> Here's what it looks like in the jump dump, right before the lower subreg
> pass:
>
> [...]
>
> (insn 63 59 61 3 memcmp.c:81 (clobber (reg:SI 75)) -1 (nil)
> (insn_list:REG_LIBCALL 62 (nil)))
>
> (insn 61 63 62 3 memcmp.c:81 (parallel [
> (set (subreg:HI (reg:SI 75) 0)
> (and:HI (subreg:HI (reg:SI 73) 0)
> (subreg:HI (reg:SI 74) 0)))
> (clobber (reg:CC 13 cc))
> ]) 120 {*andhi3} (nil)
> (expr_list:REG_NO_CONFLICT (reg:SI 73)
> (expr_list:REG_NO_CONFLICT (reg:SI 74)
> (nil))))
>
> (insn 62 61 64 3 memcmp.c:81 (parallel [
> (set (subreg:HI (reg:SI 75) 2)
> (and:HI (subreg:HI (reg:SI 73) 2)
> (subreg:HI (reg:SI 74) 2)))
> (clobber (reg:CC 13 cc))
> ]) 120 {*andhi3} (nil)
> (insn_list:REG_RETVAL 63 (expr_list:REG_NO_CONFLICT (reg:SI 73)
> (expr_list:REG_NO_CONFLICT (reg:SI 74)
> (nil)))))
What very likely happens is that the lower subreg pass only "smashes" the REGs
in place and doesn't invoke its libcall/retval compensation code because the
latter is only run on more complex moves. So it yields
(insn 61 152 62 3 memcmp.c:81 (parallel [
(set (reg:HI 93)
(and:HI (reg:HI 89)
(reg:HI 91)))
(clobber (reg:CC 13 cc))
]) 120 {*andhi3} (nil)
(nil))
(insn 62 61 64 3 memcmp.c:81 (parallel [
(set (reg:HI 94 [+2 ])
(and:HI (reg:HI 90 [+2 ])
(reg:HI 92 [+2 ])))
(clobber (reg:CC 13 cc))
]) 120 {*andhi3} (nil)
(insn_list:REG_RETVAL 63 (nil)))
(insn 64 62 65 3 memcmp.c:81 (set (reg:HI 76)
(reg:HI 93)) 23 {*movhi} (nil)
(nil))
which is in my opinion not valid because the live range of (reg:HI 93) crosses
the libcall boundary. But Ian has the final say on this stuff.
--
Eric Botcazou
