[BitcodeReader] Ensure we can read constant vector selects with an i1 condition

Summary:
Constant vectors weren't allowed to have an i1 condition in the
BitcodeReader. Make sure we have the same restrictions that are
documented, not more.

Reviewers: nlewycky, rafael, kschimpf

Subscribers: llvm-commits

Differential Revision: http://reviews.llvm.org/D12440

llvm-svn: 246459

llvm/lib/Bitcode/Reader/BitcodeReader.cpp

@@ -2475,11 +2475,12 @@ std::error_code BitcodeReader::parseConstants() {
 
       Type *SelectorTy = Type::getInt1Ty(Context);
 
-      // If CurTy is a vector of length n, then Record[0] must be a <n x i1>
-      // vector. Otherwise, it must be a single bit.
+      // The selector might be an i1 or an <n x i1>
+      // Get the type from the ValueList before getting a forward ref.
       if (VectorType *VTy = dyn_cast<VectorType>(CurTy))
-        SelectorTy = VectorType::get(Type::getInt1Ty(Context),
-                                     VTy->getNumElements());
+        if (Value *V = ValueList[Record[0]])
+          if (SelectorTy != V->getType())
+            SelectorTy = VectorType::get(SelectorTy, VTy->getNumElements());
 
       V = ConstantExpr::getSelect(ValueList.getConstantFwdRef(Record[0],
                                                               SelectorTy),