Re: [PATCH] rtl: ICE with thread_local and inline asm [PR104777]

[Marek Polacek <polacek@redhat.com>]

On Tue, Mar 08, 2022 at 09:14:56AM -0600, Segher Boessenkool wrote:
> Hi!
> 
> On Tue, Mar 08, 2022 at 10:08:25AM -0500, Marek Polacek wrote:
> > On Mon, Mar 07, 2022 at 07:19:09PM -0600, Segher Boessenkool wrote:
> > > On Mon, Mar 07, 2022 at 07:03:17PM -0500, Marek Polacek via Gcc-patches wrote:
> > > > In r270550, Jakub fixed classify_insn to handle asm goto: if the asm can
> > > > jump to a label, the insn should be a JUMP_INSN.
> > > > 
> > > > However, as the following testcase shows, non-null ASM_OPERANDS_LABEL_VEC
> > > > doesn't guarantee that the rtx has any actual labels it can branch to.
> > > 
> > > But it should.
> > 
> > Ok, that would make sense.  However...
> >  
> > > > Here, the rtvec has 0 elements because of the __thread variable: we perform
> > > > ix86_rewrite_tls_address which calls copy_isns and that allocates the rtvec:
> > > > 
> > > >     XVEC (copy, i) = rtvec_alloc (XVECLEN (orig, i));
> > > 
> > > So fix *that* instead?  Everywhere else does not use length zero RTL
> > > vectors.  copy_rtx makes sure to do the right thing here, for example.
> > 
> > ...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.

> You can do similar in copy_insn_1?

You mean copy_rtx?  It already has the same XVEC (orig, i) != NULL check.

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

Marek