On Wed, May 01, 2024 at 09:57:38AM -0400, Patrick Palka wrote: > > On Wed, 1 May 2024, Nathaniel Shead wrote: > > > Bootstrapped and regtested on x86_64-pc-linux-gnu, OK for trunk (and > > later 14.2)? I don't think making it a GTY root is necessary but I felt > > perhaps better to be safe than sorry. > > > > Potentially another approach would be to use DECL_UID instead like how > > entity_map does; would that be preferable? > > > > -- >8 -- > > > > I got notified by Linaro CI and by checking testresults that there seems > > to be some occasional failures in tpl-friend-4_b.C on some architectures > > and standards modes since r15-59-gb5f6a56940e708. I haven't been able > > to reproduce but looking at the backtrace I suspect the issue is that > > we're adding to the 'imported_temploid_friend' map a decl that is > > ultimately discarded, which then has its address reused by a later decl > > causing a failure in the assert in 'set_originating_module'. > > > > This patch attempts to fix the issue in two ways: by ensuring that we > > only store the decl if we know it's a new decl (and hence won't be > > discarded), and by making the imported_temploid_friends map a GTY root > > so that even if the decl does get discarded later the address isn't > > reused. > > > > gcc/cp/ChangeLog: > > > > * module.cc (imported_temploid_friends): Mark GTY, and... > > (init_modules): ...allocate from GGC. > > (trees_in::decl_value): Only write to imported_temploid_friends > > for new decls. > > > > Signed-off-by: Nathaniel Shead <nathanielosh...@gmail.com> > > --- > > gcc/cp/module.cc | 7 ++++--- > > 1 file changed, 4 insertions(+), 3 deletions(-) > > > > diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc > > index 5b8ff5bc483..37d38bb9654 100644 > > --- a/gcc/cp/module.cc > > +++ b/gcc/cp/module.cc > > @@ -2731,7 +2731,7 @@ static keyed_map_t *keyed_table; > > need to be attached to the same module as the temploid. This maps > > these decls to the temploid they are instantiated them, as there is > > no other easy way to get this information. */ > > -static hash_map<tree, tree> *imported_temploid_friends; > > +static GTY(()) hash_map<tree, tree> *imported_temploid_friends; > > > > /********************************************************************/ > > /* Tree streaming. The tree streaming is very specific to the tree > > @@ -8327,7 +8327,8 @@ trees_in::decl_value () > > if (TREE_CODE (inner) == FUNCTION_DECL > > || TREE_CODE (inner) == TYPE_DECL) > > if (tree owner = tree_node ()) > > - imported_temploid_friends->put (decl, owner); > > + if (is_new) > > + imported_temploid_friends->put (decl, owner); > > Hmm, I'm not seeing this code path getting reached for tpl-friend-4_b.C. > It seems we're instead adding to imported_temploid_friends from > propagate_defining_module, during tsubst_friend_function. > > What seems to be happening is that we we first tsubst_friend_function > 'foo' from TPL<int>, and then we tsubst_friend_function 'foo' from DEF<int>, > which ends up calling duplicate_decls, which ggc_frees this 'foo' > redeclaration that is still present in the imported_temploid_friends map. > > So I don't think marking imported_temploid_friends as a GC root would > help with this situation. If we want to keep imported_temploid_friends > as a tree -> tree map, I think we just need to ensure that a decl > is removed from the map upon getting ggc_free'd from e.g. duplicate_decls. > > But it seems simpler to use DECL_UID as the key instead, since those > never get reused even after the decl gets ggc_free'd IIUC. >
Ah right, thanks for digging into that further. Yup OK, I think probably the DECL_UID route feels safer to me then in case there are other places where a decl might be explicitly freed. Looking at tree.cc it looks like the relevant function is 'allocate_decl_uid' which shouldn't reuse UIDs until 2^32 decls have been created, so we should be safe on the reuse front. I'll draft and test a patch for that tomorrow morning. > > > > /* Regular typedefs will have a NULL TREE_TYPE at this point. */ > > unsigned tdef_flags = 0; > > @@ -20523,7 +20524,7 @@ init_modules (cpp_reader *reader) > > entity_map = new entity_map_t (EXPERIMENT (1, 400)); > > vec_safe_reserve (entity_ary, EXPERIMENT (1, 400)); > > imported_temploid_friends > > - = new hash_map<tree,tree> (EXPERIMENT (1, 400)); > > + = hash_map<tree,tree>::create_ggc (EXPERIMENT (1, 400)); > > } > > > > #if CHECKING_P > > -- > > 2.43.2 > > > > >
