https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103775
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Component|target |rtl-optimization
Ever confirmed|0 |1
Status|UNCONFIRMED |NEW
Last reconfirmed| |2021-12-20
Keywords|ice-on-valid-code |
CC| |pinskia at gcc dot gnu.org
--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(insn 12 9 13 2 (set (reg:SI 93 [ _2 ])
(zero_extend:SI (mem/c:QI (plus:DI (reg/f:DI 65 ap)
(const_int 16 [0x10])) [1 u128_1+0 S1 A128])))
"/app/example.cpp":5:35 117 {*zero_extendqisi2_aarch64}
(nil))
Auto-increment then turns it into:
(insn 39 9 12 2 (set (reg/f:DI 114)
(reg/f:DI 65 ap)) "/app/example.cpp":5:35 -1
(nil))
(insn 12 39 13 2 (set (reg:SI 93 [ _2 ])
(zero_extend:SI (mem/c:QI (pre_modify:DI (reg/f:DI 114)
(plus:DI (reg/f:DI 114)
(const_int 16 [0x10]))) [1 u128_1+0 S1 A128])))
"/app/example.cpp":5:35 117 {*zero_extendqisi2_aarch64}
(expr_list:REG_INC (reg/f:DI 114)
(nil)))
But this does not make sense as the result of the modify is not used
afterwards.
found pre add(17) r[115]=r[65]+20
16: r114:DI=ap:DI+0x10
REG_UNUSED r114:DI
15: r95:SI=r113:DI#0
REG_DEAD r113:DI
14: r113:DI=clrsb(r112:DI)
REG_DEAD r112:DI
13: r112:DI=zero_extend(r93:SI)
12: r93:SI=zero_extend([ap:DI+0x10])
12: r93:SI=zero_extend([ap:DI+0x10])
found mem(12) *(r[65]+16)
16: r114:DI=ap:DI+0x10
REG_UNUSED r114:DI
found post add(16) r[114]=r[65]+16
hmm before auto-increment:
(insn 16 15 17 2 (set (reg/f:DI 114)
(plus:DI (reg/f:DI 65 ap)
(const_int 16 [0x10]))) "/app/example.cpp":6:3 124
{*adddi3_aarch64}
(nil))
(insn 17 16 18 2 (set (reg/f:DI 115)
(plus:DI (reg/f:DI 65 ap)
(const_int 20 [0x14]))) "/app/example.cpp":6:3 124
{*adddi3_aarch64}
(expr_list:REG_DEAD (reg/f:DI 114)
(nil)))
114 is dead even before this.
Oh this is because at -Og we are not running DCE. I think there is some DF not
being updated before auto-increment too.
