c++: improve reference binding diagnostic [PR91849]

Here we were complaining about binding the lvalue reference to the rvalue
result of converting from float to int, but didn't mention that conversion.
Talk about the type of the initializer instead.

gcc/cp/ChangeLog:

	PR c++/91849
	* call.c (convert_like_internal): Improve reference diagnostic.

gcc/testsuite/ChangeLog:

	PR c++/91849
	* g++.dg/conversion/pr66211.C: Adjust diagnostic.
	* g++.dg/conversion/ref7.C: New test.

1 files changed, 13 insertions, 2 deletions

diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index 4b81d0f..c9a8c0d 100644
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -7898,8 +7898,19 @@ convert_like_internal (conversion *convs, tree expr, tree fn, int argnum,
                         "lvalue of type %qI", totype, extype);
 	    else if (!TYPE_REF_IS_RVALUE (ref_type) && !lvalue_p (expr)
 		     && !CP_TYPE_CONST_NON_VOLATILE_P (TREE_TYPE (ref_type)))
-	      error_at (loc, "cannot bind non-const lvalue reference of "
-			"type %qH to an rvalue of type %qI", totype, extype);
+	      {
+		conversion *next = next_conversion (convs);
+		if (next->kind == ck_std)
+		  {
+		    next = next_conversion (next);
+		    error_at (loc, "cannot bind non-const lvalue reference of "
+			      "type %qH to a value of type %qI",
+			      totype, next->type);
+		  }
+		else
+		  error_at (loc, "cannot bind non-const lvalue reference of "
+			    "type %qH to an rvalue of type %qI", totype, extype);
+	      }
 	    else if (!reference_compatible_p (TREE_TYPE (totype), extype))
 	      {
 		/* If we're converting from T[] to T[N], don't talk