Re: [patch] [gdb/testsuite] include a use of the definition of a type to cause clang to emit debug info

[Joel Brobecker <brobecker at adacore dot com>]

On Sat, Apr 12, 2014 at 11:43:40PM -0700, David Blaikie wrote:
> Clang has an optimization that causes a the debug info to only include
> the declaration of a type if the type is referenced but never used in
> a context that requires a definition (eg: pointers are handed around
> but never deferenced).
> 
> This patch introduces a variable to one test file to cause clang to
> emit the full definition of the type as well as fixing up a related
> typo in the test message of the associated expect file.
> 
> Like the difference between GCC and Clang in the emission of unused
> static entities, I think this case is also a matter of degrees - both
> GCC and Clang implement other similar optimizations* to the one
> outlined here and the GDB test suite has managed to pass without
> disabling those optimizations in GCC and I hope it's suitable to do
> the same for Clang.
> 
> Though admittedly I don't have much of the context of the history of
> the testsuite, its priorities/preferences when it comes to
> distinguishing testing compiler behavior versus debugger behavior,
> etc.
> 
> * the one I know of involves dynamic types: both GCC and Clang only
> emit the debug info definition of such a type in any translation unit
> that emits the key function. This means in many contexts where a full
> definition is provided in the source only a declaration is provided in
> the debug info.

> commit 1128f6fb45483d45668d09e0696f4a590334e0c4
> Author: David Blaikie <dblaikie@gmail.com>
> Date:   Sat Apr 12 23:27:19 2014 -0700
> 
>     Cause clang to emit the definition of a type used only by pointer
>     
>     gdb/testsuite/
>     	* gdb.stabs/gdb11479.c: introduce a variable to cause clang to
>     	emit the full definition of type required by the test
>     	* gdb.stabs/gdb11479.exp: correct a typo in a test message

The gdb11479.exp is obvious and can be pushed. The change to gdb11479.c,
on the other hand, changes the test, and I don't think we want that,
because I disagree with the outcome of Clang's optimization here.
If Clang doesn't want to fix the problem, best to just xfail the test
with Clang, and write a new one that provides the type definition as
Clang wants it.

Thanks,
-- 
Joel