One thing it depends on, that I don't think anyone has mentioned, is the compiler's register allocation logic and how that interacts with the rest of the code in the calling function.
If, at the point you call the function, all registers are used, the following statement to retrieve the value may cause a register to be spilled to the stack. That may overwrite the data. That's more likely to happen on a register-poor architecture like x86.
If, at the point you call the function, all registers are used, the following statement to retrieve the value may cause a register to be spilled to the stack. That may overwrite the data. That's more likely to happen on a register-poor architecture like x86.