A problem with field decl offsets in newly minted types

[Gary Oblock <gary@amperecomputing.com>]

I'm having some grief with creating/using some modified types.

I problem occurs in tree-ssa-sccvn.c when some code tries
to take a DECL_FIELD_OFFSET and unfortuenately gets a null
that causes a crash.

So, I traced this back the to types I created. Note, the method I used
has seemed to be fairly robust (some other engineers in our China
group even successfully copied it for thier own optimization.)
However, the DECL_FIELD_OFFSET offset is definitely null for
the fields which I created in the new versions of the types.

Here is what I'm doing.

    tree type_prime = lang_hooks.types.make_type (RECORD_TYPE);

    const char *base_type_name =
      identifier_to_locale ( IDENTIFIER_POINTER ( TYPE_NAME ( type)));
    size_t len = strlen ( MY_PREFIX) + strlen ( base_type_name);
    char *rec_name = ( char*)alloca ( len + 1);
    strcpy ( rec_name, MY_PREFIX);
    strcat ( rec_name, base_type_name);

    TYPE_NAME ( reorg_type_prime) = get_identifier ( rec_name);

    tree field;
    tree new_fields = NULL;
    for ( field = TYPE_FIELDS ( type); field; field = DECL_CHAIN ( field))
      {
        // Probably useful in creating the new field type.
        tree old_fld_type = TREE_TYPE ( field);

        // Whatever you want the new field type to be
        tree new_fld_type = ...;
        tree new_decl =
          build_decl ( DECL_SOURCE_LOCATION (field),
                              FIELD_DECL, DECL_NAME (field), new_fld_type);
         DECL_CONTEXT ( new_decl) = type_prime;
         layout_decl ( new_decl, 0);
         DECL_CHAIN ( new_decl) = new_fields;
         new_fields = new_decl;
      }

    TYPE_FIELDS ( type_prime) = nreverse ( new_fields);
    layout_type ( type_prime);

Note, when I change any declaration to have a modified type
I run relayout_decl on them.

If somebody could please tell what bit I'm missing or what I'm doing
wrong I'd really appreciate it. Looking at the code in layout_type,
it should be setting the decl field offsets with place_field and I
don't have a clue what's going on.

Thanks,

Gary


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