[Bug c/51840] asm goto enhancement request

[ktietz at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=51840

Kai Tietz <ktietz at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |NEW
   Last reconfirmed|                            |2014-06-18
                 CC|                            |ktietz at gcc dot gnu.org
     Ever confirmed|0                           |1

--- Comment #5 from Kai Tietz <ktietz at gcc dot gnu.org> ---
So original issue is caused by two issues.

For initial expand we produce the following rtl for the first code-switch:

(jump_insn 32 31 34 2 (parallel [
            (asm_operands/v ("jmp *%0") ("") 0 [
                    (mem/v/f/j:DI (plus:DI (mult:DI (reg:DI 136)
                                (const_int 8 [0x8]))
                            (reg/f:DI 135)) [0 vm_dispatch S8 A64])
                ]
                 [
                    (asm_input:DI ("m") t_asmgoto.c:65)
                ]
                 [
                    (label_ref:DI 36)
                    (label_ref:DI 56)
                    (label_ref:DI 114)
                    (label_ref:DI 120)
                ] t_asmgoto.c:65)
            (clobber (reg:QI 18 fpsr))
            (clobber (reg:QI 17 flags))
            (clobber (mem:BLK (scratch) [0  A8]))
        ]) t_asmgoto.c:65 -1
     (insn_list:REG_LABEL_TARGET 36 (insn_list:REG_LABEL_TARGET 56
(insn_list:REG_LABEL_TARGET 114 (nil))))
 -> 120)
(note 34 32 33 4 [bb 4] NOTE_INSN_BASIC_BLOCK)
(note/s 33 34 35 4 ("atop__a_dec") NOTE_INSN_DELETED_LABEL 2)
(barrier 35 33 36)
(code_label 36 35 37 5 8 "" [3 uses])
...

Of interest is here the '(note/s 33 34 35 4 ("atop__a_dec")
NOTE_INSN_DELETED_LABEL 2)'.  As long as code_label 36 (which is implementation
of "atop__a_dec" code) follows directly that note, we are fine.
That's true for -Os, -O0, and -O1.  For -O2 we exectute additional the
basic-block-reorder pass, and that moves label 36 away.  Nevertheless the
semi-deleted label-note remains and cause the wrong code-path.