Export of internal Abseil changes

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f09549625d7417fca379ff68334379d281480608 by Martijn Vels <mvels@google.com>:

Fix GetNumCPUs() for WIN32 platforms

PiperOrigin-RevId: 368245360

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e903c6690d0568f80356e03b07a895b031553977 by Abseil Team <absl-team@google.com>:

Optimize `Cord::InlineRep::InlineRep(Cord::InlineRep&& src)`.

PiperOrigin-RevId: 368198990
GitOrigin-RevId: f09549625d7417fca379ff68334379d281480608
Change-Id: I2d750c8c87f2804335a60ba8db949dedfaa462e2

1 files changed, 67 insertions, 0 deletions

diff --git a/absl/base/internal/sysinfo.cc b/absl/base/internal/sysinfo.cc
index 4a3b2050..08a1e288 100644
--- a/absl/base/internal/sysinfo.cc
+++ b/absl/base/internal/sysinfo.cc
@@ -61,9 +61,76 @@ namespace absl {
 ABSL_NAMESPACE_BEGIN
 namespace base_internal {
 
+namespace {
+
+#if defined(_WIN32)
+
+// Returns number of bits set in `bitMask`
+DWORD Win32CountSetBits(ULONG_PTR bitMask) {
+  for (DWORD bitSetCount = 0; ; ++bitSetCount) {
+    if (bitMask == 0) return bitSetCount;
+    bitMask &= bitMask - 1;
+  }
+}
+
+// Returns the number of logical CPUs using GetLogicalProcessorInformation(), or
+// 0 if the number of processors is not available or can not be computed.
+// https://docs.microsoft.com/en-us/windows/win32/api/sysinfoapi/nf-sysinfoapi-getlogicalprocessorinformation
+int Win32NumCPUs() {
+#pragma comment(lib, "kernel32.lib")
+  using Info = SYSTEM_LOGICAL_PROCESSOR_INFORMATION;
+
+  DWORD info_size = sizeof(Info);
+  Info* info(static_cast<Info*>(malloc(info_size)));
+  if (info == nullptr) return 0;
+
+  bool success = GetLogicalProcessorInformation(info, &info_size);
+  if (!success && GetLastError() == ERROR_INSUFFICIENT_BUFFER) {
+    free(info);
+    info = static_cast<Info*>(malloc(info_size));
+    if (info == nullptr) return 0;
+    success = GetLogicalProcessorInformation(info, &info_size);
+  }
+
+  DWORD logicalProcessorCount = 0;
+  if (success) {
+    Info* ptr = info;
+    DWORD byteOffset = 0;
+    while (byteOffset + sizeof(Info) <= info_size) {
+      switch (ptr->Relationship) {
+        case RelationProcessorCore:
+          logicalProcessorCount += Win32CountSetBits(ptr->ProcessorMask);
+          break;
+
+        case RelationNumaNode:
+        case RelationCache:
+        case RelationProcessorPackage:
+          // Ignore other entries
+          break;
+
+        default:
+          // Ignore unknown entries
+          break;
+      }
+      byteOffset += sizeof(Info);
+      ptr++;
+    }
+  }
+  free(info);
+  return logicalProcessorCount;
+}
+
+#endif
+
+}  // namespace
+
+
 static int GetNumCPUs() {
 #if defined(__myriad2__)
   return 1;
+#elif defined(_WIN32)
+  const unsigned hardware_concurrency = Win32NumCPUs();
+  return hardware_concurrency ? hardware_concurrency : 1;
 #else
   // Other possibilities:
   //  - Read /sys/devices/system/cpu/online and use cpumask_parse()