From 4b377e01ce6b56e0ec0276596e47bfbaacf97aa6 Mon Sep 17 00:00:00 2001
From: Martin Sebor <msebor@redhat.com>
Date: Mon, 26 Jun 2017 17:19:15 +0000
Subject: [PATCH] PR c++/81169 - -Wclass-memaccess illegitimate warning related
 to volatile

gcc/cp/ChangeLog:

	PR c++/81169
	* call.c (maybe_warn_class_memaccess): Preserve explicit conversions
	to detect casting away cv-qualifiers.

gcc/testsuite/ChangeLog:

	PR c++/81169
	* g++.dg/Wclass-memaccess-2.C: New test.

From-SVN: r249660
---
 gcc/cp/ChangeLog                          |  6 +++
 gcc/cp/call.c                             |  7 ++-
 gcc/testsuite/ChangeLog                   |  5 ++
 gcc/testsuite/g++.dg/Wclass-memaccess-2.C | 61 +++++++++++++++++++++++
 4 files changed, 77 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/Wclass-memaccess-2.C

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 040f7b79cc4..8bc268c1dcd 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,3 +1,9 @@
+2017-06-26  Martin Sebor  <msebor@redhat.com>
+
+	PR c++/81169
+	* call.c (maybe_warn_class_memaccess): Preserve explicit conversions
+	to detect casting away cv-qualifiers.
+
 2017-06-26  Nathan Sidwell  <nathan@acm.org>
 
 	* cp-tree.h (lang_decl_fn): Remove assignment_operator_p field.
diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index f480611a990..ff0a26b9335 100644
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -8340,7 +8340,10 @@ maybe_warn_class_memaccess (location_t loc, tree fndecl, tree *args)
   if (!dest || !TREE_TYPE (dest) || !POINTER_TYPE_P (TREE_TYPE (dest)))
     return;
 
-  STRIP_NOPS (dest);
+  /* Remove the outermost (usually implicit) conversion to the void*
+     argument type.  */
+  if (TREE_CODE (dest) == NOP_EXPR)
+    dest = TREE_OPERAND (dest, 0);
 
   tree srctype = NULL_TREE;
 
@@ -8357,7 +8360,7 @@ maybe_warn_class_memaccess (location_t loc, tree fndecl, tree *args)
   if (current_function_decl
       && (DECL_CONSTRUCTOR_P (current_function_decl)
 	  || DECL_DESTRUCTOR_P (current_function_decl))
-      && is_this_parameter (dest))
+      && is_this_parameter (tree_strip_nop_conversions (dest)))
     {
       tree ctx = DECL_CONTEXT (current_function_decl);
       bool special = same_type_ignoring_top_level_qualifiers_p (ctx, desttype);
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index 8b1d5af941d..d7c906aad6f 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,3 +1,8 @@
+2017-06-26  Martin Sebor  <msebor@redhat.com>
+
+	PR c++/81169
+	* g++.dg/Wclass-memaccess-2.C: New test.
+
 2017-06-26  Carl Love  <cel@us.ibm.com>
 
 	* gcc.target/powerpc/builtins-3-vec_reve-runnable.c:
diff --git a/gcc/testsuite/g++.dg/Wclass-memaccess-2.C b/gcc/testsuite/g++.dg/Wclass-memaccess-2.C
new file mode 100644
index 00000000000..49581df1204
--- /dev/null
+++ b/gcc/testsuite/g++.dg/Wclass-memaccess-2.C
@@ -0,0 +1,61 @@
+// PR c++/81169 - -Wclass-memaccess illegitimate warning related to volatile
+// { dg-do compile }
+// { dg-options "-Wclass-memaccess" }
+
+struct S { int x; };
+
+void cast_const (const S *p)
+{
+  __builtin_memset (const_cast<S*>(p), 0, sizeof *p);
+}
+
+void cast_volatile (volatile S *p)
+{
+  __builtin_memset (const_cast<S*>(p), 0, sizeof *p);
+}
+
+void cast_const_volatile (const volatile S *p)
+{
+  __builtin_memset (const_cast<S*>(p), 0, sizeof *p);
+}
+
+void c_cast_const_volatile (const volatile S *p)
+{
+  __builtin_memset ((S*)p, 0, sizeof *p);
+}
+
+// A C cast to void* suppresses the warning because it casts away
+// the qualifiers from the otherwise trivial pointed-to type..
+void c_void_cast_const_volatile (const volatile S *p)
+{
+  __builtin_memset ((void*)p, 0, sizeof *p);
+}
+
+// Also verify that casting to char* suppresses the warning for
+// non-trivial types.
+
+struct NonTrivial
+{
+  NonTrivial ();
+  NonTrivial (const NonTrivial&);
+  NonTrivial& operator= (const NonTrivial&);
+  ~NonTrivial ();
+};
+
+void cast_void (NonTrivial *p)
+{
+  __builtin_memset (reinterpret_cast<char*>(p), 0, sizeof *p);
+}
+
+// A C cast to a character (or any trivial) type suppresses the warning.
+void c_cast_uchar (NonTrivial *p)
+{
+  __builtin_memset ((unsigned char*)p, 0, sizeof *p);
+}
+
+// A cast to void* does not suppress the warning.  That is (or can be)
+// considered a feature.
+void c_cast_void (NonTrivial *p)
+{
+  __builtin_memset ((void*)p, 0, sizeof *p);   // { dg-warning "\\\[-Wclass-memaccess]" }
+}
-- 
2.30.2