On Mon, 18 Dec 2017, Jakub Jelinek wrote:
> Hi!
>
> As the testcase shows, we fold strlen (str) == 0 into *str == 0 before
> the strlen pass has a chance to optimize. The following patch optimizes
> loads from the known termination '\0' into lhs = '\0' and loads from the
> part of the string known to be non-zero results in ~[0, 0] range being
> recorded if we don't have anything better.
>
> Note that unfortunately vrp2 doesn't consider any memory loads as
> interesting, even when they have non-varying ranges from other passes,
> but guess that is something to improve later.
Yeah, it simply fails to copy a known SSA range to its private lattice
for stmts it doesn't need to iterate on.
> Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
Ok.
Richard.
> 2017-12-18 Jakub Jelinek <ja...@redhat.com>
>
> PR tree-optimization/83444
> * tree-ssa-strlen.c (strlen_check_and_optimize_stmt): Optimize
> character loads.
>
> * gcc.dg/strlenopt-36.c: New test.
>
> --- gcc/tree-ssa-strlen.c.jj 2017-12-18 14:57:20.000000000 +0100
> +++ gcc/tree-ssa-strlen.c 2017-12-18 16:45:04.689862506 +0100
> @@ -3104,6 +3104,64 @@ strlen_check_and_optimize_stmt (gimple_s
> else if (code == EQ_EXPR || code == NE_EXPR)
> fold_strstr_to_strncmp (gimple_assign_rhs1 (stmt),
> gimple_assign_rhs2 (stmt), stmt);
> + else if (gimple_assign_load_p (stmt)
> + && TREE_CODE (TREE_TYPE (lhs)) == INTEGER_TYPE
> + && TYPE_MODE (TREE_TYPE (lhs)) == TYPE_MODE (char_type_node)
> + && (TYPE_PRECISION (TREE_TYPE (lhs))
> + == TYPE_PRECISION (char_type_node))
> + && !gimple_has_volatile_ops (stmt))
> + {
> + tree off = integer_zero_node;
> + unsigned HOST_WIDE_INT coff = 0;
> + int idx = -1;
> + tree rhs1 = gimple_assign_rhs1 (stmt);
> + if (code == MEM_REF)
> + {
> + idx = get_stridx (TREE_OPERAND (rhs1, 0));
> + off = TREE_OPERAND (rhs1, 1);
> + }
> + else
> + idx = get_addr_stridx (rhs1, NULL_TREE, &coff);
> + if (idx > 0)
> + {
> + strinfo *si = get_strinfo (idx);
> + if (si
> + && si->nonzero_chars
> + && TREE_CODE (si->nonzero_chars) == INTEGER_CST)
> + {
> + widest_int w1 = wi::to_widest (si->nonzero_chars);
> + widest_int w2 = wi::to_widest (off) + coff;
> + if (w1 == w2
> + && si->full_string_p)
> + {
> + /* Reading the final '\0' character. */
> + tree zero = build_int_cst (TREE_TYPE (lhs), 0);
> + gimple_set_vuse (stmt, NULL_TREE);
> + gimple_assign_set_rhs_from_tree (gsi, zero);
> + update_stmt (gsi_stmt (*gsi));
> + }
> + else if (w1 > w2)
> + {
> + /* Reading a character before the final '\0'
> + character. Just set the value range to ~[0, 0]
> + if we don't have anything better. */
> + wide_int min, max;
> + tree type = TREE_TYPE (lhs);
> + enum value_range_type vr
> + = get_range_info (lhs, &min, &max);
> + if (vr == VR_VARYING
> + || (vr == VR_RANGE
> + && min == wi::min_value (TYPE_PRECISION (type),
> + TYPE_SIGN (type))
> + && max == wi::max_value (TYPE_PRECISION (type),
> + TYPE_SIGN (type))))
> + set_range_info (lhs, VR_ANTI_RANGE,
> + wi::zero (TYPE_PRECISION (type)),
> + wi::zero (TYPE_PRECISION (type)));
> + }
> + }
> + }
> + }
>
> if (strlen_to_stridx)
> {
> --- gcc/testsuite/gcc.dg/strlenopt-36.c.jj 2017-12-18 16:49:48.357210798
> +0100
> +++ gcc/testsuite/gcc.dg/strlenopt-36.c 2017-12-18 17:02:41.804261717
> +0100
> @@ -0,0 +1,38 @@
> +/* PR tree-optimization/83444 */
> +/* { dg-do compile } */
> +/* { dg-options "-O2 -fdump-tree-optimized" } */
> +/* { dg-final { scan-tree-dump-not "abort \\(\\)" "optimized" } } */
> +
> +#include "strlenopt.h"
> +
> +void
> +foo (void)
> +{
> + char a[5] = "012";
> + strcpy (a, "");
> + if (strlen (a) != 0)
> + abort ();
> +}
> +
> +void
> +bar (void)
> +{
> + char a[5] = "012";
> + char b[7] = "";
> + strcpy (a, b);
> + if (strlen (a) != 0)
> + abort ();
> +}
> +
> +struct S { char a[4]; char b[5]; char c[7]; };
> +
> +void
> +baz (void)
> +{
> + struct S s;
> + strcpy (s.b, "012");
> + strcpy (s.c, "");
> + strcpy (s.b, s.c);
> + if (s.b[0] != 0)
> + abort ();
> +}
>
> Jakub
>
>
--
Richard Biener <rguent...@suse.de>
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB
21284 (AG Nuernberg)
