[libc++] Instantiate hash function externally #127040

philnik777 · 2025-02-13T10:43:43Z

This has multiple benefits:

There is a single instance of our hash function, reducing object file size
The hash implementation isn't instantiated in every TU anymore, reducing compile times
Behind an ABI configuration macro it would be possible to salt the hash

llvmbot · 2025-02-19T11:35:33Z

@llvm/pr-subscribers-libcxx

Author: Nikolas Klauser (philnik777)

Changes

This has multiple benefits:

There is a single instance of our hash function, reducing object file size
The hash implementation isn't instantiated in every TU anymore, reducing compile times
Behind an ABI tag it would be possible to salt the hash

Full diff: https://github.com/llvm/llvm-project/pull/127040.diff

14 Files Affected:

(modified) libcxx/include/__configuration/availability.h (+11)
(modified) libcxx/include/__functional/hash.h (+12-4)
(modified) libcxx/include/__string/char_traits.h (+1-1)
(modified) libcxx/lib/abi/CHANGELOG.TXT (+15)
(modified) libcxx/lib/abi/arm64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist (+1)
(modified) libcxx/lib/abi/i686-linux-android21.libcxxabi.v1.stable.exceptions.nonew.abilist (+1)
(modified) libcxx/lib/abi/powerpc-ibm-aix.libcxxabi.v1.stable.exceptions.nonew.abilist (+1)
(modified) libcxx/lib/abi/powerpc64-ibm-aix.libcxxabi.v1.stable.exceptions.nonew.abilist (+1)
(modified) libcxx/lib/abi/x86_64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist (+1)
(modified) libcxx/lib/abi/x86_64-linux-android21.libcxxabi.v1.stable.exceptions.nonew.abilist (+1)
(modified) libcxx/lib/abi/x86_64-unknown-freebsd.libcxxabi.v1.stable.exceptions.nonew.abilist (+1)
(modified) libcxx/lib/abi/x86_64-unknown-linux-gnu.libcxxabi.v1.stable.exceptions.nonew.abilist (+1)
(modified) libcxx/lib/abi/x86_64-unknown-linux-gnu.libcxxabi.v1.stable.noexceptions.nonew.abilist (+1)
(modified) libcxx/src/functional.cpp (+4)

diff --git a/libcxx/include/__configuration/availability.h b/libcxx/include/__configuration/availability.h
index 261cf9c1ae9d8..d59ad352d51be 100644
--- a/libcxx/include/__configuration/availability.h
+++ b/libcxx/include/__configuration/availability.h
@@ -78,6 +78,9 @@
 // in all versions of the library are available.
 #if !_LIBCPP_HAS_VENDOR_AVAILABILITY_ANNOTATIONS
 
+#  define _LIBCPP_INTRODUCED_IN_LLVM_21 1
+#  define _LIBCPP_INTRODUCED_IN_LLVM_21_ATTRIBUTE /* nothing */
+
 #  define _LIBCPP_INTRODUCED_IN_LLVM_20 1
 #  define _LIBCPP_INTRODUCED_IN_LLVM_20_ATTRIBUTE /* nothing */
 
@@ -114,6 +117,11 @@
 
 // clang-format off
 
+// LLVM 21
+// TODO: Fill this in
+#  define _LIBCPP_INTRODUCED_IN_LLVM_21 0
+#  define _LIBCPP_INTRODUCED_IN_LLVM_21_ATTRIBUTE __attribute__((unavailable))
+
 // LLVM 20
 // TODO: Fill this in
 #  define _LIBCPP_INTRODUCED_IN_LLVM_20 0
@@ -359,6 +367,9 @@
 #define _LIBCPP_AVAILABILITY_HAS_FROM_CHARS_FLOATING_POINT _LIBCPP_INTRODUCED_IN_LLVM_20
 #define _LIBCPP_AVAILABILITY_FROM_CHARS_FLOATING_POINT _LIBCPP_INTRODUCED_IN_LLVM_20_ATTRIBUTE
 
+#define _LIBCPP_AVAILABILITY_HAS_HASH _LIBCPP_INTRODUCED_IN_LLVM_21
+// No attribute, since we've had hash in the headers before
+
 // Define availability attributes that depend on _LIBCPP_HAS_EXCEPTIONS.
 // Those are defined in terms of the availability attributes above, and
 // should not be vendor-specific.
diff --git a/libcxx/include/__functional/hash.h b/libcxx/include/__functional/hash.h
index 28b2635ab1253..f7d07dedceb83 100644
--- a/libcxx/include/__functional/hash.h
+++ b/libcxx/include/__functional/hash.h
@@ -237,6 +237,14 @@ struct __murmur2_or_cityhash<_Size, 64> {
   }
 };
 
+#if _LIBCPP_AVAILABILITY_HAS_HASH
+[[__gnu__::__pure__]] _LIBCPP_EXPORTED_FROM_ABI size_t __hash_memory(_LIBCPP_NOESCAPE const void*, size_t) _NOEXCEPT;
+#else
+_LIBCPP_HIDE_FROM_ABI inline size_t __hash_memory(const void* __ptr, size_t __size) {
+  return __murmur2_or_cityhash<size_t>()(__ptr, __size);
+}
+#endif
+
 template <class _Tp, size_t = sizeof(_Tp) / sizeof(size_t)>
 struct __scalar_hash;
 
@@ -276,7 +284,7 @@ struct __scalar_hash<_Tp, 2> : public __unary_function<_Tp, size_t> {
       } __s;
     } __u;
     __u.__t = __v;
-    return __murmur2_or_cityhash<size_t>()(&__u, sizeof(__u));
+    return std::__hash_memory(&__u, sizeof(__u));
   }
 };
 
@@ -292,7 +300,7 @@ struct __scalar_hash<_Tp, 3> : public __unary_function<_Tp, size_t> {
       } __s;
     } __u;
     __u.__t = __v;
-    return __murmur2_or_cityhash<size_t>()(&__u, sizeof(__u));
+    return std::__hash_memory(&__u, sizeof(__u));
   }
 };
 
@@ -309,7 +317,7 @@ struct __scalar_hash<_Tp, 4> : public __unary_function<_Tp, size_t> {
       } __s;
     } __u;
     __u.__t = __v;
-    return __murmur2_or_cityhash<size_t>()(&__u, sizeof(__u));
+    return std::__hash_memory(&__u, sizeof(__u));
   }
 };
 
@@ -332,7 +340,7 @@ struct _LIBCPP_TEMPLATE_VIS hash<_Tp*> : public __unary_function<_Tp*, size_t> {
       size_t __a;
     } __u;
     __u.__t = __v;
-    return __murmur2_or_cityhash<size_t>()(&__u, sizeof(__u));
+    return std::__hash_memory(&__u, sizeof(__u));
   }
 };
 
diff --git a/libcxx/include/__string/char_traits.h b/libcxx/include/__string/char_traits.h
index 9574cde642e0e..29586bfc2c116 100644
--- a/libcxx/include/__string/char_traits.h
+++ b/libcxx/include/__string/char_traits.h
@@ -534,7 +534,7 @@ __str_find_last_not_of(const _CharT* __p, _SizeT __sz, _CharT __c, _SizeT __pos)
 template <class _Ptr>
 inline _LIBCPP_HIDE_FROM_ABI size_t __do_string_hash(_Ptr __p, _Ptr __e) {
   typedef typename iterator_traits<_Ptr>::value_type value_type;
-  return __murmur2_or_cityhash<size_t>()(__p, (__e - __p) * sizeof(value_type));
+  return std::__hash_memory(__p, (__e - __p) * sizeof(value_type));
 }
 
 _LIBCPP_END_NAMESPACE_STD
diff --git a/libcxx/lib/abi/CHANGELOG.TXT b/libcxx/lib/abi/CHANGELOG.TXT
index 2b490d00e393e..524d87c6456e0 100644
--- a/libcxx/lib/abi/CHANGELOG.TXT
+++ b/libcxx/lib/abi/CHANGELOG.TXT
@@ -12,6 +12,21 @@ To generate a summary, re-generate the new ABI list using the
 
 New entries should be added directly below the "Version" header.
 
+------------
+Version 21.0
+------------
+
+* [libc++] Instantiate hash function externally
+
+  This has multiple benefits:
+  - There is a single instance of our hash function, reducing object file size
+  - The hash implementation isn't instantiated in every TU anymore, reducing compile times
+  - Behind an ABI tag it would be possible to salt the hash
+
+  All platforms
+  -------------
+  Symbol added: _ZNSt3__113__hash_memoryEPKvm
+
 ------------
 Version 20.0
 ------------
diff --git a/libcxx/lib/abi/arm64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist b/libcxx/lib/abi/arm64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist
index 7f6d1f32e28be..24cf4055e250b 100644
--- a/libcxx/lib/abi/arm64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist
+++ b/libcxx/lib/abi/arm64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist
@@ -1305,6 +1305,7 @@
 {'is_defined': True, 'name': '__ZNSt3__113shared_futureIvED1Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '__ZNSt3__113shared_futureIvED2Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '__ZNSt3__113shared_futureIvEaSERKS1_', 'type': 'FUNC'}
+{'is_defined': True, 'name': '__ZNSt3__113__hash_memoryEPKvm', 'type': 'FUNC'}
 {'is_defined': True, 'name': '__ZNSt3__114__num_get_base10__get_baseERNS_8ios_baseE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '__ZNSt3__114__num_get_base5__srcE', 'size': 0, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '__ZNSt3__114__num_put_base12__format_intEPcPKcbj', 'type': 'FUNC'}
diff --git a/libcxx/lib/abi/i686-linux-android21.libcxxabi.v1.stable.exceptions.nonew.abilist b/libcxx/lib/abi/i686-linux-android21.libcxxabi.v1.stable.exceptions.nonew.abilist
index b38cedb012e8c..4b98b19b2c6ed 100644
--- a/libcxx/lib/abi/i686-linux-android21.libcxxabi.v1.stable.exceptions.nonew.abilist
+++ b/libcxx/lib/abi/i686-linux-android21.libcxxabi.v1.stable.exceptions.nonew.abilist
@@ -941,6 +941,7 @@
 {'is_defined': True, 'name': '_ZNSt6__ndk113shared_futureIvED1Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk113shared_futureIvED2Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk113shared_futureIvEaSERKS1_', 'type': 'FUNC'}
+{'is_defined': True, 'name': '_ZNSt6__ndk113__hash_memoryEPKvj', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk114__num_get_base10__get_baseERNS_8ios_baseE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk114__num_get_base5__srcE', 'size': 33, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZNSt6__ndk114__num_put_base12__format_intEPcPKcbj', 'type': 'FUNC'}
diff --git a/libcxx/lib/abi/powerpc-ibm-aix.libcxxabi.v1.stable.exceptions.nonew.abilist b/libcxx/lib/abi/powerpc-ibm-aix.libcxxabi.v1.stable.exceptions.nonew.abilist
index 9f299d65e63f8..368ab7c62b8a8 100644
--- a/libcxx/lib/abi/powerpc-ibm-aix.libcxxabi.v1.stable.exceptions.nonew.abilist
+++ b/libcxx/lib/abi/powerpc-ibm-aix.libcxxabi.v1.stable.exceptions.nonew.abilist
@@ -418,6 +418,7 @@
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__113shared_futureIvED1Ev', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__113shared_futureIvED2Ev', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__113shared_futureIvEaSERKS1_', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
+{'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__113__hash_memoryEPKvm', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__114__num_get_base10__get_baseERNS_8ios_baseE', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__114__num_get_base5__srcE', 'storage_mapping_class': 'RO', 'type': 'OBJECT'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__114__num_put_base12__format_intEPcPKcbj', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
diff --git a/libcxx/lib/abi/powerpc64-ibm-aix.libcxxabi.v1.stable.exceptions.nonew.abilist b/libcxx/lib/abi/powerpc64-ibm-aix.libcxxabi.v1.stable.exceptions.nonew.abilist
index 3a071b9ff52d9..642fcd5c0cd12 100644
--- a/libcxx/lib/abi/powerpc64-ibm-aix.libcxxabi.v1.stable.exceptions.nonew.abilist
+++ b/libcxx/lib/abi/powerpc64-ibm-aix.libcxxabi.v1.stable.exceptions.nonew.abilist
@@ -418,6 +418,7 @@
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__113shared_futureIvED1Ev', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__113shared_futureIvED2Ev', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__113shared_futureIvEaSERKS1_', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
+{'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__113__hash_memoryEPKvm', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__114__num_get_base10__get_baseERNS_8ios_baseE', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__114__num_get_base5__srcE', 'storage_mapping_class': 'RO', 'type': 'OBJECT'}
 {'import_export': 'EXP', 'is_defined': True, 'name': '_ZNSt3__114__num_put_base12__format_intEPcPKcbj', 'storage_mapping_class': 'DS', 'type': 'FUNC'}
diff --git a/libcxx/lib/abi/x86_64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist b/libcxx/lib/abi/x86_64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist
index 39e1aaefffbc6..6571f985204a6 100644
--- a/libcxx/lib/abi/x86_64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist
+++ b/libcxx/lib/abi/x86_64-apple-darwin.libcxxabi.v1.stable.exceptions.nonew.abilist
@@ -1305,6 +1305,7 @@
 {'is_defined': True, 'name': '__ZNSt3__113shared_futureIvED1Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '__ZNSt3__113shared_futureIvED2Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '__ZNSt3__113shared_futureIvEaSERKS1_', 'type': 'FUNC'}
+{'is_defined': True, 'name': '__ZNSt3__113__hash_memoryEPKvm', 'type': 'FUNC'}
 {'is_defined': True, 'name': '__ZNSt3__114__num_get_base10__get_baseERNS_8ios_baseE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '__ZNSt3__114__num_get_base5__srcE', 'size': 0, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '__ZNSt3__114__num_put_base12__format_intEPcPKcbj', 'type': 'FUNC'}
diff --git a/libcxx/lib/abi/x86_64-linux-android21.libcxxabi.v1.stable.exceptions.nonew.abilist b/libcxx/lib/abi/x86_64-linux-android21.libcxxabi.v1.stable.exceptions.nonew.abilist
index 5c8329c1f6650..c03b4f3c8ddc5 100644
--- a/libcxx/lib/abi/x86_64-linux-android21.libcxxabi.v1.stable.exceptions.nonew.abilist
+++ b/libcxx/lib/abi/x86_64-linux-android21.libcxxabi.v1.stable.exceptions.nonew.abilist
@@ -941,6 +941,7 @@
 {'is_defined': True, 'name': '_ZNSt6__ndk113shared_futureIvED1Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk113shared_futureIvED2Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk113shared_futureIvEaSERKS1_', 'type': 'FUNC'}
+{'is_defined': True, 'name': '_ZNSt6__ndk113__hash_memoryEPKvm', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk114__num_get_base10__get_baseERNS_8ios_baseE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt6__ndk114__num_get_base5__srcE', 'size': 33, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZNSt6__ndk114__num_put_base12__format_intEPcPKcbj', 'type': 'FUNC'}
diff --git a/libcxx/lib/abi/x86_64-unknown-freebsd.libcxxabi.v1.stable.exceptions.nonew.abilist b/libcxx/lib/abi/x86_64-unknown-freebsd.libcxxabi.v1.stable.exceptions.nonew.abilist
index 3b2f99add3906..8765b49c1dce8 100644
--- a/libcxx/lib/abi/x86_64-unknown-freebsd.libcxxabi.v1.stable.exceptions.nonew.abilist
+++ b/libcxx/lib/abi/x86_64-unknown-freebsd.libcxxabi.v1.stable.exceptions.nonew.abilist
@@ -956,6 +956,7 @@
 {'is_defined': True, 'name': '_ZNSt3__113shared_futureIvED1Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__113shared_futureIvED2Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__113shared_futureIvEaSERKS1_', 'type': 'FUNC'}
+{'is_defined': True, 'name': '_ZNSt3__113__hash_memoryEPKvm', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__114__num_get_base10__get_baseERNS_8ios_baseE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__114__num_get_base5__srcE', 'size': 33, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZNSt3__114__num_put_base12__format_intEPcPKcbj', 'type': 'FUNC'}
diff --git a/libcxx/lib/abi/x86_64-unknown-linux-gnu.libcxxabi.v1.stable.exceptions.nonew.abilist b/libcxx/lib/abi/x86_64-unknown-linux-gnu.libcxxabi.v1.stable.exceptions.nonew.abilist
index 3aa9e50a7bc3d..3a4fb06edb32b 100644
--- a/libcxx/lib/abi/x86_64-unknown-linux-gnu.libcxxabi.v1.stable.exceptions.nonew.abilist
+++ b/libcxx/lib/abi/x86_64-unknown-linux-gnu.libcxxabi.v1.stable.exceptions.nonew.abilist
@@ -954,6 +954,7 @@
 {'is_defined': True, 'name': '_ZNSt3__113shared_futureIvED1Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__113shared_futureIvED2Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__113shared_futureIvEaSERKS1_', 'type': 'FUNC'}
+{'is_defined': True, 'name': '_ZNSt3__113__hash_memoryEPKvm', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__114__num_get_base10__get_baseERNS_8ios_baseE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__114__num_get_base5__srcE', 'size': 33, 'type': 'OBJECT'}
 {'is_defined': True, 'name': '_ZNSt3__114__num_put_base12__format_intEPcPKcbj', 'type': 'FUNC'}
diff --git a/libcxx/lib/abi/x86_64-unknown-linux-gnu.libcxxabi.v1.stable.noexceptions.nonew.abilist b/libcxx/lib/abi/x86_64-unknown-linux-gnu.libcxxabi.v1.stable.noexceptions.nonew.abilist
index 74681c2205a34..e5ec1424f4ae5 100644
--- a/libcxx/lib/abi/x86_64-unknown-linux-gnu.libcxxabi.v1.stable.noexceptions.nonew.abilist
+++ b/libcxx/lib/abi/x86_64-unknown-linux-gnu.libcxxabi.v1.stable.noexceptions.nonew.abilist
@@ -924,6 +924,7 @@
 {'is_defined': True, 'name': '_ZNSt3__113random_deviceclEv', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__113shared_futureIvED1Ev', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__113shared_futureIvED2Ev', 'type': 'FUNC'}
+{'is_defined': True, 'name': '_ZNSt3__113__hash_memoryEPKvm', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__113shared_futureIvEaSERKS1_', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__114__num_get_base10__get_baseERNS_8ios_baseE', 'type': 'FUNC'}
 {'is_defined': True, 'name': '_ZNSt3__114__num_get_base5__srcE', 'size': 33, 'type': 'OBJECT'}
diff --git a/libcxx/src/functional.cpp b/libcxx/src/functional.cpp
index ef53e3e84da0e..b7c287f1b7401 100644
--- a/libcxx/src/functional.cpp
+++ b/libcxx/src/functional.cpp
@@ -16,4 +16,8 @@ bad_function_call::~bad_function_call() noexcept {}
 const char* bad_function_call::what() const noexcept { return "std::bad_function_call"; }
 #endif
 
+size_t __hash_memory(_LIBCPP_NOESCAPE const void* ptr, size_t size) _NOEXCEPT {
+  return __murmur2_or_cityhash<size_t>()(ptr, size);
+}
+
 _LIBCPP_END_NAMESPACE_STD

mordante

How would this change impact us when std::map becomes constexpr?

philnik777 · 2025-02-21T12:07:50Z

How would this change impact us when std::map becomes constexpr?

std::hash is fundamentally not compatible with constexpr exectution and was not proposed to be made constexpr, so this doesn't affect us.

mordante · 2025-02-22T13:55:12Z

How would this change impact us when std::map becomes constexpr?

std::hash is fundamentally not compatible with constexpr exectution and was not proposed to be made constexpr, so this doesn't affect us.

not yet ;-) but when it's fundamentally not compatible I don't mind moving it to the dylib.

libcxx/include/__functional/hash.h

libcxx/src/functional.cpp

philnik777 · 2025-02-23T09:51:26Z

How would this change impact us when std::map becomes constexpr?

std::hash is fundamentally not compatible with constexpr exectution and was not proposed to be made constexpr, so this doesn't affect us.

not yet ;-) but when it's fundamentally not compatible I don't mind moving it to the dylib.

Even if I'm wrong and it is possible, I don't think that should stop us from improving the library this way. As long as we don't put the public API in the dylib we can just add an if consteval somewhere.

mordante · 2025-02-25T19:49:52Z

How would this change impact us when std::map becomes constexpr?

std::hash is fundamentally not compatible with constexpr exectution and was not proposed to be made constexpr, so this doesn't affect us.

not yet ;-) but when it's fundamentally not compatible I don't mind moving it to the dylib.

Even if I'm wrong and it is possible, I don't think that should stop us from improving the library this way. As long as we don't put the public API in the dylib we can just add an if consteval somewhere.

Actually std::unordered_map is constexprified, but std::hash is not.

mordante

LGTM!

libcxx/lib/abi/CHANGELOG.TXT

libcxx/include/__configuration/availability.h

philnik777 force-pushed the instantiate_hash branch 3 times, most recently from 7044422 to 52da8dd Compare February 18, 2025 18:00

philnik777 marked this pull request as ready for review February 19, 2025 11:35

philnik777 requested a review from a team as a code owner February 19, 2025 11:35

llvmbot added the libc++ libc++ C++ Standard Library. Not GNU libstdc++. Not libc++abi. label Feb 19, 2025

mordante reviewed Feb 20, 2025

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philnik777 force-pushed the instantiate_hash branch from 52da8dd to 3da1f7c Compare February 26, 2025 10:01

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[libc++] Instantiate hash function externally

4f4e9dd

philnik777 force-pushed the instantiate_hash branch from 3da1f7c to 4f4e9dd Compare March 27, 2025 12:19

philnik777 merged commit 17d0569 into llvm:main Mar 27, 2025
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philnik777 deleted the instantiate_hash branch March 27, 2025 12:20

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[libc++] Instantiate hash function externally #127040

[libc++] Instantiate hash function externally #127040

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philnik777 commented Feb 13, 2025 •

edited by ldionne

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[libc++] Instantiate hash function externally #127040

[libc++] Instantiate hash function externally #127040

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philnik777 commented Feb 13, 2025 •

edited by ldionne

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