> You rely on being able to see all FRAME accesses as component refs,
> thus nothing transforms them into just MEM[&FRAME, offset]. That's of
> course something that can be easily "broken" by means of doing
> some pointer arithmetic like (untested, but you get the idea)
>
> foo()
> {
> int c[32];
> int j;
> bar()
> {
> int *p = &c[4];
> p = p + 1;
> j = *p;
> }
> c[4] = 0;
> bar();
> return j;
> }
>
> this should get you j = MEM[<CHAIN>, 4]; in bar and thus a missing
> component-ref when inlining.
The patch compiles hundreds of thousands of lines of Ada everyday at AdaCore,
how could such a blatant hole have survived that?
> I dont' think it's easily possible to recover from this in your scheme,
> but it would be straight-forward for SRA (you basically look for the
> base variable FRAME and special-case that completely for
> replacement construction, also constraining accesses).
Well, it's implemented in the 30-line block of code under the comment:
+ /* Deal with remaining MEM_REFs, i.e. those for which the field reference
+ has been replaced with the offset. */
> Marking the FRAME VAR_DECL looks useful, maybe you can split that out
> of your patch?
Sure.
> As of doing it in SRA what I'd do there is special-case FRAME for both
> candidate consideration (so you get around the addressable issue)
> and replacement generation.
OK, but you need to be able to split the FRAME structure without necessarily
splitting its aggregate fields. Is that (easily) doable with current SRA?
> Maybe you can open an enhancement bugreport for this and link
> your patch / testcase to it?
Will do.
--
Eric Botcazou
