[Sema] Fix Sema checkArgCount function

[bsaleil]

Summary

This patch fixes the checkArgCount function in Sema that is used to check the number of arguments of a call when doing custom type-checking.
The patch fixes that function in two ways:

1. It now displays the right range in case the number of actual arguments is greater than the number of expected arguments. Example:

Without patch:

main.c:5:36: error: too many arguments to function call, expected 3, have 7
  __builtin_add_overflow(1, 2, &r, 3, 4, 5, 6);
                            ~      ^

With patch:

main.c:5:36: error: too many arguments to function call, expected 3, have 7
  __builtin_add_overflow(1, 2, &r, 3, 4, 5, 6);
                                   ^~~~~~~~~~

2. A side effect is that the patch also allows the function to properly handle the case in which the desired argument count is 0 and the number of actual arguments is 1. No test case is provided for that because currently no builtin with 0 expected argument is checked with that function.

[Yi-Hong.Lyu]

Please add tests

[bsaleil]

Adding test case

clang/lib/Sema/SemaChecking.cpp

return S.Diag(call->getEndLoc(), diag::err_typecheck_call_too_few_args)
            << 0 /*function call*/ << desiredArgCount << argCount
            << call->getSourceRange();
 
   // Highlight all the excess arguments.
   SourceRange range(call->getArg(desiredArgCount)->getBeginLoc(),
                     call->getArg(argCount - 1)->getEndLoc());
 
   return S.Diag(range.getBegin(), diag::err_typecheck_call_too_many_args)
-    << 0 /*function call*/ << desiredArgCount << argCount
-    << call->getArg(1)->getSourceRange();
+    << 0 /*function call*/ << desiredArgCount << argCount << range;
 }
 
 /// Check that the first argument to __builtin_annotation is an integer
 /// and the second argument is a non-wide string literal.
 static bool SemaBuiltinAnnotation(Sema &S, CallExpr *TheCall) {
   if (checkArgCount(S, TheCall, 2))
     return true;
 

clang/test/Sema/custom-checking.c

+// RUN: not %clang_cc1 -fsyntax-only %s 2>&1 | FileCheck %s -strict-whitespace
+
+int few_args() {
+  int r = 0;
+  __builtin_add_overflow(1, 2);
+  return r;
+}
+
+// CHECK: error: too few arguments to function call, expected 3, have 2
+// CHECK:   __builtin_add_overflow(1, 2);
+// CHECK:   ~~~~~~~~~~~~~~~~~~~~~~~~~~~^
+
+int many_args() {
+  int r = 0;
+  __builtin_add_overflow(1, 2, &r, 3, 4, 5, 6);
+  return r;
+}
+
+// CHECK: error: too many arguments to function call, expected 3, have 7
+// CHECK:   __builtin_add_overflow(1, 2, &r, 3, 4, 5, 6);
+// CHECK:                                    ^~~~~~~~~~
+
+int equal_args() {
+  int r = 0;
+  __builtin_add_overflow(1, 2, &r);
+  return r;
+}
+
+// CHECK: 2 errors generated.