LRFRC系列:解读MIR基础

pub enum Operand<'tcx> {   /// Copy: The value must be available for use afterwards.   /// This implies that the type of the place must be `Copy`;   Copy(Place<'tcx>),   /// Move: The value (including old borrows of it)   /// will not be used again.   Move(Place<'tcx>),   /// Synthesizes a constant value.   Constant(Box<Constant<'tcx>>),}

pub struct Body<'tcx> {    /// 函数包含的所有基础块，引用基础块需要通过基础块编号BasicBlock；    basic_blocks: IndexVec<BasicBlock, BasicBlockData<'tcx>>,        /// 函数本地Locals声明    /// 第1个Local用作返回值，紧接arg_count个Locals用作函数参数，    /// 后续Local用作记录用户定义的任何变量和临时变量；    /// Locals类似于维护函数的调用栈，在实现函数内部操作的过程中，    /// 对需要用到的任何变量或临时变量都记录在此；    /// 要访问Local的内容需要通过索引编号的方式；    pub local_decls: LocalDecls<'tcx>,    /// 这个函数的参数的数量，从本地索引1开始到arg_count的Locals，    /// 假定由调用者来提供并初始化；    pub arg_count: usize,    /// A span representing this MIR, for error reporting.    pub span: Span,    /// 函数体需要用到的Constants    pub required_consts: Vec<Constant<'tcx>>,    pub is_polymorphic: bool,    //..............................}rustc_index::newtype_index! {    /// A node in the MIR [control-flow graph][CFG].    pub struct BasicBlock {        derive [HashStable]        DEBUG_FORMAT = "bb{}",        const START_BLOCK = 0,    }}pub struct BasicBlockData<'tcx> {    /// List of statements in this block.    pub statements: Vec<Statement<'tcx>>,    /// Terminator for this block.    /// N.B., this should generally ONLY    /// be `None` during construction.    pub terminator: Option<Terminator<'tcx>>,    /// If true, this block lies on an unwind path.    pub is_cleanup: bool,}

pub struct Statement<'tcx> {    pub source_info: SourceInfo,    pub kind: StatementKind<'tcx>,}pub enum StatementKind<'tcx> {    /// 将右值Rvalue写到左边的访问路径    Assign(Box<(Place<'tcx>, Rvalue<'tcx>)>),    /// Local具有有效存储的开始    StorageLive(Local),    /// Local具有有效存储的结束    StorageDead(Local),    /// 省略部分其他语句.........    /// 空语句 用来删除指令而无须影响语句编号    Nop,}pub struct Terminator<'tcx> {    pub source_info: SourceInfo,    pub kind: TerminatorKind<'tcx>,}pub enum TerminatorKind<'tcx> {    /// 跳转到图中一个有效的块    Goto { target: BasicBlock },    /// 评估操作数，根据其值跳转到某一个目标；    SwitchInt {        /// 将被评估的操作数        discr: Operand<'tcx>,        /// 操作数类型，存在冗余        switch_ty: Ty<'tcx>,        /// 跳转目标列表        targets: SwitchTargets,    },    /// 表示landing pad已完成，unwinding可继续    Resume,    /// 表示landing pad已完成，需要终止后续unwinding    Abort,    /// 描述正常的返回。执行Return前，返回路径中的值应该已填充；    /// 可以在不同基础块中被调用多次    Return,    /// Indicates a terminator that can never be reached.    /// 描述该终结者不可达    Unreachable,    /// 析构指定访问路径中的Local，完成后跳转到target，    /// 发生异常则unwind    Drop { place: Place<'tcx>, target: BasicBlock           , unwind: Option<BasicBlock> },    /// 析构Place中值之后并为它赋上新值    DropAndReplace {        place: Place<'tcx>,        value: Operand<'tcx>,        target: BasicBlock,        unwind: Option<BasicBlock>,    },    /// Block ends with a call of a function.    /// 描述一次函数调用，func表示正被调用的函数，    /// args表示其参数，参数内容由调用者作为拥有者，函数可以自由修改，    /// destination表示返回值，    Call {        func: Operand<'tcx>,        args: Vec<Operand<'tcx>>,        destination: Option<(Place<'tcx>, BasicBlock)>,        /// Cleanups to be done if the call unwinds.        cleanup: Option<BasicBlock>,        from_hir_call: bool,        fn_span: Span,    },    /// 省略部分其他类型.........}

pub type LocalDecls<'tcx> = IndexVec<Local, LocalDecl<'tcx>>;/// Local表示LocalDecls中的LocalDecl索引rustc_index::newtype_index! {    pub struct Local {        derive [HashStable]        DEBUG_FORMAT = "_{}",        const RETURN_PLACE = 0,    }}pub enum LocalKind {    /// 用户声明的变量    Var,    /// 临时变量    Temp,    /// 函数参数    Arg,    /// 函数返回值    ReturnPointer,}pub struct LocalDecl<'tcx> {  pub mutability: Mutability,  pub local_info: Option<Box<LocalInfo<'tcx>>>,  pub internal: bool,  pub is_block_tail: Option<BlockTailInfo>,  /// The type of this local.  /// Local的类型，它决定Local存储空间大小及其可否Move/Copy等  pub ty: Ty<'tcx>,  pub user_ty: Option<Box<UserTypeProjections>>,    pub source_info: SourceInfo,}/// A path to a value; something that can be evaluated without/// changing or disturbing program state./// 指向一个值的路径pub struct Place<'tcx> {    pub local: Local,    /// projection out of a place    /// (access a field, deref a pointer, etc)    pub projection: &'tcx List<PlaceElem<'tcx>>,}pub enum ProjectionElem<V, T> {    Deref,    Field(Field, T),    Index(V),    Subslice {        from: u64,        to: u64,        /// Whether `to` counts from the start         /// or end of the array/slice.        from_end: bool,    },    /// 省略部分其他类型.........}

pub enum Rvalue<'tcx> {    /// x (either a move or copy, depending on type of x)    Use(Operand<'tcx>),    /// [x; 32]    Repeat(Operand<'tcx>, &'tcx ty::Const<'tcx>),    /// &x or &mut x    /// 对指定路径的值的引用或借用    Ref(Region<'tcx>, BorrowKind, Place<'tcx>),    /// Accessing a thread local static.     /// This is inherently a runtime operation.    ThreadLocalRef(DefId),    /// Create a raw pointer to the given place    /// Can be generated by raw address of expressions    /// (`&raw const x`),    /// or when casting a reference to a raw pointer.    AddressOf(Mutability, Place<'tcx>),    /// length of a `[X]` or `[X;n]` value    Len(Place<'tcx>),    Cast(CastKind, Operand<'tcx>, Ty<'tcx>),    BinaryOp(BinOp, Box<(Operand<'tcx>, Operand<'tcx>)>),    CheckedBinaryOp(BinOp, Box<(Operand<'tcx>        , Operand<'tcx>)>),    NullaryOp(NullOp, Ty<'tcx>),    UnaryOp(UnOp, Operand<'tcx>),    /// Read the discriminant of an ADT.    /// 用于match语句    Discriminant(Place<'tcx>),    /// 省略部分其他类型.........}pub enum BinOp {    /// The `+` operator (addition)    Add,    /// The `-` operator (subtraction)    Sub,    /// The `*` operator (multiplication)    Mul,    /// The `/` operator (division)    Div,    /// The `%` operator (modulus)    Rem,    /// The `^` operator (bitwise xor)    BitXor,    /// The `&` operator (bitwise and)    BitAnd,    /// The `|` operator (bitwise or)    BitOr,    /// The `<<` operator (shift left)    Shl,    /// The `>>` operator (shift right)    Shr,    /// The `==` operator (equality)    Eq,    /// The `<` operator (less than)    Lt,    /// The `<=` operator (less than or equal to)    Le,    /// The `!=` operator (not equal to)    Ne,    /// The `>=` operator (greater than or equal to)    Ge,    /// The `>` operator (greater than)    Gt,    /// The `ptr.offset` operator    Offset,}pub enum NullOp {    /// Returns the size of a value of that type    SizeOf,    /// 为指定类型的值创建一个新未初始化的空间    Box,}pub enum UnOp {    /// The `!` operator for logical inversion    Not,    /// The `-` operator for negation    Neg,}