C++ PATCH for c++/91868 - improve -Wshadow location.

[Marek Polacek]

We can improve various -Wshadow warnings by using DECL_SOURCE_LOCATION
rather than whatever is in input_location.

Bootstrapped/regtested on x86_64-linux, ok for trunk?

2019-09-23  Marek Polacek  <pola...@redhat.com>

        PR c++/91868 - improve -Wshadow location.
        * name-lookup.c (check_local_shadow): Use DECL_SOURCE_LOCATION
        instead of input_location.

        * g++.dg/warn/Wshadow-16.C: New test.

diff --git gcc/cp/name-lookup.c gcc/cp/name-lookup.c
index 8bbb92ddc9f..74f1072fa8c 100644
--- gcc/cp/name-lookup.c
+++ gcc/cp/name-lookup.c
@@ -2771,7 +2771,7 @@ check_local_shadow (tree decl)
        msg = "declaration of %qD shadows a previous local";
 
       auto_diagnostic_group d;
-      if (warning_at (input_location, warning_code, msg, decl))
+      if (warning_at (DECL_SOURCE_LOCATION (decl), warning_code, msg, decl))
        inform_shadowed (old);
       return;
     }
@@ -2798,7 +2798,7 @@ check_local_shadow (tree decl)
            || TYPE_PTRMEMFUNC_P (TREE_TYPE (decl)))
          {
            auto_diagnostic_group d;
-           if (warning_at (input_location, OPT_Wshadow,
+           if (warning_at (DECL_SOURCE_LOCATION (decl), OPT_Wshadow,
                            "declaration of %qD shadows a member of %qT",
                            decl, current_nonlambda_class_type ())
                && DECL_P (member))
@@ -2818,7 +2818,7 @@ check_local_shadow (tree decl)
     /* XXX shadow warnings in outer-more namespaces */
     {
       auto_diagnostic_group d;
-      if (warning_at (input_location, OPT_Wshadow,
+      if (warning_at (DECL_SOURCE_LOCATION (decl), OPT_Wshadow,
                      "declaration of %qD shadows a global declaration",
                      decl))
        inform_shadowed (old);
diff --git gcc/testsuite/g++.dg/warn/Wshadow-16.C 
gcc/testsuite/g++.dg/warn/Wshadow-16.C
new file mode 100644
index 00000000000..1ba54ec107d
--- /dev/null
+++ gcc/testsuite/g++.dg/warn/Wshadow-16.C
@@ -0,0 +1,24 @@
+// PR c++/91868 - improve -Wshadow location.
+// { dg-options "-Wshadow" }
+
+int global; // { dg-message "shadowed declaration" }
+
+struct S
+{
+  static int bar; // { dg-message "shadowed declaration" }
+  S (int i) { int bar // { dg-warning "19:declaration of .bar. shadows a 
member" }
+      (1);
+    int global // { dg-warning "9:declaration of .global. shadows a global 
declaration" }
+      (42);
+  }
+};
+
+void
+foo ()
+{
+  int xx; // { dg-message "shadowed declaration" }
+  {
+    S xx // { dg-warning "7:declaration of .xx. shadows a previous local" }
+    (42);
+  }
+}