[Bug middle-end/20408] New: Unnessasary code generated for empty structs

["chris at bubblescope dot net" <gcc-bugzilla at gcc dot gnu dot org>]

Given an empty struct (ie struct X { };), even at high optimisation levels g++
will insist on always allocating and zeroing some memory for empty structs.

This actually effects C++ code, including libstdc++-v3, as empty structs are
often used as a means of passing around functions.

EXAMPLE
------------------
struct X {};

void foo(X);

void call_foo()
{ foo(X()); }
------------------

generates (from -O3, t70.final_cleanup is:)
-------------------------------------------------
;; Function void call_foo() (_Z8call_foov)

void call_foo() ()
{
  struct X D.1597;

<bb 0>:
  D.1597 = 0;
  foo (D.1597) [tail call];
  return;

}
---------------------------------------------

-- 
           Summary: Unnessasary code generated for empty structs
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: minor
          Priority: P2
         Component: middle-end
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: chris at bubblescope dot net
                CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20408