Method infer_typevar

cranelift/reader/src/parser.rs:2360–2437

Type inference for polymorphic instructions. The controlling type variable can be specified explicitly as 'splat.i32x4 v5', or it can be inferred from `inst_data.typevar_operand` for some opcodes. Returns the controlling typevar for a polymorphic opcode, or `INVALID` for a non-polymorphic opcode.

(
        &self,
        ctx: &Context,
        opcode: Opcode,
        explicit_ctrl_type: Option<Type>,
        inst_data: &InstructionData,
    )

    // Returns the controlling typevar for a polymorphic opcode, or `INVALID` for a non-polymorphic
    // opcode.
    fn infer_typevar(
        &self,
        ctx: &Context,
        opcode: Opcode,
        explicit_ctrl_type: Option<Type>,
        inst_data: &InstructionData,
    ) -> ParseResult<Type> {
        let constraints = opcode.constraints();
        let ctrl_type = match explicit_ctrl_type {
            Some(t) => t,
            None => {
                if constraints.use_typevar_operand() {
                    // This is an opcode that supports type inference, AND there was no
                    // explicit type specified. Look up `ctrl_value` to see if it was defined
                    // already.
                    // TBD: If it is defined in another block, the type should have been
                    // specified explicitly. It is unfortunate that the correctness of IR
                    // depends on the layout of the blocks.
                    let ctrl_src_value = inst_data
                        .typevar_operand(&ctx.function.dfg.value_lists)
                        .expect("Constraints <-> Format inconsistency");
                    if !ctx.map.contains_value(ctrl_src_value) {
                        return err!(
                            self.loc,
                            "type variable required for polymorphic opcode, e.g. '{}.{}'; \
                             can't infer from {} which is not yet defined",
                            opcode,
                            constraints.ctrl_typeset().unwrap().example(),
                            ctrl_src_value
                        );
                    }
                    if !ctx.function.dfg.value_is_valid_for_parser(ctrl_src_value) {
                        return err!(
                            self.loc,
                            "type variable required for polymorphic opcode, e.g. '{}.{}'; \
                             can't infer from {} which is not yet resolved",
                            opcode,
                            constraints.ctrl_typeset().unwrap().example(),
                            ctrl_src_value
                        );
                    }
                    ctx.function.dfg.value_type(ctrl_src_value)
                } else if constraints.is_polymorphic() {
                    // This opcode does not support type inference, so the explicit type
                    // variable is required.
                    return err!(
                        self.loc,
                        "type variable required for polymorphic opcode, e.g. '{}.{}'",
                        opcode,
                        constraints.ctrl_typeset().unwrap().example()
                    );
                } else {
                    // This is a non-polymorphic opcode. No typevar needed.
                    INVALID
                }
            }
        };