diff --git a/lib/Analysis/BasicAliasAnalysis.cpp b/lib/Analysis/BasicAliasAnalysis.cpp
index a1bf69e..c4aa3b5 100644
--- a/lib/Analysis/BasicAliasAnalysis.cpp
+++ b/lib/Analysis/BasicAliasAnalysis.cpp
@@ -21,10 +21,12 @@
 #include "llvm/ParameterAttributes.h"
 #include "llvm/GlobalVariable.h"
 #include "llvm/Instructions.h"
+#include "llvm/Intrinsics.h"
 #include "llvm/Pass.h"
 #include "llvm/Target/TargetData.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/StringMap.h"
+#include "llvm/ADT/BitVector.h"
 #include "llvm/Support/Compiler.h"
 #include "llvm/Support/GetElementPtrTypeIterator.h"
 #include "llvm/Support/ManagedStatic.h"
@@ -874,6 +876,9 @@
 static ManagedStatic<std::vector<const char*> > NoMemoryTable;
 static ManagedStatic<std::vector<const char*> > OnlyReadsMemoryTable;
 
+static ManagedStatic<BitVector> NoMemoryIntrinsics;
+static ManagedStatic<BitVector> OnlyReadsMemoryIntrinsics;
+
 
 AliasAnalysis::ModRefBehavior
 BasicAliasAnalysis::getModRefBehavior(Function *F, CallSite CS,
@@ -891,16 +896,30 @@
                                 OnlyReadsMemoryFns, 
                                 OnlyReadsMemoryFns+
                       sizeof(OnlyReadsMemoryFns)/sizeof(OnlyReadsMemoryFns[0]));
-#define GET_MODREF_BEHAVIOR
-#include "llvm/Intrinsics.gen"
-#undef GET_MODREF_BEHAVIOR
-    
+
     // Sort the table the first time through.
     std::sort(NoMemoryTable->begin(), NoMemoryTable->end(), StringCompare());
     std::sort(OnlyReadsMemoryTable->begin(), OnlyReadsMemoryTable->end(),
               StringCompare());
+    
+    NoMemoryIntrinsics->resize(Intrinsic::num_intrinsics);
+    OnlyReadsMemoryIntrinsics->resize(Intrinsic::num_intrinsics);
+#define GET_MODREF_BEHAVIOR
+#include "llvm/Intrinsics.gen"
+#undef GET_MODREF_BEHAVIOR
+    
     Initialized = true;
   }
+
+  // If this is an intrinsic, we can use lookup tables
+  if (unsigned id = F->getIntrinsicID()) {
+    if (NoMemoryIntrinsics->test(id))
+      return DoesNotAccessMemory;
+    if (OnlyReadsMemoryIntrinsics->test(id))
+      return OnlyReadsMemory;
+
+    return UnknownModRefBehavior;
+  }
   
   ValueName *Name = F->getValueName();
   unsigned NameLen = Name->getKeyLength();
diff --git a/test/Analysis/BasicAA/2007-08-05-GetOverloadedModRef.ll b/test/Analysis/BasicAA/2007-08-05-GetOverloadedModRef.ll
new file mode 100644
index 0000000..c555f63
--- /dev/null
+++ b/test/Analysis/BasicAA/2007-08-05-GetOverloadedModRef.ll
@@ -0,0 +1,17 @@
+; PR1600
+; RUN: llvm-as < %s | opt -basicaa -load-vn -gcse -instcombine | llvm-dis | \
+; RUN:   grep {ret i32 0}
+; END.
+
+declare i16 @llvm.cttz.i16(i16)
+
+define i32 @test(i32* %P, i16* %Q) {
+        %A = load i16* %Q               ; <i16> [#uses=1]
+        %x = load i32* %P               ; <i32> [#uses=1]
+        %B = call i16 @llvm.cttz.i16( i16 %A )          ; <i16> [#uses=1]
+        %y = load i32* %P               ; <i32> [#uses=1]
+        store i16 %B, i16* %Q
+        %z = sub i32 %x, %y             ; <i32> [#uses=1]
+        ret i32 %z
+}
+
diff --git a/utils/TableGen/IntrinsicEmitter.cpp b/utils/TableGen/IntrinsicEmitter.cpp
index ebc0c32..f5df933 100644
--- a/utils/TableGen/IntrinsicEmitter.cpp
+++ b/utils/TableGen/IntrinsicEmitter.cpp
@@ -299,11 +299,11 @@
     switch (Ints[i].ModRef) {
     default: break;
     case CodeGenIntrinsic::NoMem:
-      OS << "  NoMemoryTable->push_back(\"" << Ints[i].Name << "\");\n";
+      OS << "  NoMemoryIntrinsics->set(Intrinsic::" << Ints[i].EnumName << ");\n";
       break;
     case CodeGenIntrinsic::ReadArgMem:
     case CodeGenIntrinsic::ReadMem:
-      OS << "  OnlyReadsMemoryTable->push_back(\"" << Ints[i].Name << "\");\n";
+      OS << "  OnlyReadsMemoryIntrinsics->set(Intrinsic::" << Ints[i].EnumName << ");\n";
       break;
     }
   }