[Bug lto/43455] ICE in fold_convert_loc, at fold-const.c:2670 with -O2 -flto

["rguenth at gcc dot gnu dot org" <gcc-bugzilla at gcc dot gnu dot org>]

------- Comment #3 from rguenth at gcc dot gnu dot org  2010-03-22 10:30 -------
I get on x86_64-linux

> ./xgcc -B. -flto t1.c t2.c -O2
In file included from t2.c:2:0,
                 from t1.c:2,
                 from :0:
t1.c: In function 'main':
t1.c:5:22: internal compiler error: in fold_convert_loc, at fold-const.c:2792
Please submit a full bug report,
with preprocessed source if appropriate.
See <http://gcc.gnu.org/bugs.html> for instructions.
lto-wrapper: ././xgcc returned 1 exit status
collect2: lto-wrapper returned 1 exit status

same with the less reduced testcase on x86_64 and i?86 linux.

Thanks for the report.


This is because we do not merge

  struct bar {int x;};

and

  typedef struct{int x;} bar;

but we expect to be able to convert them into each other during inlining:

#2  0x0000000000c120ac in declare_return_variable (id=0x7fffffffd9d0, 
    return_slot=0x0, modify_dest=0x7ffff5af03c0)
    at /space/rguenther/src/svn/trunk/gcc/tree-inline.c:2690
2690        use = fold_convert (caller_type, var);
(gdb) l
2685
2686      /* Build the use expr.  If the return type of the function was
2687         promoted, convert it back to the expected type.  */
2688      use = var;
2689      if (!useless_type_conversion_p (caller_type, TREE_TYPE (var)))
2690        use = fold_convert (caller_type, var);


This is really invalid C as bar is re-declared in an incompatible way
(which you'd see if you combine both TUs).

Now, we shouldn't ICE here anyway and LTO should be forgiving to this
kind of errors.

The following fixes the symptoms.

Index: gcc/tree-inline.c
===================================================================
--- gcc/tree-inline.c   (revision 157619)
+++ gcc/tree-inline.c   (working copy)
@@ -2687,7 +2687,12 @@ declare_return_variable (copy_body_data
      promoted, convert it back to the expected type.  */
   use = var;
   if (!useless_type_conversion_p (caller_type, TREE_TYPE (var)))
-    use = fold_convert (caller_type, var);
+    {
+      if (fold_convertible_p (caller_type, var))
+       use = fold_convert (caller_type, var);
+      else
+       use = fold_build1 (VIEW_CONVERT_EXPR, caller_type, var);
+    }

   STRIP_USELESS_TYPE_CONVERSION (use);


-- 

rguenth at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2010-03-22 10:30:26
               date|                            |
            Summary|Compiler hang with -O2 -flto|ICE in fold_convert_loc, at
                   |                            |fold-const.c:2670 with -O2 -
                   |                            |flto


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=43455