Recog - unrecognized insn when clobber present

[Vasanth <geekvasanth at gmail dot com>]

Hi,

I am working on a port of GCC to a 32-bit RISC machine. I am having
trouble with .combine pass adding clobbers to instruction patterns. To
be more specific,

(define_insn "lshrsi3_internal_reg_nohwshift"
  [(set (match_operand:SI 0 "register_operand" "=d")
        (lshiftrt:SI (match_operand:SI 1 "register_operand" "d")
                     (match_operand:SI 2 "register_operand" "d")))
   (clobber (reg:SI R_TMP))]
  "!(TARGET_HW_SHIFT)"
  {
 ...
  } 

is what I have in my md file. When compiling __lshrdi3 in libgcc2, I
see the following RTL produced

libgcc2.i.19.life:

(insn 43 41 44 4 (set (reg:SI 93)
        (lshiftrt:SI (subreg:SI (reg/v:DI 87 [ uu ]) 0)
            (reg/v:SI 85 [ b ]))) -1 (nil)
    (expr_list:REG_EQUAL (lshiftrt:SI (subreg:SI (reg/v:DI 84 [ u ]) 0)
            (reg/v:SI 85 [ b ]))
        (nil)))

(insn 44 43 46 4 (set (subreg:SI (reg/v:DI 89 [ w ]) 0)
        (reg:SI 93)) 46 {movsi_internal2} (insn_list 43 (nil))
    (expr_list:REG_DEAD (reg:SI 93)
        (nil)))

(insn 46 44 47 4 (set (reg:SI 94)
        (lshiftrt:SI (subreg:SI (reg/v:DI 87 [ uu ]) 4)
            (reg/v:SI 85 [ b ]))) -1 (nil)
    (expr_list:REG_DEAD (reg/v:DI 87 [ uu ])
        (expr_list:REG_DEAD (reg/v:SI 85 [ b ])
            (expr_list:REG_EQUAL (lshiftrt:SI (subreg:SI (reg/v:DI 84 [ u ]) 4)
                    (reg/v:SI 85 [ b ]))
                (nil)))))

After combine, I expect recog to take insn 43 and 46 and cause both to
match lshrsi3_internal_reg_nohwshift. However, insn 46 seems to not
get the clobber attached in a parallel while 43 does.

libgcc2.i.20.combine:

(insn 44 43 46 4 (parallel [
            (set (subreg:SI (reg/v:DI 89 [ w ]) 0)
                (lshiftrt:SI (subreg:SI (reg/v:DI 87 [ uu ]) 0)
                    (reg/v:SI 85 [ b ])))
            (clobber (reg:SI 18 r18))
        ]) 72 {lshrsi3_internal_reg_nohwshift} (nil)
    (expr_list:REG_UNUSED (reg:SI 18 r18)
        (nil)))

(insn 46 44 47 4 (set (reg:SI 94)
        (lshiftrt:SI (subreg:SI (reg/v:DI 87 [ uu ]) 4)
            (reg/v:SI 85 [ b ]))) -1 (nil)
    (expr_list:REG_DEAD (reg/v:DI 87 [ uu ])
        (expr_list:REG_DEAD (reg/v:SI 85 [ b ])
            (expr_list:REG_EQUAL (lshiftrt:SI (subreg:SI (reg/v:DI 84 [ u ]) 4)
                    (reg/v:SI 85 [ b ]))
                (nil)))))


Hence, I get an unrecognized insn error soon after. The only
difference between 43 and 46 seems to be that 43 underwent a
combination with 44 and is subregging 0, while 46 is subregging to
byte 4.

Taking away the clobber makes the insn match and the code to compile.

Any ideas what/where I should start checking? Help is greatly appreciated..

thanks,
Vasanth