[PATCH] Fix part of PR87314, folding of &decl != "foo"

[Richard Biener]

On Thu, Jan 10, 2019 at 2:41 PM Richard Biener <rguenther@suse.de> wrote:
>
>
> This fixes $subject and also "foo" != "bar" folding which was
> somehow missing.  It fixes only parts of the PR since the PR
> is about PTA tracking string constants.
>
> It might help PR88775 but unless I can confirm that this is
> just queued for GCC10.
>
> You might notice I'm treating string merging possibilities
> conservatively (defer to runtime).
>
> Bootstrapped and tested on x86_64-unknown-linux-gnu.

Applied as r270845.

> Richard.
>
> From 8f14bac370b8334a42f985027394e9f3fdf9e2f1 Mon Sep 17 00:00:00 2001
> From: Richard Guenther <rguenther@suse.de>
> Date: Thu, 10 Jan 2019 10:24:20 +0100
> Subject: [PATCH] fix-pr87314-1
>
> 2019-01-10  Richard Biener  <rguenther@suse.de>
>
>         PR middle-end/87314
>         * match.pd (cmp (convert1?@2 addr@0) (convert2? addr@1)):
>         Handle STRING_CST vs DECL or STRING_CST.
>
>         * gcc.dg/pr87314-1.c: New testcase.
>
> diff --git a/gcc/match.pd b/gcc/match.pd
> index 60b12f94f9e..95fa4e4a4dd 100644
> --- a/gcc/match.pd
> +++ b/gcc/match.pd
> @@ -3896,6 +3896,9 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
>                     || TREE_CODE (base1) == SSA_NAME
>                     || TREE_CODE (base1) == STRING_CST))
>           equal = (base0 == base1);
> +       HOST_WIDE_INT ioff0 = -1, ioff1 = -1;
> +       off0.is_constant (&ioff0);
> +       off1.is_constant (&ioff1);
>       }
>       (if (equal == 1
>           && (cmp == EQ_EXPR || cmp == NE_EXPR
> @@ -3919,10 +3922,23 @@ DEFINE_INT_AND_FLOAT_ROUND_FN (RINT)
>         (if (cmp == GT_EXPR && (known_gt (off0, off1) || known_le (off0, off1)))
>         { constant_boolean_node (known_gt (off0, off1), type); }))
>        (if (equal == 0
> -          && DECL_P (base0) && DECL_P (base1)
> -          /* If we compare this as integers require equal offset.  */
> -          && (!INTEGRAL_TYPE_P (TREE_TYPE (@2))
> -              || known_eq (off0, off1)))
> +          && ((DECL_P (base0) && DECL_P (base1)
> +               /* If we compare this as integers require equal offset.  */
> +               && (!INTEGRAL_TYPE_P (TREE_TYPE (@2))
> +                   || known_eq (off0, off1)))
> +              || (DECL_P (base0) && TREE_CODE (base1) == STRING_CST)
> +              || (TREE_CODE (base0) == STRING_CST && DECL_P (base1))
> +              || (TREE_CODE (base0) == STRING_CST
> +                  && TREE_CODE (base1) == STRING_CST
> +                  && ioff0 >= 0 && ioff1 >= 0
> +                  && ioff0 < TREE_STRING_LENGTH (base0)
> +                  && ioff1 < TREE_STRING_LENGTH (base1)
> +                  /* This is a too conservative test that the STRING_CSTs
> +                     will not end up being string-merged.  */
> +                  && strncmp (TREE_STRING_POINTER (base0) + ioff0,
> +                              TREE_STRING_POINTER (base1) + ioff1,
> +                              MIN (TREE_STRING_LENGTH (base0) - ioff0,
> +                                   TREE_STRING_LENGTH (base1) - ioff1)) != 0)))
>         (switch
>         (if (cmp == EQ_EXPR)
>          { constant_boolean_node (false, type); })
> diff --git a/gcc/testsuite/gcc.dg/pr87314-1.c b/gcc/testsuite/gcc.dg/pr87314-1.c
> new file mode 100644
> index 00000000000..4dc85c8eee6
> --- /dev/null
> +++ b/gcc/testsuite/gcc.dg/pr87314-1.c
> @@ -0,0 +1,11 @@
> +/* { dg-do compile } */
> +/* { dg-options "-O -fdump-tree-original" } */
> +
> +int f(){ int a; return &a==(void *)"hello"; }
> +int g(){ return "bye"=="hello"; }
> +int h() { return "bye"=="hellobye"+5; }
> +
> +/* { dg-final { scan-tree-dump-times "hello" 1 "original" } } */
> +/* The test in h() should be retained because the result depends on
> +   string merging.  */
> +/* { dg-final { scan-assembler "hello" } } */