[clang] [flang] [llvm] [Driver] Move CommonArgs to a location visible by the Frontend Drivers (PR #142800)

[Eugene Epshteyn via llvm-commits]

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@@ -3167,3 +3167,25 @@ void tools::handleInterchangeLoopsArgs(const ArgList &Args,
                    options::OPT_fno_loop_interchange, EnableInterchange))
     CmdArgs.push_back("-floop-interchange");
 }
+
+// Parse -mprefer-vector-width=. Return the Value string if well-formed.
+// Otherwise, return an empty string and issue a diagnosic message if needed.
+StringRef tools::ParseMPreferVectorWidthOption(clang::DiagnosticsEngine &Diags,
+                                               const llvm::opt::ArgList &Args) {
+  Arg *A = Args.getLastArg(clang::driver::options::OPT_mprefer_vector_width_EQ);
+  if (!A)
+    return "";
+
+  StringRef Value = A->getValue();
+  unsigned Width LLVM_ATTRIBUTE_UNINITIALIZED;
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eugeneepshteyn wrote:

This is fine, but FWIW, there's C++ `[[maybe_unused]]` that could possibly work here: https://en.cppreference.com/w/cpp/language/attributes/maybe_unused

https://github.com/llvm/llvm-project/pull/142800