Re: [C++ PATCH] Fix constexpr OBJ_TYPE_REF handling on array elts (PR c++/87398)

[Jakub Jelinek <jakub at redhat dot com>]

On Tue, Sep 25, 2018 at 11:07:19AM -0400, Jason Merrill wrote:
> > You're right.  So like this (only look through COMPONENT_REFs where the
> > FIELD_DECL is DECL_FIELD_IS_BASE)?
> > Only checked
> > make check-c++-all RUNTESTFLAGS="dg.exp='constexpr-virt* pr87398*'"
> > so far, but it also fixes the PR87425 testcase and doesn't regress anything.
> 
> Looks good.

Thanks, will bootstrap/regtest it now.  I also took your testcase and turned it into
something that ICEd without this patch too, is that testcase also ok
(constexpr-virtual11.C)?

2018-09-25  Jakub Jelinek  <jakub@redhat.com>

	PR c++/87398
	* constexpr.c (cxx_eval_constant_expression) <case OBJ_TYPE_REF>: Only
	look through COMPONENT_REFs with DECL_FIELD_IS_BASE FIELD_DECLs.

	* g++.dg/other/pr87398.C: New test.
	* g++.dg/cpp2a/constexpr-virtual10.C: New test.
	* g++.dg/cpp2a/constexpr-virtual11.C: New test.

--- gcc/cp/constexpr.c.jj	2018-09-25 15:14:36.335386401 +0200
+++ gcc/cp/constexpr.c	2018-09-25 16:50:38.085334475 +0200
@@ -4812,7 +4812,8 @@ cxx_eval_constant_expression (const cons
 	    return t;
 	  }
 	obj = TREE_OPERAND (obj, 0);
-	while (handled_component_p (obj))
+	while (TREE_CODE (obj) == COMPONENT_REF
+	       && DECL_FIELD_IS_BASE (TREE_OPERAND (obj, 1)))
 	  obj = TREE_OPERAND (obj, 0);
 	tree objtype = TREE_TYPE (obj);
 	/* Find the function decl in the virtual functions list.  TOKEN is
--- gcc/testsuite/g++.dg/other/pr87398.C.jj	2018-09-25 16:49:40.458304980 +0200
+++ gcc/testsuite/g++.dg/other/pr87398.C	2018-09-25 16:49:40.458304980 +0200
@@ -0,0 +1,12 @@
+// PR c++/87398
+// { dg-do compile }
+
+struct A { virtual int foo (); };
+
+int
+bar (int x)
+{
+  A e[5][2];
+  int f = e[4][x].foo ();
+  return f;
+}
--- gcc/testsuite/g++.dg/cpp2a/constexpr-virtual10.C.jj	2018-09-25 16:49:40.458304980 +0200
+++ gcc/testsuite/g++.dg/cpp2a/constexpr-virtual10.C	2018-09-25 16:49:40.458304980 +0200
@@ -0,0 +1,18 @@
+// P1064R0
+// { dg-do compile }
+// { dg-options "-std=c++2a" }
+
+struct X
+{
+  constexpr virtual int f() const { return 1; };
+};
+
+struct Y : public X
+{
+  constexpr virtual int f() const { return 2; };
+};
+
+constexpr X a[2][1][3];
+constexpr Y b[3][12];
+static_assert (a[1][0][1].f() == 1);
+static_assert (b[2][11].f() == 2);
--- gcc/testsuite/g++.dg/cpp2a/constexpr-virtual11.C.jj	2018-09-01 11:09:41.506153390 +0200
+++ gcc/testsuite/g++.dg/cpp2a/constexpr-virtual11.C	2018-09-25 17:11:30.563244029 +0200
@@ -0,0 +1,26 @@
+// P1064R0
+// { dg-do compile }
+// { dg-options "-std=c++2a" }
+
+struct A
+{
+  constexpr virtual int f () const { return 1; }
+};
+
+struct B : public A
+{
+  constexpr virtual int f () const { return 2; }
+};
+
+struct C
+{
+  A a;
+  B b;
+};
+
+constexpr C c;
+constexpr const A &d = c.a;
+constexpr const A &e = c.b;
+constexpr const B &f = c.b;
+static_assert (c.a.f () == 1 && c.b.f () == 2);
+static_assert (d.f () == 1 && e.f () == 2 && f.f () == 2);


	Jakub