It's technically possible to give perfect debug information even with a highly optimized binary. In a typical Linux/BSD ELF file the debug information is stored

It's technically possible to give perfect debug information even with a highly optimized binary. In a typical Linux/BSD ELF file the debug information is stored as a DWARF program that effectively emulates the state of all the registers in the target machine, and that program gets executed from the saved frame state of the current function to produce the state at the current breakpoint complete with tracking backpointers into the source. To track all information properly would require much much more state to be preserved over optimization passes and saved with each executable. The end result would effectively end up embedding the compiler internal state inside each and every target executable. The cost, of course, would be massive (terabyte) executables that take minutes or so to execute every step in the debugger, and compile times orders of magnitude greater than they are today. The current assumption is that the programmer knows enough about what they are doing and how their tools work under the hood that they can live with the current limitations when they try to debug non-debug builds.