c++: Tweak tsubst_qualified_id location.

Retain the location when tsubstituting a qualified-id so that our
static_assert diagnostic can benefit.  Don't create useless location
wrappers for temporary variables.

gcc/ChangeLog:

	PR c++/97518
	* tree.c (maybe_wrap_with_location): Don't add a location
	wrapper around an artificial and ignored decl.

gcc/cp/ChangeLog:

	PR c++/97518
	* pt.c (tsubst_qualified_id): Use EXPR_LOCATION of the qualified-id.
	Use it to maybe_wrap_with_location the final expression.

gcc/testsuite/ChangeLog:

	PR c++/97518
	* g++.dg/diagnostic/static_assert3.C: New test.

3 files changed, 43 insertions, 2 deletions

diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 6ba114c..c592461 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -16214,7 +16214,7 @@ tsubst_qualified_id (tree qualified_id, tree args,
   tree name;
   bool is_template;
   tree template_args;
-  location_t loc = UNKNOWN_LOCATION;
+  location_t loc = EXPR_LOCATION (qualified_id);
 
   gcc_assert (TREE_CODE (qualified_id) == SCOPE_REF);
 
@@ -16223,7 +16223,6 @@ tsubst_qualified_id (tree qualified_id, tree args,
   if (TREE_CODE (name) == TEMPLATE_ID_EXPR)
     {
       is_template = true;
-      loc = EXPR_LOCATION (name);
       template_args = TREE_OPERAND (name, 1);
       if (template_args)
 	template_args = tsubst_template_args (template_args, args,
@@ -16351,6 +16350,8 @@ tsubst_qualified_id (tree qualified_id, tree args,
   if (REF_PARENTHESIZED_P (qualified_id))
     expr = force_paren_expr (expr);
 
+  expr = maybe_wrap_with_location (expr, loc);
+
   return expr;
 }
 
diff --git a/gcc/testsuite/g++.dg/diagnostic/static_assert3.C b/gcc/testsuite/g++.dg/diagnostic/static_assert3.C
new file mode 100644
index 0000000..5d36388
--- /dev/null
+++ b/gcc/testsuite/g++.dg/diagnostic/static_assert3.C
@@ -0,0 +1,36 @@
+// PR c++/97518
+// { dg-do compile { target c++17 } }
+// { dg-options "-fdiagnostics-show-caret" }
+
+template <typename T, typename U> struct is_same { static constexpr bool value = false; };
+template <typename T> struct is_same<T, T> { static constexpr bool value = true; };
+
+template <typename T, typename U>
+void f(T, U)
+{
+  static_assert(is_same<T, T>::value && is_same<T, U>::value); // { dg-error "56:static assertion failed" }
+/* { dg-begin-multiline-output "" }
+   static_assert(is_same<T, T>::value && is_same<T, U>::value);
+                                                        ^~~~~
+   { dg-end-multiline-output "" } */
+// { dg-message ".is_same<int, double>::value. evaluates to false" "" { target *-*-* } .-5 }
+  static_assert(is_same<U, T>::value && is_same<U, U>::value); // { dg-error "32:static assertion failed" }
+/* { dg-begin-multiline-output "" }
+   static_assert(is_same<U, T>::value && is_same<U, U>::value);
+                                ^~~~~
+   { dg-end-multiline-output "" } */
+// { dg-message ".is_same<double, int>::value. evaluates to false" "" { target *-*-* } .-5 }
+  static_assert(is_same<U, U>::value
+		&& is_same<U, T>::value // { dg-error "35:static assertion failed" }
+		&& is_same<T, T>::value);
+/* { dg-begin-multiline-output "" }
+                 && is_same<U, T>::value
+                                   ^~~~~
+   { dg-end-multiline-output "" } */
+// { dg-message ".is_same<double, int>::value. evaluates to false" "" { target *-*-* } .-6 }
+}
+
+void g()
+{
+ f(0, 1.3);
+}
diff --git a/gcc/tree.c b/gcc/tree.c
index 1d4a1da..1ad4ad5 100644
--- a/gcc/tree.c
+++ b/gcc/tree.c
@@ -15041,6 +15041,10 @@ maybe_wrap_with_location (tree expr, location_t loc)
   if (EXCEPTIONAL_CLASS_P (expr))
     return expr;
 
+  /* Compiler-generated temporary variables don't need a wrapper.  */
+  if (DECL_P (expr) && DECL_ARTIFICIAL (expr) && DECL_IGNORED_P (expr))
+    return expr;
+
   /* If any auto_suppress_location_wrappers are active, don't create
      wrappers.  */
   if (suppress_location_wrappers > 0)