[pushed] c++: no clobber for C++20 destroying delete [PR91859]

Jason Merrill jason@redhat.com
Tue Jun 1 15:40:50 GMT 2021


Before C++20 added destroying operator delete, by the time we called
operator delete for a pointer, the object would already be gone.  But that
isn't true for destroying delete.  Since the optimizers' assumptions about
operator delete are based on either DECL_IS_REPLACEABLE_OPERATOR (which
already is not set) or CALL_FROM_NEW_OR_DELETE_P, let's avoid setting the
latter flag in this case.

Tested x86_64-pc-linux-gnu, applying to trunk.

	PR c++/91859

gcc/ChangeLog:

	* tree.h (CALL_FROM_NEW_OR_DELETE_P): Adjust comment.

gcc/cp/ChangeLog:

	* call.c (build_op_delete_call): Don't set CALL_FROM_NEW_OR_DELETE_P
	for destroying delete.
	* init.c (build_delete): Don't clobber before destroying delete.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp2a/destroying-delete5.C: New test.
---
 gcc/tree.h                                    |  2 +-
 gcc/cp/call.c                                 |  4 ++-
 gcc/cp/init.c                                 |  5 ++-
 .../g++.dg/cpp2a/destroying-delete5.C         | 36 +++++++++++++++++++
 4 files changed, 44 insertions(+), 3 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp2a/destroying-delete5.C

diff --git a/gcc/tree.h b/gcc/tree.h
index 260a3ae6c83..62b2de46479 100644
--- a/gcc/tree.h
+++ b/gcc/tree.h
@@ -937,7 +937,7 @@ extern void omp_clause_range_check_failed (const_tree, const char *, int,
 
 /* In a CALL_EXPR, if the function being called is DECL_IS_OPERATOR_NEW_P or
    DECL_IS_OPERATOR_DELETE_P, true for allocator calls from C++ new or delete
-   expressions.  */
+   expressions.  Not set for C++20 destroying delete operators.  */
 #define CALL_FROM_NEW_OR_DELETE_P(NODE) \
   (CALL_EXPR_CHECK (NODE)->base.protected_flag)
 
diff --git a/gcc/cp/call.c b/gcc/cp/call.c
index bf524b50bc4..90192b1b8aa 100644
--- a/gcc/cp/call.c
+++ b/gcc/cp/call.c
@@ -7206,8 +7206,10 @@ build_op_delete_call (enum tree_code code, tree addr, tree size,
 	 treat that as an implicit delete-expression.  This is also called for
 	 the delete if the constructor throws in a new-expression, and for a
 	 deleting destructor (which implements a delete-expression).  */
+      /* But leave this flag off for destroying delete to avoid wrong
+	 assumptions in the optimizers.  */
       tree call = extract_call_expr (ret);
-      if (TREE_CODE (call) == CALL_EXPR)
+      if (TREE_CODE (call) == CALL_EXPR && !destroying_delete_p (fn))
 	CALL_FROM_NEW_OR_DELETE_P (call) = 1;
 
       return ret;
diff --git a/gcc/cp/init.c b/gcc/cp/init.c
index a85f4d50750..04d495807ef 100644
--- a/gcc/cp/init.c
+++ b/gcc/cp/init.c
@@ -4881,7 +4881,10 @@ build_delete (location_t loc, tree otype, tree addr,
 			    complain);
     }
 
-  if (!destroying_delete && type_build_dtor_call (type))
+  if (destroying_delete)
+    /* The operator delete will call the destructor.  */
+    expr = addr;
+  else if (type_build_dtor_call (type))
     expr = build_dtor_call (cp_build_fold_indirect_ref (addr),
 			    auto_delete, flags, complain);
   else
diff --git a/gcc/testsuite/g++.dg/cpp2a/destroying-delete5.C b/gcc/testsuite/g++.dg/cpp2a/destroying-delete5.C
new file mode 100644
index 00000000000..553c964b9e9
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp2a/destroying-delete5.C
@@ -0,0 +1,36 @@
+// PR c++/91859
+// { dg-do run { target c++20 } }
+// { dg-additional-options -O2 }
+
+#include <cstdlib>
+#include <new>
+
+struct Expression {
+  int i = 0;
+  void *operator new(std::size_t);
+  void operator delete(Expression *, std::destroying_delete_t);
+};
+
+void * Expression::operator new(std::size_t sz)
+{
+  return std::malloc(sz);
+}
+
+int i;
+
+void Expression::operator delete(Expression *p, std::destroying_delete_t)
+{
+  Expression * e = p;
+  ::i = e->i;
+  p->~Expression();
+  std::free(p);
+}
+
+int main()
+{
+  auto p = new Expression();
+  p->i = 1;
+  delete p;
+  if (i != 1)
+    __builtin_abort();
+}
-- 
2.27.0



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