＆QUOT; Enter]键。 VS＆QUOT;推EBP; MOV EBP，ESP;子ESP，IMM＆QUOT;和＆QUOT;假＆QUOT; VS＆QUOT; MOV ESP，EBP;流行EBP＆QUOT; [英] "enter" vs "push ebp; mov ebp, esp; sub esp, imm" and "leave" vs "mov esp, ebp; pop ebp"

问题描述

之间有什么区别的输入和

push ebp
mov  ebp, esp
sub  esp, imm

说明？是否有一个性能自动区别吗？如果是这样，这是更快，为什么编译器始终将后者？

instructions? Is there a performence difference? If so, which is faster and why do compilers always use the latter?

与相若的离开和

mov  esp, ebp
pop  ebp

指令。

推荐答案

有一个性能的差异，尤其是对输入。现代处理器本德codeS到约10至20μops，而3个指令序列是约4至6，这取决于结构。有关详情请咨询瓦格纳雾的指令表。

There is a performance difference, especially for enter. On modern processors this decodes to some 10 to 20 µops, while the three instruction sequence is about 4 to 6, depending on the architecture. For details consult Agner Fog's instruction tables.

此外在输入指令通常具有相当高的延迟，例如8个时钟上酷睿2相比，3个指令序列的3个时钟依赖链。

Additionally the enter instruction usually has a quite high latency, for example 8 clocks on a core2, compared to the 3 clocks dependency chain of the three instruction sequence.

另外三个指令序列可能为s $ P $垫了编译器为调度宗旨，视场周围code，允许进一步的指令并行执行。

Furthermore the three instruction sequence may be spread out by the compiler for scheduling purposes, depending on the surrounding code of course, to allow more parallel execution of instructions.

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