Re: [PATCH] Add -fextra-libc-function=memcmpeq for __memcmpeq

[Richard Biener <richard.guenther@gmail.com>]

> Am 13.06.2022 um 16:36 schrieb H.J. Lu <hjl.tools@gmail.com>:
> 
> On Mon, Jun 13, 2022 at 3:11 AM Richard Biener
> <richard.guenther@gmail.com> wrote:
>> 
>>> On Tue, Jun 7, 2022 at 9:02 PM H.J. Lu via Gcc-patches
>>> <gcc-patches@gcc.gnu.org> wrote:
>>> 
>>> Add -fextra-libc-function=memcmpeq to map
>>> 
>>> extern int __memcmpeq (const void *, const void *, size_t);
>>> 
>>> which was added to GLIBC 2.35, to __builtin_memcmp_eq.
>> 
>> Humm.  Can't we instead use the presence of a declaration
>> of __memcmpeq with a GNU standard dialect as this instead of
>> adding a weird -fextra-libc-function= option?  Maybe that's even
>> reasonable with a non-GNU dialect standard in effect since
>> __ prefixed names are in the implementation namespace?
> 
> But not all source codes include <string.h> and GCC may generate
> memcmp directly.  How should we handle these cases?

Not.  Similar as to vectorized math functions.
I think it’s not worth optimizing for this case.

Richard.

> 
>> Richard.
>> 
>>> gcc/
>>> 
>>>        * builtins.cc: Include "opts.h".
>>>        (expand_builtin): Generate BUILT_IN_MEMCMP_EQ if __memcmpeq is
>>>        available.
>>>        * builtins.def (BUILT_IN___MEMCMPEQ): New.
>>>        * common.opt: Add -fextra-libc-function=.
>>>        * opts.cc (extra_libc_functions): New.
>>>        (parse_extra_libc_function): New function.
>>>        (common_handle_option): Handle -fextra-libc-function=.
>>>        * opts.h (extra_libc_function_list): New.
>>>        (extra_libc_functions): Likewise.
>>>        * doc/invoke.texi: Document -fextra-libc-function=memcmpeq.
>>> 
>>> gcc/testsuite/
>>> 
>>>        * c-c++-common/memcmpeq-1.c: New test.
>>>        * c-c++-common/memcmpeq-2.c: Likewise.
>>>        * c-c++-common/memcmpeq-3.c: Likewise.
>>>        * c-c++-common/memcmpeq-4.c: Likewise.
>>>        * c-c++-common/memcmpeq-5.c: Likewise.
>>>        * c-c++-common/memcmpeq-6.c: Likewise.
>>>        * c-c++-common/memcmpeq-7.c: Likewise.
>>> ---
>>> gcc/builtins.cc                         |  5 ++++-
>>> gcc/builtins.def                        |  4 ++++
>>> gcc/common.opt                          |  4 ++++
>>> gcc/doc/invoke.texi                     |  6 ++++++
>>> gcc/opts.cc                             | 23 +++++++++++++++++++++++
>>> gcc/opts.h                              |  7 +++++++
>>> gcc/testsuite/c-c++-common/memcmpeq-1.c | 11 +++++++++++
>>> gcc/testsuite/c-c++-common/memcmpeq-2.c | 11 +++++++++++
>>> gcc/testsuite/c-c++-common/memcmpeq-3.c | 11 +++++++++++
>>> gcc/testsuite/c-c++-common/memcmpeq-4.c | 11 +++++++++++
>>> gcc/testsuite/c-c++-common/memcmpeq-5.c | 11 +++++++++++
>>> gcc/testsuite/c-c++-common/memcmpeq-6.c | 11 +++++++++++
>>> gcc/testsuite/c-c++-common/memcmpeq-7.c | 11 +++++++++++
>>> 13 files changed, 125 insertions(+), 1 deletion(-)
>>> create mode 100644 gcc/testsuite/c-c++-common/memcmpeq-1.c
>>> create mode 100644 gcc/testsuite/c-c++-common/memcmpeq-2.c
>>> create mode 100644 gcc/testsuite/c-c++-common/memcmpeq-3.c
>>> create mode 100644 gcc/testsuite/c-c++-common/memcmpeq-4.c
>>> create mode 100644 gcc/testsuite/c-c++-common/memcmpeq-5.c
>>> create mode 100644 gcc/testsuite/c-c++-common/memcmpeq-6.c
>>> create mode 100644 gcc/testsuite/c-c++-common/memcmpeq-7.c
>>> 
>>> diff --git a/gcc/builtins.cc b/gcc/builtins.cc
>>> index b9d89b409b8..22269318e8c 100644
>>> --- a/gcc/builtins.cc
>>> +++ b/gcc/builtins.cc
>>> @@ -81,6 +81,7 @@ along with GCC; see the file COPYING3.  If not see
>>> #include "demangle.h"
>>> #include "gimple-range.h"
>>> #include "pointer-query.h"
>>> +#include "opts.h"
>>> 
>>> struct target_builtins default_target_builtins;
>>> #if SWITCHABLE_TARGET
>>> @@ -7410,7 +7411,9 @@ expand_builtin (tree exp, rtx target, rtx subtarget, machine_mode mode,
>>>        return target;
>>>       if (fcode == BUILT_IN_MEMCMP_EQ)
>>>        {
>>> -         tree newdecl = builtin_decl_explicit (BUILT_IN_MEMCMP);
>>> +         tree newdecl = builtin_decl_explicit
>>> +           (extra_libc_functions.has_memcmpeq
>>> +            ? BUILT_IN___MEMCMPEQ : BUILT_IN_MEMCMP);
>>>          TREE_OPERAND (exp, 1) = build_fold_addr_expr (newdecl);
>>>        }
>>>       break;
>>> diff --git a/gcc/builtins.def b/gcc/builtins.def
>>> index 005976f34e9..eb8d33b16e9 100644
>>> --- a/gcc/builtins.def
>>> +++ b/gcc/builtins.def
>>> @@ -965,6 +965,10 @@ DEF_BUILTIN_STUB (BUILT_IN_ALLOCA_WITH_ALIGN_AND_MAX, "__builtin_alloca_with_ali
>>>    equality with zero.  */
>>> DEF_BUILTIN_STUB (BUILT_IN_MEMCMP_EQ, "__builtin_memcmp_eq")
>>> 
>>> +/* Similar to BUILT_IN_MEMCMP_EQ, but is mapped to __memcmpeq only with
>>> +   -fextra-libc-function=memcmpeq.  */
>>> +DEF_EXT_LIB_BUILTIN (BUILT_IN___MEMCMPEQ, "__memcmpeq", BT_FN_INT_CONST_PTR_CONST_PTR_SIZE, ATTR_PURE_NOTHROW_NONNULL_LEAF)
>>> +
>>> /* An internal version of strcmp/strncmp, used when the result is only
>>>    tested for equality with zero.  */
>>> DEF_BUILTIN_STUB (BUILT_IN_STRCMP_EQ, "__builtin_strcmp_eq")
>>> diff --git a/gcc/common.opt b/gcc/common.opt
>>> index 7ca0cceed82..7a7631682b0 100644
>>> --- a/gcc/common.opt
>>> +++ b/gcc/common.opt
>>> @@ -1587,6 +1587,10 @@ Enum(excess_precision) String(standard) Value(EXCESS_PRECISION_STANDARD)
>>> EnumValue
>>> Enum(excess_precision) String(16) Value(EXCESS_PRECISION_FLOAT16)
>>> 
>>> +fextra-libc-function=
>>> +Common Driver Joined
>>> +Specify the extra function in the C library.
>>> +
>>> ; Whether we permit the extended set of values for FLT_EVAL_METHOD
>>> ; introduced in ISO/IEC TS 18661-3, or limit ourselves to those in C99/C11.
>>> fpermitted-flt-eval-methods=
>>> diff --git a/gcc/doc/invoke.texi b/gcc/doc/invoke.texi
>>> index 8cd5bdddc5d..fe1e3709953 100644
>>> --- a/gcc/doc/invoke.texi
>>> +++ b/gcc/doc/invoke.texi
>>> @@ -676,6 +676,7 @@ Objective-C and Objective-C++ Dialects}.
>>> -ffixed-@var{reg}  -fexceptions @gol
>>> -fnon-call-exceptions  -fdelete-dead-exceptions  -funwind-tables @gol
>>> -fasynchronous-unwind-tables @gol
>>> +-fextra-libc-function=memcmpeq @gol
>>> -fno-gnu-unique @gol
>>> -finhibit-size-directive  -fcommon  -fno-ident @gol
>>> -fpcc-struct-return  -fpic  -fPIC  -fpie  -fPIE  -fno-plt @gol
>>> @@ -17250,6 +17251,11 @@ Generate unwind table in DWARF format, if supported by target machine.  The
>>> table is exact at each instruction boundary, so it can be used for stack
>>> unwinding from asynchronous events (such as debugger or garbage collector).
>>> 
>>> +@item -fextra-libc-function=memcmpeq
>>> +@opindex fextra-libc-function
>>> +Generate @code{__memcmpeq}, which was added to GLIBC 2.35, for
>>> +@code{__builtin_memcmp_eq}.
>>> +
>>> @item -fno-gnu-unique
>>> @opindex fno-gnu-unique
>>> @opindex fgnu-unique
>>> diff --git a/gcc/opts.cc b/gcc/opts.cc
>>> index bf06a55456a..e77f0922acc 100644
>>> --- a/gcc/opts.cc
>>> +++ b/gcc/opts.cc
>>> @@ -38,6 +38,9 @@ along with GCC; see the file COPYING3.  If not see
>>> /* In this file all option sets are explicit.  */
>>> #undef OPTION_SET_P
>>> 
>>> +/* The list of extra functions in the C library.  */
>>> +extra_libc_function_list extra_libc_functions;
>>> +
>>> static void set_Wstrict_aliasing (struct gcc_options *opts, int onoff);
>>> 
>>> /* Names of fundamental debug info formats indexed by enum
>>> @@ -2269,6 +2272,22 @@ parse_no_sanitize_attribute (char *value)
>>>   return flags;
>>> }
>>> 
>>> +/* Parse -fextra-libc-function= suboptions from ARG.  */
>>> +
>>> +static void
>>> +parse_extra_libc_function (const char *arg)
>>> +{
>>> +  /* Check to see if the string matches a sub-option name.  */
>>> +  if (strcmp (arg, "memcmpeq") == 0)
>>> +    {
>>> +      extra_libc_functions.has_memcmpeq = 1;
>>> +      return;
>>> +    }
>>> +
>>> +  error ("unrecognized argument to %<-fextra-libc-function=%>: %qs",
>>> +        arg);
>>> +}
>>> +
>>> /* Parse -fzero-call-used-regs suboptions from ARG, return the FLAGS.  */
>>> 
>>> unsigned int
>>> @@ -2940,6 +2959,10 @@ common_handle_option (struct gcc_options *opts,
>>>       SET_OPTION_IF_UNSET (opts, opts_set, flag_profile_correction, value);
>>>       break;
>>> 
>>> +    case OPT_fextra_libc_function_:
>>> +      parse_extra_libc_function (arg);
>>> +      break;
>>> +
>>>     case OPT_fprofile_generate_:
>>>       opts->x_profile_data_prefix = xstrdup (arg);
>>>       value = true;
>>> diff --git a/gcc/opts.h b/gcc/opts.h
>>> index a43ce66cffe..e8d8835ba23 100644
>>> --- a/gcc/opts.h
>>> +++ b/gcc/opts.h
>>> @@ -345,6 +345,13 @@ struct cl_option_handlers
>>> extern const char *opt_fstack_limit_symbol_arg;
>>> extern int opt_fstack_limit_register_no;
>>> 
>>> +/* The list of extra functions in the C library.  */
>>> +struct extra_libc_function_list
>>> +{
>>> +  unsigned int has_memcmpeq : 1;
>>> +};
>>> +extern extra_libc_function_list extra_libc_functions;
>>> +
>>> /* Input file names.  */
>>> 
>>> extern const char **in_fnames;
>>> diff --git a/gcc/testsuite/c-c++-common/memcmpeq-1.c b/gcc/testsuite/c-c++-common/memcmpeq-1.c
>>> new file mode 100644
>>> index 00000000000..487f6cd98db
>>> --- /dev/null
>>> +++ b/gcc/testsuite/c-c++-common/memcmpeq-1.c
>>> @@ -0,0 +1,11 @@
>>> +/* { dg-do compile } */
>>> +/* { dg-options "-O2 -fextra-libc-function=memcmpeq" } */
>>> +/* { dg-final { scan-assembler "__memcmpeq" } } */
>>> +
>>> +#include <stddef.h>
>>> +
>>> +int
>>> +foo (const char *s1, const char *s2, size_t len)
>>> +{
>>> +  return __builtin_memcmp (s1, s2, len) != 0;
>>> +}
>>> diff --git a/gcc/testsuite/c-c++-common/memcmpeq-2.c b/gcc/testsuite/c-c++-common/memcmpeq-2.c
>>> new file mode 100644
>>> index 00000000000..1773dc2bee1
>>> --- /dev/null
>>> +++ b/gcc/testsuite/c-c++-common/memcmpeq-2.c
>>> @@ -0,0 +1,11 @@
>>> +/* { dg-do compile } */
>>> +/* { dg-options "-O2 -fextra-libc-function=memcmpeq" } */
>>> +/* { dg-final { scan-assembler "__memcmpeq" } } */
>>> +
>>> +#include <string.h>
>>> +
>>> +int
>>> +foo (const char *s1, const char *s2, size_t len)
>>> +{
>>> +  return memcmp (s1, s2, len) == 0;
>>> +}
>>> diff --git a/gcc/testsuite/c-c++-common/memcmpeq-3.c b/gcc/testsuite/c-c++-common/memcmpeq-3.c
>>> new file mode 100644
>>> index 00000000000..69c9537d572
>>> --- /dev/null
>>> +++ b/gcc/testsuite/c-c++-common/memcmpeq-3.c
>>> @@ -0,0 +1,11 @@
>>> +/* { dg-do compile } */
>>> +/* { dg-options "-O2 -fextra-libc-function=memcmpeq" } */
>>> +/* { dg-final { scan-assembler-not "__memcmpeq" } } */
>>> +
>>> +#include <string.h>
>>> +
>>> +int
>>> +foo (const char *s1, const char *s2, size_t len)
>>> +{
>>> +  return memcmp (s1, s2, len);
>>> +}
>>> diff --git a/gcc/testsuite/c-c++-common/memcmpeq-4.c b/gcc/testsuite/c-c++-common/memcmpeq-4.c
>>> new file mode 100644
>>> index 00000000000..a448312ea96
>>> --- /dev/null
>>> +++ b/gcc/testsuite/c-c++-common/memcmpeq-4.c
>>> @@ -0,0 +1,11 @@
>>> +/* { dg-do compile } */
>>> +/* { dg-options "-O2" } */
>>> +/* { dg-final { scan-assembler-not "__memcmpeq" } } */
>>> +
>>> +#include <stddef.h>
>>> +
>>> +int
>>> +foo (const char *s1, const char *s2, size_t len)
>>> +{
>>> +  return __builtin_memcmp (s1, s2, len) != 0;
>>> +}
>>> diff --git a/gcc/testsuite/c-c++-common/memcmpeq-5.c b/gcc/testsuite/c-c++-common/memcmpeq-5.c
>>> new file mode 100644
>>> index 00000000000..4ef33a1c238
>>> --- /dev/null
>>> +++ b/gcc/testsuite/c-c++-common/memcmpeq-5.c
>>> @@ -0,0 +1,11 @@
>>> +/* { dg-do compile } */
>>> +/* { dg-options "-O2" } */
>>> +/* { dg-final { scan-assembler-not "__memcmpeq" } } */
>>> +
>>> +#include <string.h>
>>> +
>>> +int
>>> +foo (const char *s1, const char *s2, size_t len)
>>> +{
>>> +  return memcmp (s1, s2, len) == 0;
>>> +}
>>> diff --git a/gcc/testsuite/c-c++-common/memcmpeq-6.c b/gcc/testsuite/c-c++-common/memcmpeq-6.c
>>> new file mode 100644
>>> index 00000000000..52304df7079
>>> --- /dev/null
>>> +++ b/gcc/testsuite/c-c++-common/memcmpeq-6.c
>>> @@ -0,0 +1,11 @@
>>> +/* { dg-do compile } */
>>> +/* { dg-options "-O2 -fextra-libc-function=memcmpeq" } */
>>> +/* { dg-final { scan-assembler "__memcmpeq" } } */
>>> +
>>> +#include <stddef.h>
>>> +
>>> +int
>>> +foo (const char *s1, const char *s2, size_t len)
>>> +{
>>> +  return __builtin_memcmp_eq (s1, s2, len) != 0;
>>> +}
>>> diff --git a/gcc/testsuite/c-c++-common/memcmpeq-7.c b/gcc/testsuite/c-c++-common/memcmpeq-7.c
>>> new file mode 100644
>>> index 00000000000..d59765894e7
>>> --- /dev/null
>>> +++ b/gcc/testsuite/c-c++-common/memcmpeq-7.c
>>> @@ -0,0 +1,11 @@
>>> +/* { dg-do compile } */
>>> +/* { dg-options "-O2" } */
>>> +/* { dg-final { scan-assembler-not "__memcmpeq" } } */
>>> +
>>> +#include <stddef.h>
>>> +
>>> +int
>>> +foo (const char *s1, const char *s2, size_t len)
>>> +{
>>> +  return __builtin_memcmp_eq (s1, s2, len) != 0;
>>> +}
>>> --
>>> 2.36.1
>>> 
> 
> 
> 
> -- 
> H.J.