+/// RemoveDeadArgumentsFromCallers - Checks if the given function has any
+/// arguments that are unused, and changes the caller parameters to be undefined
+/// instead.
+bool DAE::RemoveDeadArgumentsFromCallers(Function &Fn)
+{
+ if (Fn.isDeclaration() || Fn.mayBeOverridden())
+ return false;
+
+ // Functions with local linkage should already have been handled, except the
+ // fragile (variadic) ones which we can improve here.
+ if (Fn.hasLocalLinkage() && !Fn.getFunctionType()->isVarArg())
+ return false;
+
+ // If a function seen at compile time is not necessarily the one linked to
+ // the binary being built, it is illegal to change the actual arguments
+ // passed to it. These functions can be captured by isWeakForLinker().
+ // *NOTE* that mayBeOverridden() is insufficient for this purpose as it
+ // doesn't include linkage types like AvailableExternallyLinkage and
+ // LinkOnceODRLinkage. Take link_odr* as an example, it indicates a set of
+ // *EQUIVALENT* globals that can be merged at link-time. However, the
+ // semantic of *EQUIVALENT*-functions includes parameters. Changing
+ // parameters breaks this assumption.
+ //
+ if (Fn.isWeakForLinker())
+ return false;
+
+ if (Fn.use_empty())
+ return false;
+
+ SmallVector<unsigned, 8> UnusedArgs;
+ for (Function::arg_iterator I = Fn.arg_begin(), E = Fn.arg_end();
+ I != E; ++I) {
+ Argument *Arg = I;
+
+ if (Arg->use_empty() && !Arg->hasByValOrInAllocaAttr())
+ UnusedArgs.push_back(Arg->getArgNo());
+ }
+
+ if (UnusedArgs.empty())
+ return false;
+
+ bool Changed = false;
+
+ for (Use &U : Fn.uses()) {
+ CallSite CS(U.getUser());
+ if (!CS || !CS.isCallee(&U))
+ continue;
+
+ // Now go through all unused args and replace them with "undef".
+ for (unsigned I = 0, E = UnusedArgs.size(); I != E; ++I) {
+ unsigned ArgNo = UnusedArgs[I];
+
+ Value *Arg = CS.getArgument(ArgNo);
+ CS.setArgument(ArgNo, UndefValue::get(Arg->getType()));
+ ++NumArgumentsReplacedWithUndef;
+ Changed = true;
+ }
+ }
+
+ return Changed;
+}
+