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Subject: [Bug rtl-optimization/55719] [4.8 Regression] ICE: Segmentation fault
Date: Wed, 09 Jan 2013 18:46:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=55719

Aldy Hernandez <aldyh at gcc dot gnu.org> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |rsandifo at gcc dot gnu.org

--- Comment #5 from Aldy Hernandez <aldyh at gcc dot gnu.org> 2013-01-09 18:45:34 UTC ---
I'm out of my depth here, but perhaps someone can give me a hint on how to
debug this further.

As alluded to earlier, this ICE only happens with sched-pressure scheduling.

The actual ICE happens in find_reloads_address_part(), where we have are
analyzing X=:

(const:DI (plus:DI (symbol_ref:DI ("glob_b"))
        (const_int 3 [0x3])))

prefer_reload_class() returns NO_REGS, because legitimate_reload_constant_p()
returns false for the X above.  So when we call force_const_mem() in
find_reloads_address_part...

  if (CONSTANT_P (x)
      && (!targetm.legitimate_constant_p (mode, x)
      || targetm.preferred_reload_class (x, rclass) == NO_REGS))
    {
      x = force_const_mem (mode, x);   <-- HERE

force_const_mem() returns NULL because s390_cannot_force_const_mem() returns
true for the SYMBOL_REF in -fPIC mode.

Bottom line-- force_const_mem() returns NULL for a (const (plus SYMBOL_REF
CONST)) with -fPIC, and then we dereference this NULL.

Is the RTL correct?

Any hints?