Re: [PATCH][1/n] Improve vectorization in PR53355

["William J. Schmidt" <wschmidt at linux dot vnet dot ibm dot com>]

On Tue, 2012-05-15 at 14:17 +0200, Richard Guenther wrote:
> This is the first patch to make the generated code for the testcase
> in PR53355 better.  It teaches VRP about LSHIFT_EXPRs (albeit only
> of a very simple form).
> 
> Bootstrapped on x86_64-unknown-linux-gnu, testing in progress.

This appears to have caused
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=53385.

Thanks,
Bill

> 
> Richard.
> 
> 2012-05-15  Richard Guenther  <rguenther@suse.de>
> 
> 	PR tree-optimization/53355
> 	* tree-vrp.c (extract_range_from_binary_expr_1): Handle LSHIFT_EXPRs
> 	by constants.
> 
> 	* gcc.dg/tree-ssa/vrp67.c: New testcase.
> 
> Index: gcc/tree-vrp.c
> ===================================================================
> *** gcc/tree-vrp.c	(revision 187503)
> --- gcc/tree-vrp.c	(working copy)
> *************** extract_range_from_binary_expr_1 (value_
> *** 2403,2408 ****
> --- 2403,2409 ----
>         && code != ROUND_DIV_EXPR
>         && code != TRUNC_MOD_EXPR
>         && code != RSHIFT_EXPR
> +       && code != LSHIFT_EXPR
>         && code != MIN_EXPR
>         && code != MAX_EXPR
>         && code != BIT_AND_EXPR
> *************** extract_range_from_binary_expr_1 (value_
> *** 2596,2601 ****
> --- 2597,2636 ----
>         extract_range_from_multiplicative_op_1 (vr, code, &vr0, &vr1);
>         return;
>       }
> +   else if (code == LSHIFT_EXPR)
> +     {
> +       /* If we have a LSHIFT_EXPR with any shift values outside [0..prec-1],
> + 	 then drop to VR_VARYING.  Outside of this range we get undefined
> + 	 behavior from the shift operation.  We cannot even trust
> + 	 SHIFT_COUNT_TRUNCATED at this stage, because that applies to rtl
> + 	 shifts, and the operation at the tree level may be widened.  */
> +       if (vr1.type != VR_RANGE
> + 	  || !value_range_nonnegative_p (&vr1)
> + 	  || TREE_CODE (vr1.max) != INTEGER_CST
> + 	  || compare_tree_int (vr1.max, TYPE_PRECISION (expr_type) - 1) == 1)
> + 	{
> + 	  set_value_range_to_varying (vr);
> + 	  return;
> + 	}
> + 
> +       /* We can map shifts by constants to MULT_EXPR handling.  */
> +       if (range_int_cst_singleton_p (&vr1))
> + 	{
> + 	  value_range_t vr1p = { VR_RANGE, NULL_TREE, NULL_TREE, NULL };
> + 	  vr1p.min
> + 	    = double_int_to_tree (expr_type,
> + 				  double_int_lshift (double_int_one,
> + 						     TREE_INT_CST_LOW (vr1.min),
> + 						     TYPE_PRECISION (expr_type),
> + 						     false));
> + 	  vr1p.max = vr1p.min;
> + 	  extract_range_from_multiplicative_op_1 (vr, MULT_EXPR, &vr0, &vr1p);
> + 	  return;
> + 	}
> + 
> +       set_value_range_to_varying (vr);
> +       return;
> +     }
>     else if (code == TRUNC_DIV_EXPR
>   	   || code == FLOOR_DIV_EXPR
>   	   || code == CEIL_DIV_EXPR
> Index: gcc/testsuite/gcc.dg/tree-ssa/vrp67.c
> ===================================================================
> *** gcc/testsuite/gcc.dg/tree-ssa/vrp67.c	(revision 0)
> --- gcc/testsuite/gcc.dg/tree-ssa/vrp67.c	(revision 0)
> ***************
> *** 0 ****
> --- 1,38 ----
> + /* { dg-do compile } */
> + /* { dg-options "-O2 -fdump-tree-vrp1" } */
> + 
> + unsigned foo (unsigned i)
> + {
> +   if (i == 2)
> +     {
> +       i = i << 2;
> +       if (i != 8)
> + 	link_error ();
> +     }
> +   return i;
> + }
> + unsigned bar (unsigned i)
> + {
> +   if (i == 1 << (sizeof (unsigned) * 8 - 1))
> +     {
> +       i = i << 1;
> +       if (i != 0)
> + 	link_error ();
> +     }
> +   return i;
> + }
> + unsigned baz (unsigned i)
> + {
> +   i = i & 15;
> +   if (i == 0)
> +     return 0;
> +   i = 1000 - i;
> +   i >>= 1;
> +   i <<= 1;
> +   if (i == 0)
> +     link_error ();
> +   return i;
> + }
> + 
> + /* { dg-final { scan-tree-dump-times "Folding predicate" 3 "vrp1" } } */
> + /* { dg-final { cleanup-tree-dump "vrp1" } } */