http://gcc.gnu.org/bugzilla/show_bug.cgi?id=48837
--- Comment #6 from Steven Bosscher <steven at gcc dot gnu.org> 2011-05-01
19:56:37 UTC ---
In the tail recursion optimization:
Breakpoint 3, gimple_call_set_tail (s=0x7ffff7ed3680, tail_p=1 '\001') at
../../trunk/gcc/gimple.h:2241
2241 GIMPLE_CHECK (s, GIMPLE_CALL);
(gdb) bt 2
#0 gimple_call_set_tail (s=0x7ffff7ed3680, tail_p=1 '\001') at
../../trunk/gcc/gimple.h:2241
#1 0x0000000000f6d5a3 in optimize_tail_call (t=0x1cd7820, opt_tailcalls=1
'\001') at ../../trunk/gcc/tree-tailcall.c:917
(More stack frames follow...)
(gdb) up
#1 0x0000000000f6d5a3 in optimize_tail_call (t=0x1cd7820, opt_tailcalls=1
'\001') at ../../trunk/gcc/tree-tailcall.c:917
917 gimple_call_set_tail (stmt, true);
(gdb) l
912
913 if (opt_tailcalls)
914 {
915 gimple stmt = gsi_stmt (t->call_gsi);
916
917 gimple_call_set_tail (stmt, true);
918 if (dump_file && (dump_flags & TDF_DETAILS))
919 {
920 fprintf (dump_file, "Found tail call ");
921 print_gimple_stmt (dump_file, stmt, 0, dump_flags);
(gdb) disp debug_bb_n(5)
3: debug_bb_n (5) = ;; basic block 5, loop depth 0, count 0
;; prev block 4, next block 1
;; pred: 3 [100.0%] (fallthru,exec)
;; succ: EXIT [100.0%]
<bb 5>:
Invalid sum of incoming frequencies 3900, should be 6950
# D.2081_1 = PHI <D.2081_5(3)>
return D.2081_1;
(struct basic_block_def *) 0x7ffff7227548
(gdb) p debug_bb_n(3)
;; basic block 3, loop depth 0, count 0
;; prev block 2, next block 4
;; pred: 2 [39.0%] (true,exec)
;; succ: 5 [100.0%] (fallthru,exec)
<bb 3>:
D.2081_5 = baz (); [tail call]
goto <bb 5>;
$9 = (struct basic_block_def *) 0x7ffff7227478
(gdb)
So far so good. But now compensation code must be inserted for the
recursive-call-turned-loop:
(gdb)
3: debug_bb_n (5) = ;; basic block 5, loop depth 0, count 0
;; prev block 4, next block 1
;; pred: 3 [100.0%] (fallthru,exec)
;; succ: EXIT [100.0%]
<bb 5>:
Invalid sum of incoming frequencies 3900, should be 6950
# D.2081_1 = PHI <D.2081_5(3)>
return D.2081_1;
(struct basic_block_def *) 0x7ffff7227548
(gdb)
1040 adjust_return_value (e->src, m_acc, a_acc);
3: debug_bb_n (5) = ;; basic block 5, loop depth 0, count 0
;; prev block 4, next block 1
;; pred: 3 [100.0%] (fallthru,exec)
;; succ: EXIT [100.0%]
<bb 5>:
Invalid sum of incoming frequencies 3900, should be 6950
# D.2081_1 = PHI <D.2081_5(3)>
return D.2081_1;
(struct basic_block_def *) 0x7ffff7227548
(gdb)
1034 FOR_EACH_EDGE (e, ei, EXIT_BLOCK_PTR->preds)
3: debug_bb_n (5) = ;; basic block 5, loop depth 0, count 0
;; prev block 4, next block 1
;; pred: 3 [100.0%] (fallthru,exec)
;; succ: EXIT [100.0%]
<bb 5>:
Invalid sum of incoming frequencies 3900, should be 6950
# D.2081_1 = PHI <D.2081_5(3)>
acc_tmp.13_10 = add_acc.12_19 + D.2081_1;
return acc_tmp.13_10;
(struct basic_block_def *) 0x7ffff7227548
(gdb)
(I don't see now r127491 can be the cause of this, FWIW.)
