Index: gcc/optabs.c
===================================================================
*** gcc/optabs.c	(revision 127069)
--- gcc/optabs.c	(working copy)
*************** static void prepare_float_lib_cmp (rtx *
*** 122,127 ****
--- 122,129 ----
  				   enum machine_mode *, int *);
  static rtx widen_clz (enum machine_mode, rtx, rtx);
  static rtx expand_parity (enum machine_mode, rtx, rtx);
+ static rtx expand_ffs (enum machine_mode, rtx, rtx);
+ static rtx expand_ctz (enum machine_mode, rtx, rtx);
  static enum rtx_code get_rtx_code (enum tree_code, bool);
  static rtx vector_compare_rtx (tree, bool, enum insn_code);
  
*************** expand_parity (enum machine_mode mode, r
*** 2560,2565 ****
--- 2562,2629 ----
    return 0;
  }
  
+ /* Try calculating ffs(x) using clz(x).  Since the ffs builtin promises
+    to return zero for a zero value and clz may have an undefined value
+    in that case, only do this if we know clz returns the right thing so
+    that we don't have to generate a test and branch.  */
+ static rtx
+ expand_ffs (enum machine_mode mode, rtx op0, rtx target)
+ {
+   HOST_WIDE_INT val;
+   if (clz_optab->handlers[(int) mode].insn_code != CODE_FOR_nothing
+       && CLZ_DEFINED_VALUE_AT_ZERO (mode, val)
+       && val == GET_MODE_BITSIZE (mode))
+     {
+       rtx last = get_last_insn ();
+       rtx temp;
+ 
+       temp = expand_unop (mode, neg_optab, op0, NULL_RTX, true);
+       if (temp)
+ 	temp = expand_binop (mode, and_optab, op0, temp, NULL_RTX,
+ 			     true, OPTAB_DIRECT);
+       if (temp)
+ 	temp = expand_unop (mode, clz_optab, temp, NULL_RTX, true);
+       if (temp)
+ 	temp = expand_binop (mode, sub_optab,
+ 			     GEN_INT (GET_MODE_BITSIZE (mode)),
+ 			     temp,
+ 			     target, true, OPTAB_DIRECT);
+       if (temp == 0)
+ 	delete_insns_since (last);
+       return temp;
+     }
+   return 0;
+ }
+ 
+ /* We can compute ctz(x) using clz(x) with a similar recipe.  Here the ctz
+    builtin has an undefined result on zero, just like clz, so we don't have
+    to do that check.  */
+ static rtx
+ expand_ctz (enum machine_mode mode, rtx op0, rtx target)
+ {
+   if (clz_optab->handlers[(int) mode].insn_code != CODE_FOR_nothing)
+     {
+       rtx last = get_last_insn ();
+       rtx temp;
+ 
+       temp = expand_unop (mode, neg_optab, op0, NULL_RTX, true);
+       if (temp)
+ 	temp = expand_binop (mode, and_optab, op0, temp, NULL_RTX,
+ 			     true, OPTAB_DIRECT);
+       if (temp)
+ 	temp = expand_unop (mode, clz_optab, temp, NULL_RTX, true);
+       if (temp)
+ 	temp = expand_binop (mode, xor_optab, temp,
+ 			     GEN_INT (GET_MODE_BITSIZE (mode) - 1),
+ 			     target,
+ 			     true, OPTAB_DIRECT);
+       if (temp == 0)
+ 	delete_insns_since (last);
+       return temp;
+     }
+   return 0;
+ }
+ 
  /* Extract the OMODE lowpart from VAL, which has IMODE.  Under certain
     conditions, VAL may already be a SUBREG against which we cannot generate
     a further SUBREG.  In this case, we expect forcing the value into a
*************** expand_unop (enum machine_mode mode, opt
*** 2885,2890 ****
--- 2949,2970 ----
  	return temp;
      }
  
+   /* Try implementing ffs (x) in terms of clz (x).  */
+   if (unoptab == ffs_optab)
+     {
+       temp = expand_ffs (mode, op0, target);
+       if (temp)
+ 	return temp;
+     }
+ 
+   /* Try implementing ctz (x) in terms of clz (x).  */
+   if (unoptab == ctz_optab)
+     {
+       temp = expand_ctz (mode, op0, target);
+       if (temp)
+ 	return temp;
+     }
+ 
   try_libcall:
    /* Now try a library call in this mode.  */
    if (unoptab->handlers[(int) mode].libfunc)