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wasm: Reverse the order of error and payload

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This will set us up to correctly retrieve the error local index and payload index
depending on that of the multi_value's index. As from now, the error will always use
the multi_value's index, and the payload will use the following locals.
This commit is contained in:
Luuk de Gram 2021-05-28 10:50:16 +02:00
parent 967a299c34
commit 8a81dfc999
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GPG Key ID: A002B174963DBB7D
1 changed files with 22 additions and 17 deletions
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39
src/codegen/wasm.zig
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@ -623,7 +623,8 @@ pub const Context = struct {
.Struct => {
// for each struct field, generate a local
const struct_data: *Module.Struct = ty.castTag(.@"struct").?.data;
try self.locals.ensureCapacity(self.gpa, self.locals.items.len + struct_data.fields.count());
const fields_len = @intCast(u32, struct_data.fields.count());
try self.locals.ensureCapacity(self.gpa, self.locals.items.len + fields_len);
for (struct_data.fields.items()) |entry| {
const val_type = try self.genValtype(
.{ .node_offset = struct_data.node_offset },
@ -634,19 +635,20 @@ pub const Context = struct {
}
return WValue{ .multi_value = .{
.index = initial_index,
.count = @intCast(u32, struct_data.fields.count()),
.count = fields_len,
} };
},
.ErrorUnion => {
// generate a local for both the error and the payload.
const payload_type = ty.errorUnionChild();
// we emit the payload value as the first local, and the error as the second
// The first local is also used to find the index of the error.
try self.locals.ensureCapacity(self.gpa, self.locals.items.len + 2);
const val_type = try self.genValtype(.{ .node_offset = 0 }, payload_type);
self.locals.appendAssumeCapacity(val_type);
// we emit the error value as the first local, and the payload as the following.
// The first local is also used to find the index of the error and payload.
//
// TODO: Add support where the payload is a type that contains multiple locals such as a struct.
try self.locals.ensureCapacity(self.gpa, self.locals.items.len + 2);
self.locals.appendAssumeCapacity(wasm.valtype(.i32)); // error values are always i32
self.locals.appendAssumeCapacity(val_type);
self.local_index += 2;
return WValue{ .multi_value = .{
@ -1039,6 +1041,9 @@ pub const Context = struct {
const error_type = ty.errorUnionSet();
const payload_type = ty.errorUnionChild();
if (value.getError()) |_| {
// write the error value
try self.emitConstant(src, data, error_type);
// no payload, so write a '0' const
const opcode: wasm.Opcode = buildOpcode(.{
.op = .@"const",
@ -1046,15 +1051,12 @@ pub const Context = struct {
});
try writer.writeByte(wasm.opcode(opcode));
try leb.writeULEB128(writer, @as(u32, 0));
// write the error value
try self.emitConstant(src, data, error_type);
} else {
// payload first
try self.emitConstant(src, data, payload_type);
// no error, so write a '0' const
try writer.writeByte(wasm.opcode(.i32_const));
try leb.writeULEB128(writer, @as(u32, 0));
// after the error code, we emit the payload
try self.emitConstant(src, data, payload_type);
}
},
else => |zig_type| return self.fail(src, "Wasm TODO: emitConstant for zigTypeTag {s}", .{zig_type}),
@ -1278,8 +1280,8 @@ pub const Context = struct {
const offset = self.code.items.len;
const writer = self.code.writer();
// load the error value which is the payload's multi_value index + 1
try self.emitWValue(.{ .local = operand.multi_value.index + 1 });
// load the error value which is positioned at multi_value's index
try self.emitWValue(.{ .local = operand.multi_value.index });
// Compare the error value with '0'
try writer.writeByte(wasm.opcode(.i32_const));
try leb.writeILEB128(writer, @as(i32, 0));
@ -1293,8 +1295,11 @@ pub const Context = struct {
fn genUnwrapErrUnionPayload(self: *Context, inst: *Inst.UnOp) InnerError!WValue {
const operand = self.resolveInst(inst.operand);
// payload's local index is that of its multi_value index, so convert it to a `WValue.local`
return WValue{ .local = operand.multi_value.index };
// The index of multi_value contains the error code. To get the initial index of the payload we get
// the following index. Next, convert it to a `WValue.local`
//
// TODO: Check if payload is a type that requires a multi_value as well and emit that instead. i.e. a struct.
return WValue{ .local = operand.multi_value.index + 1 };
}
fn genWrapErrUnionPayload(self: *Context, inst: *Inst.UnOp) InnerError!WValue {