From 73a737681502c4880bee7b1825a4ff0c30f97e79 Mon Sep 17 00:00:00 2001
From: Nathan Sidwell <nathan@codesourcery.com>
Date: Tue, 1 Oct 2002 19:11:07 +0000
Subject: [PATCH] re PR c/8083 (GCC does not warn for aliasing violations)

	PR c/8083
	* c-typeck.c (build_c_cast): Warn about type punning which breaks
	type based aliasing.
testsuite:
	* gcc.dg/alias-1.c: New test.

From-SVN: r57698
---
 gcc/ChangeLog                  |  7 +++++++
 gcc/c-typeck.c                 | 17 +++++++++++++++++
 gcc/testsuite/ChangeLog        |  4 ++++
 gcc/testsuite/gcc.dg/alias-1.c | 28 ++++++++++++++++++++++++++++
 4 files changed, 56 insertions(+)
 create mode 100644 gcc/testsuite/gcc.dg/alias-1.c

diff --git a/gcc/ChangeLog b/gcc/ChangeLog
index a860318aa12..600b7ea4a6e 100644
--- a/gcc/ChangeLog
+++ b/gcc/ChangeLog
@@ -1,3 +1,9 @@
+2002-10-01  Nathan Sidwell  <nathan@codesourcery.com>
+
+	PR c/8083
+	* c-typeck.c (build_c_cast): Warn about type punning which breaks
+	type based aliasing.
+
 2002-10-01  Mark Mitchell  <mark@codesourcery.com>
 
 	* stor-layout.c (update_alignment_for_field): New function.
@@ -6,6 +12,7 @@
 	
 2002-10-01  Nathan Sidwell  <nathan@codesourcery.com>
 
+	PR other/8077
 	* gcc.c (cc1_options): Add space on -auxbase-strip.
 
 2002-10-01  Jim Wilson  <wilson@redhat.com>
diff --git a/gcc/c-typeck.c b/gcc/c-typeck.c
index 1bca1bfb858..6fd14e5e743 100644
--- a/gcc/c-typeck.c
+++ b/gcc/c-typeck.c
@@ -3759,6 +3759,23 @@ build_c_cast (type, expr)
 	  && !TREE_CONSTANT (value))
 	warning ("cast to pointer from integer of different size");
 
+      if (TREE_CODE (type) == POINTER_TYPE
+	  && TREE_CODE (otype) == POINTER_TYPE
+	  && TREE_CODE (expr) == ADDR_EXPR
+	  && DECL_P (TREE_OPERAND (expr, 0))
+	  && flag_strict_aliasing && extra_warnings
+	  && !VOID_TYPE_P (TREE_TYPE (type)))
+	{
+ 	  /* Casting the address of a decl to non void pointer. Warn
+	     if the cast breaks type based aliasing.  */
+	  if (!COMPLETE_TYPE_P (TREE_TYPE (type)))
+	    warning ("type punning to incomplete type might not be type based aliasing safe");
+	  else if (!alias_sets_conflict_p
+		   (get_alias_set (TREE_TYPE (TREE_OPERAND (expr, 0))),
+		    get_alias_set (TREE_TYPE (type))))
+	    warning ("type punning cast is not type based aliasing safe");
+	}
+      
       ovalue = value;
       value = convert (type, value);
 
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 57d265fe7f6..ccfba4efc33 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,7 @@
+2002-10-01  Nathan Sidwell  <nathan@codesourcery.com>
+
+	* gcc.dg/alias-1.c: New test.
+
 2002-10-01  Mark Mitchell  <mark@codesourcery.com>
 
 	* gcc.dg/empty1.C: New test.
diff --git a/gcc/testsuite/gcc.dg/alias-1.c b/gcc/testsuite/gcc.dg/alias-1.c
new file mode 100644
index 00000000000..71056e9b6d8
--- /dev/null
+++ b/gcc/testsuite/gcc.dg/alias-1.c
@@ -0,0 +1,28 @@
+// { dg-do compile }
+// { dg-options "-W -fstrict-aliasing" }
+
+// Copyright (C) 2002 Free Software Foundation, Inc.
+// Contributed by Nathan Sidwell 29 Sep 2002 <nathan@codesourcery.com>
+
+// 8083. warn about odd casts
+
+typedef int YYSTYPE;
+typedef struct tDefEntry 
+{
+  unsigned t;
+  
+} tDefEntry;
+struct incomplete;
+
+
+YYSTYPE
+ addSibMacro(
+         YYSTYPE  list )
+ {
+     tDefEntry** ppT   = (tDefEntry**)&list; // { dg-warning "type punning cast" "" }
+ 
+     struct incomplete *p = (struct incomplete *)&list; // { dg-warning "type punning to incomplete" "" }
+     
+     return list;
+ }
+
-- 
2.30.2