Re: [PATCH v2] Simplify memchr with small constant strings

["H.J. Lu" <hjl.tools@gmail.com>]

On Wed, Jul 13, 2022 at 5:35 AM Richard Biener
<richard.guenther@gmail.com> wrote:
>
> On Tue, Jul 12, 2022 at 6:59 PM H.J. Lu <hjl.tools@gmail.com> wrote:
> >
> > On Fri, Jul 8, 2022 at 5:54 AM Richard Biener
> > <richard.guenther@gmail.com> wrote:
> > >
> > > On Thu, Jul 7, 2022 at 6:45 PM H.J. Lu <hjl.tools@gmail.com> wrote:
> > > >
> > > > When memchr is applied on a constant string of no more than the bytes of
> > > > a word, simplify memchr by checking each byte in the constant string.
> > > >
> > > > int f (int a)
> > > > {
> > > >    return  __builtin_memchr ("AE", a, 2) != 0;
> > > > }
> > > >
> > > > is simplified to
> > > >
> > > > int f (int a)
> > > > {
> > > >   return ((char) a == 'A' || (char) a == 'E') != 0;
> > > > }
> > > >
> > > > gcc/
> > > >
> > > >         PR tree-optimization/103798
> > > >         * tree-ssa-forwprop.cc: Include "tree-ssa-strlen.h".
> > > >         (simplify_builtin_call): Inline memchr with constant strings of
> > > >         no more than the bytes of a word.
> > > >         * tree-ssa-strlen.cc (use_in_zero_equality): Make it global.
> > > >         * tree-ssa-strlen.h (use_in_zero_equality): New.
> > > >
> > > > gcc/testsuite/
> > > >
> > > >         PR tree-optimization/103798
> > > >         * c-c++-common/pr103798-1.c: New test.
> > > >         * c-c++-common/pr103798-2.c: Likewise.
> > > >         * c-c++-common/pr103798-3.c: Likewise.
> > > >         * c-c++-common/pr103798-4.c: Likewise.
> > > >         * c-c++-common/pr103798-5.c: Likewise.
> > > >         * c-c++-common/pr103798-6.c: Likewise.
> > > >         * c-c++-common/pr103798-7.c: Likewise.
> > > >         * c-c++-common/pr103798-8.c: Likewise.
> > > > ---
> > > >  gcc/testsuite/c-c++-common/pr103798-1.c | 28 +++++++++++
> > > >  gcc/testsuite/c-c++-common/pr103798-2.c | 30 ++++++++++++
> > > >  gcc/testsuite/c-c++-common/pr103798-3.c | 28 +++++++++++
> > > >  gcc/testsuite/c-c++-common/pr103798-4.c | 28 +++++++++++
> > > >  gcc/testsuite/c-c++-common/pr103798-5.c | 26 ++++++++++
> > > >  gcc/testsuite/c-c++-common/pr103798-6.c | 27 +++++++++++
> > > >  gcc/testsuite/c-c++-common/pr103798-7.c | 27 +++++++++++
> > > >  gcc/testsuite/c-c++-common/pr103798-8.c | 27 +++++++++++
> > > >  gcc/tree-ssa-forwprop.cc                | 64 +++++++++++++++++++++++++
> > > >  gcc/tree-ssa-strlen.cc                  |  4 +-
> > > >  gcc/tree-ssa-strlen.h                   |  2 +
> > > >  11 files changed, 289 insertions(+), 2 deletions(-)
> > > >  create mode 100644 gcc/testsuite/c-c++-common/pr103798-1.c
> > > >  create mode 100644 gcc/testsuite/c-c++-common/pr103798-2.c
> > > >  create mode 100644 gcc/testsuite/c-c++-common/pr103798-3.c
> > > >  create mode 100644 gcc/testsuite/c-c++-common/pr103798-4.c
> > > >  create mode 100644 gcc/testsuite/c-c++-common/pr103798-5.c
> > > >  create mode 100644 gcc/testsuite/c-c++-common/pr103798-6.c
> > > >  create mode 100644 gcc/testsuite/c-c++-common/pr103798-7.c
> > > >  create mode 100644 gcc/testsuite/c-c++-common/pr103798-8.c
> > > >
> > > > diff --git a/gcc/testsuite/c-c++-common/pr103798-1.c b/gcc/testsuite/c-c++-common/pr103798-1.c
> > > > new file mode 100644
> > > > index 00000000000..cd3edf569fc
> > > > --- /dev/null
> > > > +++ b/gcc/testsuite/c-c++-common/pr103798-1.c
> > > > @@ -0,0 +1,28 @@
> > > > +/* { dg-do run } */
> > > > +/* { dg-options "-O2 -fdump-tree-optimized -save-temps" } */
> > > > +
> > > > +__attribute__ ((weak))
> > > > +int
> > > > +f (char a)
> > > > +{
> > > > +   return  __builtin_memchr ("a", a, 1) == 0;
> > > > +}
> > > > +
> > > > +__attribute__ ((weak))
> > > > +int
> > > > +g (char a)
> > > > +{
> > > > +  return a != 'a';
> > > > +}
> > > > +
> > > > +int
> > > > +main ()
> > > > +{
> > > > + for (int i = 0; i < 255; i++)
> > > > +   if (f (i) != g (i))
> > > > +     __builtin_abort ();
> > > > +
> > > > + return 0;
> > > > +}
> > > > +
> > > > +/* { dg-final { scan-assembler-not "memchr" } } */
> > > > diff --git a/gcc/testsuite/c-c++-common/pr103798-2.c b/gcc/testsuite/c-c++-common/pr103798-2.c
> > > > new file mode 100644
> > > > index 00000000000..e7e99c3679e
> > > > --- /dev/null
> > > > +++ b/gcc/testsuite/c-c++-common/pr103798-2.c
> > > > @@ -0,0 +1,30 @@
> > > > +/* { dg-do run } */
> > > > +/* { dg-options "-O2 -fdump-tree-optimized -save-temps" } */
> > > > +
> > > > +#include <string.h>
> > > > +
> > > > +__attribute__ ((weak))
> > > > +int
> > > > +f (int a)
> > > > +{
> > > > +   return memchr ("aE", a, 2) != NULL;
> > > > +}
> > > > +
> > > > +__attribute__ ((weak))
> > > > +int
> > > > +g (char a)
> > > > +{
> > > > +  return a == 'a' || a == 'E';
> > > > +}
> > > > +
> > > > +int
> > > > +main ()
> > > > +{
> > > > + for (int i = 0; i < 255; i++)
> > > > +   if (f (i + 256) != g (i + 256))
> > > > +     __builtin_abort ();
> > > > +
> > > > + return 0;
> > > > +}
> > > > +
> > > > +/* { dg-final { scan-assembler-not "memchr" } } */
> > > > diff --git a/gcc/testsuite/c-c++-common/pr103798-3.c b/gcc/testsuite/c-c++-common/pr103798-3.c
> > > > new file mode 100644
> > > > index 00000000000..ddcedc7e238
> > > > --- /dev/null
> > > > +++ b/gcc/testsuite/c-c++-common/pr103798-3.c
> > > > @@ -0,0 +1,28 @@
> > > > +/* { dg-do run } */
> > > > +/* { dg-options "-O2 -fdump-tree-optimized -save-temps" } */
> > > > +
> > > > +__attribute__ ((weak))
> > > > +int
> > > > +f (char a)
> > > > +{
> > > > +   return  __builtin_memchr ("aEgZ", a, 3) == 0;
> > > > +}
> > > > +
> > > > +__attribute__ ((weak))
> > > > +int
> > > > +g (char a)
> > > > +{
> > > > +  return a != 'a' && a != 'E' && a != 'g';
> > > > +}
> > > > +
> > > > +int
> > > > +main ()
> > > > +{
> > > > + for (int i = 0; i < 255; i++)
> > > > +   if (f (i) != g (i))
> > > > +     __builtin_abort ();
> > > > +
> > > > + return 0;
> > > > +}
> > > > +
> > > > +/* { dg-final { scan-assembler-not "memchr" } } */
> > > > diff --git a/gcc/testsuite/c-c++-common/pr103798-4.c b/gcc/testsuite/c-c++-common/pr103798-4.c
> > > > new file mode 100644
> > > > index 00000000000..00e8302a833
> > > > --- /dev/null
> > > > +++ b/gcc/testsuite/c-c++-common/pr103798-4.c
> > > > @@ -0,0 +1,28 @@
> > > > +/* { dg-do run } */
> > > > +/* { dg-options "-O2 -fdump-tree-optimized -save-temps" } */
> > > > +
> > > > +__attribute__ ((weak))
> > > > +int
> > > > +f (char a)
> > > > +{
> > > > +   return  __builtin_memchr ("aEgi", a, 4) != 0;
> > > > +}
> > > > +
> > > > +__attribute__ ((weak))
> > > > +int
> > > > +g (char a)
> > > > +{
> > > > +  return a == 'a' || a == 'E' || a == 'g' || a == 'i';
> > > > +}
> > > > +
> > > > +int
> > > > +main ()
> > > > +{
> > > > + for (int i = 0; i < 255; i++)
> > > > +   if (f (i) != g (i))
> > > > +     __builtin_abort ();
> > > > +
> > > > + return 0;
> > > > +}
> > > > +
> > > > +/* { dg-final { scan-assembler-not "memchr" } } */
> > > > diff --git a/gcc/testsuite/c-c++-common/pr103798-5.c b/gcc/testsuite/c-c++-common/pr103798-5.c
> > > > new file mode 100644
> > > > index 00000000000..0d6487a13df
> > > > --- /dev/null
> > > > +++ b/gcc/testsuite/c-c++-common/pr103798-5.c
> > > > @@ -0,0 +1,26 @@
> > > > +/* { dg-do run { target int128 } } */
> > > > +/* { dg-options "-O2 -fdump-tree-optimized -save-temps" } */
> > > > +
> > > > +__attribute__ ((weak))
> > > > +int f(char a)
> > > > +{
> > > > +   return  __builtin_memchr ("aEgiH", a, 5) == 0;
> > > > +}
> > > > +
> > > > +__attribute__ ((weak))
> > > > +int g(char a)
> > > > +{
> > > > +  return a != 'a' && a != 'E' && a != 'g' && a != 'i' && a != 'H';
> > > > +}
> > > > +
> > > > +int
> > > > +main ()
> > > > +{
> > > > + for (int i = 0; i < 255; i++)
> > > > +   if (f (i) != g (i))
> > > > +     __builtin_abort ();
> > > > +
> > > > + return 0;
> > > > +}
> > > > +
> > > > +/* { dg-final { scan-assembler-not "memchr" } } */
> > > > diff --git a/gcc/testsuite/c-c++-common/pr103798-6.c b/gcc/testsuite/c-c++-common/pr103798-6.c
> > > > new file mode 100644
> > > > index 00000000000..5ccb5ee66e0
> > > > --- /dev/null
> > > > +++ b/gcc/testsuite/c-c++-common/pr103798-6.c
> > > > @@ -0,0 +1,27 @@
> > > > +/* { dg-do run { target int128 } } */
> > > > +/* { dg-options "-O2 -fdump-tree-optimized -save-temps" } */
> > > > +
> > > > +__attribute__ ((weak))
> > > > +int f(char a)
> > > > +{
> > > > +   return  __builtin_memchr ("aEgiHx", a, 6) != 0;
> > > > +}
> > > > +
> > > > +__attribute__ ((weak))
> > > > +int g(char a)
> > > > +{
> > > > +  return (a == 'a' || a == 'E' || a == 'g' || a == 'i' || a == 'H'
> > > > +         || a == 'x');
> > > > +}
> > > > +
> > > > +int
> > > > +main ()
> > > > +{
> > > > + for (int i = 0; i < 255; i++)
> > > > +   if (f (i) != g (i))
> > > > +     __builtin_abort ();
> > > > +
> > > > + return 0;
> > > > +}
> > > > +
> > > > +/* { dg-final { scan-assembler-not "memchr" } } */
> > > > diff --git a/gcc/testsuite/c-c++-common/pr103798-7.c b/gcc/testsuite/c-c++-common/pr103798-7.c
> > > > new file mode 100644
> > > > index 00000000000..40fd38257d1
> > > > --- /dev/null
> > > > +++ b/gcc/testsuite/c-c++-common/pr103798-7.c
> > > > @@ -0,0 +1,27 @@
> > > > +/* { dg-do run { target int128 } } */
> > > > +/* { dg-options "-O2 -fdump-tree-optimized -save-temps" } */
> > > > +
> > > > +__attribute__ ((weak))
> > > > +int f(char a)
> > > > +{
> > > > +   return  __builtin_memchr ("aEgiHjZ", a, 7) == 0;
> > > > +}
> > > > +
> > > > +__attribute__ ((weak))
> > > > +int g(char a)
> > > > +{
> > > > +  return (a != 'a' && a != 'E' && a != 'g' && a != 'i' && a != 'H'
> > > > +         && a != 'j' && a != 'Z');
> > > > +}
> > > > +
> > > > +int
> > > > +main ()
> > > > +{
> > > > + for (int i = 0; i < 255; i++)
> > > > +   if (f (i) != g (i))
> > > > +     __builtin_abort ();
> > > > +
> > > > + return 0;
> > > > +}
> > > > +
> > > > +/* { dg-final { scan-assembler-not "memchr" } } */
> > > > diff --git a/gcc/testsuite/c-c++-common/pr103798-8.c b/gcc/testsuite/c-c++-common/pr103798-8.c
> > > > new file mode 100644
> > > > index 00000000000..0841b18cea4
> > > > --- /dev/null
> > > > +++ b/gcc/testsuite/c-c++-common/pr103798-8.c
> > > > @@ -0,0 +1,27 @@
> > > > +/* { dg-do run { target int128 } } */
> > > > +/* { dg-options "-O2 -fdump-tree-optimized -save-temps" } */
> > > > +
> > > > +__attribute__ ((weak))
> > > > +int f(int a)
> > > > +{
> > > > +   return  __builtin_memchr ("aEgiHx19ABC", a, 8) != 0;
> > > > +}
> > > > +
> > > > +__attribute__ ((weak))
> > > > +int g(char a)
> > > > +{
> > > > +  return (a == 'a' || a == 'E' || a == 'g' || a == 'i' || a == 'H'
> > > > +         || a == 'x' || a == '1' || a == '9');
> > > > +}
> > > > +
> > > > +int
> > > > +main ()
> > > > +{
> > > > + for (int i = 0; i < 255; i++)
> > > > +   if (f (i + 256) != g (i + 256))
> > > > +     __builtin_abort ();
> > > > +
> > > > + return 0;
> > > > +}
> > > > +
> > > > +/* { dg-final { scan-assembler-not "memchr" } } */
> > > > diff --git a/gcc/tree-ssa-forwprop.cc b/gcc/tree-ssa-forwprop.cc
> > > > index 69567ab3275..edd1277c23b 100644
> > > > --- a/gcc/tree-ssa-forwprop.cc
> > > > +++ b/gcc/tree-ssa-forwprop.cc
> > > > @@ -42,6 +42,7 @@ along with GCC; see the file COPYING3.  If not see
> > > >  #include "tree-dfa.h"
> > > >  #include "tree-ssa-propagate.h"
> > > >  #include "tree-ssa-dom.h"
> > > > +#include "tree-ssa-strlen.h"
> > > >  #include "builtins.h"
> > > >  #include "tree-cfgcleanup.h"
> > > >  #include "cfganal.h"
> > > > @@ -1177,6 +1178,15 @@ constant_pointer_difference (tree p1, tree p2)
> > > >     memcpy (p, "abcd   ", 7);
> > > >     call if the latter can be stored by pieces during expansion.
> > > >
> > > > +   Optimize
> > > > +   memchr ("abcd", a, 4) == 0;
> > > > +   or
> > > > +   memchr ("abcd", a, 4) != 0;
> > > > +   to
> > > > +   (a == 'a' || a == 'b' || a == 'c' || a == 'd') == 0
> > > > +   or
> > > > +   (a == 'a' || a == 'b' || a == 'c' || a == 'd') != 0
> > > > +
> > > >     Also canonicalize __atomic_fetch_op (p, x, y) op x
> > > >     to __atomic_op_fetch (p, x, y) or
> > > >     __atomic_op_fetch (p, x, y) iop x
> > > > @@ -1193,8 +1203,62 @@ simplify_builtin_call (gimple_stmt_iterator *gsi_p, tree callee2)
> > > >      return false;
> > > >    stmt1 = SSA_NAME_DEF_STMT (vuse);
> > > >
> > > > +  tree res;
> > > > +
> > > >    switch (DECL_FUNCTION_CODE (callee2))
> > > >      {
> > > > +    case BUILT_IN_MEMCHR:
> > > > +      if (gimple_call_num_args (stmt2) == 3
> > > > +         && (res = gimple_call_lhs (stmt2)) != nullptr
> > > > +         && use_in_zero_equality (res) != nullptr
> > > > +         && CHAR_BIT == 8
> > > > +         && BITS_PER_UNIT == 8)
> > > > +       {
> > > > +         tree ptr = gimple_call_arg (stmt2, 0);
> > > > +         if (TREE_CODE (ptr) != ADDR_EXPR
> > > > +             || TREE_CODE (TREE_OPERAND (ptr, 0)) != STRING_CST)
> > > > +           break;
> > > > +         unsigned HOST_WIDE_INT slen
> > > > +           = TREE_STRING_LENGTH (TREE_OPERAND (ptr, 0));
> > > > +         /* It must be a non-empty string constant.  */
> > > > +         if (slen < 2)
> > > > +           break;
> > > > +         tree size = gimple_call_arg (stmt2, 2);
> > > > +         /* Size must be a constant which is <= UNITS_PER_WORD and
> > > > +            <= the string length.  */
> > > > +         if (TREE_CODE (size) != INTEGER_CST
> > > > +             || integer_zerop (size)
> > > > +             || wi::gtu_p (wi::to_wide (size), UNITS_PER_WORD)
> > > > +             || wi::geu_p (wi::to_wide (size), slen))
> > >
> > > it might be convenient to check tree_fits_uhwi_p (size) and
> > > do unsigned HOST_WIDE_INT sz = tree_to_uhwi (size); instead
> > > of playing with wide-int here.
> >
> > Fixed.
> >
> > > > +           break;
> > > > +         tree ch = gimple_call_arg (stmt2, 1);
> > > > +         location_t loc = gimple_location (stmt2);
> > > > +         if (!useless_type_conversion_p (char_type_node,
> > > > +                                         TREE_TYPE (ch)))
> > > > +           ch = fold_convert_loc (loc, char_type_node, ch);
> > > > +         const char *p = TREE_STRING_POINTER (TREE_OPERAND (ptr, 0));
> > > > +         unsigned int isize = TREE_INT_CST_LOW (size);
> > > > +         tree *op = new tree[isize];
> > > > +         for (unsigned int i = 0; i < isize; i++)
> > > > +           {
> > > > +             op[i] = build_int_cst (char_type_node, p[i]);
> > > > +             op[i] = fold_build2_loc (loc, EQ_EXPR, boolean_type_node,
> > > > +                                      op[i], ch);
> > > > +           }
> > > > +         for (unsigned int i = isize - 1; i >= 1; i--)
> > > > +           op[i - 1] = fold_convert_loc (loc, boolean_type_node,
> > > > +                                         fold_build2_loc (loc,
> > > > +                                                          BIT_IOR_EXPR,
> > > > +                                                          boolean_type_node,
> > > > +                                                          op[i - 1],
> > > > +                                                          op[i]));
> > > > +         res = fold_convert_loc (loc, TREE_TYPE (res), op[0]);
> > > > +         gimplify_and_update_call_from_tree (gsi_p, res);
> > >
> > > my worry about -Os remains, can you please add a check
> > > like optimize_bb_for_speed (gimple_bb (stmt2)) || sz <= 2
> >
> > Fixed.
> >
> > > (so we allow inline expanding two comparisons when not optimizing
> > > for speed)?  For UNITS_PER_WORD == 8 this is possibly a
> > > lot of compares, don't we have some _BY_PIECEs limit we
> >
> > There are a few comparisons.  Should I limit it to 4 bytes?
>
> Not sure, if we don't have any existing target configurable limit
> then using UNITS_PER_WORD is fine for now I guess.
>
> > > can use here?  There's no COMPARE_RATIO it seems,
> > > not sure what we use there.
> > >
> > > Since we only inline expand memchr(..) != 0 we're leaving
> > > 'a' != x | 'b' != x | ... optimization to possibly
> >
> > memchr("abcd", a, 4) == 0 is optimized to
> >
> > (a == 'a' || a == 'b' || a == 'c' || a == 'd') == 0
> >
> > by this patch.
> >
> > > 'ab...' != (x|x<<8|x<<12|...) for followup (I'm quite sure we don't
> >
> > It works only for memchr("aaaa", a, 4) == 0.  It is optimized to
> > x != 'a' by this patch.
>
> Hmm, true ;)
>
> Btw, no updated patch in your mail?

Here is the v3 patch:

https://gcc.gnu.org/pipermail/gcc-patches/2022-July/598362.html

Thanks.

> Thanks
> Richard.
>
> >
> > Thanks.
> >
> > > do anything like that).  The x "splat" needs log2 (sz) operations
> > > (but they might be slow?), but in the end it might pay off
> > > for power-of-two (sz) (one could even do this in chunks)?
> > > Anyway, this might be for a followup.
> > >
> > > Otherwise it looks OK.
> > >
> > > Thanks,
> > > Richard.
> > >
> > > > +         delete[] op;
> > > > +         return true;
> > > > +       }
> > > > +      break;
> > > > +
> > > >      case BUILT_IN_MEMSET:
> > > >        if (gimple_call_num_args (stmt2) != 3
> > > >           || gimple_call_lhs (stmt2)
> > > > diff --git a/gcc/tree-ssa-strlen.cc b/gcc/tree-ssa-strlen.cc
> > > > index 7b3e3899ea2..5afbae1b72e 100644
> > > > --- a/gcc/tree-ssa-strlen.cc
> > > > +++ b/gcc/tree-ssa-strlen.cc
> > > > @@ -3913,8 +3913,8 @@ strlen_pass::handle_builtin_memset (bool *zero_write)
> > > >     nonnull if and only RES is used in such expressions exclusively and
> > > >     in none other.  */
> > > >
> > > > -static gimple *
> > > > -use_in_zero_equality (tree res, bool exclusive = true)
> > > > +gimple *
> > > > +use_in_zero_equality (tree res, bool exclusive)
> > > >  {
> > > >    gimple *first_use = NULL;
> > > >
> > > > diff --git a/gcc/tree-ssa-strlen.h b/gcc/tree-ssa-strlen.h
> > > > index 8d155450db8..fdb4d9d7783 100644
> > > > --- a/gcc/tree-ssa-strlen.h
> > > > +++ b/gcc/tree-ssa-strlen.h
> > > > @@ -35,6 +35,8 @@ struct c_strlen_data;
> > > >  extern void get_range_strlen_dynamic (tree, gimple *, c_strlen_data *,
> > > >                                       pointer_query &);
> > > >
> > > > +extern gimple *use_in_zero_equality (tree, bool = true);
> > > > +
> > > >  /* APIs internal to strlen pass.  Defined in gimple-ssa-sprintf.cc.  */
> > > >  extern bool handle_printf_call (gimple_stmt_iterator *, pointer_query &);
> > > >
> > > > --
> > > > 2.36.1
> > > >
> >
> >
> >
> > --
> > H.J.



-- 
H.J.