Re: rtl_verify_flow_info fix

[Jakub Jelinek <jakub at redhat dot com>]

On Mon, Sep 05, 2011 at 10:29:18AM +0200, Tom de Vries wrote:
> Hi Eric,
> 
> During testing the approved-for-commit middle-end patch for bug 43864 on ARM, I
> ran into a gcc.dg/torture/pr46068.c ICE.
> 
> An asm jump is not recognized as an unconditional jump, so its followed by a
> fall-through block rather than a barrier.
> ...
> (jump_insn 10 9 19 4 (asm_operands/v ("") ("") 0 []
>          []
>          [
>             (label_ref:SI 16)
>         ] pr46068.c:16) pr46068.c:6 -1
>      (nil)
>  -> 16)
> ...
> 
> ce3 then turns the asm jump into an asm return, still without a barrier after it:
> ...
> (jump_insn 10 9 19 4 (asm_operands/v ("") ("") 0 []
>          []
>          [
>             (return)
>         ] pr46068.c:16) pr46068.c:6 -1
>      (nil)
>  -> return)
> ...

I'd say the above transformation shouldn't be valid, asm goto is given some
possible labels it can jump to, but what will be emitted when the operand is
RETURN?  I think final.c does:
            else if (letter == 'l')
              output_asm_label (operands[opnum]);
here and when operands[opnum] isn't a label or deleted label, that function
will
  output_operand_lossage ("'%%l' operand isn't a label");
You don't get it only because this testcase uses empty inline asm string
and thus doesn't use any of the labels.

	Jakub