From 1b81b7891b82b0d5bbb5ff760423f3d6ad3c701e Mon Sep 17 00:00:00 2001
From: Jason Merrill <jason@redhat.com>
Date: Tue, 7 Aug 2001 07:13:54 -0400
Subject: [PATCH] alias.c (get_alias_set): Return a previously calculated alias
 set for a VAR_DECL.

        * alias.c (get_alias_set): Return a previously calculated
        alias set for a VAR_DECL.

From-SVN: r44683
---
 gcc/ChangeLog                     |  5 +++++
 gcc/alias.c                       |  7 +++++++
 gcc/testsuite/g++.dg/opt/alias1.C | 25 +++++++++++++++++++++++++
 3 files changed, 37 insertions(+)
 create mode 100644 gcc/testsuite/g++.dg/opt/alias1.C

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index 7c66b670f56..760dd9574d0 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,8 @@
+2001-08-07  Jason Merrill  <jason_merrill@redhat.com>
+
+	* alias.c (get_alias_set): Return a previously calculated
+	alias set for a VAR_DECL.
+
 2001-08-06  Richard Henderson  <rth@redhat.com>
 
 	* varasm.c (assemble_gc_entry): Remove.
diff --git a/gcc/alias.c b/gcc/alias.c
index e7417183c21..a529a01cfa6 100644
--- a/gcc/alias.c
+++ b/gcc/alias.c
@@ -527,6 +527,13 @@ get_alias_set (t)
 	    return 0;
 	}
 
+      /* If we've already determined the alias set for this decl, just
+	 return it.  This is necessary for C++ anonymous unions, whose
+	 component variables don't look like union members (boo!).  */
+      if (TREE_CODE (t) == VAR_DECL
+	  && DECL_RTL_SET_P (t) && GET_CODE (DECL_RTL (t)) == MEM)
+	return MEM_ALIAS_SET (DECL_RTL (t));
+
       /* Give the language another chance to do something special.  */
       if (orig_t != t
 	  && (set = lang_get_alias_set (t)) != -1)
diff --git a/gcc/testsuite/g++.dg/opt/alias1.C b/gcc/testsuite/g++.dg/opt/alias1.C
new file mode 100644
index 00000000000..34aed593532
--- /dev/null
+++ b/gcc/testsuite/g++.dg/opt/alias1.C
@@ -0,0 +1,25 @@
+// Test that type punning using an anonymous union works with strict aliasing.
+// { dg-do run }
+// { dg-options -O2 -fstrict-aliasing }
+
+extern "C" void abort ();
+
+void f (int i)
+{
+  union
+  {
+    int ui;
+    float uf[2];
+  };
+
+  ui = i;
+  if (uf[0] != 42.0)
+    abort ();
+}
+
+int main ()
+{
+  union U { int i; float f[2]; } u;
+  u.f[0] = 42.0;
+  f (u.i);
+}