Delay initialization of OptBisect

When LLVM is used in other projects, it may happen that global cons-
tructors will execute before the call to ParseCommandLineOptions.
Since OptBisect is initialized via a constructor, and has no ability
to be updated at a later time, passing "-opt-bisect-limit" to the
parse function may have no effect.

To avoid this problem use a cl::cb (callback) to set the bisection
limit when the option is actually processed.

Differential Revision: https://reviews.llvm.org/D104551

include/llvm/IR/OptBisect.h

@@ -16,6 +16,7 @@
 
 #include "llvm/ADT/StringRef.h"
 #include "llvm/Support/ManagedStatic.h"
+#include <limits>
 
 namespace llvm {
 
@@ -43,14 +44,12 @@ public:
 /// optimization-related problems.
 class OptBisect : public OptPassGate {
 public:
-  /// Default constructor, initializes the OptBisect state based on the
-  /// -opt-bisect-limit command line argument.
-  ///
-  /// By default, bisection is disabled.
-  ///
+  /// Default constructor. Initializes the state to "disabled". The bisection
+  /// will be enabled by the cl::opt call-back when the command line option
+  /// is processed.
   /// Clients should not instantiate this class directly.  All access should go
   /// through LLVMContext.
-  OptBisect();
+  OptBisect() = default;
 
   virtual ~OptBisect() = default;
 
@@ -60,7 +59,11 @@ public:
   bool shouldRunPass(const Pass *P, StringRef IRDescription) override;
 
   /// isEnabled() should return true before calling shouldRunPass().
-  bool isEnabled() const override { return BisectEnabled; }
+  bool isEnabled() const override { return BisectLimit != Disabled; }
+
+  /// Set the new optimization limit. Passing OptBisect::Disabled disables
+  /// the limiting.
+  void setLimit(int Limit) { BisectLimit = Limit; }
 
   /// Checks the bisect limit to determine if the specified pass should run.
   ///
@@ -75,9 +78,11 @@ public:
   /// instance, function passes should call FunctionPass::skipFunction().
   bool checkPass(const StringRef PassName, const StringRef TargetDesc);
 
+  static const int Disabled = std::numeric_limits<int>::max();
+
 private:
-  bool BisectEnabled = false;
-  unsigned LastBisectNum = 0;
+  int BisectLimit = Disabled;
+  int LastBisectNum = 0;
 };
 
 /// Singleton instance of the OptBisect class, so multiple pass managers don't

lib/IR/OptBisect.cpp

@@ -22,14 +22,12 @@
 using namespace llvm;
 
 static cl::opt<int> OptBisectLimit("opt-bisect-limit", cl::Hidden,
-                                   cl::init(std::numeric_limits<int>::max()),
-                                   cl::Optional,
+                                   cl::init(OptBisect::Disabled), cl::Optional,
+                                   cl::cb<void, int>([](int Limit) {
+                                     llvm::OptBisector->setLimit(Limit);
+                                   }),
                                    cl::desc("Maximum optimization to perform"));
 
-OptBisect::OptBisect() : OptPassGate() {
-  BisectEnabled = OptBisectLimit != std::numeric_limits<int>::max();
-}
-
 static void printPassMessage(const StringRef &Name, int PassNum,
                              StringRef TargetDesc, bool Running) {
   StringRef Status = Running ? "" : "NOT ";
@@ -38,17 +36,17 @@ static void printPassMessage(const StringRef &Name, int PassNum,
 }
 
 bool OptBisect::shouldRunPass(const Pass *P, StringRef IRDescription) {
-  assert(BisectEnabled);
+  assert(isEnabled());
 
   return checkPass(P->getPassName(), IRDescription);
 }
 
 bool OptBisect::checkPass(const StringRef PassName,
                           const StringRef TargetDesc) {
-  assert(BisectEnabled);
+  assert(isEnabled());
 
   int CurBisectNum = ++LastBisectNum;
-  bool ShouldRun = (OptBisectLimit == -1 || CurBisectNum <= OptBisectLimit);
+  bool ShouldRun = (BisectLimit == -1 || CurBisectNum <= BisectLimit);
   printPassMessage(PassName, CurBisectNum, TargetDesc, ShouldRun);
   return ShouldRun;
 }