On Tue, 2013-09-17 at 08:08 -0700, Ian Lance Taylor wrote: > In your example code you are using the attribute on a local variable. > The used attribute is only meaningful on a function or global > variable. Aha. OK thanks. It would be very helpful if the manual made this more clear: it simply says "variable" and I see no obvious way to infer that it applies only to global variables or functions. > It's intended to be used to force the function or global variable to > be emitted even if it is not used. > > It sounds like you are looking for the ability to disable optimization > for a local variable. It doesn't make sense to say that you want to > force a local variable to exist even at high levels of optimization. > At high levels of optimization local variables more or less disappear, > though debug info is able to track some cases. In any case, GCC has > no such ability. IMO it is not nonsensical to ask the compiler to preserve a variable on the stack even at high levels of optimization, so that its value can be queried from a coredump or even live debugging. The variables I'm referring to are typically of the type in my example (although their value is not so simply reproduced obviously): they are local variables which are assigned but never read. They exist solely to keep track of a value which may be interesting in a debugging session. Ideally we'd not be debugging highly optimized code but real life is not always ideal :-). However, I understand that this capability is not currently available. Cheers!
