Make PGO builds deterministic again

some environment dependent execution (e.g. pid) were being std::hash'ed, and
net filenames put in unordered maps.  Also uses sprintf instead of
std::to_string.  Depending on precise content, this could lead to different
PGO'ed binaries. This is mitigated by using a basic hash function.

This also fixes a potential issue in net filename generation, in cases where
std::hash would use invocation dependent salt, which is not the cases today for
typical std libraries.

Closes https://github.com/official-stockfish/Stockfish/pull/6562

No functional change

src/misc.h

@@ -34,6 +34,7 @@
 #include <memory>
 #include <string>
 #include <string_view>
+#include <type_traits>
 #include <vector>
 
 #define stringify2(x) #x
@@ -305,24 +306,38 @@ inline uint64_t mul_hi64(uint64_t a, uint64_t b) {
 #endif
 }
 
-
+inline std::uint64_t hash_bytes(const char* data, std::size_t size) {
-template<typename T>
+    // FNV-1a 64-bit
-inline void hash_combine(std::size_t& seed, const T& v) {
+    const char*   p = data;
-    std::hash<T> hasher;
+    std::uint64_t h = 14695981039346656037ull;
-    seed ^= hasher(v) + 0x9e3779b9 + (seed << 6) + (seed >> 2);
+    for (std::size_t i = 0; i < size; ++i)
-}
+        h = (h ^ p[i]) * 1099511628211ull;
-
+    return h;
-template<>
-inline void hash_combine(std::size_t& seed, const std::size_t& v) {
-    seed ^= v + 0x9e3779b9 + (seed << 6) + (seed >> 2);
 }
 
 template<typename T>
 inline std::size_t get_raw_data_hash(const T& value) {
-    return std::hash<std::string_view>{}(
+    // We must have no padding bytes because we're reinterpreting as char
-      std::string_view(reinterpret_cast<const char*>(&value), sizeof(value)));
+    static_assert(std::has_unique_object_representations<T>());
+
+    return static_cast<std::size_t>(
+      hash_bytes(reinterpret_cast<const char*>(&value), sizeof(value)));
 }
 
+template<typename T>
+inline void hash_combine(std::size_t& seed, const T& v) {
+    std::size_t x;
+    // For primitive types we avoid using the default hasher, which may be
+    // nondeterministic across program invocations
+    if constexpr (std::is_integral<T>())
+        x = v;
+    else
+        x = std::hash<T>{}(v);
+    seed ^= x + 0x9e3779b9 + (seed << 6) + (seed >> 2);
+}
+
+inline std::uint64_t hash_string(const std::string& sv) { return hash_bytes(sv.data(), sv.size()); }
+
 template<std::size_t Capacity>
 class FixedString {
    public:
@@ -450,7 +465,7 @@ void move_to_front(std::vector<T>& vec, Predicate pred) {
 template<std::size_t N>
 struct std::hash<Stockfish::FixedString<N>> {
     std::size_t operator()(const Stockfish::FixedString<N>& fstr) const noexcept {
-        return std::hash<std::string_view>{}((std::string_view) fstr);
+        return Stockfish::hash_bytes(fstr.data(), fstr.size());
     }
 };
 

src/numa.h

@@ -1586,7 +1586,7 @@ class LazyNumaReplicatedSystemWide: public NumaReplicatedBase {
         CpuIndex    cpu     = *cfg.nodes[idx].begin();  // get a CpuIndex from NumaIndex
         NumaIndex   sys_idx = cfg_sys.is_cpu_assigned(cpu) ? cfg_sys.nodeByCpu.at(cpu) : 0;
         std::string s       = cfg_sys.to_string() + "$" + std::to_string(sys_idx);
-        return std::hash<std::string>{}(s);
+        return static_cast<std::size_t>(hash_string(s));
     }
 
     void ensure_present(NumaIndex idx) const {

src/shm.h

@@ -20,6 +20,7 @@
 #define SHM_H_INCLUDED
 
 #include <algorithm>
+#include <cinttypes>
 #include <cstddef>
 #include <cstdint>
 #include <cstring>
@@ -512,12 +513,9 @@ template<typename T>
 struct SystemWideSharedConstant {
    private:
     static std::string createHashString(const std::string& input) {
-        size_t hash = std::hash<std::string>{}(input);
+        char buf[1024];
-
+        std::snprintf(buf, sizeof(buf), "%016" PRIx64, hash_string(input));
-        std::stringstream ss;
+        return buf;
-        ss << std::hex << std::setfill('0') << hash;
-
-        return ss.str();
     }
 
    public:
@@ -534,11 +532,11 @@ struct SystemWideSharedConstant {
     // that are not present in the content, for example NUMA node allocation.
     SystemWideSharedConstant(const T& value, std::size_t discriminator = 0) {
         std::size_t content_hash    = std::hash<T>{}(value);
-        std::size_t executable_hash = std::hash<std::string>{}(getExecutablePathHash());
+        std::size_t executable_hash = hash_string(getExecutablePathHash());
 
-        std::string shm_name = std::string("Local\\sf_") + std::to_string(content_hash) + "$"
+        char buf[1024];
-                             + std::to_string(executable_hash) + "$"
+        std::snprintf(buf, sizeof(buf), "Local\\sf_%zu$%zu$%zu", content_hash, executable_hash, discriminator);
-                             + std::to_string(discriminator);
+        std::string shm_name = buf;
 
 #if !defined(_WIN32)
         // POSIX shared memory names must start with a slash

src/shm_linux.h

@@ -33,7 +33,6 @@
 #include <string>
 #include <inttypes.h>
 #include <type_traits>
-#include <unordered_set>
 
 #include <fcntl.h>
 #include <signal.h>
@@ -51,6 +50,7 @@
     #define SF_MAX_SEM_NAME_LEN 255
 #endif
 
+#include "misc.h"
 
 namespace Stockfish::shm {
 
@@ -74,17 +74,18 @@ class SharedMemoryBase {
 class SharedMemoryRegistry {
    private:
     static std::mutex                            registry_mutex_;
-    static std::unordered_set<SharedMemoryBase*> active_instances_;
+    static std::vector<SharedMemoryBase*> active_instances_;
 
    public:
     static void register_instance(SharedMemoryBase* instance) {
         std::scoped_lock lock(registry_mutex_);
-        active_instances_.insert(instance);
+        active_instances_.push_back(instance);
     }
 
     static void unregister_instance(SharedMemoryBase* instance) {
         std::scoped_lock lock(registry_mutex_);
-        active_instances_.erase(instance);
+        active_instances_.erase(
+            std::remove(active_instances_.begin(), active_instances_.end(), instance), active_instances_.end());
     }
 
     static void cleanup_all(bool skip_unmap = false) noexcept {
@@ -96,7 +97,7 @@ class SharedMemoryRegistry {
 };
 
 inline std::mutex                            SharedMemoryRegistry::registry_mutex_;
-inline std::unordered_set<SharedMemoryBase*> SharedMemoryRegistry::active_instances_;
+inline std::vector<SharedMemoryBase*> SharedMemoryRegistry::active_instances_;
 
 class CleanupHooks {
    private:
@@ -181,9 +182,10 @@ class SharedMemory: public detail::SharedMemoryBase {
     }
 
     static std::string make_sentinel_base(const std::string& name) {
-        uint64_t hash = std::hash<std::string>{}(name);
         char     buf[32];
-        std::snprintf(buf, sizeof(buf), "sfshm_%016" PRIx64, static_cast<uint64_t>(hash));
+        // Using std::to_string here causes non-deterministic PGO builds.
+        // snprintf, being part of libc, is insensitive to the formatted values.
+        std::snprintf(buf, sizeof(buf), "sfshm_%016" PRIu64, hash_string(name));
         return buf;
     }
 
@@ -442,11 +444,10 @@ class SharedMemory: public detail::SharedMemoryBase {
     }
 
     std::string sentinel_full_path(pid_t pid) const {
-        std::string path = "/dev/shm/";
+        char buf[1024];
-        path += sentinel_base_;
+        // See above snprintf comment
-        path.push_back('.');
+        std::snprintf(buf, sizeof(buf), "/dev/shm/%s.%ld", sentinel_base_.c_str(), long(pid));
-        path += std::to_string(pid);
+        return buf;
-        return path;
     }
 
     void decrement_refcount_relaxed() noexcept {