optimization/10185: [3.3/3.4 regression] Wrong code with 3-int-structs & optimization

[Jan Hubicka]

> The regression appeared with this patch:
> 
> Sun Jul 21 00:54:54 CEST 2002  Jan Hubicka  <jh@suse.cz>
> 
> 	* gcse.c: Include cselib.h
> 	(constptop_register): Break out from ...
> 	(cprop_insn): ... here; kill basic_block argument.
> 	(do_local_cprop, local_cprop_pass): New functions.
> 	(one_cprop_pass): Call local_cprop_pass.
> 
> My testing used the submitter's test case with -O2 on
> i686-pc-linux-gnu.

As described in the audit, the bug is really latent problem in BIV
discovery code.  This patch fixes the reason why gcse now manifest it.
I am now using cselib to discover noop moves and remove them more
aggresivly than delete_trivially_dead_insns can.  15 such noops are
found in combine.c compilation and resulting insn chain is reduced by 7
instructions, so this arrise in real programs too.

Bootstrapped/regtested x86-64.  OK?

Mon Mar 24 19:00:35 CET 2003  Jan Hubicka  <jh@suse.cz>
	* gcse.c (local_cprop_pass):  Do not copy propagate noop sets;
	attempt to turn set into noop.
	* cselib.c (cselib_set_noop_p): New function.
	* cselib.h (cselib_set_noop_p): Declare.
Index: gcse.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/gcse.c,v
retrieving revision 1.239
diff -c -3 -p -r1.239 gcse.c
*** gcse.c	8 Mar 2003 09:47:28 -0000	1.239
--- gcse.c	24 Mar 2003 18:12:32 -0000
*************** local_cprop_pass (alter_jumps)
*** 4437,4442 ****
--- 4437,4443 ----
        if (INSN_P (insn))
  	{
  	  rtx note = find_reg_note (insn, REG_LIBCALL, NULL_RTX);
+ 	  rtx set;
  
  	  if (note)
  	    {
*************** local_cprop_pass (alter_jumps)
*** 4448,4453 ****
--- 4449,4499 ----
  	  if (note)
  	    libcall_sp++;
  	  note = find_reg_equal_equiv_note (insn);
+ 
+ 	  if (noop_move_p (insn)
+ 	      && !find_reg_note (insn, REG_LIBCALL, NULL_RTX))
+ 	    {
+ 	      delete_insn (insn);
+ 	      continue;
+ 	    }
+ 	  
+ 	  set = single_set (insn);
+ 
+ 	  /* Don't do copy propagation on noop moves as it only
+ 	     results in these being in the insn chain longer  */
+ 	  if (set && set_noop_p (set))
+ 	    continue;
+ 	  /* Attempt to turn (set A B) where A B are known to be equivalent
+ 	     into (set A A) or (set B B) so the instruction is removed later.
+ 	     */
+ 	  if (set && cselib_set_noop_p (set)
+ 	      && (!SMALL_REGISTER_CLASSES
+ 		  || ((!REG_P (SET_DEST (set))
+ 		       || REGNO (SET_DEST (set)) >= FIRST_PSEUDO_REGISTER)
+ 		      && (GET_CODE (SET_DEST (set)) != SUBREG
+ 		          || (REGNO (SUBREG_REG (SET_DEST (set)))
+ 			      >= FIRST_PSEUDO_REGISTER)))))
+ 	    {
+ 	      bool converted = false;
+ 
+ 	      if (validate_change (insn, &SET_DEST (set),
+ 				   copy_rtx (SET_SRC (set)), 0))
+ 		converted = true;
+ 	      else if (validate_change (insn, &SET_SRC (set),
+ 					copy_rtx (SET_DEST (set)), 0))
+ 		converted = true;
+ 	      if (converted)
+ 		{
+ 		  if (gcse_file)
+ 		    fprintf (gcse_file,
+ 			     "LOCAL COPY-PROP: Set in insn %d turned into noop",
+ 			     INSN_UID (insn));
+ 		  if (noop_move_p (insn)
+ 		      && !find_reg_note (insn, REG_LIBCALL, NULL_RTX))
+ 		    delete_insn (insn);
+ 		  continue;
+ 		}
+ 	    }
  	  do
  	    {
  	      reg_use_count = 0;
Index: cselib.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/cselib.c,v
retrieving revision 1.26
diff -c -3 -p -r1.26 cselib.c
*** cselib.c	14 Mar 2003 20:15:11 -0000	1.26
--- cselib.c	24 Mar 2003 18:12:33 -0000
*************** rtx_equal_for_cselib_p (x, y)
*** 541,546 ****
--- 541,570 ----
    return 1;
  }
  
+ /* Return nonzero if the destination of SET equals the source
+    and there are no side effects.  Use cselib infromation to recognize
+    nontrivial cases.  */
+ 
+ bool
+ cselib_set_noop_p (set)
+      rtx set;
+ {
+   rtx src = SET_SRC (set);
+   rtx dst = SET_DEST (set);
+ 
+   if (GET_CODE (dst) == STRICT_LOW_PART)
+     dst = XEXP (dst, 0);
+   if ((GET_CODE (dst) == SIGN_EXTRACT
+        || GET_CODE (dst) == ZERO_EXTRACT)
+       && ! BYTES_BIG_ENDIAN && XEXP (dst, 2) == const0_rtx)
+     dst = XEXP (dst, 0);
+ 
+   if (rtx_equal_for_cselib_p (src, dst))
+     return !side_effects_p (src) && !side_effects_p (dst);
+ 
+   return false;
+ }
+ 
  /* We need to pass down the mode of constants through the hash table
     functions.  For that purpose, wrap them in a CONST of the appropriate
     mode.  */
Index: cselib.h
===================================================================
RCS file: /cvs/gcc/gcc/gcc/cselib.h,v
retrieving revision 1.7
diff -c -3 -p -r1.7 cselib.h
*** cselib.h	11 Mar 2003 21:52:41 -0000	1.7
--- cselib.h	24 Mar 2003 18:12:33 -0000
*************** extern void cselib_update_varray_sizes	P
*** 67,72 ****
--- 67,73 ----
  extern void cselib_init			PARAMS ((void));
  extern void cselib_finish		PARAMS ((void));
  extern void cselib_process_insn		PARAMS ((rtx));
+ extern bool cselib_set_noop_p		PARAMS ((rtx));
  extern int rtx_equal_for_cselib_p	PARAMS ((rtx, rtx));
  extern int references_value_p		PARAMS ((rtx, int));
  extern rtx cselib_subst_to_values	PARAMS ((rtx));