Another bootstrap failure on vax: label referred to in addr_vec deleted when basic block is moved to the fallthru position after the addr_vec

["John David Anglin" <dave at hiauly1 dot hia dot nrc dot ca>]

After adding this patch
<http://gcc.gnu.org/ml/gcc-patches/2001-09/msg01155.html> to a build
on vax-dec-ultrix4.3, the build goes somewhat further but again trips
on an addr_diff_vec problem:

stage1/xgcc -Bstage1/ -B/usr/local/vax-dec-ultrix4.3/bin/ -c  -DIN_GCC    -g -O2 -W -Wall -Wwrite-strings -Wstrict-prototypes -Wmissing-prototypes -Wtraditional -pedantic -Wno-long-long  -DHAVE_CONFIG_H -DGENERATOR_FILE    -I. -I. -I../../gcc -I../../gcc/. -I../../gcc/config -I../../gcc/../include ../../gcc/rtl.c -o rtl.o
/usr/tmp//ccVcGZ6G.s: Assembler messages:
/usr/tmp//ccVcGZ6G.s:2801: Error: subtraction of two symbols in different sections `L112' {unknown section} - `L124' {text section} at file address 7805
/usr/tmp//ccVcGZ6G.s:2801: Error: subtraction of two symbols in different sections `L112' {unknown section} - `L124' {text section} at file address 7803
...

The label L112 is deleted in the bbro pass:

;; Function rtx_equal_p

try_optimize_cfg iteration 1
...
Forwarding edge 5->6 to 14 failed.
...
Reordering block 14 after 6
...
Basic block 14: first insn 138, last 566, loop_depth 0, count 0, freq 424.
Predecessors:  6 [100.0%]  5 [16.7%] 
Successors:  15 [68.5%]  (fallthru) 34 [31.5%] 
Registers live at start: 0 [r0] 6 [r6] 7 [r7] 9 [r9] 10 [r10] 11 [r11] 12 [ap] 1
3 [fp] 14 [sp]
Registers live at end: 6 [r6] 7 [r7] 8 [r8] 9 [r9] 10 [r10] 11 [r11] 12 [ap] 13 
[fp] 14 [sp]
...
Reordered sequence:
...
 7 bb 6 freq 212
 8 bb 14 freq 424
...
try_optimize_cfg iteration 1

Forwarding edge 6->7 to 8 failed.
Removing jump 136.
Deleting fallthru block 7.
Deleted label in block 7.

Jump 136 was to code_label 138 which in the previous pass was the first insn
in bb 14.  The label deleted was label 138.  After bbro we have,

;; Start of basic block 6, registers live: 0 [r0] 6 [r6] 7 [r7] 8 [r8] 9 [r9] 10 [r10] 11 [r11] 12 [ap] 13 [fp] 14 [sp]
(note 504 712 64 [bb 6] NOTE_INSN_BASIC_BLOCK)

(note 64 504 133 ("../../gcc/rtl.c") 589)

(jump_insn 133 64 134 (set (pc)
        (if_then_else (leu (minus:SI (reg/v:SI 0 r0 [26])
                    (const_int 52 [0x34]))
                (const_int 13 [0xd]))
            (plus:SI (sign_extend:SI (mem:HI (plus:SI (pc)
                            (mult:SI (minus:SI (reg/v:SI 0 r0 [26])
                                    (const_int 52 [0x34]))
                                (const_int 2 [0x2]))) 0))
                (label_ref:SI 134))
            (pc))) 142 {casesi1} (nil)
    (nil))
;; End of basic block 6, registers live:
 0 [r0] 6 [r6] 7 [r7] 8 [r8] 9 [r9] 10 [r10] 11 [r11] 12 [ap] 13 [fp] 14 [sp]

;; Insn is not within a basic block
(code_label 134 133 135 124 "" "" [1 uses])

;; Insn is not within a basic block
(jump_insn 135 134 122 (addr_diff_vec:HI (label_ref:SI 134)
        [ 
            (label_ref:SI 739)
            (label_ref:SI 739)
            (label_ref:SI 138)
            (label_ref:SI 138)
            (label_ref:SI 138)
            (label_ref:SI 138)
            (label_ref:SI 67)
            (label_ref:SI 739)
            (label_ref:SI 138)
            (label_ref:SI 138)
            (label_ref:SI 138)
            (label_ref:SI 138)
            (label_ref:SI 105)
            (label_ref:SI 105)
        ] 
        (const_int 0 [0x0])
        (const_int 0 [0x0])) -1 (nil)
    (nil))

(note 122 135 704 ("../../gcc/rtl.c") 609)

(note 704 122 339 ("../../gcc/rtl.c") 673)

(note 339 704 700 ("../../gcc/rtl.c") 643)

(note 700 339 129 ("../../gcc/rtl.c") 673)

(note 129 700 522 ("../../gcc/rtl.c") 612)

;; Start of basic block 7, registers live: 0 [r0] 6 [r6] 7 [r7] 9 [r9] 10 [r10] 11 [r11] 12 [ap] 13 [fp] 14 [sp]
(note 522 129 139 [bb 7] NOTE_INSN_BASIC_BLOCK)

(note 139 522 141 ("../../gcc/rtl.c") 618)

(note 141 139 142 NOTE_INSN_DELETED)

(note 142 141 143 NOTE_INSN_DELETED)

(insn 143 142 144 (set (reg:SI 0 r0 [52])
        (ashift:SI (reg/v:SI 0 r0 [26])
            (const_int 2 [0x2]))) 92 {ashlsi3} (nil)
    (nil))

Clearly, the label shouldn't have been deleted because there were still
references to it in the addr_diff_vec.

Dave
-- 
J. David Anglin                                  dave.anglin@nrc.ca
National Research Council of Canada              (613) 990-0752 (FAX: 952-6605)