https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112760
Jakub Jelinek <jakub at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords|needs-bisection |
--- Comment #4 from Jakub Jelinek <jakub at gcc dot gnu.org> ---
In reload dump I see no changes (except function_decl/var_decl addresses), in
vzeroupper, postreload, split2, ree and cmpelim dumps a bunch of extra REG_DEAD
notes
here and there in r14-5355 compared to r14-5354, and finally pro_and_epilogue
deletes
(insn 20 19 62 2 (set (reg:CCZ 17 flags)
(compare:CCZ (reg:SI 0 ax [110])
(reg:SI 1 dx [111]))) "pr112760.c":6:22 11 {*cmpsi_1}
(expr_list:REG_UNUSED (reg:CCZ 17 flags)
(nil)))
insn.
In reload dump there is:
(insn 20 19 44 2 (set (reg:CCZ 17 flags)
(compare:CCZ (reg:SI 0 ax [110])
(reg:SI 1 dx [111]))) "pr112760.c":6:22 11 {*cmpsi_1}
(nil))
(insn 44 20 62 2 (set (reg:CCZ 17 flags)
(compare:CCZ (reg:SI 0 ax [110])
(reg:SI 1 dx [111]))) "pr112760.c":6:22 11 {*cmpsi_1}
(nil))
(insn 62 44 46 2 (set (reg:HI 0 ax [118])
(const_int 1 [0x1])) "pr112760.c":6:22 86 {*movhi_internal}
(expr_list:REG_EQUIV (const_int 1 [0x1])
(nil)))
(insn 46 62 25 2 (set (reg:HI 3 bx [orig:103 _8+2 ] [103])
(if_then_else:HI (eq (reg:CCZ 17 flags)
(const_int 0 [0]))
(reg:HI 3 bx [orig:103 _8+2 ] [103])
(reg:HI 0 ax [118]))) "pr112760.c":6:22 1381 {*movhicc_noc}
(nil))
so the insn 20 is indeed useless and in vzeroupper pass that was correctly
marked in
the notes:
(insn 20 19 44 2 (set (reg:CCZ 17 flags)
(compare:CCZ (reg:SI 0 ax [110])
(reg:SI 1 dx [111]))) "pr112760.c":6:22 11 {*cmpsi_1}
(expr_list:REG_UNUSED (reg:CCZ 17 flags)
(nil)))
(insn 44 20 62 2 (set (reg:CCZ 17 flags)
(compare:CCZ (reg:SI 0 ax [110])
(reg:SI 1 dx [111]))) "pr112760.c":6:22 11 {*cmpsi_1}
(expr_list:REG_DEAD (reg:SI 1 dx [111])
(expr_list:REG_DEAD (reg:SI 0 ax [110])
(nil))))
(insn 62 44 46 2 (set (reg:HI 0 ax [118])
(const_int 1 [0x1])) "pr112760.c":6:22 86 {*movhi_internal}
(expr_list:REG_EQUIV (const_int 1 [0x1])
(nil)))
(insn 46 62 25 2 (set (reg:HI 3 bx [orig:103 _8+2 ] [103])
(if_then_else:HI (eq (reg:CCZ 17 flags)
(const_int 0 [0]))
(reg:HI 3 bx [orig:103 _8+2 ] [103])
(reg:HI 0 ax [118]))) "pr112760.c":6:22 1381 {*movhicc_noc}
(expr_list:REG_DEAD (reg:CCZ 17 flags)
(expr_list:REG_DEAD (reg:HI 0 ax [118])
(nil))))
But then postreload deletes insn 44 rather than 20 and keeps the notes around
unchanged.
Insn 20 is deleted in
#2 0x0000000000cce9df in copyprop_hardreg_forward_1 (bb=<basic_block
0x7fffea2f7c60 (2)>, vd=0x3bd2be0) at ../../gcc/regcprop.cc:829
#3 0x0000000000ccfe1c in copyprop_hardreg_forward_bb_without_debug_insn
(bb=<basic_block 0x7fffea2f7c60 (2)>) at ../../gcc/regcprop.cc:1235
#4 0x0000000000d5b371 in prepare_shrink_wrap (entry_block=<basic_block
0x7fffea2f7c60 (2)>) at ../../gcc/shrink-wrap.cc:451
#5 0x0000000000d5bb70 in try_shrink_wrapping (entry_edge=0x7fffffffd900,
prologue_seq=0x7fffe9f25240) at ../../gcc/shrink-wrap.cc:674
#6 0x00000000008b4320 in thread_prologue_and_epilogue_insns () at
../../gcc/function.cc:6056
and regcprop.cc documents it relies on up to date REG_DEAD/REG_UNUSED notes;
after all
the removal happens in
/* Detect obviously dead sets (via REG_UNUSED notes) and remove them. */
if (set
&& !RTX_FRAME_RELATED_P (insn)
&& NONJUMP_INSN_P (insn)
&& !may_trap_p (set)
&& find_reg_note (insn, REG_UNUSED, SET_DEST (set))
&& !side_effects_p (SET_SRC (set))
&& !side_effects_p (SET_DEST (set)))
{
bool last = insn == BB_END (bb);
delete_insn (insn);
if (last)
break;
continue;
}
and regcprop.cc calls df_note_add_problem (); before calling df_analyze ().
Except
in the pro_and_epilogue case it is done elsewhere and it just calls into the
regcprop.cc functions.
