I have a problem where the optimizer seems to be removing lines of code that are quite necessary. Some background: I have a program that interfaces a PCIe driver. I have an integer pointer UINT32 *bar_reg; that points to the user space address of the BAR register I am communicating to. To write to the register I just de-reference the pointer. *(bar_reg + OFFSET) = value;
With no optimizations, this works fine. However as soon as I turn on any level of optimization, all the lines that de-reference the pointer get removed. The way I finally discovered this was by stepping through in Visual Studio. However it happens independent of platform. I've been able to get by up to now with the optimizer off, but someone using my library code in Linux wants to turn on optimization now. So I'm curious as to why this problem occurs and what the most reasonable fix/workaround is.
Use volatile keyword in order to prevent the optimization of that variable.
For example:
volatile UINT32 *bar_reg;
The issue here is that the compiler assumes that since the memory is not accessed by the program, then it means that the memory will remain unchanged and hence it might try to optimize some of the writes to that memory.
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