[Bug regression/21897] New: Segementation fault in fold_ternary

[e9925248 at stud4 dot tuwien dot ac dot at]

Example code:
#define vector64 __attribute__((vector_size(8)))

main(){

 vector64 short  c;
vector64 short a = {1, -1};
vector64 short b = {2, -2};
c = -a + b*b*(-1LL);

 printf("result is %llx\n", (long long)c);
}

If it is compiled with -O3 a Segmentation fault happens.
GNU C version 4.1.0 20050603 (experimental) (i686-pc-linux-gnu)
        compiled by GNU C version 4.1.0 20050302 (experimental).
GGC heuristics: --param ggc-min-expand=0 --param ggc-min-heapsize=0

gcc (GCC) 4.1.0 20050302 (experimental)
and later (at least till 20050501) can compile this file with -O3.

The fold of this expression causes the segmentation fault:
 <bit_field_ref 0xb7f56118
    type <integer_type 0xb7ef6438 short int public HI
        size <integer_cst 0xb7eee318 constant invariant 16>
        unit size <integer_cst 0xb7eee330 constant invariant 2>
        align 16 symtab 0 alias set -1 precision 16 min <integer_cst 0xb7eee2b8
-32768> max <integer_cst 0xb7eee2e8 32767>
        pointer_to_this <pointer_type 0xb7f069b4>>

    arg 0 <vector_cst 0xb7f1d018
        type <vector_type 0xb7f06b64 type <integer_type 0xb7ef6438 short int>
            sizes-gimplified DI
            size <integer_cst 0xb7eee540 constant invariant 64>
            unit size <integer_cst 0xb7eee558 constant invariant 8>
            align 64 symtab 0 alias set -1 nunits 4>
        constant invariant
        elt0:  <integer_cst 0xb7f07bb8 constant invariant 1>
        elt1:  <integer_cst 0xb7f0a510 constant invariant -1>> arg 1
<integer_cst 0xb7eee318 16>
    arg 2 <integer_cst 0xb7eee408 type <integer_type 0xb7ef6288 bit_size_type>
constant invariant 32>>

The problem is, that fold_ternary wants to access the third element of the
constant vector, which is not present.

The cause of this is, that fold_ternary fails, if it an element of the vector is
not initialized.

The change seem to be done by 
2005-06-01  Jakub Jelinek  <jakub@redhat.com>
* fold-const.c (fold_ternary): Optimize BIT_FIELD_REF of VECTOR_CST.

Replacing (in fold_ternary case BIT_FIELD_REF:)
        while (idx-- > 0)
                elements = TREE_CHAIN (elements);
              return TREE_VALUE (elements);
with
        while (idx-- > 0 && elements)
                elements = TREE_CHAIN (elements);
          if(elements)
              return TREE_VALUE (elements);
          else return build_int_cst_type(type,0);

should solve the problem.

-- 
           Summary: Segementation fault in fold_ternary
           Product: gcc
           Version: 4.1.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: regression
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: e9925248 at stud4 dot tuwien dot ac dot at
                CC: gcc-bugs at gcc dot gnu dot org,jakub at redhat dot com
 GCC build triplet: i686-pc-linux-gnu
  GCC host triplet: i686-pc-linux-gnu
GCC target triplet: i686-pc-linux-gnu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=21897