Re: C++ PATCH for c++/49003 (DR 1207, use of 'this' in trailing return type)

[Jason Merrill <jason at redhat dot com>]

On 06/29/2011 05:15 PM, Jason Merrill wrote:
> This patch adds support for use of 'this' (implicitly or explicitly) in
> the trailing-return-type of a member function.

The above patch wasn't enough, though.  The following patch fixes some 
issues that arose with real uses, including mangling.

Tested x86_64-pc-linux-gnu, applying to trunk.
commit ef43a979a3f46150f383b9deab70dd412d66f96b
Author: Jason Merrill <jason@redhat.com>
Date:   Sun Jul 3 17:14:56 2011 -0400

    	DR 1207
    	PR c++/49589
    	* mangle.c (write_expression): Handle 'this'.
    	* parser.c (cp_parser_postfix_dot_deref_expression): Allow
    	incomplete *this.
    	* semantics.c (potential_constant_expression_1): Check that
    	DECL_CONTEXT is set on 'this'.

diff --git a/gcc/cp/mangle.c b/gcc/cp/mangle.c
index 134c9ea..81b772f 100644
--- a/gcc/cp/mangle.c
+++ b/gcc/cp/mangle.c
@@ -2495,6 +2495,11 @@ write_expression (tree expr)
   else if (TREE_CODE_CLASS (code) == tcc_constant
 	   || (abi_version_at_least (2) && code == CONST_DECL))
     write_template_arg_literal (expr);
+  else if (code == PARM_DECL && DECL_ARTIFICIAL (expr))
+    {
+      gcc_assert (!strcmp ("this", IDENTIFIER_POINTER (DECL_NAME (expr))));
+      write_string ("fpT");
+    }
   else if (code == PARM_DECL)
     {
       /* A function parameter used in a late-specified return type.  */
diff --git a/gcc/cp/parser.c b/gcc/cp/parser.c
index d79326d..6bb15ed 100644
--- a/gcc/cp/parser.c
+++ b/gcc/cp/parser.c
@@ -5281,7 +5281,11 @@ cp_parser_postfix_dot_deref_expression (cp_parser *parser,
 		    postfix_expression);
 	  scope = NULL_TREE;
 	}
-      else
+      /* Unlike the object expression in other contexts, *this is not
+	 required to be of complete type for purposes of class member
+	 access (5.2.5) outside the member function body.  */
+      else if (scope != current_class_ref
+	       && !(processing_template_decl && scope == current_class_type))
 	scope = complete_type_or_else (scope, NULL_TREE);
       /* Let the name lookup machinery know that we are processing a
 	 class member access expression.  */
diff --git a/gcc/cp/semantics.c b/gcc/cp/semantics.c
index e29705c..619c058 100644
--- a/gcc/cp/semantics.c
+++ b/gcc/cp/semantics.c
@@ -7791,7 +7791,8 @@ potential_constant_expression_1 (tree t, bool want_rval, tsubst_flags_t flags)
         STRIP_NOPS (x);
         if (is_this_parameter (x))
 	  {
-	    if (DECL_CONSTRUCTOR_P (DECL_CONTEXT (x)) && want_rval)
+	    if (want_rval && DECL_CONTEXT (x)
+		&& DECL_CONSTRUCTOR_P (DECL_CONTEXT (x)))
 	      {
 		if (flags & tf_error)
 		  sorry ("use of the value of the object being constructed "
diff --git a/gcc/testsuite/g++.dg/abi/mangle48.C b/gcc/testsuite/g++.dg/abi/mangle48.C
new file mode 100644
index 0000000..dc9c492
--- /dev/null
+++ b/gcc/testsuite/g++.dg/abi/mangle48.C
@@ -0,0 +1,23 @@
+// Testcase for 'this' mangling
+// { dg-options -std=c++0x }
+
+struct B
+{
+  template <class U> U f();
+};
+
+struct A
+{
+  B b;
+  // { dg-final { scan-assembler "_ZN1A1fIiEEDTcldtdtdefpT1b1fIT_EEEv" } }
+  template <class U> auto f() -> decltype (b.f<U>());
+  // { dg-final { scan-assembler "_ZN1A1gIiEEDTcldtptfpT1b1fIT_EEEv" } }
+  template <class U> auto g() -> decltype (this->b.f<U>());
+};
+
+int main()
+{
+  A a;
+  a.f<int>();
+  a.g<int>();
+}

commit acbc60694bf95f13f9088ed4d5b3d18780aaf754
Author: Jason Merrill <jason@redhat.com>
Date:   Mon Jul 4 10:44:29 2011 -0400

    	* cp-demangle.c (d_expression): Handle 'this'.
    	(d_print_comp) [DEMANGLE_COMPONENT_FUNCTION_PARAM]: Likewise.

diff --git a/libiberty/cp-demangle.c b/libiberty/cp-demangle.c
index f136322..29badbb 100644
--- a/libiberty/cp-demangle.c
+++ b/libiberty/cp-demangle.c
@@ -2738,10 +2738,18 @@ d_expression (struct d_info *di)
       /* Function parameter used in a late-specified return type.  */
       int index;
       d_advance (di, 2);
-      index = d_compact_number (di);
-      if (index < 0)
-	return NULL;
-
+      if (d_peek_char (di) == 'T')
+	{
+	  /* 'this' parameter.  */
+	  d_advance (di, 1);
+	  index = 0;
+	}
+      else
+	{
+	  index = d_compact_number (di) + 1;
+	  if (index == 0)
+	    return NULL;
+	}
       return d_make_function_param (di, index);
     }
   else if (IS_DIGIT (peek)
@@ -4400,9 +4408,17 @@ d_print_comp (struct d_print_info *dpi, int options,
       return;
 
     case DEMANGLE_COMPONENT_FUNCTION_PARAM:
-      d_append_string (dpi, "{parm#");
-      d_append_num (dpi, dc->u.s_number.number + 1);
-      d_append_char (dpi, '}');
+      {
+	long num = dc->u.s_number.number;
+	if (num == 0)
+	  d_append_string (dpi, "this");
+	else
+	  {
+	    d_append_string (dpi, "{parm#");
+	    d_append_num (dpi, num);
+	    d_append_char (dpi, '}');
+	  }
+      }
       return;
 
     case DEMANGLE_COMPONENT_GLOBAL_CONSTRUCTORS:
diff --git a/libiberty/testsuite/demangle-expected b/libiberty/testsuite/demangle-expected
index 4980cf1..2dc74be 100644
--- a/libiberty/testsuite/demangle-expected
+++ b/libiberty/testsuite/demangle-expected
@@ -3905,6 +3905,10 @@ decltype ({parm#1}+{parm#2}) add<int, double>(int, double)
 --format=gnu-v3
 _Z4add3IidEDTclL_Z1gEfp_fp0_EET_T0_
 decltype (g({parm#1}, {parm#2})) add3<int, double>(int, double)
+# 'this' test
+--format=gnu-v3
+_ZN1A1fIiEEDTcldtdtdefpT1b1fIT_EEEv
+decltype ((((*this).b).(f<int>))()) A::f<int>()
 # new (2008) built in types test
 --format=gnu-v3
 _Z1fDfDdDeDhDsDi