Confirmed.  slsr replaces:
  D.2219_3 = *row_2(D);
  D.2220_4 = (int) D.2219_3;
  a1_5 = D.2220_4 * 22725;
  D.2222_6 = MEM[(short int *)row_2(D) + 4B];
  D.2223_7 = (int) D.2222_6;
  D.2224_8 = D.2223_7 * 21407;
  a0_9 = D.2224_8 + a1_5;
  D.2225_10 = D.2223_7 * 8867;
- a1_11 = a1_5 + D.2225_10;
+ slsr.4_25 = D.2222_6 * 12540;
+ slsr.5_26 = (int) slsr.4_25;
+ a1_11 = a0_9 - slsr.5_26;

The multiplication is newly performed in short int, supposedly that is the problem here.  Anyway, while the number of multiplications in the end is the same, with slsr the code sequence is also 3 insns/4 bytes longer on x86_64.

I'll take a look.  Might be a day or two as my queue is kind of full.

I'm putting together a for-now patch that disables the optimization when a widening cast produces the stride.  In the long run this can be re-enabled so long as we can retain the original cast and base the new multiply on that value rather than doing it in the smaller type.  This is a bit subtle to get right so I plan to defer that work until I have more time to concentrate on it.

I.e., there are two problems in this example: we did the multiply in a smaller type and we introduced an extra cast that wasn't necessary if we were smart enough (causing the longer sequence as Jakub noted).  The replacement would be ok with a little re-design.

Author: wschmidt
Date: Wed Aug 15 13:27:29 2012
New Revision: 190412

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=190412
Log:
gcc:

2012-08-15  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>

	PR tree-optimization/54245
	* gimple-ssa-strength-reduction.c (legal_cast_p_1): New function.
	(legal_cast_p): Split out logic to legal_cast_p_1.
	(analyze_increments): Avoid introducing multiplies in smaller types.


gcc/testsuite:

2012-08-15  Bill Schmidt  <wschmidt@linux.vnet.ibm.com>

	PR tree-optimization/54245
	* gcc.dg/tree-ssa/pr54245.c: New test.


Added:
    trunk/gcc/testsuite/gcc.dg/tree-ssa/pr54245.c
Modified:
    trunk/gcc/ChangeLog
    trunk/gcc/gimple-ssa-strength-reduction.c
    trunk/gcc/testsuite/ChangeLog

Fixed.