[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-add-01.ll b/llvm/test/CodeGen/SystemZ/vec-add-01.ll
index a59a8da..1de2aa2 100644
--- a/llvm/test/CodeGen/SystemZ/vec-add-01.ll
+++ b/llvm/test/CodeGen/SystemZ/vec-add-01.ll
@@ -37,3 +37,13 @@
   %ret = add <2 x i64> %val1, %val2
   ret <2 x i64> %ret
 }
+
+; Test a v2f64 addition.
+define <2 x double> @f5(<2 x double> %dummy, <2 x double> %val1,
+                        <2 x double> %val2) {
+; CHECK-LABEL: f5:
+; CHECK: vfadb %v24, %v26, %v28
+; CHECK: br %r14
+  %ret = fadd <2 x double> %val1, %val2
+  ret <2 x double> %ret
+}