Updates per review.

Author: JonPsson1

llvm/docs/LangRef.rst

@@ -1189,9 +1189,12 @@ Currently, only the following parameter attributes are defined:
     value should be sign-extended to the extent required by the target's
     ABI (which is usually 32-bits) by the caller (for a parameter) or
     the callee (for a return value).
-``noext`` This indicates to the code generator that the parameter or return
+``noext``
+    This indicates to the code generator that the parameter or return
     value has the high bits undefined, as for a struct in register, and
-    therefore does not need to be sign or zero extended.
+    therefore does not need to be sign or zero extended. This is the same
+    as default behavior and is only actually used (by some targets) to
+    validate that one of the attributes is always present.
 ``inreg``
     This indicates that this parameter or return value should be treated
     in a special target-dependent fashion while emitting code for

llvm/lib/Target/SystemZ/SystemZISelLowering.cpp

@@ -9820,8 +9820,7 @@ SDValue SystemZTargetLowering::lowerVECREDUCE_ADD(SDValue Op,
 
 // Only consider a function fully internal as long as it has local linkage
 // and is not used in any other way than acting as the called function at
-// call sites.  TODO: Remove this when/if all internal functions adhere to
-// the ABI.
+// call sites.
 bool SystemZTargetLowering::isFullyInternal(const Function *Fn) const {
   if (!Fn->hasLocalLinkage())
     return false;
@@ -9842,9 +9841,15 @@ verifyNarrowIntegerArgs(const SmallVectorImpl<ISD::OutputArg> &Outs,
   if (IsInternal || !Subtarget.isTargetELF())
     return;
 
-  // Temporarily only do the check when explicitly requested.
-  if (/* !getTargetMachine().Options.VerifyArgABICompliance && */
-      !EnableIntArgExtCheck)
+  // Temporarily only do the check when explicitly requested, until it can be
+  // enabled by default.
+  if (!EnableIntArgExtCheck)
+    return;
+
+  if (EnableIntArgExtCheck.getNumOccurrences()) {
+    if (!EnableIntArgExtCheck)
+      return;
+  } else if (!getTargetMachine().Options.VerifyArgABICompliance)
     return;
 
   for (unsigned i = 0; i < Outs.size(); ++i) {