Use ManagedStatic and lazy initialization of cl::opt in libSupport to make it free of global initializer

We can build it with -Werror=global-constructors now. This helps
in situation where libSupport is embedded as a shared library,
potential with dlopen/dlclose scenario, and when command-line
parsing or other facilities may not be involved. Avoiding the
implicit construction of these cl::opt can avoid double-registration
issues and other kind of behavior.

Reviewed By: lattner, jpienaar

Differential Revision: https://reviews.llvm.org/D105959

1 files changed, 17 insertions, 7 deletions

diff --git a/llvm/lib/Support/RandomNumberGenerator.cpp b/llvm/lib/Support/RandomNumberGenerator.cpp
index f9c41ee..aea0132 100644
--- a/llvm/lib/Support/RandomNumberGenerator.cpp
+++ b/llvm/lib/Support/RandomNumberGenerator.cpp
@@ -13,6 +13,9 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/Support/RandomNumberGenerator.h"
+
+#include "DebugOptions.h"
+
 #include "llvm/Support/CommandLine.h"
 #include "llvm/Support/Debug.h"
 #include "llvm/Support/raw_ostream.h"
@@ -25,13 +28,20 @@
 using namespace llvm;
 
 #define DEBUG_TYPE "rng"
-
-static cl::opt<uint64_t> Seed("rng-seed", cl::value_desc("seed"), cl::Hidden,
-                              cl::desc("Seed for the random number generator"),
-                              cl::init(0));
+namespace {
+struct CreateSeed {
+  static void *call() {
+    return new cl::opt<uint64_t>(
+        "rng-seed", cl::value_desc("seed"), cl::Hidden,
+        cl::desc("Seed for the random number generator"), cl::init(0));
+  }
+};
+} // namespace
+static ManagedStatic<cl::opt<uint64_t>, CreateSeed> Seed;
+void llvm::initRandomSeedOptions() { *Seed; }
 
 RandomNumberGenerator::RandomNumberGenerator(StringRef Salt) {
-  LLVM_DEBUG(if (Seed == 0) dbgs()
+  LLVM_DEBUG(if (*Seed == 0) dbgs()
              << "Warning! Using unseeded random number generator.\n");
 
   // Combine seed and salts using std::seed_seq.
@@ -41,8 +51,8 @@ RandomNumberGenerator::RandomNumberGenerator(StringRef Salt) {
   // twister constructor copies these correctly into its initial state.
   std::vector<uint32_t> Data;
   Data.resize(2 + Salt.size());
-  Data[0] = Seed;
-  Data[1] = Seed >> 32;
+  Data[0] = *Seed;
+  Data[1] = *Seed >> 32;
 
   llvm::copy(Salt, Data.begin() + 2);