Dwarf says (Section 188.8.131.52. of DWARF v5) that these operations should
push "generic" (pointer-sized) values. This was not the case for
DW_OP_const operations (which were pushing values based on the size of
arguments), nor DW_OP_litN (which were always pushing 64-bit values).
The practical effect of this that were were unable to display the values
of variables if the size of the DW_OP_const opcode was smaller than the
value of the variable it was describing. This would happen because we
would store this (small) result into a buffer and then would not be able
to read sufficient data out of it (in Value::GetValueAsData). Gcc emits
debug info like this.
Other (more subtle) effects are also possible.
The same fix should be applied to DW_OP_const[us] (leb128 versions), but
I'm not doing that right now, because that would cause us to display
wrong (truncated) values of variables on 32-bit targets (pr48087).