[LLVMdev] .debug_info section size in arm executable

[Eric Christopher]

On Nov 9, 2011, at 2:12 PM, Chris Lattner wrote:

> On Nov 9, 2011, at 1:08 PM, Jim Grosbach wrote:
>>> On Nov 9, 2011, at 10:49 AM, Jim Grosbach wrote:
>>>>> 
>>>>> It's not good, but people do it. Also constructing enums via & and | etc. It'd be nice to be able to get the name of whatever it is that the code generator actually produced :)
>>>>> 
>>>> 
>>>> Agreed. LLVM itself does this sort of thing pretty frequently, actually, and having the enum names and values available in the debugger is very nice.
>>> 
>>> Wouldn't it be better to emit the enumerators that are actually used in a translation unit, instead of emitting all of them?  If we're not emitting them when used, that would be a problem, but I don't see a reason to care about enumerators that are never used anywhere in a program.
> 
>> Say something is going wrong for value E of the enum because the default case doesn't work for it. I want to put a conditional breakpoint on the switch statement for 'a == E', but E isn't explicitly used anywhere in the program since the call to foo passes the value as an int, constructed in some arbitrary manner.
> 
> So long as E is used in another file, you'll be able to do this.  If E isn't used anywhere in your app, then it's dead and doesn't seem interesting.
> 

In this case though it's not dead as long as there's a switch on the enum with a default case :) i.e. "We should never get here, but yet we are, what type that I'm not expecting did we get here with?"

>> Also consider the case where the caller of foo() (which does explicitly use E) is in a dylib we haven't loaded yet, and thus haven't looked at the debug info for. I want to set that same breakpoint.
> 
> -flimit-debug-info=0.  The entire idea of -gused is that you're building (almost) all of your app with debug info.  It's the default because this matches the common scenario.
> 
> In short, I still don't understand why we'd want to emit all the enumerators just because an enum type is used. :)

The above :)

That said if we want to conditionalize this on flimit-debug-info that's fine, however, I think that since the type is used all elements of the type are used. Also, I doubt that (except for pathological cases) enum switch values are our greatest worry for size of the string table :)

-eric