如何IA32'CMP'指令转换为Y86？

问题描述

IA32 为 Y86

ATT大会

我有以下IA32组装code：

I have the following IA32 assembly code:

Bubble:
.LFB0:
    pushl   %esi
    pushl   %ebx
    movl    16(%esp), %esi
    movl    12(%esp), %edx
    subl    $1, %esi
    andl    %esi, %esi
    jle .L1
.L7:
    xorl    %eax, %eax
.L5:
    movl    4(%edx,%eax,4), %ecx
    movl    (%edx,%eax,4), %ebx
    cmpl    %ebx, %ecx
    jge .L4
    movl    %ebx, 4(%edx,%eax,4)
    movl    %ecx, (%edx,%eax,4)
.L4:
    addl    $1, %eax
    cmpl    %eax, %esi
    jg  .L5
    subl    $1, %esi
    jne .L7
.L1:
    popl    %ebx
    popl    %esi
    ret

我试图将其转换为Y86组装code。我无法翻译的比较指令：

I'm trying to convert it to Y86 assembly code. I'm having trouble translating the compare instruction:

 cmpl    %ebx, %ecx

感谢。

推荐答案

看来，Y86没有 CMP 指令。但是，它有分，推和弹出。

It seems that Y86 does not have cmp instruction. However, it has sub, push and pop.

所以 CMPL％EBX，ECX％可转换为以下code：

So cmpl %ebx, %ecx can be converted to the following code:

pushl %ecx
subl  %ebx, %ecx
popl  %ecx

CMP 是完全一样的分与 CMP 不存储结果，只更新标志。因此， CMP 总是可以用推，分取代， 弹出（如果在堆栈中的足够的空间）。

cmp is exactly the same as sub, with the difference that cmp does not store the result, it only updates the flags. So cmp can always be replaced with push, sub, pop (if there's enough space in the stack).

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