Re: [PATCH] Finish implementing P0426R1 "Constexpr for std::char_traits" for C++17

2017-06-13 Thread Jonathan Wakely 

On 12/06/17 23:28 +0100, Pedro Alves wrote:

On 06/05/2017 03:27 PM, Jonathan Wakely wrote:


Pedro, this is OK for trunk now we're in stage 1. Please go ahead and
commit it - thanks.


Thanks Jonathan.  I've pushed it in now.



It's probably safe for gcc-7-branch too, but let's leave it on trunk
for a while first.


OK.

BTW, for extra thoroughness, to confirm we're handling both
const & non-const arrays correctly, I had written this testsuite
tweak too.  Would you like to have this in?


Yes please, this looks useful.



@@ -98,7 +220,12 @@ static_assert( test_compare() );
static_assert( test_length() );
static_assert( test_find() );

-struct C { unsigned char c; };
+struct C
+{
+  C() = default;
+  constexpr C(auto c_) : c(c_) {}


Placeholder types as function parameters are non-standard, so this
would fail with -pedantic-errors.

How about:

struct C {
 constexpr C(unsigned char c_ = 0) : c(c_) { }
 unsigned char c;
};



+  unsigned char c;
+};
constexpr bool operator==(const C& c1, const C& c2) { return c1.c == c2.c; }
constexpr bool operator<(const C& c1, const C& c2) { return c1.c < c2.c; }
static_assert( test_assign() );
--
2.5.5

Re: [PATCH] Finish implementing P0426R1 "Constexpr for std::char_traits" for C++17

2017-06-12 Thread Pedro Alves 
On 06/05/2017 03:27 PM, Jonathan Wakely wrote:

> Pedro, this is OK for trunk now we're in stage 1. Please go ahead and
> commit it - thanks.

Thanks Jonathan.  I've pushed it in now.

> 
> It's probably safe for gcc-7-branch too, but let's leave it on trunk
> for a while first.

OK.

BTW, for extra thoroughness, to confirm we're handling both
const & non-const arrays correctly, I had written this testsuite
tweak too.  Would you like to have this in?

>From 3f7adab8bab68955aafd760467bb860057140d40 Mon Sep 17 00:00:00 2001
From: Pedro Alves 
Date: Mon, 12 Jun 2017 20:23:23 +0100
Subject: [PATCH] constexpr char_traits: Test non-const strings/arrays too

libstdc++-v3/ChangeLog
-mm-dd  Pedro Alves  

* 
testsuite/21_strings/char_traits/requirements/constexpr_functions_c++17.cc
(test_assign, test_compare, test_length, test_find): Test
non-const strings/arrays too.
(struct C): Add a generic conversion ctor.
---
 .../requirements/constexpr_functions_c++17.cc  | 173 ++---
 1 file changed, 150 insertions(+), 23 deletions(-)

diff --git 
a/libstdc++-v3/testsuite/21_strings/char_traits/requirements/constexpr_functions_c++17.cc
 
b/libstdc++-v3/testsuite/21_strings/char_traits/requirements/constexpr_functions_c++17.cc
index efd280f..c41b490 100644
--- 
a/libstdc++-v3/testsuite/21_strings/char_traits/requirements/constexpr_functions_c++17.cc
+++ 
b/libstdc++-v3/testsuite/21_strings/char_traits/requirements/constexpr_functions_c++17.cc
@@ -25,10 +25,40 @@ template
   test_assign()
   {
 using char_type = typename CT::char_type;
-char_type s1[2] = {};
-const char_type s2[2] = {1, 0};
-CT::assign(s1[0], s2[0]);
-return s1[0] == char_type{1};
+
+auto check = [](char_type* s1, const char_type* s2)
+  {
+   CT::assign(s1[0], s2[0]);
+   return s1[0] == char_type{1};
+  };
+
+// const strings.
+
+{
+  char_type s1[2] = {};
+  const char_type s2[2] = {1, 0};
+  if (!check (s1, s2))
+   return false;
+}
+
+// non-const strings.
+
+{
+  char_type s1[2] = {};
+  char_type s2[2] = {1, 0};
+  if (!check (s1, s2))
+   return false;
+}
+
+{
+  char_type s1[2] = {};
+  char_type s2[2] = {};
+  s2[0] = char_type{1};
+  if (!check (s1, s2))
+   return false;
+}
+
+return true;
   }
 
 template
@@ -36,14 +66,48 @@ template
   test_compare()
   {
 using char_type = typename CT::char_type;
-const char_type s1[3] = {1, 2, 3};
-const char_type s2[3] = {1, 2, 3};
-if (CT::compare(s1, s2, 3) != 0)
-  return false;
-if (CT::compare(s2, s1, 3) != 0)
-  return false;
-if (CT::compare(s1+1, s2, 2) <= 0)
-  return false;
+
+auto check = [](const char_type* s1, const char_type* s2)
+  {
+   if (CT::compare(s1, s2, 3) != 0)
+ return false;
+   if (CT::compare(s2, s1, 3) != 0)
+ return false;
+   if (CT::compare(s1+1, s2, 2) <= 0)
+ return false;
+   return true;
+  };
+
+// const arrays.
+
+{
+  const char_type s1[3] = {1, 2, 3};
+  const char_type s2[3] = {1, 2, 3};
+  if (!check (s1, s2))
+   return false;
+}
+
+// non-const arrays.
+
+{
+  char_type s1[3] = {1, 2, 3};
+  char_type s2[3] = {1, 2, 3};
+  if (!check (s1, s2))
+   return false;
+}
+
+{
+  char_type s1[3] = {};
+  char_type s2[3] = {};
+  for (size_t i = 0; i < 3; i++)
+   {
+ s1[i] = char_type(i+1);
+ s2[i] = char_type(i+1);
+   }
+  if (!check (s1, s2))
+   return false;
+}
+
 return true;
   }
 
@@ -52,11 +116,40 @@ template
   test_length()
   {
 using char_type = typename CT::char_type;
-const char_type s1[4] = {1, 2, 3, 0};
-if (CT::length(s1) != 3)
-  return false;
-if (CT::length(s1+1) != 2)
-  return false;
+
+auto check = [](const char_type* s)
+  {
+   if (CT::length(s) != 3)
+ return false;
+   if (CT::length(s+1) != 2)
+ return false;
+   return true;
+  };
+
+// const strings.
+
+{
+  const char_type s[4] = {1, 2, 3, 0};
+  if (!check (s))
+   return false;
+}
+
+// non-const strings.
+
+{
+  char_type s[4] = {1, 2, 3, 0};
+  if (!check (s))
+   return false;
+}
+
+{
+  char_type s[4] = {};
+  for (size_t i = 0; i < 3; i++)
+   s[i] = char_type(i+1);
+  if (!check (s))
+   return false;
+}
+
 return true;
   }
 
@@ -65,11 +158,40 @@ template
   test_find()
   {
 using char_type = typename CT::char_type;
-const char_type s1[3] = {1, 2, 3};
-if (CT::find(s1, 3, char_type{2}) != s1+1)
-  return false;
-if (CT::find(s1, 3, char_type{4}) != nullptr)
-  return false;
+
+auto check = [](const char_type* s)
+  {
+   if (CT::find(s, 3, char_type{2}) != s+1)
+ return false;
+

Re: [PATCH] Finish implementing P0426R1 "Constexpr for std::char_traits" for C++17

2017-06-05 Thread Jonathan Wakely 

On 23/04/17 19:33 +0100, Pedro Alves wrote:

On 04/23/2017 06:54 PM, Pedro Alves wrote:

Hi!

As I had suggested in PR c++/80265, here's a patch that uses
__builtin_constant_p to tell whether we can defer to a constexpr
algorithm, which avoids having to wait for compiler support.

Unfortunately I ran out of cycles today to run a full bootstrap/regtest
cycle, but constexpr_functions_c++17.cc passes cleanly on
x86_64 GNU/Linux at least.

If this looks like a reasonable approach, I can maybe try running
full tests on the gcc compile farm next week.

WDYT?


Reading the patch via the list made me spot something
that was incorrect.



-  static char_type*
+  static _GLIBCXX17_CONSTEXPR char_type*
   assign(char_type* __s, size_t __n, char_type __a)
   {
+#if __cplusplus > 201402
+   if (__constant_string_p(__s)


This should probably have been __constant_char_array_p, but now
that I look again at the paper, I see I got myself confused -- this
assign overload is not meant to be constexpr in the first place.

So here's an updated patch that drops that bit.  (Same testing
as before.)


Pedro, this is OK for trunk now we're in stage 1. Please go ahead and
commit it - thanks.

It's probably safe for gcc-7-branch too, but let's leave it on trunk
for a while first.

Re: [PATCH] Finish implementing P0426R1 "Constexpr for std::char_traits" for C++17

2017-04-23 Thread Pedro Alves 
On 04/23/2017 06:54 PM, Pedro Alves wrote:
> Hi!
> 
> As I had suggested in PR c++/80265, here's a patch that uses
> __builtin_constant_p to tell whether we can defer to a constexpr
> algorithm, which avoids having to wait for compiler support.
> 
> Unfortunately I ran out of cycles today to run a full bootstrap/regtest
> cycle, but constexpr_functions_c++17.cc passes cleanly on
> x86_64 GNU/Linux at least.
> 
> If this looks like a reasonable approach, I can maybe try running
> full tests on the gcc compile farm next week.
> 
> WDYT?

Reading the patch via the list made me spot something
that was incorrect.

>  
> -  static char_type*
> +  static _GLIBCXX17_CONSTEXPR char_type*
>assign(char_type* __s, size_t __n, char_type __a)
>{
> +#if __cplusplus > 201402
> + if (__constant_string_p(__s)

This should probably have been __constant_char_array_p, but now
that I look again at the paper, I see I got myself confused -- this
assign overload is not meant to be constexpr in the first place.

So here's an updated patch that drops that bit.  (Same testing
as before.)

>From 71cf9b9a3ea79bd790d792c9a02e5a577f1af156 Mon Sep 17 00:00:00 2001
From: Pedro Alves <pal...@redhat.com>
Date: Sun, 23 Apr 2017 14:16:09 +0100
Subject: [PATCH] Finish implementing P0426R1 "Constexpr for std::char_traits"
 for C++17

As discussed in PR c++/80265 (__builtin_{memcmp,memchr,strlen} are not
usable in constexpr functions), use __builtin_constant_p to tell
whether we can defer to a constexpr algorithm.

I used __always_inline__ just to be thorough.  It isn't really really
necessary as far as I could determine.

Changes like these:

 if (__n == 0)
   return 0;
 -  return wmemcmp(__s1, __s2, __n);
 +  else
 +return wmemcmp(__s1, __s2, __n);

are necessary otherwise G++ complains that we're calling a
non-constexpr function, which looks like a a manifestation of PR67026
to me.

libstdc++-v3:
2017-04-23  Pedro Alves  <pal...@redhat.com>

* doc/xml/manual/status_cxx2017.xml: Update C++17 constexpr
char_traits status.
* doc/html/*: Regenerate.

* include/bits/char_traits.h (_GLIBCXX_ALWAYS_INLINE): Define if
not already defined.
(__cpp_lib_constexpr_char_traits): Uncomment.
(__constant_string_p, __constant_char_array_p): New.
(std::char_traits, std::char_traits): Add
_GLIBCXX17_CONSTEXPR on compare, length and find and use
__constant_string_p, __constant_char_array_p and
__builtin_constant_p to defer to __gnu_cxx::char_traits at compile
time.

* testsuite/21_strings/char_traits/requirements/
constexpr_functions_c++17.cc: Uncomment
__cpp_lib_constexpr_char_traits tests.  Uncomment
test_compare, test_length, test_find,
test_compare, test_length and test_find
static_assert tests.
---
 libstdc++-v3/doc/xml/manual/status_cxx2017.xml |   4 +-
 libstdc++-v3/include/bits/char_traits.h| 101 ++---
 .../requirements/constexpr_functions_c++17.cc  |  16 ++--
 3 files changed, 100 insertions(+), 21 deletions(-)

diff --git a/libstdc++-v3/doc/xml/manual/status_cxx2017.xml 
b/libstdc++-v3/doc/xml/manual/status_cxx2017.xml
index 0e35f75..fed91f9 100644
--- a/libstdc++-v3/doc/xml/manual/status_cxx2017.xml
+++ b/libstdc++-v3/doc/xml/manual/status_cxx2017.xml
@@ -489,8 +489,8 @@ Feature-testing recommendations for C++.
P0426R1

   
-   7 (partial) 
-   ??? 
+   7 
+   __cpp_lib_constexpr_char_traits >= 201611 
 
 
 
diff --git a/libstdc++-v3/include/bits/char_traits.h 
b/libstdc++-v3/include/bits/char_traits.h
index 75db5b8..3ecc30e 100644
--- a/libstdc++-v3/include/bits/char_traits.h
+++ b/libstdc++-v3/include/bits/char_traits.h
@@ -40,6 +40,10 @@
 #include   // For streampos
 #include// For WEOF, wmemmove, wmemset, etc.
 
+#ifndef _GLIBCXX_ALWAYS_INLINE
+#define _GLIBCXX_ALWAYS_INLINE inline __attribute__((__always_inline__))
+#endif
+
 namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
 {
 _GLIBCXX_BEGIN_NAMESPACE_VERSION
@@ -139,7 +143,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   { return !eq_int_type(__c, eof()) ? __c : to_int_type(char_type()); }
 };
 
-// #define __cpp_lib_constexpr_char_traits 201611
+#define __cpp_lib_constexpr_char_traits 201611
 
   template
 _GLIBCXX14_CONSTEXPR int
@@ -212,6 +216,42 @@ namespace std _GLIBCXX_VISIBILITY(default)
 {
 _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
+#if __cplusplus > 201402
+  /**
+   *  @brief Determine whether the characters of a NULL-terminated
+   *  string are known at compile time.
+   *  @param  __s  The string.
+   *
+   *  Assumes that _CharT is a built-in character type.
+   */
+  template
+static _GLIBCXX_ALWAYS_INLINE constexpr bool
+__constant_string_p(const _CharT* __s)
+{
+

[PATCH] Finish implementing P0426R1 "Constexpr for std::char_traits" for C++17

2017-04-23 Thread Pedro Alves 
Hi!

As I had suggested in PR c++/80265, here's a patch that uses
__builtin_constant_p to tell whether we can defer to a constexpr
algorithm, which avoids having to wait for compiler support.

Unfortunately I ran out of cycles today to run a full bootstrap/regtest
cycle, but constexpr_functions_c++17.cc passes cleanly on
x86_64 GNU/Linux at least.

If this looks like a reasonable approach, I can maybe try running
full tests on the gcc compile farm next week.

WDYT?

Thanks,
Pedro Alves

>From 91606ca1f51309121e292559bcb6b2cfc126737b Mon Sep 17 00:00:00 2001
From: Pedro Alves <pal...@redhat.com>
Date: Sun, 23 Apr 2017 14:16:09 +0100
Subject: [PATCH] Finish implementing P0426R1 "Constexpr for std::char_traits"
 for C++17

As discussed in PR c++/80265 (__builtin_{memcmp,memchr,strlen} are not
usable in constexpr functions), use __builtin_constant_p to tell
whether we can defer to a constexpr algorithm.

I used __always_inline__ just to be thorough.  It isn't really really
necessary as far as I could determine.

Changes like these:

 if (__n == 0)
   return 0;
 -  return wmemcmp(__s1, __s2, __n);
 +  else
 +return wmemcmp(__s1, __s2, __n);

are necessary otherwise G++ complains that we're calling a
non-constexpr function, which looks like a a manifestation of PR67026
to me.

libstdc++-v3:
2017-04-23  Pedro Alves  <pal...@redhat.com>

* doc/xml/manual/status_cxx2017.xml: Update C++17 constexpr
char_traits status.
* doc/html/*: Regenerate.

* include/bits/char_traits.h (_GLIBCXX_ALWAYS_INLINE): Define if
not already defined.
(__cpp_lib_constexpr_char_traits): Uncomment.
(__constant_string_p, __constant_char_array_p): New.
(std::char_traits, std::char_traits): Add
_GLIBCXX17_CONSTEXPR on compare, length, find and assign and use
__constant_string_p, __constant_char_array_p and
__builtin_constant_p to defer to __gnu_cxx::char_traits at compile
time.

* testsuite/21_strings/char_traits/requirements/
constexpr_functions_c++17.cc: Uncomment
__cpp_lib_constexpr_char_traits tests.  Uncomment
test_compare, test_length, test_find,
test_compare, test_length and test_find
static_assert tests.
---
 libstdc++-v3/doc/xml/manual/status_cxx2017.xml |   4 +-
 libstdc++-v3/include/bits/char_traits.h| 120 ++---
 .../requirements/constexpr_functions_c++17.cc  |  16 +--
 3 files changed, 116 insertions(+), 24 deletions(-)

diff --git a/libstdc++-v3/doc/xml/manual/status_cxx2017.xml 
b/libstdc++-v3/doc/xml/manual/status_cxx2017.xml
index 0e35f75..fed91f9 100644
--- a/libstdc++-v3/doc/xml/manual/status_cxx2017.xml
+++ b/libstdc++-v3/doc/xml/manual/status_cxx2017.xml
@@ -489,8 +489,8 @@ Feature-testing recommendations for C++.
P0426R1

   
-   7 (partial) 
-   ??? 
+   7 
+   __cpp_lib_constexpr_char_traits >= 201611 
 
 
 
diff --git a/libstdc++-v3/include/bits/char_traits.h 
b/libstdc++-v3/include/bits/char_traits.h
index 75db5b8..cc636a9 100644
--- a/libstdc++-v3/include/bits/char_traits.h
+++ b/libstdc++-v3/include/bits/char_traits.h
@@ -40,6 +40,10 @@
 #include   // For streampos
 #include// For WEOF, wmemmove, wmemset, etc.
 
+#ifndef _GLIBCXX_ALWAYS_INLINE
+#define _GLIBCXX_ALWAYS_INLINE inline __attribute__((__always_inline__))
+#endif
+
 namespace __gnu_cxx _GLIBCXX_VISIBILITY(default)
 {
 _GLIBCXX_BEGIN_NAMESPACE_VERSION
@@ -139,7 +143,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
   { return !eq_int_type(__c, eof()) ? __c : to_int_type(char_type()); }
 };
 
-// #define __cpp_lib_constexpr_char_traits 201611
+#define __cpp_lib_constexpr_char_traits 201611
 
   template
 _GLIBCXX14_CONSTEXPR int
@@ -212,6 +216,42 @@ namespace std _GLIBCXX_VISIBILITY(default)
 {
 _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
+#if __cplusplus > 201402
+  /**
+   *  @brief Determine whether the characters of a NULL-terminated
+   *  string are known at compile time.
+   *  @param  __s  The string.
+   *
+   *  Assumes that _CharT is a built-in character type.
+   */
+  template
+static _GLIBCXX_ALWAYS_INLINE constexpr bool
+__constant_string_p(const _CharT* __s)
+{
+  while (__builtin_constant_p(*__s) && *__s)
+   __s++;
+  return __builtin_constant_p(*__s);
+}
+
+  /**
+   *  @brief Determine whether the characters of a character array are
+   *  known at compile time.
+   *  @param  __a  The character array.
+   *  @param  __n  Number of characters.
+   *
+   *  Assumes that _CharT is a built-in character type.
+   */
+  template
+static _GLIBCXX_ALWAYS_INLINE constexpr bool
+__constant_char_array_p(const _CharT* __a, size_t __n)
+{
+  size_t __i = 0;
+  while (__builtin_constant_p(__a[__i]) && __i < __n)
+   __i++;
+  return __i == __n;
+}
+#endif
+
   // 21