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Lecture 5

:material-circle-edit-outline: 约 449 个字 :fontawesome-solid-code: 2 行代码 :material-clock-time-two-outline: 预计阅读时间 2 分钟

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!!! bug “我真的服了” 这个老师会传统点名

接上周没讲完的 jump 跳转

Jump

Basic Blocks

跳转让优化变得很困难，因为跳转是未知的、不确定的。

为了方面预测并优化，将指令集合分为多个basic block，每个block里面不会进行jump，还有一些其它的性质：

  • A basic block is a sequence of instructions with
    • No embedded branches (except at end)
    • No branch targets (except at beginning)

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2.8 Supporting Procedures

Procedure/function

  • Procedure/function be used to structure programs
    • A stored subroutine that performs a specific task based on the parameters with which it is provided
    • Six step
  1. Place Parameters in a place where the procedure can access them
  2. Transfer control to the procedure(jump to)
  3. Acquire the storage resources needed for the procedure
  4. Perform the desired task
  5. Place the result value in a place where the calling program can access it
  6. Return control to the point of origin

Procedure Call Instructions

  • Instruction for procedures: jal ( jump-and-link )
    • Address of following instruction put in x1
    • Jumps to target address
Caller jal x1, ProcedureAddress
  • Procedure return:jalr (jump and link register)
    • Like jal, but jumps to 0 + address in x1
    • Use x0 as rd (x0 cannot be changed)
    • Can also be used for computed jumps
Callee jalr x0, 0(x1)

Using More Registers

  • Registers for procedure calling
    • a0 ~ a7(x10-x17): eight argument registers to pass parameters & return values
    • ra/x1：one return address register to return to origin point
  • Stack
    • ideal data structure for spilling registers
    • Stack pointer sp
  • Stack grow from higher address to lower address
    • 约定起始位置在高位，往低位扩张
    • Push: sp= sp - 8 addi sp,sp,-8 sd …,8(sp)
    • Pop: sp = sp + 8 ld …,8(sp) addi sp,sp,
    • 8 是字长

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Example

这里没听没看

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下面虚线部分是运算部分，可以忽略

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记成tx是方便，就一个临时记号

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Nested Procedures

下面都没看

嵌套程序

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一个stack不够用，用多个stack

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Memory Layout

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Local Data on the Stack

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RISC-V assembly language

这张表经常要查

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2.9 Communicating with People Character Data

  • Byte-encoded character sets
    • ASCII ( American Standard Code for Information Interchange )
  • Unicode: 32-bit character set

Byte/Halfword/Word Operations

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String Copy Example

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2.10 Addressing for 32-Bit Immediate and Addresses

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Addressing

Branch Addressing

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Jump Addressing

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Show branch offset in machine language

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Instructions Addressing and their Offset

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