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Re: [debug-early] C++ clones and limbo DIEs


On 02/12/2015 11:27 AM, Jason Merrill wrote:
On 02/12/2015 01:04 PM, Aldy Hernandez wrote:
On 02/10/2015 02:52 AM, Richard Biener wrote:
On Fri, Feb 6, 2015 at 5:42 PM, Aldy Hernandez <aldyh@redhat.com> wrote:

Of course I wonder why you need to separate handling of functions and
variables

The variables need to be handled earlier, else the call to
analyze_functions() will remove some optimized global variables away,
and we'll never see them.  I believe that Jason said they were needed
up-thread.

variables.  What breaks if you emit debug info for functions before
the first analyze_functions () call?
 >
 > I also wonder why you restrict it to functions with a GIMPLE body.

The functions, on the other hand, need to be handled after the second
call to analyze_function (and with a GIMPLE body) else we get far more
function DIEs than mainline currently does, especially wrt C++ clones.
Otherwise, we get DIEs for base constructors, complete constructors, and
what-have-yous.  Jason wanted less DIEs, more attune to what mainline is
currently doing.

I think it makes sense to generate DIEs for everything defined in the TU
if we don't have -feliminate-unused-debug-symbols.  But since clones are
artificial, emit them only if they're used.

Ok, just so we're on the same page. I'm thinking that for -fNO-eliminate-unused-debug-symbols, we can iterate through FOR_EACH_DEFINED_FUNCTION before unreachable functions have been removed. There we can output all non-clones.

Then for the -feliminate-unused-debug-symbols case, we can output reachable functions after the unreachable ones have been removed. Here we can also dump the clones we ignored for -fNO-eliminate-unused-debug-symbols above, since we only want to emit them if they're reachable (regardless of -feliminate-unused-debug-symbols).

In either case, we always ignore those without a gimple body, otherwise we end up generating DIEs for the _ZN1AC2Ei constructor in the attached function unnecessarily. See how the bits end up in the attached testcase:

(Oh, and we determine clonehood with DECL_ABSTRACT_ORIGIN)

Before any calls to analyze_functions()
---------------------------------------
Function: 'int main()' (Mangled: main) gimple_body=1 DECL_ABSTRACT_ORIGIN=0
Function: 'A::A(int)' (Mangled: _ZN1AC1Ei) gimple_body=0 DECL_ABSTRACT_ORIGIN=1 Function: 'A::A(int)' (Mangled: _ZN1AC2Ei) gimple_body=1 DECL_ABSTRACT_ORIGIN=1 Function: 'void foo(int)' (Mangled: _Z3fooi) gimple_body=1 DECL_ABSTRACT_ORIGIN=0 Function: 'int bar()' (Mangled: _Z3barv) gimple_body=1 DECL_ABSTRACT_ORIGIN=0 Function: 'void unreachable_func()' (Mangled: _ZL16unreachable_funcv) gimple_body=1 DECL_ABSTRACT_ORIGIN=0

After reachability analysis
(after first call to analyze_functions())
-----------------------------------------
Function: 'int main()' (Mangled: main) gimple_body=1 DECL_ABSTRACT_ORIGIN=0
Function: 'A::A(int)' (Mangled: _ZN1AC1Ei) gimple_body=0 DECL_ABSTRACT_ORIGIN=1 Function: 'A::A(int)' (Mangled: _ZN1AC2Ei) gimple_body=1 DECL_ABSTRACT_ORIGIN=1 Function: 'void foo(int)' (Mangled: _Z3fooi) gimple_body=1 DECL_ABSTRACT_ORIGIN=0 Function: 'int bar()' (Mangled: _Z3barv) gimple_body=1 DECL_ABSTRACT_ORIGIN=0

Is this what you had in mind?  I can provide a patch to make things clearer.

Aldy

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