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Re: [PATCH] Fix PR81719


On Tue, Aug 8, 2017 at 1:20 PM, Richard Biener <rguenther@suse.de> wrote:
>
> The following improves niter analysis for range-based for loops
> by handling ADDR_EXPR in expand_simple_operations.
>
> Bootstrapped on x86_64-unknown-linux-gnu, testing in progress.
>
> Richard.
>
> 2017-08-08  Richard Biener  <rguenther@suse.de>
>
>         PR middle-end/81719
>         * tree-ssa-loop-niter.c: Include tree-dfa.h.
>         (expand_simple_operations): Also look through ADDR_EXPRs with
>         MEM_REF bases treating them as POINTER_PLUS_EXPR.
>
>         * g++.dg/tree-ssa/pr81719.C: New testcase.
>
> Index: gcc/tree-ssa-loop-niter.c
> ===================================================================
> *** gcc/tree-ssa-loop-niter.c   (revision 250813)
> --- gcc/tree-ssa-loop-niter.c   (working copy)
> *************** along with GCC; see the file COPYING3.
> *** 42,47 ****
> --- 42,48 ----
>   #include "tree-chrec.h"
>   #include "tree-scalar-evolution.h"
>   #include "params.h"
> + #include "tree-dfa.h"
>
>
>   /* The maximum number of dominator BBs we search for conditions
> *************** expand_simple_operations (tree expr, tre
> *** 1980,1985 ****
> --- 1981,2001 ----
>
>         if (code == SSA_NAME)
>         return expand_simple_operations (e, stop);
> +       else if (code == ADDR_EXPR)
> +       {
> +         HOST_WIDE_INT offset;
> +         tree base = get_addr_base_and_unit_offset (TREE_OPERAND (e, 0),
> +                                                    &offset);
> +         if (base
> +             && TREE_CODE (base) == MEM_REF)
> +           {
> +             ee = expand_simple_operations (TREE_OPERAND (base, 0), stop);
> +             return fold_build2 (POINTER_PLUS_EXPR, TREE_TYPE (expr), ee,
> +                                 wide_int_to_tree (sizetype,
> +                                                   mem_ref_offset (base)
> +                                                   + offset));
> +           }
> +       }
>
>         return expr;
>       }
There are various places we need to look into ADDR_EXPR (MEM_REF), is
it possible/beneficial to generally simplify &MEM_REF[base + offset]?

Thanks,
bin
> Index: gcc/testsuite/g++.dg/tree-ssa/pr81719.C
> ===================================================================
> *** gcc/testsuite/g++.dg/tree-ssa/pr81719.C     (nonexistent)
> --- gcc/testsuite/g++.dg/tree-ssa/pr81719.C     (working copy)
> ***************
> *** 0 ****
> --- 1,24 ----
> + /* { dg-do compile { target c++11 } } */
> + /* { dg-options "-O3 -fdump-tree-optimized" } */
> +
> + typedef int Items[2];
> +
> + struct ItemArray
> + {
> +   Items items;
> +   int sum_x2() const;
> + };
> +
> + int ItemArray::sum_x2() const
> + {
> +   int total = 0;
> +   for (int item : items)
> +     {
> +       total += item;
> +     }
> +   return total;
> + }
> +
> + /* We should be able to compute the number of iterations to two, unroll
> +    the loop and end up with a single basic-block in sum_x2.  */
> + /* { dg-final { scan-tree-dump-times "bb" 1 "optimized" } } */


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