Re: [PATCH] Fix PR37795

[Andrew Thomas Pinski <pinskia at gmail dot com>]

Sent from my iPhone

On Oct 12, 2008, at 11:50 AM, Richard Guenther <rguenther@suse.de>  
wrote:

> This fixes PR37795, a missed optimization with optimizing consecutive
> (and-ed) tests as we already do for or-ed ones.
Does this do the correct thing for floating point comparisons?  That  
is it if we had a >= b and b < a does not change as NaN would give  
true and the false.

Thanks,
Andrew Pinski


> Bootstrapped and tested on x86_64-unknown-linux-gnu, queued for 4.5.
>
> Richard.
>
>
> 2008-10-12  Richard Guenther  <rguenther@suse.de>
>
>    PR tree-optimization/37795
>    * tree-ssa-ifcombine.c (ifcombine_ifandif): Optimize two successive
>    comparisons.
>
>    * gcc.dg/tree-ssa/ssa-ifcombine-7.c: New testcase.
>
> Index: gcc/tree-ssa-ifcombine.c
> ===================================================================
> *** gcc/tree-ssa-ifcombine.c    (revision 141074)
> --- gcc/tree-ssa-ifcombine.c    (working copy)
> *************** ifcombine_ifandif (basic_block inner_con
> *** 380,385 ****
> --- 380,441 ----
>        return true;
>      }
>
> +   /* See if we have two comparisons that we can merge into one.  */
> +   else if (TREE_CODE_CLASS (gimple_cond_code (inner_cond)) ==  
> tcc_comparison
> +       && TREE_CODE_CLASS (gimple_cond_code (outer_cond)) ==  
> tcc_comparison
> +       && operand_equal_p (gimple_cond_lhs (inner_cond),
> +                   gimple_cond_lhs (outer_cond), 0)
> +       && operand_equal_p (gimple_cond_rhs (inner_cond),
> +                   gimple_cond_rhs (outer_cond), 0))
> +     {
> +       enum tree_code code1 = gimple_cond_code (inner_cond);
> +       enum tree_code code2 = gimple_cond_code (outer_cond);
> +       enum tree_code code;
> +       tree t;
> +
> + #define CHK(a,b) ((code1 == a ## _EXPR && code2 == b ## _EXPR) \
> +          || (code2 == a ## _EXPR && code1 == b ## _EXPR))
> +       /* Merge the two condition codes if possible.  */
> +       if (code1 == code2)
> +    code = code1;
> +       else if (CHK (EQ, LE))
> +    code = EQ_EXPR;
> +       else if (CHK (EQ, GE))
> +    code = EQ_EXPR;
> +       else if (CHK (NE, LE))
> +    code = LT_EXPR;
> +       else if (CHK (NE, GE))
> +    code = GT_EXPR;
> +       else if (CHK (LE, GE))
> +    code = EQ_EXPR;
> +       /* We could check for combinations leading to trivial true/ 
> false.  */
> +       else
> +    return false;
> + #undef CHK
> +
> +       /* Do it.  */
> +       t = fold_build2 (code, boolean_type_node, gimple_cond_lhs  
> (outer_cond),
> +               gimple_cond_rhs (outer_cond));
> +       t = canonicalize_cond_expr_cond (t);
> +       if (!t)
> +    return false;
> +       gimple_cond_set_condition_from_tree (inner_cond, t);
> +       update_stmt (inner_cond);
> +
> +       /* Leave CFG optimization to cfg_cleanup.  */
> +       gimple_cond_set_condition_from_tree (outer_cond,  
> boolean_true_node);
> +       update_stmt (outer_cond);
> +
> +       if (dump_file)
> +    {
> +      fprintf (dump_file, "optimizing two comparisons to ");
> +      print_generic_expr (dump_file, t, 0);
> +      fprintf (dump_file, "\n");
> +    }
> +
> +       return true;
> +     }
> +
>    return false;
>  }
>
> Index: gcc/testsuite/gcc.dg/tree-ssa/ssa-ifcombine-7.c
> ===================================================================
> *** gcc/testsuite/gcc.dg/tree-ssa/ssa-ifcombine-7.c    (revision 0)
> --- gcc/testsuite/gcc.dg/tree-ssa/ssa-ifcombine-7.c    (revision 0)
> ***************
> *** 0 ****
> --- 1,15 ----
> + /* { dg-do compile } */
> + /* { dg-options "-O -fdump-tree-optimized" } */
> +
> + int test1 (int i, int j)
> + {
> +   if (i >= j)
> +     if (i != j)
> +       return 0;
> +   return -1;
> + }
> +
> + /* The above should be optimized to a i > j test by ifcombine.  */
> +
> + /* { dg-final { scan-tree-dump " > " "optimized" } } */
> + /* { dg-final { cleanup-tree-dump "optimized" } } */