Hello, I want to check the alias for the argument of 'free' operation, and I use gimple, gimple_stmt_iterator and gimple_call_arg to get the argument. > gimple *stmt = gsi_stmt (gsi); > stmt = gsi_stmt (gsi); > tree arg = gimple_call_arg (stmt, 0); Then I put this argument into refs_may_alias_p (tree ref1, tree ref2), and get the wrong message: internal compiler error: Segmentation fault 0x11c11a8 crash_signal /home/cc/gcc/src/gcc/toplev.c:337 0x1233d7c get_ref_base_and_extent(tree_node*, long*, long*, long*, bool*) /home/cc/gcc/src/gcc/tree-dfa.c:393 0x131be04 ao_ref_base(ao_ref*) /home/cc/gcc/src/gcc/tree-ssa-alias.c:641 0x131f3c6 refs_may_alias_p_1(ao_ref*, ao_ref*, bool) /home/cc/gcc/src/gcc/tree-ssa-alias.c:1417 0x1c7ec35 search_table_alias(pointer_table*, tree_node*, bool) ... How can I resolve this problem?