[C++ PATCH] Avoid NRV optimization for members of anon union (PR c++/32992)

[C++ PATCH] Avoid NRV optimization for members of anon union (PR c++/32992)

[Jakub Jelinek]

Hi!

Until GCC 3.4.x the fields of anon unions were represented as ALIAS_DECL
and thus check_return_expr wouldn't consider them for NRV.  Since 4.0.x
they are represented using VAR_DECL with DECL_ANON_UNION_VAR_P
and DECL_VALUE_EXPR.
This patch restores the 3.4.x behavior where anon union fields aren't
considered for NRV.
Tested on x86_64-linux, ok for 4.3/4.2/4.1?

2007-08-13  Jakub Jelinek  <jakub@redhat.com>

	PR c++/32992
	* typeck.c (check_return_expr): Don't NRV optimize vars in
	anonymous unions.
	* decl.c (finish_function): Comment fix.

	* g++.dg/opt/nrv14.C: New test.

--- gcc/cp/typeck.c.jj	2007-08-13 15:10:19.000000000 +0200
+++ gcc/cp/typeck.c	2007-08-13 18:00:15.000000000 +0200
@@ -6701,6 +6701,7 @@ check_return_expr (tree retval, bool *no
      && TREE_CODE (retval) == VAR_DECL
      && DECL_CONTEXT (retval) == current_function_decl
      && ! TREE_STATIC (retval)
+     && ! DECL_ANON_UNION_VAR_P (retval)
      && (DECL_ALIGN (retval)
          >= DECL_ALIGN (DECL_RESULT (current_function_decl)))
      /* The cv-unqualified type of the returned value must be the
--- gcc/cp/decl.c.jj	2007-08-13 15:10:19.000000000 +0200
+++ gcc/cp/decl.c	2007-08-13 18:09:33.000000000 +0200
@@ -11566,7 +11566,7 @@ finish_function (int flags)
   gcc_assert (stmts_are_full_exprs_p ());
 
   /* Set up the named return value optimization, if we can.  Candidate
-     variables are selected in check_return_value.  */
+     variables are selected in check_return_expr.  */
   if (current_function_return_value)
     {
       tree r = current_function_return_value;
--- gcc/testsuite/g++.dg/opt/nrv14.C.jj	2007-08-13 18:07:09.000000000 +0200
+++ gcc/testsuite/g++.dg/opt/nrv14.C	2007-08-13 18:07:46.000000000 +0200
@@ -0,0 +1,39 @@
+// PR c++/32992
+// { dg-do run }
+// { dg-options "-O2" }
+
+extern "C" void abort (void);
+
+struct A
+{
+  long int a1;
+  long int a2;
+  long int a3;
+};
+
+struct B
+{
+  long int f[3];
+  operator A ()
+  {
+    union
+    {
+      long int t[3];
+      A a;
+    };
+    for (int i = 0; i < 3; i++)
+      t[i] = f[i];
+    return a;
+  }
+};
+
+int
+main ()
+{
+  B b = { {1, 3, 5} };
+  A a = b;
+
+  if (a.a1 != b.f[0] || a.a2 != b.f[1] || a.a3 != b.f[2])
+    abort ();
+  return 0;
+}

	Jakub

Re: [C++ PATCH] Avoid NRV optimization for members of anon union (PR c++/32992)

[Mark Mitchell]

Jakub Jelinek wrote:

> 2007-08-13  Jakub Jelinek  <jakub@redhat.com>
> 
> 	PR c++/32992
> 	* typeck.c (check_return_expr): Don't NRV optimize vars in
> 	anonymous unions.
> 	* decl.c (finish_function): Comment fix.
> 
> 	* g++.dg/opt/nrv14.C: New test.

OK, thanks!

-- 
Mark Mitchell
CodeSourcery
mark@codesourcery.com
(650) 331-3385 x713