Hi, today I have encountered an unpleasant problem with the function get_ref_base_and_extent() when it claimed a known and constant offset for the expression insn_4(D)->u.fld[arg.82_3].rt_rtvec. (arg being a default_def parameter of the function, insn is an rtx). Moreover, it also returned constant size and max_size, all three equal to 64 (bits).
This is certainly wrong (I believe the function got confused by unions) but after looking at the function and what it did in debugger, I grew unsure what the expected behavior is. The two alternatives I consider possibly correct are returned offset equal to -1 or, alternatively, offset equal to the offset of the array (+ offset of rt_rtvec which is zero) and max_size equal either to the size of the array or -1 if it is unknown. At the moment, the function never returns offset equal to -1, the comment above it does not even mention such possibility and, from the limited research I did, its callers do not expect and check for it. However, at the same time, the special handling of non-constants in array indices after the label "done" does not trigger in this particular case (here I suspect the unions come to play because it is the last part of the conjunction that evaluates to false). Which (or what else) is the correct semantics of the function? Both make sense to me (I would prefer the former but I suspect other users rely on the latter). What would be the correct fix, when a union field is itself a record ending with a variable-length array? How much would I pessimize things if I just returned -1 max_size if both a non-constant index and a union was encountered? Or did I miss something else? Thanks a lot in advance, Martin
