Re: [PATCH] Fix PR88301

[Christophe Lyon <christophe.lyon@linaro.org>]

Hi Richard,
On Mon, 3 Dec 2018 at 14:37, Richard Biener <rguenther@suse.de> wrote:
>
>
> This fixes a missed optimization in EVRP by teaching the code
> figuring out conditional asserts about conversions that preserve
> the converted value.
>
> Bootstrapped and tested on x86_64-unknown-linux-gnu, applied to trunk
> sofar.
>
> Richard.
>
> 2018-12-03  Richard Biener  <rguenther@suse.de>
>
>         PR tree-optimization/88301
>         * tree-vrp.c (register_edge_assert_for_2): Handle conversions
>         that do not change the value by registering the same assert
>         for the operand.
>
>         * gcc.dg/tree-ssa/evrp13.c: New testcase.
>

I noticed a regression in g++ on aarch64, and git bisect indicates
this commits is the culprit.
    g++.dg/warn/Wstringop-overflow-1.C  -std=c++14  (test for warnings, line 14)
    g++.dg/warn/Wstringop-overflow-1.C  -std=c++14 (test for excess errors)
    g++.dg/warn/Wstringop-overflow-1.C  -std=c++17  (test for warnings, line 14)
    g++.dg/warn/Wstringop-overflow-1.C  -std=c++17 (test for excess errors)
    g++.dg/warn/Wstringop-overflow-1.C  -std=c++98  (test for warnings, line 14)
    g++.dg/warn/Wstringop-overflow-1.C  -std=c++98 (test for excess errors)

g++.log says:
Excess errors:
/gcc/testsuite/g++.dg/warn/Wstringop-overflow-1.C:14:21: warning:
'char* __builtin_strncpy(char*, const char*, long unsigned int)'
writing between 6 and 2147483647 bytes into a region of size 5
overflows the destination [-Wstringop-overflow=]

Christophe

> Index: gcc/tree-vrp.c
> ===================================================================
> --- gcc/tree-vrp.c      (revision 266733)
> +++ gcc/tree-vrp.c      (working copy)
> @@ -2966,6 +2966,23 @@ register_edge_assert_for_2 (tree name, e
>             add_assert_info (asserts, name2, tmp, new_comp_code, new_val);
>         }
>
> +      /* If we have a conversion that doesn't change the value of the source
> +         simply register the same assert for it.  */
> +      if (CONVERT_EXPR_CODE_P (rhs_code))
> +       {
> +         wide_int rmin, rmax;
> +         tree rhs1 = gimple_assign_rhs1 (def_stmt);
> +         if (INTEGRAL_TYPE_P (TREE_TYPE (rhs1))
> +             && int_fits_type_p (val, TREE_TYPE (rhs1))
> +             && ((TYPE_PRECISION (TREE_TYPE (name))
> +                  > TYPE_PRECISION (TREE_TYPE (rhs1)))
> +                 || (get_range_info (rhs1, &rmin, &rmax) == VR_RANGE
> +                     && wi::fits_to_tree_p (rmin, TREE_TYPE (name))
> +                     && wi::fits_to_tree_p (rmax, TREE_TYPE (name)))))
> +           add_assert_info (asserts, rhs1, rhs1,
> +                            comp_code, fold_convert (TREE_TYPE (rhs1), val));
> +       }
> +
>        /* Add asserts for NAME cmp CST and NAME being defined as
>          NAME = NAME2 & CST2.
>
> Index: gcc/testsuite/gcc.dg/tree-ssa/evrp13.c
> ===================================================================
> --- gcc/testsuite/gcc.dg/tree-ssa/evrp13.c      (revision 0)
> +++ gcc/testsuite/gcc.dg/tree-ssa/evrp13.c      (working copy)
> @@ -0,0 +1,7 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-evrp" } */
> +
> +#define ADD_NW(A,B) (__extension__({ __typeof(A+B) R; if(__builtin_add_overflow(A,B,&R)) __builtin_unreachable(); R ;}))
> +_Bool a_b2(unsigned A,  unsigned B) { return ADD_NW(A,B) >= B; }
> +
> +/* { dg-final { scan-tree-dump "return 1;" "evrp" } } */