[llvm-dev] (in x86, ) Use ebp or esp to access local variable? what's different?

[PenYiWang via llvm-dev]

Hi

I use LLVM/Clang to compile some program.

I found that if we use -O0 flag, the program will use ebp to access local
variables.

For example :  mov ecx,DWORD PTR [ebp-0x8]

If we use -O2 flag, the program will use esp to access local variables.

For example : mov eax,DWORD PTR [esp+0x8]

Is there any different between them?

Can user decide esp or ebp to access the local variable?

Or can I modify LLVM backend code to do it?

Is there any calling convention related to it?
I  found it is the same in gcc.

Thank you!
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