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As discussed in https://sourceware.org/bugzilla/show_bug.cgi?id=26987 , for very large bounds (which don't fit into HOST_WIDE_INT) GCC emits invalid DWARF. In DWARF2, DW_AT_{lower,upper}_bound were constant reference class. In DWARF3 they are block constant reference and the Static and Dynamic Properties of Types chapter says: "For a block, the value is interpreted as a DWARF expression; evaluation of the expression yields the value of the attribute." In DWARF4/5 they are constant exprloc reference class. Now, for add_AT_wide we use DW_FORM_data16 (valid in constant class) when -gdwarf-5, but otherwise just use DW_FORM_block1, which is not constant class, but block. For DWARF3 this means emitting clearly invalid DWARF, because the DW_FORM_block1 should contain a DWARF expression, not random bytes containing the constant directly. For DWARF2/DWARF4/5 it could be considered a GNU extension, but a very badly designed one when it means something different in DWARF3. The following patch uses add_AT_wide only if we know we'll be using DW_FORM_data16, and otherwise wastes 2 extra bytes and emits in there DW_OP_implicit_value <size> before the constant. 2020-12-03 Jakub Jelinek <jakub@redhat.com> * dwarf2out.c (add_scalar_info): Only use add_AT_wide for 128-bit constants and only in dwarf-5 or later, where DW_FORM_data16 is available. Otherwise use DW_FORM_block*/DW_FORM_exprloc with DW_OP_implicit_value to describe the constant.
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