1 files changed, 37 insertions, 11 deletions
diff --git a/llvm/lib/Support/Windows/Process.inc b/llvm/lib/Support/Windows/Process.inc
index 3526e3dee6fa1..8064d4e17b295 100644
--- a/llvm/lib/Support/Windows/Process.inc
+++ b/llvm/lib/Support/Windows/Process.inc
@@ -19,7 +19,7 @@
 #include <malloc.h>
 
 // The Windows.h header must be after LLVM and standard headers.
-#include "WindowsSupport.h"
+#include "llvm/Support/Windows/WindowsSupport.h"
 
 #include <direct.h>
 #include <io.h>
@@ -43,6 +43,12 @@
 
 using namespace llvm;
 
+Process::Pid Process::getProcessId() {
+  static_assert(sizeof(Pid) >= sizeof(DWORD),
+                "Process::Pid should be big enough to store DWORD");
+  return Pid(::GetCurrentProcessId());
+}
+
 // This function retrieves the page size using GetNativeSystemInfo() and is
 // present solely so it can be called once to initialize the self_process member
 // below.
@@ -439,18 +445,38 @@ const char *Process::ResetColor() {
   return 0;
 }
 
+static unsigned GetRandomNumberSeed() {
+  // Generate a random number seed from the millisecond-resolution Windows
+  // system clock and the current process id.
+  FILETIME Time;
+  GetSystemTimeAsFileTime(&Time);
+  DWORD Pid = GetCurrentProcessId();
+  return hash_combine(Time.dwHighDateTime, Time.dwLowDateTime, Pid);
+}
+
+static unsigned GetPseudoRandomNumber() {
+  // Arrange to call srand once when this function is first used, and
+  // otherwise (if GetRandomNumber always succeeds in using
+  // CryptGenRandom) don't bother at all.
+  static int x = (static_cast<void>(::srand(GetRandomNumberSeed())), 0);
+  (void)x;
+  return ::rand();
+}
+
 unsigned Process::GetRandomNumber() {
+  // Try to use CryptGenRandom.
   HCRYPTPROV HCPC;
-  if (!::CryptAcquireContextW(&HCPC, NULL, NULL, PROV_RSA_FULL,
-                              CRYPT_VERIFYCONTEXT))
-    ReportLastErrorFatal("Could not acquire a cryptographic context");
-
-  ScopedCryptContext CryptoProvider(HCPC);
-  unsigned Ret;
-  if (!::CryptGenRandom(CryptoProvider, sizeof(Ret),
-                        reinterpret_cast<BYTE *>(&Ret)))
-    ReportLastErrorFatal("Could not generate a random number");
-  return Ret;
+  if (::CryptAcquireContextW(&HCPC, NULL, NULL, PROV_RSA_FULL,
+                             CRYPT_VERIFYCONTEXT)) {
+    ScopedCryptContext CryptoProvider(HCPC);
+    unsigned Ret;
+    if (::CryptGenRandom(CryptoProvider, sizeof(Ret),
+                         reinterpret_cast<BYTE *>(&Ret)))
+      return Ret;
+  }
+
+  // If that fails, fall back to pseudo-random numbers.
+  return GetPseudoRandomNumber();
 }
 
 typedef NTSTATUS(WINAPI* RtlGetVersionPtr)(PRTL_OSVERSIONINFOW);