Re: Fix two ICEs with C++ destructors and LTO
Hi Jan, > these two PRs are about C++ destructors that are not virtual but have > virtual alias. The devirtualization machinery walks from alias to symbol > and is then confused by not knowing the class symbol belongs to. > > I think it would make more sense to avoid these walks but that require > more of surgery, so for GCC9 I think it is best to stop freeing contexts > for desctructors. This does not save any stremaing because THIS pointer > of the destructor has the same type. > > Bootstrapped/regtested x86_64-linux, OK? > > Honza > > PR lto/87809 > PR lto/89335 > * tree.c (free_lang_data_in_decl): Do not free context of C++ > destrutors. > > * g++.dg/lto/pr87089_0.C: New testcase. > * g++.dg/lto/pr87089_1.C: New testcase. > * g++.dg/lto/pr89335_0.C: New testcase. this test FAILs on Solaris with the native ld: FAIL: g++.dg/lto/pr89335 cp_lto_pr89335_0.o assemble, -O2 -flto -Wsuggest-final-methods /vol/gcc/src/hg/trunk/local/gcc/testsuite/g++.dg/lto/pr89335_0.C:9:7: warning: Declaring virtual destructor of 'struct List' final would enable devirtualization of 1 call [-Wsuggest-final-methods] The same failure can be seen on Linux/x86_64 with -fno-use-linker-plugin. Rainer -- - Rainer Orth, Center for Biotechnology, Bielefeld University
Re: Fix two ICEs with C++ destructors and LTO
On Mon, 18 Mar 2019, Jan Hubicka wrote:
> Hi,
> these two PRs are about C++ destructors that are not virtual but have
> virtual alias. The devirtualization machinery walks from alias to symbol
> and is then confused by not knowing the class symbol belongs to.
>
> I think it would make more sense to avoid these walks but that require
> more of surgery, so for GCC9 I think it is best to stop freeing contexts
> for desctructors. This does not save any stremaing because THIS pointer
> of the destructor has the same type.
>
> Bootstrapped/regtested x86_64-linux, OK?
OK.
Richard.
> Honza
>
> PR lto/87809
> PR lto/89335
> * tree.c (free_lang_data_in_decl): Do not free context of C++
> destrutors.
>
> * g++.dg/lto/pr87089_0.C: New testcase.
> * g++.dg/lto/pr87089_1.C: New testcase.
> * g++.dg/lto/pr89335_0.C: New testcase.
> Index: tree.c
> ===
> --- tree.c(revision 269704)
> +++ tree.c(working copy)
> @@ -5772,10 +5772,16 @@ free_lang_data_in_decl (tree decl, struc
> not do well with TREE_CHAIN pointers linking them.
>
> Also do not drop containing types for virtual methods and tables because
> - these are needed by devirtualization. */
> + these are needed by devirtualization.
> + C++ destructors are special because C++ frontends sometimes produces
> + virtual destructor as an alias of non-virtual destructor. In
> + devirutalization code we always walk through aliases and we need
> + context to be preserved too. See PR89335 */
>if (TREE_CODE (decl) != FIELD_DECL
>&& ((TREE_CODE (decl) != VAR_DECL && TREE_CODE (decl) != FUNCTION_DECL)
> - || !DECL_VIRTUAL_P (decl)))
> + || (!DECL_VIRTUAL_P (decl)
> + && (TREE_CODE (decl) != FUNCTION_DECL
> + || !DECL_CXX_DESTRUCTOR_P (decl)
> DECL_CONTEXT (decl) = fld_decl_context (DECL_CONTEXT (decl));
> }
>
> Index: testsuite/g++.dg/lto/pr87089_0.C
> ===
> --- testsuite/g++.dg/lto/pr87089_0.C (nonexistent)
> +++ testsuite/g++.dg/lto/pr87089_0.C (working copy)
> @@ -0,0 +1,21 @@
> +// { dg-lto-do link }
> +// { dg-extra-ld-options "-r -nostdlib -flinker-output=nolto-rel" }
> +namespace itpp {
> +template void b(a *c) { c[0].~a(); }
> +class CFix;
> +template class d {
> + void e(const char *);
> + CFix *data;
> +};
> +class CFix {
> +public:
> + virtual ~CFix();
> +};
> +template <> void d::e(const char *) { b(data); }
> +} // namespace itpp
> +
> +int
> +main (void)
> +{
> + return 0;
> +}
> Index: testsuite/g++.dg/lto/pr87089_1.C
> ===
> --- testsuite/g++.dg/lto/pr87089_1.C (nonexistent)
> +++ testsuite/g++.dg/lto/pr87089_1.C (working copy)
> @@ -0,0 +1,12 @@
> +namespace itpp {
> +enum a { b };
> +class CFix {
> +public:
> + virtual ~CFix();
> +};
> +template class c : CFix {
> + ~c() {}
> +};
> +template class c<>;
> +} // namespace itpp
> +
> Index: testsuite/g++.dg/lto/pr89335_0.C
> ===
> --- testsuite/g++.dg/lto/pr89335_0.C (nonexistent)
> +++ testsuite/g++.dg/lto/pr89335_0.C (working copy)
> @@ -0,0 +1,16 @@
> +// { dg-lto-do link }
> +// { dg-lto-options {{-O2 -flto -Wsuggest-final-methods}} }
> +// { dg-extra-ld-options "-r -nostdlib -flinker-output=nolto-rel" }
> +class Container
> +{
> +public:
> + virtual ~Container ();
> +};
> +class List : public Container // { dg-lto-message "final would enable
> devirtualization" }
> +{
> +};
> +static List cache[256];
> +int main (void)
> +{
> + return 0;
> +}
>
--
Richard Biener
SUSE LINUX GmbH, GF: Felix Imendoerffer, Jane Smithard, Graham Norton, HRB
21284 (AG Nuernberg)
Fix two ICEs with C++ destructors and LTO
Hi,
these two PRs are about C++ destructors that are not virtual but have
virtual alias. The devirtualization machinery walks from alias to symbol
and is then confused by not knowing the class symbol belongs to.
I think it would make more sense to avoid these walks but that require
more of surgery, so for GCC9 I think it is best to stop freeing contexts
for desctructors. This does not save any stremaing because THIS pointer
of the destructor has the same type.
Bootstrapped/regtested x86_64-linux, OK?
Honza
PR lto/87809
PR lto/89335
* tree.c (free_lang_data_in_decl): Do not free context of C++
destrutors.
* g++.dg/lto/pr87089_0.C: New testcase.
* g++.dg/lto/pr87089_1.C: New testcase.
* g++.dg/lto/pr89335_0.C: New testcase.
Index: tree.c
===
--- tree.c (revision 269704)
+++ tree.c (working copy)
@@ -5772,10 +5772,16 @@ free_lang_data_in_decl (tree decl, struc
not do well with TREE_CHAIN pointers linking them.
Also do not drop containing types for virtual methods and tables because
- these are needed by devirtualization. */
+ these are needed by devirtualization.
+ C++ destructors are special because C++ frontends sometimes produces
+ virtual destructor as an alias of non-virtual destructor. In
+ devirutalization code we always walk through aliases and we need
+ context to be preserved too. See PR89335 */
if (TREE_CODE (decl) != FIELD_DECL
&& ((TREE_CODE (decl) != VAR_DECL && TREE_CODE (decl) != FUNCTION_DECL)
- || !DECL_VIRTUAL_P (decl)))
+ || (!DECL_VIRTUAL_P (decl)
+ && (TREE_CODE (decl) != FUNCTION_DECL
+ || !DECL_CXX_DESTRUCTOR_P (decl)
DECL_CONTEXT (decl) = fld_decl_context (DECL_CONTEXT (decl));
}
Index: testsuite/g++.dg/lto/pr87089_0.C
===
--- testsuite/g++.dg/lto/pr87089_0.C(nonexistent)
+++ testsuite/g++.dg/lto/pr87089_0.C(working copy)
@@ -0,0 +1,21 @@
+// { dg-lto-do link }
+// { dg-extra-ld-options "-r -nostdlib -flinker-output=nolto-rel" }
+namespace itpp {
+template void b(a *c) { c[0].~a(); }
+class CFix;
+template class d {
+ void e(const char *);
+ CFix *data;
+};
+class CFix {
+public:
+ virtual ~CFix();
+};
+template <> void d::e(const char *) { b(data); }
+} // namespace itpp
+
+int
+main (void)
+{
+ return 0;
+}
Index: testsuite/g++.dg/lto/pr87089_1.C
===
--- testsuite/g++.dg/lto/pr87089_1.C(nonexistent)
+++ testsuite/g++.dg/lto/pr87089_1.C(working copy)
@@ -0,0 +1,12 @@
+namespace itpp {
+enum a { b };
+class CFix {
+public:
+ virtual ~CFix();
+};
+template class c : CFix {
+ ~c() {}
+};
+template class c<>;
+} // namespace itpp
+
Index: testsuite/g++.dg/lto/pr89335_0.C
===
--- testsuite/g++.dg/lto/pr89335_0.C(nonexistent)
+++ testsuite/g++.dg/lto/pr89335_0.C(working copy)
@@ -0,0 +1,16 @@
+// { dg-lto-do link }
+// { dg-lto-options {{-O2 -flto -Wsuggest-final-methods}} }
+// { dg-extra-ld-options "-r -nostdlib -flinker-output=nolto-rel" }
+class Container
+{
+public:
+ virtual ~Container ();
+};
+class List : public Container // { dg-lto-message "final would enable
devirtualization" }
+{
+};
+static List cache[256];
+int main (void)
+{
+ return 0;
+}
