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Re: [PATCH] PR middle-end/19774
Ian Lance Taylor wrote:
> Josh Conner <firstname.lastname@example.org> writes:
>> SJLJ exception handling is incompatible with alloca (and hence,
>> variable-length arrays). A function which calls alloca and then catches
>> an exception may discover upon catching that the alloca'd memory has
>> been corrupted.
> As Steven says, insn notes are considered to be declasse. And I'm not
> crazy about new register notes either.
> And I don't understand how
> your solution will work for C99 dynamically sized arrays.
It works because variable-length arrays are created using
builtin_alloca. It solved my original test case, which was a VLA in C++
code -- am I missing something obvious?
> Look at the code for SETJMP_VIA_SAVE_AREA in
> allocate_dynamic_stack_space. That shows how you can adjust the
> alloca request to avoid space on the stack frame. I think you can add
> something like that in the USING_SJLJ_EXCEPTIONS case, for cases where
> you will need to catch an exception. If you do that it should work
> for all cases which can call allocate_dynamic_stack_space.
I can look into this some more -- I'm not sure that I have enough
information in allocate_dynamic_stack_space to make this decision.
> This is a more complex solution. But I'm pretty sure your solution
> will not work reliably over time, because there is really nothing to
> tie the insn note to the stack allocation. It only works today
> because exception handling is done shortly after expansion.
That makes sense. I'll see what other alternatives I can come up with.
Thanks for the quick review -