https://gcc.gnu.org/bugzilla/show_bug.cgi?id=113994
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |krebbel at gcc dot gnu.org
--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
Reproduced on the trunk as well. So, we have before cse1:
(insn 28 27 29 6 (set (reg:CCU 33 %cc)
(compare:CCU (reg/v:DI 61 [ end ])
(reg:DI 63 [ _15 ]))) "pr113994.C":13:32 discrim 7 1436
{*cmpdi_ccu}
(nil))
(jump_insn 29 28 30 6 (set (pc)
(if_then_else (geu (reg:CCU 33 %cc)
(const_int 0 [0]))
(label_ref 39)
(pc))) "pr113994.C":13:32 discrim 7 2149 {*cjump_64}
(int_list:REG_BR_PROB 536870916 (nil))
-> 39)
;; succ: 7 [50.0% (guessed)] count:536870912 (estimated locally, freq
3.0000) (FALLTHRU)
;; 8 [50.0% (guessed)] count:536870912 (estimated locally, freq
3.0000)
...
;; basic block 8, loop depth 0, count 536870912 (estimated locally, freq
3.0000), maybe hot
;; prev block 7, next block 9, flags: (RTL, MODIFIED)
;; pred: 6 [50.0% (guessed)] count:536870912 (estimated locally, freq
3.0000)
;; bb 8 artificial_defs: { }
;; bb 8 artificial_uses: { u-1(11){ }u-1(15){ }u-1(32){ }u-1(34){ }}
(code_label 39 35 40 8 19 (nil) [1 uses])
(note 40 39 41 8 [bb 8] NOTE_INSN_BASIC_BLOCK)
(insn 41 40 42 8 (set (reg:CCU 33 %cc)
(compare:CCU (reg/v:DI 61 [ end ])
(reg:DI 63 [ _15 ])))
"/usr/include/c++/13/bits/basic_string.h":388:2 discrim 1 1436 {*cmpdi_ccu}
(nil))
(jump_insn 42 41 43 8 (set (pc)
(if_then_else (leu (reg:CCU 33 %cc)
(const_int 0 [0]))
(label_ref 53)
(pc))) "/usr/include/c++/13/bits/basic_string.h":388:2 discrim 1
2149 {*cjump_64}
(int_list:REG_BR_PROB 1073028868 (nil))
-> 53)
Next cse1 decides that the insn 41 is redundant, because insn 28 performed the
same comparison, dominates insn 41 and %cc has not been modified. REG_DEAD
note remains
on jump_insn 35, cse/gcse/postreload-cse doesn't remove REG_DEAD/REG_UNUSED
notes it invalidates.
ce1 pass then recomputes the notes and drops it, so fortunately this doesn't
seem to be about these notes.
%cc is even mentioned in
;; lr out 11 [%r11] 15 [%r15] 32 [%ap] 33 [%cc] 34 [%fp] 61 63 82 84
;; live out 11 [%r11] 15 [%r15] 32 [%ap] 33 [%cc] 34 [%fp] 61 63 82 84
after the jump_insn 29 (that actually already shows up that way in fwprop1, the
first time some pass did df_analyze after cse1).
But then something goes wrong during loop_invariant pass, jump_insn 29 above
gets (incorrect) REG_DEAD %cc note again and 33 [%cc] is dropped from lr
out/live out.
Sure, %cc is unused on one of the two successors, but on the other one is used.
And then comes loop_doloop and replaces that jump_insn 29 with
(jump_insn 226 28 225 6 (parallel [
(set (pc)
(if_then_else (ne (reg:DI 120)
(const_int 1 [0x1]))
(label_ref 225)
(pc)))
(set (reg:DI 120)
(plus:DI (reg:DI 120)
(const_int -1 [0xffffffffffffffff])))
(clobber (scratch:DI))
(clobber (reg:CC 33 %cc))
]) "pr113994.C":13:32 discrim 7 -1
(int_list:REG_BR_PROB 536870916 (nil))
-> 225)
(unsure whether because of the bogus REG_DEAD note, wrong df live out or
something else). And then the cprop3 pass just removes the dead
(insn 28 27 226 8 (set (reg:CCU 33 %cc)
(compare:CCU (reg/v:DI 61 [ end ])
(reg:DI 63 [ _15 ]))) "pr113994.C":13:32 discrim 7 1436
{*cmpdi_ccu}
(expr_list:REG_DEAD (reg:DI 63 [ _15 ])
(nil)))
comparison because nothing really consumes %cc it sets (there is a user in
jump_insn 42, but there is jump_insn 226 in between which clobbers it).
And the above brctg then clobbers %cc and so we end up with
brctg %r10,.L40
.L19:
jh .L55
in the assembly. If .L19 is reached from
jhe .L19
then it works fine, but if it is reached from falling through from brctg, %cc
is not what the code expects to (comparison of end with size()).
