loplugin:redundantcast: Do warn about convoluted dynamic_cast to self

...that the compiler is free to elide anyway.  (See
4e7ffc0a "Avoid compiler eliding#redundant
dynamic_cast" and 380d6afe "Remove redundant
asserts involving dynamic_cast".)

Change-Id: I3f75154fee3e978b7ba95a5a27589417065599bd

compilerplugins/clang/redundantcast.cxx

@@ -682,11 +682,6 @@ bool RedundantCast::VisitCXXDynamicCastExpr(CXXDynamicCastExpr const * expr) {
     if (ignoreLocation(expr)) {
         return true;
     }
-    // ignore dynamic_cast<T1>(static_cast<T1>(void*)), it's necessary
-    if (auto subStaticCast = dyn_cast<CXXStaticCastExpr>(expr->getSubExpr())) {
-        if (loplugin::TypeCheck(subStaticCast->getSubExpr()->getType()).Pointer().Void())
-            return true;
-    }
     // so far this only deals with dynamic casting from T to T
     auto const sub = compat::getSubExprAsWritten(expr);
     auto const t1 = expr->getTypeAsWritten();

compilerplugins/clang/test/redundantcast.cxx

@@ -333,15 +333,11 @@ void testDynamicCast() {
 
     S1 * s1 = nullptr;
     S2 * s2 = nullptr;
-    void * v1 = nullptr;
 
     (void) dynamic_cast<S2 *>(s1);
     (void) dynamic_cast<S1 *>(s2);
     (void) dynamic_cast<S2 *>(s2); // expected-error {{redundant dynamic cast from 'S2 *' to 'S2 *' [loplugin:redundantcast]}}
     (void) dynamic_cast<S3 *>(s2);
-    // used in some assert in vcl
-    (void) dynamic_cast<S1 *>(static_cast<S1*>(v1));
-    (void) dynamic_cast<S2 *>(static_cast<S2*>(s1));  // expected-error {{redundant dynamic cast from 'S2 *' to 'S2 *' [loplugin:redundantcast]}}
 }
 
 int main() {