Re: RFA: new execute testcase (Was: Re: bootstrap failed during 'make check')

[Joern RENNECKE <joern dot rennecke at st dot com>]

Joern Rennecke wrote:

> Andrew Haley wrote:
>
> >  > > So it seems I have to abandom the system compiler for doing 
> > bootstraps.
> >
> > Can you make a simple testcase for this?
> >
> > Andrew.
> >  
> Attached.
> This fails at -O0..-O2 for gcc 3.2.2 and gcc 3.2.3 on 
> i686-pc-linux-gnu.   For gcc 3.4.3,
> it still fails at -O1.
> 4.2.0 appears to be OK, although it might be this bug only hidden by 
> the tree optimizers
> optimizing the test case into something that doesn't trigger the bug.

I've identified this code in 3.4.0 c-typeck.c:common_type as the culprit:

   case POINTER_TYPE:
     /* For two pointers, do this recursively on the target type,
        and combine the qualifiers of the two types' targets.  */
     /* This code was turned off; I don't know why.
        But ANSI C specifies doing this with the qualifiers.
        So I turned it on again.  */
     {
       tree pointed_to_1 = TREE_TYPE (t1);
       tree pointed_to_2 = TREE_TYPE (t2);
       tree target = common_type (TYPE_MAIN_VARIANT (pointed_to_1),
                                  TYPE_MAIN_VARIANT (pointed_to_2));
       t1 = build_pointer_type (c_build_qualified_type
                                (target,
                                 TYPE_QUALS (pointed_to_1) |
                                 TYPE_QUALS (pointed_to_2)));
       return build_type_attribute_variant (t1, attributes);
     }


(gdb) s
325                                       TYPE_QUALS (pointed_to_2)));
(gdb)
c_build_qualified_type (type=0xb5988804, type_quals=1)
   at ../../srcw/gcc/c-common.c:2793
2793      if (type == error_mark_node)
(gdb) call debug_tree(type)
<function_type 0xb5988804
   type <integer_type 0xb599c4a4 int SI
       size <integer_cst 0xb599a208 constant 32>
       unit size <integer_cst 0xb599a294 constant 4>
       align 32 symtab 0 alias set -1 precision 32 min <integer_cst 
0xb599a26c -2147483648> max <integer_cst 0xb599a280 2147483647>
       pointer_to_this <pointer_type 0xb59a3ca8>>
   DI
   size <integer_cst 0xb599a5a0 type <integer_type 0xb59a3654 
bit_size_type> constant 64>
   unit size <integer_cst 0xb599a794 type <integer_type 0xb59a35e8 
unsigned int> constant 8>
   align 64 symtab 0 alias set -1
   arg-types <tree_list 0xb598485c value <integer_type 0xb599c4a4 int>
       chain <tree_list 0xb598467c value <void_type 0xb59a3870 void>>>
   pointer_to_this <pointer_type 0xb58f6360>>


One of the function pointers is TREE_READONLY, and we make the result 
TREE_READONLY.
This is wrong, since TREE_READONLY for functions means that they have no 
side effects.

There is similar code in mainline, but it is not reached with the testcase.