Re: target/7559: kdelibs miscompilation

[Gwenole Beauchesne <gbeauchesne@mandrakesoft.com>]

The following reply was made to PR target/7559; it has been noted by GNATS.

From: Gwenole Beauchesne <gbeauchesne@mandrakesoft.com>
To: gcc-gnats@gcc.gnu.org
Cc: david@mandrakesoft.com, <aj@suse.de>, <jh@suse.cz>, <nobody@gcc.gnu.org>,
        <gcc-prs@gcc.gnu.org>, <gcc-bugs@gcc.gnu.org>
Subject: Re: target/7559: kdelibs miscompilation
Date: Sat, 10 Aug 2002 13:54:00 +0200 (CEST)

 > The following C testcase is equivalent in miscompiled-behavior. If you
 > don't want to bother compiling the C++ front-end for tests. ;-)
 
 This could be a mis-classification of the other eightbyte sub-object. 
 
 1) Actually, the following testcase fails too and occurs because we have a
 two eightbytes object, "sliced" in the middle (aka two sub-aggregates). As
 a result, only the first eightbyte is actually passed in register. The
 other one vanished.
 
 [gb@gauss vrac]$ cat struct.c
 extern void abort();
 
 struct A {
   int x, y;
 };
 
 struct R {
   struct A a, b;
 };
 
 struct R R = {
   { 100, 100 },
   { 200, 200 }
 };
 
 void f(struct R r) {
   if (r.a.x != R.a.x || r.a.y != R.a.y || r.b.x != R.b.x || r.b.y != 
 R.b.y)
     abort();
 }
 
 int main() {
   f(R);
   return 0;
 }
 
 2) The following testcase *won't* fail though we have a two eightbytes 
 object, and is not "sliced" in.
 
 [gb@gauss vrac]$ cat other.c
 extern void abort();
 
 struct A {
   int a, b, c, d;
 };
 
 struct A X = {
   100, 200, 300, 400
 };
 
 void f(struct A x) {
   if (x.a != X.a || x.b != X.b || x.c != X.c || x.d != X.d)
     abort();
 }
 
 int main(void) {
   f(X);
   return 0;
 }
 
 3) The last testcase is ultra-reduced to a two eightbytes object, with 
 only one member in each one. That one do fails.
 
 extern void abort();
 
 struct A {
   long x;
 };
 
 struct R {
   struct A a, b;
 };
 
 struct R R = {
   100, 200
 };
 
 void f(struct R r) {
   if (r.a.x != R.a.x || r.b.x != R.b.x)
     abort();
 }
 
 int main() {
   f(R);
   return 0;
 }
 
 4) The <struct.c> testcase won't fail if we add some garbage in struct R, 
 because the size of the object will be > 16 bytes, thus having MEMORY 
 class.
 
 HTH,
 Gwenole.