assembly - "enter" vs "push ebp; mov ebp, esp; sub esp, imm" and "leave" vs "mov esp, ebp; pop ebp" -

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what difference between enter and

push ebp mov  ebp, esp sub  esp, imm

instructions? there performence difference? if so, faster , why compilers use latter?

similarily leave and

mov  esp, ebp pop  ebp

instructions.

there performance difference, enter. on modern processors decodes 10 20 µops, while 3 instruction sequence 4 6, depending on architecture. details consult agner fog's instruction tables.

additionally enter instruction has quite high latency, example 8 clocks on core2, compared 3 clocks dependency chain of 3 instruction sequence.

furthermore 3 instruction sequence may spread out compiler scheduling purposes, depending on surrounding code of course, allow more parallel execution of instructions.


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