diff --git a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
index 85d580b..773441f 100644
--- a/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -2088,11 +2088,13 @@
   // addressing...
   for (unsigned i = 2, e = CE->getNumOperands(); i != e; ++i)
     if (ConstantUInt *CU = dyn_cast<ConstantUInt>(CE->getOperand(i))) {
-      ConstantStruct *CS = cast<ConstantStruct>(C);
+      ConstantStruct *CS = dyn_cast<ConstantStruct>(C);
+      if (CS == 0) return 0;
       if (CU->getValue() >= CS->getValues().size()) return 0;
       C = cast<Constant>(CS->getValues()[CU->getValue()]);
     } else if (ConstantSInt *CS = dyn_cast<ConstantSInt>(CE->getOperand(i))) {
-      ConstantArray *CA = cast<ConstantArray>(C);
+      ConstantArray *CA = dyn_cast<ConstantArray>(C);
+      if (CA == 0) return 0;
       if ((uint64_t)CS->getValue() >= CA->getValues().size()) return 0;
       C = cast<Constant>(CA->getValues()[CS->getValue()]);
     } else 
diff --git a/llvm/lib/Transforms/Scalar/SCCP.cpp b/llvm/lib/Transforms/Scalar/SCCP.cpp
index 4e5e515..8304e2e 100644
--- a/llvm/lib/Transforms/Scalar/SCCP.cpp
+++ b/llvm/lib/Transforms/Scalar/SCCP.cpp
@@ -689,14 +689,16 @@
   // addressing...
   for (unsigned i = 2, e = CE->getNumOperands(); i != e; ++i)
     if (ConstantUInt *CU = dyn_cast<ConstantUInt>(CE->getOperand(i))) {
-      ConstantStruct *CS = cast<ConstantStruct>(C);
+      ConstantStruct *CS = dyn_cast<ConstantStruct>(C);
+      if (CS == 0) return 0;
       if (CU->getValue() >= CS->getValues().size()) return 0;
       C = cast<Constant>(CS->getValues()[CU->getValue()]);
     } else if (ConstantSInt *CS = dyn_cast<ConstantSInt>(CE->getOperand(i))) {
-      ConstantArray *CA = cast<ConstantArray>(C);
+      ConstantArray *CA = dyn_cast<ConstantArray>(C);
+      if (CA == 0) return 0;
       if ((uint64_t)CS->getValue() >= CA->getValues().size()) return 0;
       C = cast<Constant>(CA->getValues()[CS->getValue()]);
-    } else 
+    } else
       return 0;
   return C;
 }
diff --git a/llvm/lib/Transforms/Utils/Linker.cpp b/llvm/lib/Transforms/Utils/Linker.cpp
index 457a8b9..aa7720e 100644
--- a/llvm/lib/Transforms/Utils/Linker.cpp
+++ b/llvm/lib/Transforms/Utils/Linker.cpp
@@ -284,7 +284,8 @@
 
   // Check to see if it's a constant that we are interesting in transforming...
   if (const Constant *CPV = dyn_cast<Constant>(In)) {
-    if (!isa<DerivedType>(CPV->getType()) && !isa<ConstantExpr>(CPV))
+    if ((!isa<DerivedType>(CPV->getType()) && !isa<ConstantExpr>(CPV)) ||
+        isa<ConstantAggregateZero>(CPV))
       return const_cast<Constant*>(CPV);   // Simple constants stay identical...
 
     Constant *Result = 0;
@@ -796,12 +797,24 @@
 
       // Merge the initializer...
       Inits.reserve(NewSize);
-      ConstantArray *I = cast<ConstantArray>(G1->getInitializer());
-      for (unsigned i = 0, e = T1->getNumElements(); i != e; ++i)
-        Inits.push_back(cast<Constant>(I->getValues()[i]));
-      I = cast<ConstantArray>(G2->getInitializer());
-      for (unsigned i = 0, e = T2->getNumElements(); i != e; ++i)
-        Inits.push_back(cast<Constant>(I->getValues()[i]));
+      if (ConstantArray *I = dyn_cast<ConstantArray>(G1->getInitializer())) {
+        for (unsigned i = 0, e = T1->getNumElements(); i != e; ++i)
+          Inits.push_back(cast<Constant>(I->getValues()[i]));
+      } else {
+        assert(isa<ConstantAggregateZero>(G1->getInitializer()));
+        Constant *CV = Constant::getNullValue(T1->getElementType());
+        for (unsigned i = 0, e = T1->getNumElements(); i != e; ++i)
+          Inits.push_back(CV);
+      }
+      if (ConstantArray *I = dyn_cast<ConstantArray>(G2->getInitializer())) {
+        for (unsigned i = 0, e = T2->getNumElements(); i != e; ++i)
+          Inits.push_back(cast<Constant>(I->getValues()[i]));
+      } else {
+        assert(isa<ConstantAggregateZero>(G2->getInitializer()));
+        Constant *CV = Constant::getNullValue(T2->getElementType());
+        for (unsigned i = 0, e = T2->getNumElements(); i != e; ++i)
+          Inits.push_back(CV);
+      }
       NG->setInitializer(ConstantArray::get(NewType, Inits));
       Inits.clear();
 
diff --git a/llvm/lib/Transforms/Utils/ValueMapper.cpp b/llvm/lib/Transforms/Utils/ValueMapper.cpp
index acc433a..2cb6a9d 100644
--- a/llvm/lib/Transforms/Utils/ValueMapper.cpp
+++ b/llvm/lib/Transforms/Utils/ValueMapper.cpp
@@ -28,7 +28,7 @@
 
   if (Constant *C = const_cast<Constant*>(dyn_cast<Constant>(V))) {
     if (isa<ConstantIntegral>(C) || isa<ConstantFP>(C) ||
-        isa<ConstantPointerNull>(C))
+        isa<ConstantPointerNull>(C) || isa<ConstantAggregateZero>(C))
       return VMSlot = C;           // Primitive constants map directly
     else if (ConstantPointerRef *CPR = dyn_cast<ConstantPointerRef>(C)) {
       GlobalValue *MV = cast<GlobalValue>(MapValue((Value*)CPR->getValue(),VM));