SV: [PATCH] D11940: don't diagnose -Wunused-parameter in virtual method or method that overrides base class method

[Daniel Marjamäki via cfe-commits]

ideally there should be no -Wunused-parameter compiler warning when the parameter is used.

would it feel better to move the "FP" warnings about virtual functions, for instance to clang-tidy?

> If you enable this warning, you probably want to know about unused parameters, independent of if your function is virtual or not, no?

imho there are some compiler warnings that are too noisy. I don't like to get a warning when there is obviously no bug:

sign compare:
  if the signed value is obviously not negative then there is no bug:
    signed x;  .. if (x>10 && x < s.size())
unused parameter:
  could check in the current translation unit if the parameter is used in an overloaded method.
constructor initialization order:
  should not warn if the order obviously does not matter. for instance initialization order of pod variables using constants.
etc

Best regards,
Daniel Marjamäki

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Daniel Marjamäki Senior Engineer
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________________________________________
Från: thakis at google.com [thakis at google.com] för Nico Weber [thakis at chromium.org]
Skickat: den 11 augusti 2015 20:50
Till: David Blaikie
Kopia: reviews+D11940+public+578c1335b27aa98b at reviews.llvm.org; Daniel Marjamäki; cfe-commits at lists.llvm.org
Ämne: Re: [PATCH] D11940: don't diagnose -Wunused-parameter in virtual method or method that overrides base class method

On Tue, Aug 11, 2015 at 11:32 AM, David Blaikie <dblaikie at gmail.com<mailto:dblaikie at gmail.com>> wrote:


On Tue, Aug 11, 2015 at 8:46 AM, Nico Weber via cfe-commits <cfe-commits at lists.llvm.org<mailto:cfe-commits at lists.llvm.org>> wrote:
Can't you just change your signature to

  virtual void a(int /* x */) {}

in these cases?

You could - does it add much value to do that, though?

If you enable this warning, you probably want to know about unused parameters, independent of if your function is virtual or not, no?

(perhaps it does - it means you express the intent that the parameter is not used and the compiler helps you check that (so that for the parameters you think /should/ be used (you haven't commented out their name but accidentally shadow or otherwise fail to reference, you still get a warning))

- David


On Tue, Aug 11, 2015 at 6:43 AM, Daniel Marjamäki <cfe-commits at lists.llvm.org<mailto:cfe-commits at lists.llvm.org>> wrote:
danielmarjamaki created this revision.
danielmarjamaki added a reviewer: krememek.
danielmarjamaki added a subscriber: cfe-commits.

Don't diagnose -Wunused-parameter in methods that override other methods because the overridden methods might use the parameter

Don't diagnose -Wunused-parameter in virtual methods because these might be overriden by other methods that use the parameter.

Such diagnostics could be more accurately written if they are based on whole-program-analysis that establish if such parameter is unused in all methods.



http://reviews.llvm.org/D11940

Files:
  lib/Sema/SemaDecl.cpp
  test/SemaCXX/warn-unused-parameters.cpp

Index: test/SemaCXX/warn-unused-parameters.cpp
===================================================================
--- test/SemaCXX/warn-unused-parameters.cpp
+++ test/SemaCXX/warn-unused-parameters.cpp
@@ -32,3 +32,20 @@
   auto l = [&t...]() { return sizeof...(s); };
   return l();
 }
+
+// Don't diagnose virtual methods or methods that override base class
+// methods.
+class Base {
+public:
+  virtual void f(int x);
+};
+
+class Derived : public Base {
+public:
+  // Don't warn in overridden methods.
+  virtual void f(int x) {}
+
+  // Don't warn in virtual methods.
+  virtual void a(int x) {}
+};
+
Index: lib/Sema/SemaDecl.cpp
===================================================================
--- lib/Sema/SemaDecl.cpp
+++ lib/Sema/SemaDecl.cpp
@@ -10797,8 +10797,13 @@

     if (!FD->isInvalidDecl()) {
       // Don't diagnose unused parameters of defaulted or deleted functions.
-      if (!FD->isDeleted() && !FD->isDefaulted())
-        DiagnoseUnusedParameters(FD->param_begin(), FD->param_end());
+      if (!FD->isDeleted() && !FD->isDefaulted()) {
+        // Don't diagnose unused parameters in virtual methods or
+        // in methods that override base class methods.
+        const auto MD = dyn_cast<CXXMethodDecl>(FD);
+        if (!MD || (MD->size_overridden_methods() == 0U && !MD->isVirtual()))
+          DiagnoseUnusedParameters(FD->param_begin(), FD->param_end());
+      }
       DiagnoseSizeOfParametersAndReturnValue(FD->param_begin(), FD->param_end(),
                                              FD->getReturnType(), FD);




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