Don't introduce illegal types when creating vmull operations. <rdar://11324364>

ARM BUILD_VECTORs created after type legalization cannot use i8 or i16
operands, since those types are not legal.  Instead use i32 operands, which
will be implicitly truncated by the BUILD_VECTOR to match the element type.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@155824 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Target/ARM/ARMISelLowering.cpp b/lib/Target/ARM/ARMISelLowering.cpp
index e193672..88da263 100644
--- a/lib/Target/ARM/ARMISelLowering.cpp
+++ b/lib/Target/ARM/ARMISelLowering.cpp
@@ -4792,7 +4792,9 @@
   for (unsigned i = 0; i != NumElts; ++i) {
     ConstantSDNode *C = cast<ConstantSDNode>(N->getOperand(i));
     const APInt &CInt = C->getAPIntValue();
-    Ops.push_back(DAG.getConstant(CInt.trunc(EltSize), TruncVT));
+    // Element types smaller than 32 bits are not legal, so use i32 elements.
+    // The values are implicitly truncated so sext vs. zext doesn't matter.
+    Ops.push_back(DAG.getConstant(CInt.zextOrTrunc(32), MVT::i32));
   }
   return DAG.getNode(ISD::BUILD_VECTOR, N->getDebugLoc(),
                      MVT::getVectorVT(TruncVT, NumElts), Ops.data(), NumElts);