[Bug c/58400] gcc for h8300 internal compiler error: insn does not satisfy its constraints at fs/ext4/mballoc.c: In function 'mb_free_blocks':

["law at redhat dot com" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=58400

Jeffrey A. Law <law at redhat dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |kazu at gcc dot gnu.org,
                   |                            |law at redhat dot com

--- Comment #5 from Jeffrey A. Law <law at redhat dot com> ---
Kazu, you added these patterns many years ago...  Your thoughts would be
appreciated.

Compile the attached code with -O2 -mh -mint32 on the H8 port, using the trunk.

It'll fail due to an insn not matching its constraints problem.


The H8 port has the following insn:

(define_insn_and_split "*tstsi_variable_bit_qi"
  [(set (cc0)
        (compare (zero_extract:SI (zero_extend:SI (match_operand:QI 0
"general_operand_src" "r,U,mn>"))
                                  (const_int 1)
                                  (and:SI (match_operand:SI 1
"register_operand" "r,r,r")
                                          (const_int 7)))
                 (const_int 0)))
   (clobber (match_scratch:QI 2 "=X,X,&r"))]
  "TARGET_H8300H || TARGET_H8300S"
  "@
   btst\\t%w1,%X0
   btst\\t%w1,%X0
   #"
  "&& reload_completed
   && !satisfies_constraint_U (operands[0])"
  [(set (match_dup 2)
        (match_dup 0))
   (parallel [(set (cc0)
                   (compare (zero_extract:SI (zero_extend:SI (match_dup 2))
                                             (const_int 1)
                                             (and:SI (match_dup 1)
                                                     (const_int 7)))
                            (const_int 0)))
              (clobber (scratch:QI))])]
  ""    
  [(set_attr "length" "2,8,10")
   (set_attr "cc" "set_zn,set_zn,set_zn")])


Now assume that operand 0 is initially a pseudo, something like this;

(insn 50 49 51 5 (parallel [
            (set (cc0)
                (compare (zero_extract:SI (zero_extend:SI (reg:QI 37 [ D.1545
]))
                        (const_int 1 [0x1])
                        (and:SI (reg:SI 59 [ D.1543 ])
                            (const_int 7 [0x7])))
                    (const_int 0 [0])))
            (clobber (scratch:QI))
        ]) j.c:36 113 {*tstsi_variable_bit_qi}
     (expr_list:REG_DEAD (reg:SI 59 [ D.1543 ])
        (expr_list:REG_DEAD (reg:QI 37 [ D.1545 ])
            (nil))))


That looks fine and good.  Now assume reg:37 doesn't get a hard reg.  reload
will replace the reg with its equivalent stack slot resulting in:


(insn 50 116 51 5 (parallel [
            (set (cc0)
                (compare (zero_extract:SI (zero_extend:SI (mem/c:QI (plus:SI
(reg/f:SI 6 r6)
                                    (const_int -17 [0xffffffffffffffef])) [7
%sfp+-9 S1 A8]))
                        (const_int 1 [0x1])
                        (and:SI (reg:SI 3 r3)
                            (const_int 7 [0x7])))
                    (const_int 0 [0])))
            (clobber (scratch:QI))
        ]) j.c:36 113 {*tstsi_variable_bit_qi}
     (nil))


Note that the insn no longer matches its strict constraints.  It doesn't match
alternatives 0 or 1 because of operand 0.  It doesn't match alternative 2
because the SCRATCH is not a REG.

I'm guessing you wanted reload to give you a scratch register that you could
use for generating code when operand0 wasn't a suitable source for a single bit
extraction.  You'd then split the insn at insn output time using the scratch
register to effectively reload operand0 yourself?

Note there's another pattern tst_extzv_1_n that has potentially the same
problem.

The fundamental issue is that once reload is done, all insns must always
satisfy their constraints, no exceptions. 

Thoughts on how this is supposed to work?