X-Git-Url: http://demsky.eecs.uci.edu/git/?a=blobdiff_plain;f=lib%2FAnalysis%2FCaptureTracking.cpp;h=42a54d9d1eb3adba766363cf2ef38765a12055b9;hb=ff10341183adf74760e6118a55cbd1debf50f90f;hp=e86ad96e4a15e821852f997c8ff876aa16766130;hpb=76c638a14c1e2927e5e20040b347bc3d7ae8fb82;p=oota-llvm.git

diff --git a/lib/Analysis/CaptureTracking.cpp b/lib/Analysis/CaptureTracking.cpp
index e86ad96e4a1..42a54d9d1eb 100644
--- a/lib/Analysis/CaptureTracking.cpp
+++ b/lib/Analysis/CaptureTracking.cpp
@@ -25,6 +25,16 @@
 #include "llvm/Support/CallSite.h"
 using namespace llvm;
 
+/// As its comment mentions, PointerMayBeCaptured can be expensive.
+/// However, it's not easy for BasicAA to cache the result, because
+/// it's an ImmutablePass. To work around this, bound queries at a
+/// fixed number of uses.
+///
+/// TODO: Write a new FunctionPass AliasAnalysis so that it can keep
+/// a cache. Then we can move the code from BasicAliasAnalysis into
+/// that path, and remove this threshold.
+static int const Threshold = 20;
+
 /// PointerMayBeCaptured - Return true if this pointer value may be captured
 /// by the enclosing function (which is required to exist).  This routine can
 /// be expensive, so consider caching the results.  The boolean ReturnCaptures
@@ -34,12 +44,18 @@ using namespace llvm;
 /// counts as capturing it or not.
 bool llvm::PointerMayBeCaptured(const Value *V,
                                 bool ReturnCaptures, bool StoreCaptures) {
-  assert(isa<PointerType>(V->getType()) && "Capture is for pointers only!");
-  SmallVector<Use*, 16> Worklist;
-  SmallSet<Use*, 16> Visited;
+  assert(V->getType()->isPointerTy() && "Capture is for pointers only!");
+  SmallVector<Use*, Threshold> Worklist;
+  SmallSet<Use*, Threshold> Visited;
+  int Count = 0;
 
-  for (Value::use_const_iterator UI = V->use_begin(), UE = V->use_end();
+  for (Value::const_use_iterator UI = V->use_begin(), UE = V->use_end();
        UI != UE; ++UI) {
+    // If there are lots of uses, conservatively say that the value
+    // is captured to avoid taking too much compile time.
+    if (Count++ >= Threshold)
+      return true;
+
     Use *U = &UI.getUse();
     Visited.insert(U);
     Worklist.push_back(U);
@@ -53,7 +69,7 @@ bool llvm::PointerMayBeCaptured(const Value *V,
     switch (I->getOpcode()) {
     case Instruction::Call:
     case Instruction::Invoke: {
-      CallSite CS = CallSite::get(I);
+      CallSite CS(I);
       // Not captured if the callee is readonly, doesn't return a copy through
       // its return value and doesn't unwind (a readonly function can leak bits
       // by throwing an exception or not depending on the input value).
@@ -79,6 +95,9 @@ bool llvm::PointerMayBeCaptured(const Value *V,
     case Instruction::Load:
       // Loading from a pointer does not cause it to be captured.
       break;
+    case Instruction::VAArg:
+      // "va-arg" from a pointer does not cause it to be captured.
+      break;
     case Instruction::Ret:
       if (ReturnCaptures)
         return true;
@@ -105,25 +124,18 @@ bool llvm::PointerMayBeCaptured(const Value *V,
           Worklist.push_back(U);
       }
       break;
-    case Instruction::ICmp: {
-      // Don't count comparisons of the original value against null as captures.
-      // This allows us to ignore comparisons of malloc results with null,
-      // for example.
-      if (isIdentifiedObject(V))
+    case Instruction::ICmp:
+      // Don't count comparisons of a no-alias return value against null as
+      // captures. This allows us to ignore comparisons of malloc results
+      // with null, for example.
+      if (isNoAliasCall(V->stripPointerCasts()))
         if (ConstantPointerNull *CPN =
               dyn_cast<ConstantPointerNull>(I->getOperand(1)))
           if (CPN->getType()->getAddressSpace() == 0)
             break;
-      // Don't count comparisons of two pointers within the same identified
-      // object as captures.
-      Value *O0 = I->getOperand(0)->getUnderlyingObject();
-      if (isIdentifiedObject(O0) &&
-          O0 == I->getOperand(1)->getUnderlyingObject())
-        break;
       // Otherwise, be conservative. There are crazy ways to capture pointers
       // using comparisons.
       return true;
-    }
     default:
       // Something else - be conservative and say it is captured.
       return true;