[Bug middle-end/45632] New: const function pointer propagation issues with inlining

[Bug middle-end/45632] New: const function pointer propagation issues with inlining

[andi-gcc at firstfloor dot org]

The attached test case is testing inlining of const function pointers
in a typical "OO code written in C" situation.

The code shows two optimization problems:

- a_foo is inlined into main, b_foo is not.
The only difference is that new_a() returns a const pointer 
and new_b() does not. I would have assumed that gcc detects that the pointer
coming out of new_b() is const.

- p->ops->op2 is never inlined, not even for a, even though the compiler
should have enough information to do so (everything that is passed in is 
const). I assume this is because cloning does not work through
function pointers?


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           Summary: const function pointer propagation issues with inlining
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: andi-gcc at firstfloor dot org
  GCC host triplet: x86_64-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45632

[Bug middle-end/45632] const function pointer propagation issues with inlining

[andi-gcc at firstfloor dot org]

------- Comment #1 from andi-gcc at firstfloor dot org  2010-09-10 08:50 -------
Created an attachment (id=21763)
 --> (http://gcc.gnu.org/bugzilla/attachment.cgi?id=21763&action=view)
testcase, compiled with -O3


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45632

[Bug middle-end/45632] const function pointer propagation issues with inlining

[rguenth at gcc dot gnu dot org]

-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rguenth at gcc dot gnu dot
                   |                            |org, hubicka at gcc dot gnu
                   |                            |dot org, jamborm at gcc dot
                   |                            |gnu dot org
           Severity|normal                      |enhancement
           Keywords|                            |missed-optimization


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45632

[Bug middle-end/45632] const function pointer propagation issues with inlining

[jamborm at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45632

--- Comment #2 from Martin Jambor <jamborm at gcc dot gnu.org> 2011-10-21 14:07:53 UTC ---
Is the second call to func() in main we pass the pointer p again, p2
being basically thrown away, I think that is a mistake because this
way, there isn't actually any call to b_foo in the testcase, just two
calls to a_foo.

BTW, currently (at -O3 and on i686) not even these calls to a_foo is
inlined.  Just one of them is direct but the other one is not, presumably
because we don't believe in the constantness of *p over the first call
at this stage.  When I change the testcase to pass p2 to the second
invocation of func, neither a_foo nor b_foo are inlined either.

So it seems to me that in order to inline both cases we'd need
aggregate return functions that we would be able to combine with
indirect cgraph edges at inlining time.  Tough.