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[C++ PATCH] Fix constexpr tree sharing problem (PR c++/46526)
- From: Jakub Jelinek <jakub at redhat dot com>
- To: Jason Merrill <jason at redhat dot com>
- Cc: gcc-patches at gcc dot gnu dot org
- Date: Fri, 19 Nov 2010 20:17:16 +0100
- Subject: [C++ PATCH] Fix constexpr tree sharing problem (PR c++/46526)
- Reply-to: Jakub Jelinek <jakub at redhat dot com>
Hi!
As mentioned in the PR, this testcase is miscompiled because of a tree
sharing problem. cxx_eval_call_expression always returns the same result
(CONSTRUCTOR in this case) and cxx_eval_bare_aggregate modifies it in place,
which means on this testcase that Base's CONSTRUCTOR is first changed
to have _ZTV1A + 16 value in the first element and then to _ZTV1B + 16,
so a (with A type) ends up _ZTV1B + 16 instead of _ZTV1A + 16 pointer.
It seems that cxx_eval_constant_expression and its helpers mostly have
unsharing semantics (usually they build new trees from the old ones), so
unsharing in cxx_eval_call_expression looks best to me.
Bootstrapped/regtested on x86_64-linux and i686-linux, ok for trunk?
2010-11-19 Jakub Jelinek <jakub@redhat.com>
PR c++/46526
* semantics.c (cxx_eval_call_expression): Unshare the result.
* g++.dg/cpp0x/constexpr-base3.C: New test.
--- gcc/cp/semantics.c.jj 2010-11-11 09:04:25.000000000 +0100
+++ gcc/cp/semantics.c 2010-11-19 10:29:03.018372763 +0100
@@ -6042,7 +6042,7 @@ cxx_eval_call_expression (const constexp
}
pop_cx_call_context ();
- return result;
+ return unshare_expr (result);
}
/* FIXME speed this up, it's taking 16% of compile time on sieve testcase. */
--- gcc/testsuite/g++.dg/cpp0x/constexpr-base3.C.jj 2010-11-19 10:34:23.231529194 +0100
+++ gcc/testsuite/g++.dg/cpp0x/constexpr-base3.C 2010-11-19 10:32:22.000000000 +0100
@@ -0,0 +1,27 @@
+// PR c++/46526
+// { dg-do run }
+// { dg-options "-std=c++0x" }
+
+struct Base
+{
+ virtual int getid () = 0;
+};
+
+struct A : public Base
+{
+ virtual int getid () { return 1; }
+};
+
+struct B : public Base
+{
+ virtual int getid () { throw "here"; }
+};
+
+int
+main ()
+{
+ A a;
+ B b;
+ Base& ar = a;
+ ar.getid ();
+}
Jakub