On November 19, 2014 8:13:09 AM CET, Wei Mi <w...@google.com> wrote: >We see an inline problem as below caused by r201408 >(https://gcc.gnu.org/ml/gcc-patches/2013-08/msg00027.html). > >hoo() { > foo(); > ... >} > >foo { > goo(); > ... >} > >foo is func splitted, so its body changes to > >foo { > goo(); > ... > foo.part(); >} > >and the used_as_abstract_origin of cgraph node of foo will be set to >true after func splitting. > >In ipa-inline, when inlining foo into hoo, the original node of foo >will not be reused as clone node because used_as_abstract_origin of >cgraph node of foo is true and can_remove_node_now_p_1 will return >false, so that a new clone node of foo will be created. This is the >case in gcc-4_9. >In gcc-4_8, the original node of foo will be reused as clone node. > >gcc-4_8 >foo > | >goo > >gcc-4_9 >foo foo_clone > \ / > goo > >Because of the difference of whether to create a new clone for foo, >when inlining goo to foo, the overall growth of inlining all callsites >of goo in gcc-4_8 will be less than gcc-4_9 (goo has two callsites in >gcc-4_9 but only one in gcc-4_8). If we have many cases like this, >gcc-4_8 will actually have more inline growth budget than gcc-4_9 and >will inline more aggressively than gcc-4_9. > >I don't understand the exact usage of the check about >node->used_as_abstract_origin in can_remove_node_now_p_1, but I feel >puzzled about following two points: > >1. https://gcc.gnu.org/ml/gcc-patches/2013-08/msg00027.html said the >patch was to ensure all abstract origin functions do have nodes >attached. However, even if the node of origin function is reused as a >clone node, a new clone node will be created in following code in >symbol_table::remove_unreachable_nodes if only the node that needs >abstract origin is reachable. > > if (TREE_CODE (node->decl) == FUNCTION_DECL > && DECL_ABSTRACT_ORIGIN (node->decl)) > { > struct cgraph_node *origin_node > = cgraph_node::get_create (DECL_ABSTRACT_ORIGIN (node->decl)); > origin_node->used_as_abstract_origin = true; > enqueue_node (origin_node, &first, &reachable); > } > >2. DECL_ABSTRACT_ORIGIN(decl) seems only useful for debug info of >clone nodes. But now the check of used_as_abstract_origin affect >inline decisions, which should be the same with or without keeping >debug info.
I think we need to keep the functions but do not need to account for them in the unit size if we otherwise could remove them Richard. >Thanks, >Wei.
