Why does the compiler generate this code?

Question

I disassembled an object file (most likely generated using the Visual C++ compiler) using DumpBin and saw the following piece of code:

...         ...
mov         dword ptr [ebp-4],eax       // Why save EAX?
push        dword ptr [ebp+14h]
push        dword ptr [ebp+10h]
push        dword ptr [ebp+0Ch]
push        dword ptr [ebp+8]
mov         eax,dword ptr [ebp-4]       // Why restore EAX? Did it change at all?
call        <function>
...         ...

Could someone please explain why the EAX register is being saved and restored across these 4 push instructions?

Answer 1

Also, maybe it's compiled in release mode, but that variable has been marked as volatile, which tells the compiler that such variable may change without it knowing, so it is forced to continuously write/restore it on/from the stack

Answer 2

Was this built in debug mode? If so, the compiler stores every local variable on the stack so that the debugger can find them in a consistent way.

The elision of such unnecessary stores and reloads is one of the optimizations that constitutes "release" mode.