hubert.reinterpretcast added inline comments.

================
Comment at: clang/lib/Driver/ToolChains/Clang.cpp:5250
 
+  if (Args.hasArg(options::OPT_mroptr) || Args.hasArg(options::OPT_mno_roptr)) 
{
+    bool HasRoptr =
----------------
qiongsiwu1 wrote:
> hubert.reinterpretcast wrote:
> > This only checks for `-m[no-]roptr` when the front-end is invoked. When the 
> > driver is used just for linking, we get no diagnostic at all for using 
> > these options on other platforms.
> > 
> > @MaskRay:
> > 
> > As Clang code owner for the Driver, are you concerned if platform-specific 
> > options are sometimes silently ignored on other platforms? Is there a 
> > better place for the diagnostic?
> > 
> > For info, in this case, the option would have effects on AIX at both 
> > compile-from-C/C++ time and at link time. 
> > 
> > Also, should `-Wunused-command-line-argument` warnings be generated for 
> > cases where the option has no effect (e.g., `-emit-llvm` or 
> > `-fsyntax-only`)? I think `-flto` is a bit of an exception because it may 
> > be unfriendly to expect users to change other aspects of their compile 
> > invocations when adding `-flto`. At the same time, it can be argued instead 
> > that generating a `-Wunused-command-line-argument` warning for "back-end" 
> > options on `-flto` compiles helps the user realize that they need to 
> > provide the option on their link step.
> > 
> @MaskRay May I ask for your input on this issue where platform-specific 
> options are silently ignored on other platforms? What is our current opinion 
> on where these checks/diagnostics should go? 
> 
> Thanks!! 
Hi @MaskRay,

Thank you for your comments so far. I am particularly interested diagnostics 
for cases where the option does not take effect. We are hoping for a good 
approach to implement the diagnostic when the option is used on non-AIX 
platforms (without the current issue that we only check when the front-end is 
invoked). Additionally, I would like your opinion on whether a diagnostic is 
warranted for cases like `-emit-llvm` or `-fsyntax-only`. What existing 
command-line options are you aware of that can serve as a good design template 
that we can apply here?

Thanks again,
HT



Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D144190/new/

https://reviews.llvm.org/D144190

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