From 9cd4eeefcc641dd70d026e08e9d218101b826c52 Mon Sep 17 00:00:00 2001
From: Jonathan Wakely <jwakely@redhat.com>
Date: Mon, 17 Feb 2020 15:25:33 +0000
Subject: [PATCH] libstdc++: Reduce header dependencies for C++20 (PR 92546)

In C++20 <memory> depends on <bits/ranges_unitialized.h> which
depends on <bits/random.h> just for a single concept. Including
<bits/random.h> also requires including <cmath>, which is huge due to
the C++17 special functions.

This change moves the concept to the <bits/uniform_int_dist.h> internal
header that exists so that <bits/stl_algobase.h> doesn't need to include
<bits/random.h>.

	PR libstdc++/92546 (partial)
	* include/bits/random.h (uniform_random_bit_generator): Move definition
	to <bits/uniform_int_dist.h>.
	* include/bits/ranges_algo.h: Include <bits/uniform_int_dist.h> instead
	of <bits/random.h>.
	* include/bits/ranges_algobase.h: Do not include <cmath>.
	* include/bits/uniform_int_dist.h (uniform_random_bit_generator):
	Move here.
	* include/std/ranges: Do not include <limits>.
	* testsuite/26_numerics/random/pr60037-neg.cc: Adjust dg-error lineno.
---
 libstdc++-v3/ChangeLog                           | 11 +++++++++++
 libstdc++-v3/include/bits/random.h               | 16 +---------------
 libstdc++-v3/include/bits/ranges_algo.h          |  2 +-
 libstdc++-v3/include/bits/ranges_algobase.h      |  1 -
 libstdc++-v3/include/bits/uniform_int_dist.h     | 16 ++++++++++++++++
 libstdc++-v3/include/std/ranges                  |  1 -
 .../testsuite/26_numerics/random/pr60037-neg.cc  |  2 +-
 7 files changed, 30 insertions(+), 19 deletions(-)

diff --git a/libstdc++-v3/ChangeLog b/libstdc++-v3/ChangeLog
index 954eb673184..f4477aaa6f2 100644
--- a/libstdc++-v3/ChangeLog
+++ b/libstdc++-v3/ChangeLog
@@ -1,5 +1,16 @@
 2020-02-17  Jonathan Wakely  <jwakely@redhat.com>
 
+	PR libstdc++/92546 (partial)
+	* include/bits/random.h (uniform_random_bit_generator): Move definition
+	to <bits/uniform_int_dist.h>.
+	* include/bits/ranges_algo.h: Include <bits/uniform_int_dist.h> instead
+	of <bits/random.h>.
+	* include/bits/ranges_algobase.h: Do not include <cmath>.
+	* include/bits/uniform_int_dist.h (uniform_random_bit_generator):
+	Move here.
+	* include/std/ranges: Do not include <limits>.
+	* testsuite/26_numerics/random/pr60037-neg.cc: Adjust dg-error lineno.
+
 	PR libstdc++/92546 (partial)
 	* include/Makefile.am: Add new header.
 	* include/Makefile.in: Regenerate.
diff --git a/libstdc++-v3/include/bits/random.h b/libstdc++-v3/include/bits/random.h
index d4aebf45af0..19307fbc3ca 100644
--- a/libstdc++-v3/include/bits/random.h
+++ b/libstdc++-v3/include/bits/random.h
@@ -33,9 +33,6 @@
 
 #include <vector>
 #include <bits/uniform_int_dist.h>
-#if __cplusplus > 201703L
-# include <concepts>
-#endif
 
 namespace std _GLIBCXX_VISIBILITY(default)
 {
@@ -51,18 +48,7 @@ _GLIBCXX_BEGIN_NAMESPACE_VERSION
    * @{
    */
 
-#ifdef __cpp_lib_concepts
-  /// Requirements for a uniform random bit generator.
-  template<typename _Gen>
-    concept uniform_random_bit_generator
-      = invocable<_Gen&> && unsigned_integral<invoke_result_t<_Gen&>>
-      && requires
-      {
-	{ _Gen::min() } -> same_as<invoke_result_t<_Gen&>>;
-	{ _Gen::max() } -> same_as<invoke_result_t<_Gen&>>;
-	requires bool_constant<(_Gen::min() < _Gen::max())>::value;
-      };
-#endif
+  // std::uniform_random_bit_generator is defined in <bits/uniform_int_dist.h>
 
   /**
    * @brief A function template for converting the output of a (integral)
diff --git a/libstdc++-v3/include/bits/ranges_algo.h b/libstdc++-v3/include/bits/ranges_algo.h
index ff1b40f6ace..f3a349ef839 100644
--- a/libstdc++-v3/include/bits/ranges_algo.h
+++ b/libstdc++-v3/include/bits/ranges_algo.h
@@ -33,7 +33,7 @@
 #if __cplusplus > 201703L
 
 #include <bits/ranges_algobase.h>
-#include <bits/random.h> // concept uniform_random_bit_generator
+#include <bits/uniform_int_dist.h> // concept uniform_random_bit_generator
 
 #if __cpp_lib_concepts
 namespace std _GLIBCXX_VISIBILITY(default)
diff --git a/libstdc++-v3/include/bits/ranges_algobase.h b/libstdc++-v3/include/bits/ranges_algobase.h
index cc24483b2d3..eedd29f570a 100644
--- a/libstdc++-v3/include/bits/ranges_algobase.h
+++ b/libstdc++-v3/include/bits/ranges_algobase.h
@@ -32,7 +32,6 @@
 
 #if __cplusplus > 201703L
 
-#include <cmath>
 #include <compare>
 #include <iterator>
 // #include <bits/range_concepts.h>
diff --git a/libstdc++-v3/include/bits/uniform_int_dist.h b/libstdc++-v3/include/bits/uniform_int_dist.h
index d2a01570635..e3d7934e997 100644
--- a/libstdc++-v3/include/bits/uniform_int_dist.h
+++ b/libstdc++-v3/include/bits/uniform_int_dist.h
@@ -33,11 +33,27 @@
 
 #include <type_traits>
 #include <limits>
+#if __cplusplus > 201703L
+# include <concepts>
+#endif
 
 namespace std _GLIBCXX_VISIBILITY(default)
 {
 _GLIBCXX_BEGIN_NAMESPACE_VERSION
 
+#ifdef __cpp_lib_concepts
+  /// Requirements for a uniform random bit generator.
+  template<typename _Gen>
+    concept uniform_random_bit_generator
+      = invocable<_Gen&> && unsigned_integral<invoke_result_t<_Gen&>>
+      && requires
+      {
+	{ _Gen::min() } -> same_as<invoke_result_t<_Gen&>>;
+	{ _Gen::max() } -> same_as<invoke_result_t<_Gen&>>;
+	requires bool_constant<(_Gen::min() < _Gen::max())>::value;
+      };
+#endif
+
   namespace __detail
   {
     /* Determine whether number is a power of 2.  */
diff --git a/libstdc++-v3/include/std/ranges b/libstdc++-v3/include/std/ranges
index 970e904bddd..b9ac528fdff 100644
--- a/libstdc++-v3/include/std/ranges
+++ b/libstdc++-v3/include/std/ranges
@@ -42,7 +42,6 @@
 #include <compare>
 #include <initializer_list>
 #include <iterator>
-#include <limits>
 #include <optional>
 #include <tuple>
 
diff --git a/libstdc++-v3/testsuite/26_numerics/random/pr60037-neg.cc b/libstdc++-v3/testsuite/26_numerics/random/pr60037-neg.cc
index 91e5566c54a..f808132e9ea 100644
--- a/libstdc++-v3/testsuite/26_numerics/random/pr60037-neg.cc
+++ b/libstdc++-v3/testsuite/26_numerics/random/pr60037-neg.cc
@@ -10,6 +10,6 @@ std::__detail::_Adaptor<std::mt19937, unsigned long> aurng(urng);
 auto x = std::generate_canonical<std::size_t,
 			std::numeric_limits<std::size_t>::digits>(urng);
 
-// { dg-error "static assertion failed: template argument must be a floating point type" "" { target *-*-* } 172 }
+// { dg-error "static assertion failed: template argument must be a floating point type" "" { target *-*-* } 158 }
 
 // { dg-error "static assertion failed: template argument must be a floating point type" "" { target *-*-* } 3281 }
-- 
2.30.2