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From: "vries at gcc dot gnu.org" <gcc-bugzilla@gcc.gnu.org>
To: gcc-bugs@gcc.gnu.org
Subject: [Bug debug/66714] ICE in loc_list_from_tree with -g
Date: Mon, 06 Jul 2015 07:44:00 -0000
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X-Bugzilla-Keywords: ice-on-valid-code, openacc, openmp
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https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66714

--- Comment #14 from vries at gcc dot gnu.org ---
1.

In lower_omp_target for function fn3, we handle clause 'map(alloc:bD.1833
[pointer assign, bias: 0])' with variable-sized bD.1833.
The var bD.1833 has value-expr *b.0D.1844. For b.0D.1844, we search the
associated decl with lookup_decl, and find b.0D.1854. We set the value-expr for
b.0D.1854 to '*.omp_data_iD.1851->b.0D.1870'.

Associated code:
...
        if (DECL_SIZE (var)
            && TREE_CODE (DECL_SIZE (var)) != INTEGER_CST)
          {
            tree var2 = DECL_VALUE_EXPR (var);
            gcc_assert (TREE_CODE (var2) == INDIRECT_REF);
            var2 = TREE_OPERAND (var2, 0);
            gcc_assert (DECL_P (var2));
            var = var2;
          }

        if (!maybe_lookup_field (var, ctx))
          continue;

        if (offloaded)
          {
            x = build_receiver_ref (var, true, ctx);
            tree new_var = lookup_decl (var, ctx);
            if (OMP_CLAUSE_MAP_KIND (c) == GOMP_MAP_POINTER
                && !OMP_CLAUSE_MAP_ZERO_BIAS_ARRAY_SECTION (c)
                && TREE_CODE (TREE_TYPE (var)) == ARRAY_TYPE)
              x = build_simple_mem_ref (x);
            SET_DECL_VALUE_EXPR (new_var, x);
            DECL_HAS_VALUE_EXPR_P (new_var) = 1;
          }
...


2.

In replace_block_vars_by_duplicates, called from move_sese_region_to_fn, called
from expand_omp_target: 
- we copy the value-expr *b.0D.1854 from bD.1855 to bD.1916, and
- we copy the value-expr *.omp_data_iD.1851->b.0D.1870 from b.0D.1854 to
  b.0D.1917

Associated code:
...
      t = *tp;
      if (TREE_CODE (t) != VAR_DECL && TREE_CODE (t) != CONST_DECL)
        continue;
      replace_by_duplicate_decl (&t, vars_map, to_context);
      if (t != *tp)
        {
          if (TREE_CODE (*tp) == VAR_DECL && DECL_HAS_VALUE_EXPR_P (*tp))
            {
              SET_DECL_VALUE_EXPR (t, DECL_VALUE_EXPR (*tp));
              DECL_HAS_VALUE_EXPR_P (t) = 1;
            }
          DECL_CHAIN (t) = DECL_CHAIN (*tp);
          *tp = t;
        }
...


3.

In expand_omp_target for function fn3._omp_fn.0 we remove b.0D.1854 and bD.1855
from the local_decls, because the DECL_CONTEXT is fn3, rather than
fn3._omp_fn.0.

Associated code:
...
      /* Remove non-local VAR_DECLs from child_cfun->local_decls list.  */
      num = vec_safe_length (child_cfun->local_decls);
      for (srcidx = 0, dstidx = 0; srcidx < num; srcidx++)
        {
          t = (*child_cfun->local_decls)[srcidx];
          if (DECL_CONTEXT (t) == cfun->decl)
            continue;
          if (srcidx != dstidx)
            (*child_cfun->local_decls)[dstidx] = t;
          dstidx++;
        }
...


4.

Now that b.0D.1854 and bD.1855 are no longer declared in a function, they're no
longer live, and during garbage collection, we remove:
- cache entry (b.0D.1854, *.omp_data_iD.1851->b.0D.1870), and
- cache entry (bD.1855, *b.0D.1854)
from hash table value_expr_for_decl.


5.

During dwarf processing of fn3._omp_fn.0, we process a scope with decl bD.1916,
which has value-expr *b.0D.1854. When processing b.0D.1854 in
loc_list_from_tree, we run into the sigsegv because the value-expr for
b.0D.1854 is NULL (since the entry has been removed from the hash table).

Associated code:
...
      /* FALLTHRU */

    case PARM_DECL:
    case RESULT_DECL:
      if (DECL_HAS_VALUE_EXPR_P (loc))
        return loc_list_from_tree (DECL_VALUE_EXPR (loc),
                                   want_address, context);
...