https://gcc.gnu.org/bugzilla/show_bug.cgi?id=123020
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
Ever confirmed|0 |1
Last reconfirmed| |2025-12-06
--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Confirmed.
for aarch64 we have
```
(insn 14 13 15 3 (set (reg/v:SI 106 [ mx ])
(reg/v:SI 103 [ mx ])) 103 {*movsi_aarch64}
(nil))
(insn 15 14 16 3 (set (reg:CC 66 cc)
(compare:CC (reg/v:SI 103 [ mx ])
(reg:SI 108 [ _25 ]))) "/app/example.cpp":40:20 451 {cmpsi}
(nil))
(insn 16 15 17 3 (set (reg/v:SI 103 [ mx ])
(if_then_else:SI (geu (reg:CC 66 cc)
(const_int 0 [0]))
(reg/v:SI 103 [ mx ])
(reg:SI 108 [ _25 ]))) "/app/example.cpp":40:20 503 {*cmovsi_insn}
(expr_list:REG_DEAD (reg:CC 66 cc)
(nil)))
(insn 17 16 53 3 (set (reg:CC 66 cc)
(compare:CC (reg/v:SI 106 [ mx ])
(reg:SI 108 [ _25 ]))) "/app/example.cpp":41:21 451 {cmpsi}
(expr_list:REG_DEAD (reg/v:SI 106 [ mx ])
(nil)))
```
But (reg:CC 66) is already set to the same thing and should have been removed
But since we clobber 103 we don't notice it is the same.
x86_64 is more complex:
```
(insn 13 12 57 3 (parallel [
(set (reg/v:SI 100 [ mx ])
(umax:SI (reg/v:SI 100 [ mx ])
(reg:SI 105 [ _25 ])))
(clobber (reg:CC 17 flags))
]) "/app/example.cpp":40:20 1883 {*umaxsi3_1}
(expr_list:REG_UNUSED (reg:CC 17 flags)
(nil)))
(insn 57 13 59 3 (set (reg:DI 110 [ _27 ])
(zero_extend:DI (reg:SI 105 [ _25 ]))) "/app/example.cpp":41:13 discrim
3 179 {*zero_extendsidi2}
(nil))
(insn 59 57 60 3 (parallel [
(set (reg:DI 125)
(plus:DI (reg/v:DI 104 [ sum ])
(reg:DI 110 [ _27 ])))
(clobber (reg:CC 17 flags))
]) "/app/example.cpp":41:13 discrim 3 289 {*adddi_1}
(expr_list:REG_DEAD (reg:DI 110 [ _27 ])
(expr_list:REG_UNUSED (reg:CC 17 flags)
(nil))))
(insn 60 59 61 3 (set (reg:CC 17 flags)
(compare:CC (reg/v:SI 103 [ mx ])
(reg:SI 105 [ _25 ]))) "/app/example.cpp":41:13 discrim 3 15
{*cmpsi_1}
(expr_list:REG_DEAD (reg:SI 105 [ _25 ])
(expr_list:REG_DEAD (reg/v:SI 103 [ mx ])
(nil))))
```
For the gimple level. The problem is we convert `flag ? a[i] : mx;` into
MAX_EXPR but I had assumed ethread would have done the jump thread beforehand
...
