Richard Henderson wrote: > Try > > cst_uchar_ptr_node > = build_pointer_type_for_mode (cst_uchar_node, ptr_mode, true); > > which is apparently in use by the Ada front end, but only if a > certain pragma is given. Dunno how reliably that's likely to work.
We are seeing regressions in our local testsuite on cases exercising that pragma. Passing 'true' as CAN_ALIAS_ALL sets TYPE_REF_CAN_ALIAS_ALL (t), but this apparently has no influence on what tree-ssa-alias computes. Out of a preliminary look into this code (new to me), a possible place to address that appears to be 'get_tmt_for', which presumably should assign a zero alias set to tags for pointer types with that bit set. The current code doesn't do that: tree tag_type = TREE_TYPE (TREE_TYPE (ptr)); HOST_WIDE_INT tag_set = get_alias_set (tag_type); I'd be happy to work-on and submit a patch to deal with this the proper way. I'd welcome hints or directions on what the proper way should be, as I don't yet have a global view of the complete alias analysis circuitry. The 'tag alias set should be zero if ...' idea above seems logical to me. I still may well not yet see a number of other options.
