RTL problem with optimizations

[Petar Penchev]

Hello All,
I have defined RTL patterns for HImode in my .md files as follows :

(define_expand "ashlhi3"
   [(set (match_operand:HI 0 "register_operand" "")
	(ashift:HI (match_operand:HI 1 "register_operand" "")
	           (match_operand:HI 2 "general_operand" "")))]
    ""
    "
{
   /* If the argument is not a const, load it in a register */
   if (GET_CODE (operands[2]) != CONST_INT)
     {
       emit_insn (gen_rtx (PARALLEL, VOIDmode,
	 	 gen_rtvec (2, gen_rtx (SET, VOIDmode,
			    operand0,
			    gen_rtx_ASHIFT (HImode,
					operand1, operand2)),
			      gen_rtx (CLOBBER, VOIDmode, operand2))));
	  DONE;
     }
}")


(define_insn "*ashlhi3_reg"
[(parallel
   [
	
	 (set (match_operand:HI 0 "register_operand"       "=b,x")
           (ashift:HI (match_operand:HI 1 "register_operand"  "%0,0")
                    (match_operand:HI 2 "register_operand"  "x,b")
		   )
	  )
      (clobber (match_dup 2))
    ]
  )]
   ""
{
   mlx16_emit_shift( HImode, (which_alternative == 0), ASHIFT, operands );
   return "";
}
   [(set_attr "cc" "set_zn,set_zn")]
)

This pattern works, unless I try to compile newlib's file hash.c with -O3  
option specified.
GCC gives followintg error :

->>>
../../../../../newlib_src/newlib/libc/search/hash.c:957: error:  
unrecognizable insn:
(insn 102 101 104 6  
../../../../../newlib_src/newlib/libc/search/hash.c:955 (par
allel [
             (set (reg:HI 49)
                 (ashift:HI (reg/v:HI 18 [ i ])
                     (reg:HI 48 [ <variable>.hdr.sshift ])))
             (clobber (reg:HI 74 [ <variable>.hdr.sshift ]))
         ]) -1 (insn_list 101 (nil))
     (expr_list:REG_DEAD (reg:HI 48 [ <variable>.hdr.sshift ])
         (expr_list:REG_UNUSED (reg:HI 74 [ <variable>.hdr.sshift ])
             (expr_list:REG_EQUAL (ashift:HI (reg/v:HI 18 [ i ])
                     (reg/v:HI 69 [ <variable>.hdr.sshift ]))
                 (nil)))))
../../../../../newlib_src/newlib/libc/search/hash.c:957: internal compiler  
error
: in extract_insn, at recog.c:2083
Please submit a full bug report,
with preprocessed source if appropriate.
See <URL:http://gcc.gnu.org/bugs.html> for instructions.

->>>

When  I look at RTL dumps , I see :

hash.c.16.loop2:

(insn 102 101 104 6  
../../../../../newlib_src/newlib/libc/search/hash.c:955 (parallel [
             (set (reg:HI 49)
                 (ashift:HI (reg/v:HI 18 [ i ])
                     (reg:HI 48 [ <variable>.hdr.sshift ])))
             (clobber (reg:HI 48 [ <variable>.hdr.sshift ]))
         ]) -1 (nil)
     (expr_list:REG_EQUAL (ashift:HI (reg/v:HI 18 [ i ])
             (reg/v:HI 69 [ <variable>.hdr.sshift ]))
         (nil)))
This perfectly match to my desription in the RTL file.

However if I take a look into hash.c.17.web

(insn 102 101 104 6  
../../../../../newlib_src/newlib/libc/search/hash.c:955 (parallel [
             (set (reg:HI 49)
                 (ashift:HI (reg/v:HI 18 [ i ])
                     (reg:HI 48 [ <variable>.hdr.sshift ])))
             (clobber (reg:HI 74 [ <variable>.hdr.sshift ]))
         ]) -1 (nil)
     (expr_list:REG_EQUAL (ashift:HI (reg/v:HI 18 [ i ])
             (reg/v:HI 69 [ <variable>.hdr.sshift ]))
         (nil)))

I tried to find something about .web but I couldn't. I am wondering why  
gcc replaces reg 48 with reg 75 and if there is a way to
explain it not to do that :). Of course I can define pattern to match such  
instruction, but this seems to me to be wrong.
I have the same problem with -O4 optimizations. This problem does not  
appear with other -Ox options.

GCCINT does not say anything about .web, i.e. after which compilation  
phase it is being generated.
My questions are about this .web file , what it is ? and why compiler  
decides to replace clobber register ?

Regards
-- 
Petar Penchev
Software engineer