When we instantiate char_type_node in tree.c:build_common_tree_nodes we very explicitly create a char_type_node that is signed or unsigned based on the value of -funsigned-char, but instead of make char_type_node point to signed_char_type_node or unsigned_char_type_node, we explicitly instantiate a different type.
This is causing trouble in lto1 because when we stream out gimple, assignments between char and unsigned char go through without a cast. However, the LTO front end has no knowledge of the C/C++ FE flags, so it creates a signed char_type_node. This causes a SEGV in PRE because the assignment between char and unsigned char confuses it. This is trivially fixable by making char_type_node be 'unsigned char', so that when we stream out the types for the variables the types are explicitly signed or unsigned, instead of taking its sign implicitly from an FE flag. @@ -7674,12 +7713,8 @@ build_common_tree_nodes (bool signed_cha unsigned_char_type_node = make_unsigned_type (CHAR_TYPE_SIZE); TYPE_STRING_FLAG (unsigned_char_type_node) = 1; - /* Define `char', which is like either `signed char' or `unsigned char' - but not the same as either. */ - char_type_node - = (signed_char - ? make_signed_type (CHAR_TYPE_SIZE) - : make_unsigned_type (CHAR_TYPE_SIZE)); + /* Define `char', which is like either `signed char' or `unsigned char'. */ + char_type_node = signed_char ? signed_char_type_node : unsigned_char_type_node; TYPE_STRING_FLAG (char_type_node) = 1; short_integer_type_node = make_signed_type (SHORT_TYPE_SIZE); However, this has other side effects in the FE, as we now can't build libstdc++ (a PCH failure). So, do we really need a third, distinct, char_type_node? Is there some language or FE rule that causes us to do this? The comment in build_common_tree_nodes is not very illuminating. I could fix this in a slower way by crawling through the whole callgraph and changing 'char' to 'unsigned char' everywhere once the whole compilation unit is in GIMPLE form, but I'd like to consider doing that only if it's really necessary. Thanks. Diego.
