[SystemZ] Add CodeGen support for v2f64

This adds ABI and CodeGen support for the v2f64 type, which is natively
supported by z13 instructions.

Based on a patch by Richard Sandiford.

llvm-svn: 236522
diff --git a/llvm/test/CodeGen/SystemZ/vec-move-13.ll b/llvm/test/CodeGen/SystemZ/vec-move-13.ll
index e103aff..c50c94a 100644
--- a/llvm/test/CodeGen/SystemZ/vec-move-13.ll
+++ b/llvm/test/CodeGen/SystemZ/vec-move-13.ll
@@ -45,3 +45,13 @@
   %ret = insertelement <2 x i64> zeroinitializer, i64 %val, i32 1
   ret <2 x i64> %ret
 }
+
+; Test v2f64 insertion into 0.
+define <2 x double> @f6(double %val) {
+; CHECK-LABEL: f6:
+; CHECK: vgbm [[REG:%v[0-9]+]], 0
+; CHECK: vmrhg %v24, [[REG]], %v0
+; CHECK: br %r14
+  %ret = insertelement <2 x double> zeroinitializer, double %val, i32 1
+  ret <2 x double> %ret
+}