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Date: Tue, 8 Mar 2022 09:49:15 -0600
From: Segher Boessenkool <segher@kernel.crashing.org>
To: Marek Polacek <polacek@redhat.com>
Cc: Jakub Jelinek <jakub@redhat.com>, GCC Patches <gcc-patches@gcc.gnu.org>
Subject: Re: [PATCH] rtl: ICE with thread_local and inline asm  [PR104777]
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On Tue, Mar 08, 2022 at 10:25:45AM -0500, Marek Polacek wrote:
> On Tue, Mar 08, 2022 at 09:14:56AM -0600, Segher Boessenkool wrote:
> > On Tue, Mar 08, 2022 at 10:08:25AM -0500, Marek Polacek wrote:
> > > ...I don't see that.  In fact copy_rtx does the same thing as
> > > copy_insn:
> > > 
> > >        case 'V':
> > >          if (XVEC (orig, i) != NULL)
> > >            {
> > >              XVEC (copy, i) = rtvec_alloc (XVECLEN (orig, i));
> > > 
> > > which will copy a zero-length vector too, right?
> > 
> > It doesn't.  It copies NULL as NULL.  That is what that "if" is for.
> 
> But XVEC (orig, i) is not null, it just has XVECLEN 0.

So where did *that* come from?  This isn't correct RTL.

> > You can do similar in copy_insn_1?
> 
> You mean copy_rtx?  It already has the same XVEC (orig, i) != NULL check.

No, I mean do similar in copy_insn_1 as what copy_rtx already
(correctly) does.

> But like I said above, even if we didn't copy these XVECLEN 0 rtvecs,
> the crash would not go away.

An rtvec should never have length 0.  Look at gen_rtvec for another
example.

You can get rid of the crash, sure.  But it is a much better plan to try
and get rid of the actual problem!  (And then add some more checking to
make sure this doesn't happen in the future.)


Segher