https://gcc.gnu.org/bugzilla/show_bug.cgi?id=94846
Uroš Bizjak <ubizjak at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Ever confirmed|0 |1
Last reconfirmed| |2020-11-25
Status|UNCONFIRMED |NEW
CC| |rguenth at gcc dot gnu.org
Component|rtl-optimization |tree-optimization
--- Comment #3 from Uroš Bizjak <ubizjak at gmail dot com> ---
This looks like a tree-optimization problem. A store to *p_5(D) could sink all
the way to bb5. RTL gets expanded from:
...
if (_10 != 0)
goto <bb 4>; [50.00%]
else
goto <bb 3>; [50.00%]
<bb 3> [local count: 536870912]:
*p_5(D) = _1;
goto <bb 5>; [100.00%]
<bb 4> [local count: 536870913]:
_2 = _1 + 1;
*p_5(D) = _2;
<bb 5> [local count: 1073741824]:
# prephitmp_11 = PHI <_1(3), _2(4)>
return prephitmp_11;
ifcvt RTL pass (_.ce1) is unable to convert:
...
17: r86:SI=r89:SI
REG_DEAD r89:SI
18: flags:CCZ=cmp(r85:SI,0)
REG_DEAD r85:SI
19: pc={(flags:CCZ!=0)?L24:pc}
REG_DEAD flags:CCZ
REG_BR_PROB 536870916
20: NOTE_INSN_BASIC_BLOCK 5
21: [r87:DI]=r89:SI
REG_DEAD r87:DI
; pc falls through to BB 7
24: L24:
25: NOTE_INSN_BASIC_BLOCK 6
26: {r86:SI=r89:SI+0x1;clobber flags:CC;}
REG_UNUSED flags:CC
27: [r87:DI]=r86:SI
REG_DEAD r87:DI
32: L32:
35: NOTE_INSN_BASIC_BLOCK 7
...
IF-THEN-ELSE-JOIN block found, pass 2, test 2, then 5, else 6, join 7
===
In case p is not a pointer, RTL optimizers start with:
...
if (_8 != 0)
goto <bb 3>; [50.00%]
else
goto <bb 4>; [50.00%]
<bb 3> [local count: 536870913]:
p_5 = p_4 + 1;
<bb 4> [local count: 1073741824]:
# p_1 = PHI <p_4(2), p_5(3)>
return p_1;
and RTL ifcvt pass is able to convert this form to addcc:
IF-THEN-JOIN block found, pass 2, test 2, then 5, join 6
if-conversion succeeded through noce_try_addcc
