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? But even if it didn't
we'd still ICE on the original rtx as I found out. The zero-length
rtvec is originally created in expand_asm_stmt:
rtvec labelvec = rtvec_alloc (nlabels);
where nlabels is 0 but using NULL_RTVEC instead just means crashes everywhere.
So I'm afraid I don't have a better fix (except that I should have used
ASM_OPERANDS_LABEL_LENGTH).
> We do not have notation to create zero-length vectors in RTL source
> code either, btw.:
> case 'V':
> /* 'V' is an optional vector: if a closeparen follows,
> just store NULL for this element. */
> (optional vectors are at the end of an RTX), and if you write [] you
> will hit
> fatal_with_file_and_line ("vector must have at least one element");
Marek
