[Bug target/28574] [4.2 regression] switch statement points to unreferenced label at -O2

[steven at gcc dot gnu dot org]

------- Comment #8 from steven at gcc dot gnu dot org  2006-08-02 21:10 -------
Happens when we are in find_if_case_1, where we call:

  delete_basic_block (then_bb);

The basic block we try to remove is this one:

;; basic block 5, loop depth 1, count 0
;; prev block 9, next block 6
;; pred:
;; succ:       6 [100.0%]
;; Registers live at start:  12 [r12] 32 [r34] 33 [r35] 34 [r36] 35 [r37] 36
[r38] 37 [r39] 38 [r40] 112 [r32] 113 [r33] 272 [p16] 273 [p17]
(note 129 214 47 5 [bb 5] NOTE_INSN_BASIC_BLOCK)
(jump_insn 47 129 48 5 (parallel [
            (set (pc)
                (reg:DI 326 b6))
            (use (label_ref 48))
        ]) 331 {*tablejump_internal} (nil)
    (expr_list:REG_DEAD (reg:DI 326 b6)
        (nil)))
;; Registers live at end:  12 [r12] 32 [r34] 33 [r35] 34 [r36] 35 [r37] 36
[r38] 37 [r39] 38 [r40] 112 [r32] 113 [r33] 272 [p16] 273 [p17]
$72 = void


But the jump table follows right after this block:
;; Start of basic block 5, registers live: 12 [r12] 32 [r34] 33 [r35] 34 [r36]
35 [r37] 36 [r38] 37 [r39] 38 [r40] 112 [r32] 113 [r33] 272 [p16] 273 [p17]
(note 129 214 47 5 [bb 5] NOTE_INSN_BASIC_BLOCK)

(jump_insn 47 129 48 5 (parallel [
            (set (pc)
                (reg:DI 326 b6))
            (use (label_ref 48))
        ]) 331 {*tablejump_internal} (nil)
    (expr_list:REG_DEAD (reg:DI 326 b6)
        (nil)))
;; End of basic block 5, registers live:
 12 [r12] 32 [r34] 33 [r35] 34 [r36] 35 [r37] 36 [r38] 37 [r39] 38 [r40] 112
[r32] 113 [r33] 272 [p16] 273 [p17]

;; Insn is not within a basic block
(code_label 48 47 49 11 "" [3 uses])

;; Insn is not within a basic block
(jump_insn 49 48 50 (addr_diff_vec:DI (label_ref:DI 48)
         [
            (label_ref:DI 103)
            (label_ref:DI 103)
            (label_ref:DI 103)
            (label_ref:DI 103)
            (label_ref:DI 103)
        ]
        (const_int 0 [0x0])
        (const_int 0 [0x0])) -1 (nil)
    (nil))

(barrier 50 49 103)


And rtl_delete_block (the cfgrtl hook for delete_basic_block) says:

  /* Include any jump table following the basic block.  */
  end = BB_END (b);
  if (tablejump_p (end, NULL, &tmp))
    end = tmp;

So there we lose.

Part of the problem is (should I say now "as always"?) missing REG_LABEL notes:

(insn 185 35 186 3 (set (reg/f:DI 14 r14 [386])
        (plus:DI (high:DI (label_ref:DI 48))
            (reg:DI 1 r1))) 76 {*load_symptr_high} (nil)
    (nil))

But even with a REG_LABEL note, this label is going to disappear AFAICT because 
can_delete_label_p will return true for it.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=28574

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