Re: [SFN+LVU+IEPM v4 7/9] [LVU] Introduce location views

[Alexandre Oliva <aoliva@redhat.com>]

On Feb 12, 2018, Andreas Schwab <schwab@linux-m68k.org> wrote:

> On Feb 12 2018, Alexandre Oliva <aoliva@redhat.com> wrote:
>> On Feb 11, 2018, Andreas Schwab <schwab@linux-m68k.org> wrote:
>> 
>>> On Feb 09 2018, Alexandre Oliva <aoliva@redhat.com> wrote:
>> 
>>>> +  if (list_head->vl_symbol && dwarf2out_locviews_in_attribute ())
>>>> +    {
>>>> +      ASM_OUTPUT_LABEL (asm_out_file, list_head->vl_symbol);
>> 
>>> That needs to use ASM_OUTPUT_DEBUG_LABEL.
>> 
>> Note this is always output in the .debug_loclist section, not in code
>> sections, so I don't get why it should matter.  Care to clarify, please?

> Perhaps I'm misunderstanding it, but I see .LM labels emitted in the
> middle of code bundles, which breaks them apart.

That line would only output .LVUS symbols.

The only line that outputs LM symbols is 

      targetm.asm_out.internal_label (asm_out_file, LINE_CODE_LABEL, label_num);

It's not ASM_OUTPUT_DEBUG_LABEL, but it was there before.

What may have changed is that, using an assembler without .loc view
support, GCC would switch to internal line number tables, which requires
it to emit LM labels at points in which it would otherwise have output
.loc directives.

The patch I posted last night should work around this problem, in that
it will disable LVU by default if the assembler doesn't support .loc
views, and then you won't get this error any more, unless you explicitly
ask for location views.  If you can give it a try on ia64-linux-gnu,
that would be appreciated.  You might also want to give it a spin with
GNU as 2.30: the assembler view mismatch errors you'd get before that
patch should now be gone too, because we no longer trust min insn
lengths to compute view reset points internally.

If you force that on, with -ginternal-reset-location-views, you'll get
errors in at meast some of the cases in which the assembler finds the
GCC-computed insn length mismatches the assembler's, and then you can
fix the lengths in GCC, so that eventually we can mark this port as one
whose lengths can be used to this end.  See also the reset_location_view
target hook introduced in the same patch.

https://gcc.gnu.org/ml/gcc-patches/2018-02/msg00624.html

-- 
Alexandre Oliva, freedom fighter    http://FSFLA.org/~lxoliva/
You must be the change you wish to see in the world. -- Gandhi
Be Free! -- http://FSFLA.org/   FSF Latin America board member
Free Software Evangelist|Red Hat Brasil GNU Toolchain Engineer