[Bug target/66563] [4.9 Regression] ICE (segmentation fault) on sh4-linux-gnu

[olegendo at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66563

--- Comment #31 from Oleg Endo <olegendo at gcc dot gnu.org> ---
(In reply to Kazumoto Kojima from comment #29)
> Unfortunately, 4.9 and later compilers 'optimize' the above code
> to the code like

Just for my understanding ...

In the pattern ...

(define_expand "GOTaddr2picreg"
  [(set (reg:SI R0_REG)
        (unspec:SI [(const:SI (unspec:SI [(match_dup 1)] UNSPEC_PIC))]
                   UNSPEC_MOVA))
   (set (match_dup 0) (const:SI (unspec:SI [(match_dup 1)] UNSPEC_PIC)))
   (set (match_dup 0) (plus:SI (match_dup 0) (reg:SI R0_REG)))]

... the 2nd (set ...) becomes the mov.l load from the constant pool, which is
CSE'ed by some other optimization after the initial RTL expansion.  If so,
wouldn't it be a bit cleaner to avoid CSE by hiding the constant/symref load
from CSE passes by doing something like the following ...

(define_expand "GOTaddr2picreg"
  [(parallel [(set (reg:SI R0_REG)
        (unspec:SI [(const:SI (unspec:SI [(match_dup 1)] UNSPEC_PIC))]
                   UNSPEC_MOVA))
   (set (match_dup 0) (const:SI (unspec:SI [(match_dup 1)] UNSPEC_PIC)))
   (set (match_dup 0) (plus:SI (match_dup 0) (reg:SI R0_REG)))])]
  <... everything else stays the same ...>


(define_insn_and_split "*GOTaddr2picreg"
  [(set (reg:SI R0_REG)
        (unspec:SI [(const:SI (unspec:SI [(match_dup 1)] UNSPEC_PIC))]
                   UNSPEC_MOVA))
   (set (match_dup 0) (const:SI (unspec:SI [(match_dup 1)] UNSPEC_PIC)))
   (set (match_dup 0) (plus:SI (match_dup 0) (reg:SI R0_REG)))]
  ""
  "#"
  "&& reload_completed"
  [(set (reg:SI R0_REG)
        (unspec:SI [(const:SI (unspec:SI [(match_dup 1)] UNSPEC_PIC))]
                   UNSPEC_MOVA))
   (set (match_dup 0) (const:SI (unspec:SI [(match_dup 1)] UNSPEC_PIC)))
   (set (match_dup 0) (plus:SI (match_dup 0) (reg:SI R0_REG)))])

Alternatively, can't the mov.l constant load insn be marked as "volatile" so
that it doesn't get optimized away for sure?