSERT(bf_type->kind == Type_BitField);
+
+				lbValue a = lb_addr_get_ptr(p, addr);
+				Selection sub_sel = sel;
+				sub_sel.index.count -= 1;
+				i32 index = sel.index[sel.index.count-1];
+
+				Entity *f = bf_type->BitField.fields[index];
+				u8 bit_size = bf_type->BitField.bit_sizes[index];
+				i64 bit_offset = bf_type->BitField.bit_offsets[index];
+
+				return lb_addr_bit_field(a, f->type, index, bit_offset, bit_size);
+			}
 			if (sel.pseudo_field) {
 				GB_ASSERT(sel.entity->kind == Entity_Procedure || sel.entity->kind == Entity_ProcGroup);
 				Entity *e = entity_of_node(sel_node);
diff --git a/src/llvm_backend_general.cpp b/src/llvm_backend_general.cpp
index 2102420f8..4ff8482a7 100644
--- a/src/llvm_backend_general.cpp
+++ b/src/llvm_backend_general.cpp
@@ -451,6 +451,20 @@ gb_internal lbAddr lb_addr_swizzle_large(lbValue addr, Type *array_type, Slice<i
 	return v;
 }
 
+gb_internal lbAddr lb_addr_bit_field(lbValue addr, Type *type, i64 index, i64 bit_offset, i64 bit_size) {
+	GB_ASSERT(is_type_pointer(addr.type));
+	Type *mt = type_deref(addr.type);
+	GB_ASSERT(is_type_bit_field(mt));
+
+	lbAddr v = {lbAddr_BitField, addr};
+	v.bitfield.type       = type;
+	v.bitfield.index      = index;
+	v.bitfield.bit_offset = bit_offset;
+	v.bitfield.bit_size   = bit_size;
+	return v;
+}
+
+
 gb_internal Type *lb_addr_type(lbAddr const &addr) {
 	if (addr.addr.value == nullptr) {
 		return nullptr;
@@ -759,7 +773,17 @@ gb_internal void lb_addr_store(lbProcedure *p, lbAddr addr, lbValue value) {
 		addr = lb_addr(lb_address_from_load(p, lb_addr_load(p, addr)));
 	}
 
-	if (addr.kind == lbAddr_RelativePointer) {
+	if (addr.kind == lbAddr_BitField) {
+		lbValue dst = addr.addr;
+
+		auto args = array_make<lbValue>(temporary_allocator(), 4);
+		args[0] = dst;
+		args[1] = lb_address_from_load_or_generate_local(p, value);
+		args[2] = lb_const_int(p->module, t_uintptr, addr.bitfield.bit_offset);
+		args[3] = lb_const_int(p->module, t_uintptr, addr.bitfield.bit_size);
+		lb_emit_runtime_call(p, "__write_bits", args);
+		return;
+	} else if (addr.kind == lbAddr_RelativePointer) {
 		Type *rel_ptr = base_type(lb_addr_type(addr));
 		GB_ASSERT(rel_ptr->kind == Type_RelativePointer ||
 		          rel_ptr->kind == Type_RelativeMultiPointer);
@@ -1074,8 +1098,31 @@ gb_internal lbValue lb_emit_load(lbProcedure *p, lbValue value) {
 gb_internal lbValue lb_addr_load(lbProcedure *p, lbAddr const &addr) {
 	GB_ASSERT(addr.addr.value != nullptr);
 
+	if (addr.kind == lbAddr_BitField) {
+		lbAddr dst = lb_add_local_generated(p, addr.bitfield.type, true);
+		lbValue src = addr.addr;
 
-	if (addr.kind == lbAddr_RelativePointer) {
+		auto args = array_make<lbValue>(temporary_allocator(), 4);
+		args[0] = dst.addr;
+		args[1] = src;
+		args[2] = lb_const_int(p->module, t_uintptr, addr.bitfield.bit_offset);
+		args[3] = lb_const_int(p->module, t_uintptr, addr.bitfield.bit_size);
+		lb_emit_runtime_call(p, "__read_bits", args);
+
+		lbValue r = lb_addr_load(p, dst);
+
+		if (!is_type_unsigned(core_type(addr.bitfield.type))) {
+			// Sign extension
+			// m := 1<<(bit_size-1)
+			// r = (r XOR m) - m
+			Type *t = addr.bitfield.type;
+			lbValue m = lb_const_int(p->module, t, 1ull<<(addr.bitfield.bit_size-1));
+			r = lb_emit_arith(p, Token_Xor, r, m, t);
+			r = lb_emit_arith(p, Token_Sub, r, m, t);
+		}
+
+		return r;
+	} else if (addr.kind == lbAddr_RelativePointer) {
 		Type *rel_ptr = base_type(lb_addr_type(addr));
 		Type *base_integer = nullptr;
 		Type *pointer_type = nullptr;
diff --git a/src/parser.hpp b/src/parser.hpp
index ff77c88c7..1f4ec8726 100644
--- a/src/parser.hpp
+++ b/src/parser.hpp
@@ -429,6 +429,7 @@ AST_KIND(_ExprBegin,  "",  bool) \
 		Ast *expr, *selector; \
 		u8 swizzle_count; /*maximum of 4 components, if set, count >= 2*/ \
 		u8 swizzle_indices; /*2 bits per component*/ \
+		bool is_bit_field; \
 	}) \
 	AST_KIND(ImplicitSelectorExpr, "implicit selector expression",    struct { Token token; Ast *selector; }) \
 	AST_KIND(SelectorCallExpr, "selector call expression", struct { \
diff --git a/src/types.cpp b/src/types.cpp
index 1c28e6583..be4b8944b 100644
--- a/src/types.cpp
+++ b/src/types.cpp
@@ -287,6 +287,7 @@ struct TypeProc {
 		Type *          backing_type;                     \
 		Slice<Entity *> fields;                           \
 		Slice<u8>       bit_sizes;                        \
+		Slice<i64>      bit_offsets;                      \
 		Ast *           node;                             \
 	})                                                        \
 	TYPE_KIND(SoaPointer, struct { Type *elem; })
@@ -408,6 +409,7 @@ struct Selection {
 	bool       indirect; // Set if there was a pointer deref anywhere down the line
 	u8 swizzle_count;    // maximum components = 4
 	u8 swizzle_indices;  // 2 bits per component, representing which swizzle index
+	bool is_bit_field;
 	bool pseudo_field;
 };
 gb_global Selection const empty_selection = {0};
@@ -3187,6 +3189,21 @@ gb_internal Selection lookup_field_with_selection(Type *type_, String field_name
 			else if (field_name == "a") mapped_field_name = str_lit("w");
 			return lookup_field_with_selection(type, mapped_field_name, is_type, sel, allow_blank_ident);
 		}
+	} else if (type->kind == Type_BitField) {
+		for_array(i, type->BitField.fields) {
+			Entity *f = type->BitField.fields[i];
+			if (f->kind != Entity_Variable || (f->flags & EntityFlag_Field) == 0) {
+				continue;
+			}
+			String str = f->token.string;
+			if (field_name == str) {
+				selection_add_index(&sel, i);  // HACK(bill): Leaky memory
+				sel.entity = f;
+				sel.is_bit_field = true;
+				return sel;
+			}
+		}
+
 	} else if (type->kind == Type_Basic) {
 		switch (type->Basic.kind) {
 		case Basic_any: {
@@ -4551,6 +4568,23 @@ gb_internal gbString write_type_to_string(gbString str, Type *type, bool shortha
 		str = gb_string_appendc(str, gb_bprintf("matrix[%d, %d]", cast(int)type->Matrix.row_count, cast(int)type->Matrix.column_count));
 		str = write_type_to_string(str, type->Matrix.elem);
 		break;
+
+	case Type_BitField:
+		str = gb_string_appendc(str, "bit_field ");
+		str = write_type_to_string(str, type->BitField.backing_type);
+		str = gb_string_appendc(str, " {");
+		for (isize i = 0; i < type->BitField.fields.count; i++) {
+			Entity *f = type->BitField.fields[i];
+			if (i > 0) {
+				str = gb_string_appendc(str, ", ");
+			}
+			str = gb_string_append_length(str, f->token.string.text, f->token.string.len);
+			str = gb_string_appendc(str, ": ");
+			str = write_type_to_string(str, f->type);
+			str = gb_string_append_fmt(str, " | %u", type->BitField.bit_sizes[i]);
+		}
+		str = gb_string_appendc(str, " }");
+		break;
 	}
 
 	return str;