[gcc r13-4095] c++: Fix up calls to static operator() or operator[] [PR107624]

[gcc r13-4095] c++: Fix up calls to static operator() or operator[] [PR107624]

[Jakub Jelinek]

https://gcc.gnu.org/g:cf958f8f168f695d49e29297ef9fb37f6efa5d0f

commit r13-4095-gcf958f8f168f695d49e29297ef9fb37f6efa5d0f
Author: Jakub Jelinek <jakub@redhat.com>
Date:   Wed Nov 16 14:42:54 2022 +0100

    c++: Fix up calls to static operator() or operator[] [PR107624]
    
    One thing that doesn't work properly is the same problem as I've filed
    yesterday for static operator() - PR107624 - that side-effects of
    the postfix-expression on which the call or subscript operator are
    applied are thrown away, I assume we have to add them into COMPOUND_EXPR
    somewhere after we find out that the we've chosen a static member function
    operator.
    
    On Mon, Nov 14, 2022 at 06:29:44PM -0500, Jason Merrill wrote:
    > Indeed.  The code in build_new_method_call for this case has the comment
    >
    >               /* In an expression of the form `a->f()' where `f' turns
    >                  out to be a static member function, `a' is
    >                  none-the-less evaluated.  */
    
    Had to tweak 3 spots for this.  Furthermore, found that if in non-pedantic
    C++20 compilation static operator[] is accepted, we required that it has 2
    arguments, I think it is better to require exactly one because that case
    is the only one that will actually work in C++20 and older.
    
    2022-11-16  Jakub Jelinek  <jakub@redhat.com>
    
            PR c++/107624
            * call.cc (keep_unused_object_arg): New function.
            (build_op_call): Use it.
            (build_op_subscript): Likewise.
            (build_new_op): Similarly for ARRAY_REF.
            (build_new_method_call): Use it.
            * decl.cc (grok_op_properties): For C++20 and earlier, if operator[]
            is static member function, require exactly one parameter rather than
            exactly two parameters.
    
            * g++.dg/cpp23/static-operator-call4.C: New test.
            * g++.dg/cpp23/subscript10.C: New test.
            * g++.dg/cpp23/subscript11.C: New test.

Diff:
---
 gcc/cp/call.cc                                     | 66 ++++++++++++++++------
 gcc/cp/decl.cc                                     |  4 ++
 gcc/testsuite/g++.dg/cpp23/static-operator-call4.C | 37 ++++++++++++
 gcc/testsuite/g++.dg/cpp23/subscript10.C           | 46 +++++++++++++++
 gcc/testsuite/g++.dg/cpp23/subscript11.C           | 11 ++++
 5 files changed, 148 insertions(+), 16 deletions(-)

diff --git a/gcc/cp/call.cc b/gcc/cp/call.cc
index dbb01ec6ee5..459e86b5f09 100644
--- a/gcc/cp/call.cc
+++ b/gcc/cp/call.cc
@@ -5017,6 +5017,33 @@ build_operator_new_call (tree fnname, vec<tree, va_gc> **args,
    return ret;
 }
 
+/* Evaluate side-effects from OBJ before evaluating call
+   to FN in RESULT expression.
+   This is for expressions of the form `obj->fn(...)'
+   where `fn' turns out to be a static member function and
+   `obj' needs to be evaluated.  `fn' could be also static operator[]
+   or static operator(), in which cases the source expression
+   would be `obj[...]' or `obj(...)'.  */
+
+static tree
+keep_unused_object_arg (tree result, tree obj, tree fn)
+{
+  if (result == NULL_TREE
+      || result == error_mark_node
+      || TREE_CODE (TREE_TYPE (fn)) == METHOD_TYPE
+      || !TREE_SIDE_EFFECTS (obj))
+    return result;
+
+  /* But avoid the implicit lvalue-rvalue conversion when `obj' is
+     volatile.  */
+  tree a = obj;
+  if (TREE_THIS_VOLATILE (a))
+    a = build_this (a);
+  if (TREE_SIDE_EFFECTS (a))
+    return build2 (COMPOUND_EXPR, TREE_TYPE (result), a, result);
+  return result;
+}
+
 /* Build a new call to operator().  This may change ARGS.  */
 
 tree
@@ -5137,7 +5164,13 @@ build_op_call (tree obj, vec<tree, va_gc> **args, tsubst_flags_t complain)
       else if (TREE_CODE (cand->fn) == FUNCTION_DECL
 	       && DECL_OVERLOADED_OPERATOR_P (cand->fn)
 	       && DECL_OVERLOADED_OPERATOR_IS (cand->fn, CALL_EXPR))
-	result = build_over_call (cand, LOOKUP_NORMAL, complain);
+	{
+	  result = build_over_call (cand, LOOKUP_NORMAL, complain);
+	  /* In an expression of the form `a()' where cand->fn
+	     which is operator() turns out to be a static member function,
+	     `a' is none-the-less evaluated.  */
+	  result = keep_unused_object_arg (result, obj, cand->fn);
+	}
       else
 	{
 	  if (TREE_CODE (cand->fn) == FUNCTION_DECL)
@@ -7046,6 +7079,12 @@ build_new_op (const op_location_t &loc, enum tree_code code, int flags,
 		  gcc_unreachable ();
 		}
 	    }
+
+	  /* In an expression of the form `a[]' where cand->fn
+	     which is operator[] turns out to be a static member function,
+	     `a' is none-the-less evaluated.  */
+	  if (code == ARRAY_REF)
+	    result = keep_unused_object_arg (result, arg1, cand->fn);
 	}
       else
 	{
@@ -7302,6 +7341,11 @@ build_op_subscript (const op_location_t &loc, tree obj,
 	      /* Specify evaluation order as per P0145R2.  */
 	      CALL_EXPR_ORDERED_ARGS (call) = op_is_ordered (ARRAY_REF) == 1;
 	    }
+
+	  /* In an expression of the form `a[]' where cand->fn
+	     which is operator[] turns out to be a static member function,
+	     `a' is none-the-less evaluated.  */
+	  result = keep_unused_object_arg (result, obj, cand->fn);
 	}
       else
 	gcc_unreachable ();
@@ -11494,21 +11538,11 @@ build_new_method_call (tree instance, tree fns, vec<tree, va_gc> **args,
 	      /* In an expression of the form `a->f()' where `f' turns
 		 out to be a static member function, `a' is
 		 none-the-less evaluated.  */
-	      if (TREE_CODE (TREE_TYPE (fn)) != METHOD_TYPE
-		  && !is_dummy_object (instance)
-		  && TREE_SIDE_EFFECTS (instance))
-		{
-		  /* But avoid the implicit lvalue-rvalue conversion when 'a'
-		     is volatile.  */
-		  tree a = instance;
-		  if (TREE_THIS_VOLATILE (a))
-		    a = build_this (a);
-		  if (TREE_SIDE_EFFECTS (a))
-		    call = build2 (COMPOUND_EXPR, TREE_TYPE (call), a, call);
-		}
-	      else if (call != error_mark_node
-		       && DECL_DESTRUCTOR_P (cand->fn)
-		       && !VOID_TYPE_P (TREE_TYPE (call)))
+	      if (!is_dummy_object (instance))
+		call = keep_unused_object_arg (call, instance, fn);
+	      if (call != error_mark_node
+		  && DECL_DESTRUCTOR_P (cand->fn)
+		  && !VOID_TYPE_P (TREE_TYPE (call)))
 		/* An explicit call of the form "x->~X()" has type
 		   "void".  However, on platforms where destructors
 		   return "this" (i.e., those where
diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 0234919ea57..d28889ed865 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -15404,6 +15404,10 @@ grok_op_properties (tree decl, bool complain)
 	    pedwarn (loc, OPT_Wc__23_extensions, "%qD may be a static member "
 		     "function only with %<-std=c++23%> or %<-std=gnu++23%>",
 		     decl);
+	  if (operator_code == ARRAY_REF)
+	    /* static operator[] should have exactly one argument
+	       for C++20 and earlier, so that it isn't multidimensional.  */
+	    op_flags = OVL_OP_FLAG_UNARY;
 	}
       else if (DECL_STATIC_FUNCTION_P (decl))
 	{
diff --git a/gcc/testsuite/g++.dg/cpp23/static-operator-call4.C b/gcc/testsuite/g++.dg/cpp23/static-operator-call4.C
new file mode 100644
index 00000000000..83ccde3b9c5
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp23/static-operator-call4.C
@@ -0,0 +1,37 @@
+// PR c++/107624
+// { dg-do run { target c++11 } }
+// { dg-options "" }
+
+int n[3];
+struct S {
+  static void operator() (int x) { n[0] |= (1 << x); }	// { dg-warning "may be a static member function only with" "" { target c++20_down } }
+  static void baz (int x) { n[1] |= (1 << x); }
+  int s;
+};
+volatile S s[2];
+
+S &
+foo (int x)
+{
+  static S t;
+  n[2] |= (1 << x);
+  return t;
+}
+
+int
+main ()
+{
+  int i = 0;
+  foo (0) (0);
+  if (n[0] != 1 || n[1] || n[2] != 1)
+    __builtin_abort ();
+  foo (1).baz (1);
+  if (n[0] != 1 || n[1] != 2 || n[2] != 3)
+    __builtin_abort ();
+  s[i++] (2);
+  if (i != 1 || n[0] != 5 || n[1] != 2 || n[2] != 3)
+    __builtin_abort ();
+  s[--i].baz (3);
+  if (i != 0 || n[0] != 5 || n[1] != 10 || n[2] != 3)
+    __builtin_abort ();
+}
diff --git a/gcc/testsuite/g++.dg/cpp23/subscript10.C b/gcc/testsuite/g++.dg/cpp23/subscript10.C
new file mode 100644
index 00000000000..96e5e1f3ed2
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp23/subscript10.C
@@ -0,0 +1,46 @@
+// PR c++/107624
+// { dg-do run { target c++11 } }
+// { dg-options "" }
+
+int n[3];
+struct S {
+  static int &operator[] (int x) { n[0] |= (1 << x); return n[2]; }	// { dg-warning "may be a static member function only with" "" { target c++20_down } }
+#if __cpp_multidimensional_subscript >= 202211L
+  static int &operator[] () { n[0] |= (1 << 8); return n[2]; }
+  static int &operator[] (int y, int z, int w) { n[0] |= (1 << y) | (1 << z) | (1 << w); return n[2]; }
+#endif
+  int s;
+};
+volatile S s[2];
+
+S &
+foo (int x)
+{
+  static S t;
+  n[1] |= (1 << x);
+  return t;
+}
+
+int
+main ()
+{
+  int i = 0;
+  foo (0) [0]++;
+  if (n[0] != 1 || n[1] != 1 || n[2] != 1)
+    __builtin_abort ();
+  s[i++][2]++;
+  if (i != 1 || n[0] != 5 || n[1] != 1 || n[2] != 2)
+    __builtin_abort ();
+#if __cpp_multidimensional_subscript >= 202211L
+  foo (3) []++;
+  if (n[0] != 261 || n[1] != 9 || n[2] != 3)
+    __builtin_abort ();
+  int y = 10;
+  int z = 10;
+  int w = 13;
+  foo (4) [y++, ++z, w++]++;
+  if (n[0] != 11525 || n[1] != 25 || n[2] != 4
+      || y != 11 || z != 11 || w != 14)
+    __builtin_abort ();
+#endif
+}
diff --git a/gcc/testsuite/g++.dg/cpp23/subscript11.C b/gcc/testsuite/g++.dg/cpp23/subscript11.C
new file mode 100644
index 00000000000..990a70327b2
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp23/subscript11.C
@@ -0,0 +1,11 @@
+// { dg-do compile { target c++11 } }
+// { dg-options "" }
+
+struct S {
+  static int &operator[] (int);	// { dg-warning "may be a static member function only with" "" { target c++20_down } }
+  static int &operator[] ();	// { dg-warning "may be a static member function only with" "" { target c++20_down } }
+				// { dg-error "'static int& S::operator\\\[\\\]\\\(\\\)' must have exactly one argument" "" { target c++20_down } .-1 }
+  static int &operator[] (int, int, int);	// { dg-warning "may be a static member function only with" "" { target c++20_down } }
+				// { dg-error "'static int& S::operator\\\[\\\]\\\(int, int, int\\\)' must have exactly one argument" "" { target c++20_down } .-1 }
+  int s;
+};