比较跳转指令为一条指令 [英] Compare and jump instruction as one instruction

问题描述

有没有一种方法，我可以比较和跳跃在一个指令：

Is there a way I can compare and jump in one instruction:

C code：结果
 1. 而（I＆LT; 10）结果
 2. {我++}

C code:
1. while(i<10)
2. {i++}

大会code：（EAX = 0）（ECX = 10）

1. 。而


2. CMP EAX，ECX


3. JGE .endofwhile


4. 添加EAX，1


5. JMP。而


6. .endofwhile：

1. .while:
2. cmp eax, ecx
3. jge .endofwhile
4. add eax, 1
5. jmp .while
6. .endofwhile:

有没有一种方法，我可以在一个指令做线2和3？

Is there a way i can do line 2 and 3 in one instruction?

推荐答案

是的，你可以测试并作为一个单一的指令处理分支，做的方式，这是写他们两个指令像你这样，要用现代的Intel处理器，并遵循一些简单的规则（分支指令必须包含在code，测试指令结束的相同的16个字节线，两条指令，不要通过其他任何指令分离，... ）。

Yes, you can have the test and branch treated as a single instruction, and the way to do this is to write them as two instructions like you did, to use a modern Intel processor and to follow a few simple rules (the branch instruction must be contained in the same 16-bytes line of code that the test instruction ends, the two instructions must not be separated by any other instruction, …).

的机制被称为<一href=\"https://web.archive.org/web/20120922053925/http://www.behardware.com/articles/623-7/intel-core-2-duo-test.html\"相对=nofollow>宏观融合。更详细的信息，包括在宏观融合应用可从瓦格纳雾的手册中的precise条件，第82页。

The mechanism is called macro-fusion. More detailed information including the precise conditions in which macro-fusion apply is available from Agner Fog's manual, page 82.

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