https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103197
--- Comment #1 from acsawdey at gcc dot gnu.org ---
Looking at trunk, after expand we have this:
(note 5 1 2 2 [bb 2] NOTE_INSN_BASIC_BLOCK)
(insn 2 5 3 2 (set (reg/v/f:DI 117 [ a ])
(reg:DI 3 3 [ a ])) "bug2.c":3:1 -1
(nil))
(insn 3 2 4 2 (set (reg/v/f:DI 118 [ b ])
(reg:DI 4 4 [ b ])) "bug2.c":3:1 -1
(nil))
(note 4 3 7 2 NOTE_INSN_FUNCTION_BEG)
(insn 7 4 9 2 (set (reg:DI 119)
(mem:DI (reg/v/f:DI 118 [ b ]) [0 MEM <char[1:9]> [(void *)b_3(D)]+0 S8
A8])) "bug2.c":4:3 -1
(nil))
(insn 9 7 8 2 (set (reg:QI 120)
(mem:QI (plus:DI (reg/v/f:DI 118 [ b ])
(const_int 8 [0x8])) [0 MEM <char[1:9]> [(void *)b_3(D)]+8 S1
A8])) "bug2.c":4:3 -1
(nil))
(insn 8 9 10 2 (set (mem:DI (reg/v/f:DI 117 [ a ]) [0 MEM <char[1:9]> [(void
*)a_2(D)]+0 S8 A8])
(reg:DI 119)) "bug2.c":4:3 -1
(nil))
(insn 10 8 0 2 (set (mem:QI (plus:DI (reg/v/f:DI 117 [ a ])
(const_int 8 [0x8])) [0 MEM <char[1:9]> [(void *)a_2(D)]+8 S1
A8])
(reg:QI 120)) "bug2.c":4:3 -1
(nil))
Which is the expected code, DI and QI loads/stores that should produce D-form
instructions.
But it looks like reload put the QI into hard reg 32 which is a fp reg:
(insn 9 17 8 2 (set (reg:QI 32 0 [orig:120 MEM <char[1:9]> [(void *)b_3(D)]+8 ]
[120])
(mem:QI (reg:DI 10 10 [124]) [0 MEM <char[1:9]> [(void *)b_3(D)]+8 S1
A8])) "bug2.c":4:3 549 {*movqi_internal}
which leads to the lxsibzx/stxsibx on output.
