[CaptureTracking] Replace hardcoded constant to option. NFC.

The motivation is to be able to play with the option and change if it is required.

Reviewers: fedor.sergeev, apilipenko, rnk, jdoerfert
Reviewed By: fedor.sergeev
Subscribers: hiraditya, dantrushin, llvm-commits
Differential Revision: https://reviews.llvm.org/D78624

include/llvm/Analysis/CaptureTracking.h

@@ -21,13 +21,10 @@ namespace llvm {
   class Instruction;
   class DominatorTree;
 
-  /// The default value for MaxUsesToExplore argument. It's relatively small to
-  /// keep the cost of analysis reasonable for clients like BasicAliasAnalysis,
-  /// where the results can't be cached.
-  /// TODO: we should probably introduce a caching CaptureTracking analysis and
-  /// use it where possible. The caching version can use much higher limit or
-  /// don't have this cap at all.
-  unsigned constexpr DefaultMaxUsesToExplore = 20;
+  /// getDefaultMaxUsesToExploreForCaptureTracking - Return default value of
+  /// the maximal number of uses to explore before giving up. It is used by
+  /// PointerMayBeCaptured family analysys.
+  unsigned getDefaultMaxUsesToExploreForCaptureTracking();
 
   /// PointerMayBeCaptured - Return true if this pointer value may be captured
   /// by the enclosing function (which is required to exist).  This routine can
@@ -38,10 +35,10 @@ namespace llvm {
   /// automatically counts as capturing it or not.
   /// MaxUsesToExplore specifies how many uses should the analysis explore for
   /// one value before giving up due too "too many uses".
-  bool PointerMayBeCaptured(const Value *V,
-                            bool ReturnCaptures,
+  bool PointerMayBeCaptured(const Value *V, bool ReturnCaptures,
                             bool StoreCaptures,
-                            unsigned MaxUsesToExplore = DefaultMaxUsesToExplore);
+                            unsigned MaxUsesToExplore =
+                                getDefaultMaxUsesToExploreForCaptureTracking());
 
   /// PointerMayBeCapturedBefore - Return true if this pointer value may be
   /// captured by the enclosing function (which is required to exist). If a
@@ -55,10 +52,11 @@ namespace llvm {
   /// final parameter is true.
   /// MaxUsesToExplore specifies how many uses should the analysis explore for
   /// one value before giving up due too "too many uses".
-  bool PointerMayBeCapturedBefore(const Value *V, bool ReturnCaptures,
-                                  bool StoreCaptures, const Instruction *I,
-                                  const DominatorTree *DT, bool IncludeI = false,
-                                  unsigned MaxUsesToExplore = DefaultMaxUsesToExplore);
+  bool PointerMayBeCapturedBefore(
+      const Value *V, bool ReturnCaptures, bool StoreCaptures,
+      const Instruction *I, const DominatorTree *DT, bool IncludeI = false,
+      unsigned MaxUsesToExplore =
+          getDefaultMaxUsesToExploreForCaptureTracking());
 
   /// This callback is used in conjunction with PointerMayBeCaptured. In
   /// addition to the interface here, you'll need to provide your own getters
@@ -94,7 +92,8 @@ namespace llvm {
   /// MaxUsesToExplore specifies how many uses should the analysis explore for
   /// one value before giving up due too "too many uses".
   void PointerMayBeCaptured(const Value *V, CaptureTracker *Tracker,
-                            unsigned MaxUsesToExplore = DefaultMaxUsesToExplore);
+                            unsigned MaxUsesToExplore =
+                                getDefaultMaxUsesToExploreForCaptureTracking());
 } // end namespace llvm
 
 #endif

lib/Analysis/CaptureTracking.cpp

@@ -28,6 +28,21 @@
 
 using namespace llvm;
 
+/// The default value for MaxUsesToExplore argument. It's relatively small to
+/// keep the cost of analysis reasonable for clients like BasicAliasAnalysis,
+/// where the results can't be cached.
+/// TODO: we should probably introduce a caching CaptureTracking analysis and
+/// use it where possible. The caching version can use much higher limit or
+/// don't have this cap at all.
+static cl::opt<unsigned>
+DefaultMaxUsesToExplore("capture-tracking-max-uses-to-explore", cl::Hidden,
+                        cl::desc("Maximal number of uses to explore."),
+                        cl::init(20));
+
+unsigned llvm::getDefaultMaxUsesToExploreForCaptureTracking() {
+  return DefaultMaxUsesToExplore;
+}
+
 CaptureTracker::~CaptureTracker() {}
 
 bool CaptureTracker::shouldExplore(const Use *U) { return true; }
@@ -215,8 +230,9 @@ bool llvm::PointerMayBeCapturedBefore(const Value *V, bool ReturnCaptures,
 void llvm::PointerMayBeCaptured(const Value *V, CaptureTracker *Tracker,
                                 unsigned MaxUsesToExplore) {
   assert(V->getType()->isPointerTy() && "Capture is for pointers only!");
-  SmallVector<const Use *, DefaultMaxUsesToExplore> Worklist;
-  SmallSet<const Use *, DefaultMaxUsesToExplore> Visited;
+  SmallVector<const Use *, 20> Worklist;
+  Worklist.reserve(getDefaultMaxUsesToExploreForCaptureTracking());
+  SmallSet<const Use *, 20> Visited;
 
   auto AddUses = [&](const Value *V) {
     unsigned Count = 0;

lib/Transforms/IPO/AttributorAttributes.cpp

@@ -4170,7 +4170,8 @@ ChangeStatus AANoCaptureImpl::updateImpl(Attributor &A) {
   // defined in AACaptureUseTracker, that can look at in-flight abstract
   // attributes and directly updates the assumed state.
   SmallVector<const Value *, 4> PotentialCopies;
-  unsigned RemainingUsesToExplore = DefaultMaxUsesToExplore;
+  unsigned RemainingUsesToExplore =
+      getDefaultMaxUsesToExploreForCaptureTracking();
   AACaptureUseTracker Tracker(A, *this, IsDeadAA, T, PotentialCopies,
                               RemainingUsesToExplore);