[flohofwoe]

That's why step-debugging usually is done on unoptimized builds where there's a clear relationship between the original source code lines and variables and the generated machine code.

But there's a wide "grey area" depending on optimization level where the debug information is more or less off yet the mapping is still "good enough". Debugging on optimized builds can work surprisingly well if you know what to expect (e.g. the debugging cursor might jump to unexpected places in the source code because the line mapping is off, or you can't step into a function because it has been inlined).