[PATCH] Fix bogus address costs in ivopts

["Ulrich Weigand" <weigand at i1 dot informatik dot uni-erlangen dot de>]

Hello,

some of the loop optimization tests (loop-2.c, loop-4.c) fail on s390x
because the reference to the arr_base symbol is not moved out of the
loop.

This turned out to be caused simply by bogus cost metrics returned
from get_address_cost, leading to suboptimal selection of iv candidates.

There were two problems in get_address_cost:

- it did not recognize that offset zero is special and may be 
  implemented more efficiently than any non-zero offset (even though
  this is not an issue on s390, it may well be e.g. on rs6000).

- it would generate non-canonical RTL of the form
      (plus (const_int) (reg))
  in some cases, which caused the cost functions to return too
  high costs for simple addresses

Both are fixed by the following patch.  (Note that the whole concept
behind get_address_cost still appears to be too simplistic IMHO:
e.g. the assumption that every type of symbol has the same cost is
just wrong.  A local static will be cheaper that a global symbol 
with -fPIC, which will be cheaper than thread-local symbols etc.)

Bootstrapped/regtested on s390-ibm-linux and s390x-ibm-linux,
fixes the loop-2/loop-4 test cases.

OK for mainline?

Bye,
Ulrich


ChangeLog:

	* tree-ssa-loop-ivopts.c (get_address_cost): Offset zero does not
	cause extra costs.  Generate canonical RTL.

Index: gcc/tree-ssa-loop-ivopts.c
===================================================================
RCS file: /cvs/gcc/gcc/gcc/tree-ssa-loop-ivopts.c,v
retrieving revision 2.20
diff -c -p -r2.20 tree-ssa-loop-ivopts.c
*** gcc/tree-ssa-loop-ivopts.c	18 Oct 2004 18:01:09 -0000	2.20
--- gcc/tree-ssa-loop-ivopts.c	20 Oct 2004 13:05:19 -0000
*************** get_address_cost (bool symbol_present, b
*** 2485,2491 ****
    s_offset = offset;
  
    cost = 0;
!   offset_p = (min_offset <= s_offset && s_offset <= max_offset);
    ratio_p = (ratio != 1
  	     && -MAX_RATIO <= ratio && ratio <= MAX_RATIO
  	     && TEST_BIT (valid_mult, ratio + MAX_RATIO));
--- 2485,2492 ----
    s_offset = offset;
  
    cost = 0;
!   offset_p = (s_offset != 0
! 	      && min_offset <= s_offset && s_offset <= max_offset);
    ratio_p = (ratio != 1
  	     && -MAX_RATIO <= ratio && ratio <= MAX_RATIO
  	     && TEST_BIT (valid_mult, ratio + MAX_RATIO));
*************** get_address_cost (bool symbol_present, b
*** 2509,2514 ****
--- 2510,2518 ----
        if (ratio_p)
  	addr = gen_rtx_fmt_ee (MULT, Pmode, addr, GEN_INT (rat));
  
+       if (var_present)
+ 	addr = gen_rtx_fmt_ee (PLUS, Pmode, reg1, addr);
+ 
        if (symbol_present)
  	{
  	  base = gen_rtx_SYMBOL_REF (Pmode, ggc_strdup (""));
*************** get_address_cost (bool symbol_present, b
*** 2517,2531 ****
  				  gen_rtx_fmt_ee (PLUS, Pmode,
  						  base,
  						  GEN_INT (off)));
- 	  if (var_present)
- 	    base = gen_rtx_fmt_ee (PLUS, Pmode, reg1, base);
- 	}
- 
-       else if (var_present)
- 	{
- 	  base = reg1;
- 	  if (offset_p)
- 	    base = gen_rtx_fmt_ee (PLUS, Pmode, base, GEN_INT (off));
  	}
        else if (offset_p)
  	base = GEN_INT (off);
--- 2521,2526 ----
-- 
  Dr. Ulrich Weigand
  weigand@informatik.uni-erlangen.de