https://gcc.gnu.org/bugzilla/show_bug.cgi?id=60874
--- Comment #8 from Uroš Bizjak <ubizjak at gmail dot com> ---
After lots of debugging...
The problem is with the label that is passed as an argument to
__go_set_defer_retaddr. In function main.$thunk0, in _.179r.cse1 dump, we have:
...
(insn 7 3 8 2 (set (reg:DI 84)
(high:DI (label_ref:DI 47))) rr.go:57 236 {*movdi}
(insn_list:REG_LABEL_OPERAND 47 (nil)))
(insn 8 7 9 2 (set (reg:DI 83)
(lo_sum:DI (reg:DI 84)
(label_ref:DI 47))) rr.go:57 230 {*movdi_er_low_l}
(insn_list:REG_LABEL_OPERAND 47 (expr_list:REG_EQUAL (label_ref:DI 47)
(nil))))
(insn 9 8 10 2 (set (reg:DI 16 $16)
(reg:DI 83)) rr.go:57 236 {*movdi}
(nil))
(call_insn 10 9 11 2 (parallel [
(set (reg:DI 0 $0)
(call (mem:DI (symbol_ref:DI ("__go_set_defer_retaddr") [flags
0x41] <function_decl 0x2000066a900 __go_set_defer_retaddr>) [0
__go_set_defer_retaddr S8 A64])
(const_int 0 [0])))
(use (reg:DI 29 $29))
(clobber (reg:DI 26 $26))
]) rr.go:57 357 {*call_value_osf_1_er}
(expr_list:REG_CALL_DECL (symbol_ref:DI ("__go_set_defer_retaddr") [flags
0x41] <function_decl 0x2000066a900 __go_set_defer_retaddr>)
(nil))
(expr_list:DI (use (reg:DI 16 $16))
(nil)))
...
(call_insn 46 45 47 5 (parallel [
(call (mem:DI (reg/f:DI 80 [ D.1014 ]) [0 *_42 S8 A64])
(const_int 4048 [0xfd0]))
(use (reg:DI 29 $29))
(clobber (reg:DI 26 $26))
]) rr.go:57 210 {*call_osf_1_er}
(expr_list:REG_DEAD (reg/f:DI 80 [ D.1014 ])
(expr_list:REG_DEAD (reg:DI 21 $21)
(expr_list:REG_DEAD (reg:DI 20 $20)
(expr_list:REG_DEAD (reg:DI 19 $19)
(expr_list:REG_DEAD (reg:DI 18 $18)
(expr_list:REG_DEAD (reg:DI 17 $17)
(expr_list:REG_DEAD (reg:DI 16 $16)
(expr_list:REG_CALL_DECL (nil)
(nil)))))))))
(expr_list (use (reg:DI 21 $21))
(expr_list (use (reg:DI 20 $20))
(expr_list (use (reg:DI 19 $19))
(expr_list (use (reg:DI 18 $18))
(expr_list (use (reg:DI 17 $17))
(expr_list (use (reg:DI 16 $16))
(expr_list:BLK (use (mem:BLK (reg/f:DI 30 $30) [0
S4048 A64]))
(nil)))))))))
;; succ: 6 [100.0%] (FALLTHRU)
;; lr out 15 [$15] 26 [$26] 29 [$29] 30 [$30] 31 [AP] 63 [FP]
;; live out 15 [$15] 29 [$29] 30 [$30] 31 [AP] 63 [FP]
;; basic block 6, loop depth 0, count 0, freq 10000, maybe hot
;; prev block 5, next block 7, flags: (REACHABLE, RTL, MODIFIED)
;; pred: 2 [39.0%]
;; 5 [100.0%] (FALLTHRU)
;; bb 6 artificial_defs: { }
;; bb 6 artificial_uses: { u-1(15){ }u-1(29){ }u-1(30){ }u-1(31){ }u-1(63){ }}
;; lr in 15 [$15] 26 [$26] 29 [$29] 30 [$30] 31 [AP] 63 [FP]
;; lr use 15 [$15] 29 [$29] 30 [$30] 31 [AP] 63 [FP]
;; lr def 81
;; live in 15 [$15] 29 [$29] 30 [$30] 31 [AP] 63 [FP]
;; live gen 81
;; live kill
(code_label/s 47 46 48 6 2 ("retaddr") [5 uses])
(note 48 47 49 6 [bb 6] NOTE_INSN_BASIC_BLOCK)
(insn 49 48 52 6 (set (reg:DI 81 [ <retval> ])
(const_int 0 [0])) rr.go:57 236 {*movdi}
(nil))
succ: 8 [100.0%] (FALLTHRU)
Unfortunatelly, this is not a robust approach, since in a follow-up
_.180r.fwprop1 pass (insn 49) propagates to function return value, leaving:
(code_label/s 47 46 48 6 2 ("retaddr") [5 uses])
(note 48 47 52 6 [bb 6] NOTE_INSN_BASIC_BLOCK)
;; succ: 8 [100.0%] (FALLTHRU)
The following 181r.cprop pass removes the label (also updates passed argument
to __go_set_defer_retaddr in (insn 7) and (insn 8)) and merges bb after a thunk
call:
(insn 7 3 8 2 (set (reg/f:DI 84)
(high:DI (label_ref:DI [47 deleted]))) rr.go:57 236 {*movdi}
(insn_list:REG_LABEL_OPERAND 47 (nil)))
(insn 8 7 9 2 (set (reg/f:DI 83)
(lo_sum:DI (reg/f:DI 84)
(label_ref:DI [47 deleted]))) rr.go:57 230 {*movdi_er_low_l}
(expr_list:REG_DEAD (reg/f:DI 84)
(insn_list:REG_LABEL_OPERAND 47 (expr_list:REG_EQUAL (label_ref:DI [47
deleted])
(nil)))))
...
(call_insn 46 45 47 5 (parallel [
(call (mem:DI (reg/f:DI 80 [ D.1014 ]) [0 *_42 S8 A64])
(const_int 4048 [0xfd0]))
(use (reg:DI 29 $29))
(clobber (reg:DI 26 $26))
]) rr.go:57 210 {*call_osf_1_er}
(expr_list:REG_DEAD (reg/f:DI 80 [ D.1014 ])
(expr_list:REG_DEAD (reg:DI 21 $21)
(expr_list:REG_DEAD (reg:DI 20 $20)
(expr_list:REG_DEAD (reg:DI 19 $19)
(expr_list:REG_DEAD (reg:DI 18 $18)
(expr_list:REG_DEAD (reg:DI 17 $17)
(expr_list:REG_DEAD (reg:DI 16 $16)
(expr_list:REG_CALL_DECL (nil)
(nil)))))))))
(expr_list (use (reg:DI 21 $21))
(expr_list (use (reg:DI 20 $20))
(expr_list (use (reg:DI 19 $19))
(expr_list (use (reg:DI 18 $18))
(expr_list (use (reg:DI 17 $17))
(expr_list (use (reg:DI 16 $16))
(expr_list:BLK (use (mem:BLK (reg/f:DI 30 $30) [0
S4048 A64]))
(nil)))))))))
(note/s 47 46 52 5 ("retaddr") NOTE_INSN_DELETED_LABEL 2)
;; succ: 8 [100.0%] (FALLTHRU)
The missing label is substituted with a reference to some nearby label,
resulting in:
[+] ldah $16,$L8($29) !gprelhigh
stq $26,4048($30)
stq $9,4056($30)
[+] lda $16,$L8($16) !gprellow
jsr $26,($27),__go_set_defer_retaddr !lituse_jsr!22
...
$L10:
$L8:
ldq $27,memcpy($29) !literal!12
lda $17,56($9)
mov $30,$16
lda $18,4048($31)
jsr $26,($27),memcpy !lituse_jsr!12
...
[++] jsr $26,($27),0
ldah $29,0($26) !gpdisp!24
lda $29,0($29) !gpdisp!24
$L11:
mov $31,$0
The [+] marks wrong label load and [++] marks thunk call. $L8 is an unrelated
label that gets loaded as an argument to __go_set_defer_retaddr.
Since $L8 is "far" away from thunk call, this fails the test in
__go_can_recover (runtime/go-recover.c):
dret = (const char *) d->__retaddr;
if (ret <= dret && ret + 16 >= dret)
return 1;
Manually changing $L8 to $L11 in the call to __go_set_defer_retaddr (in an
assembly) results in a successful test.
