On Wed, Nov 19, 2014 at 8:21 AM, Richard Biener <richard.guent...@gmail.com> wrote: > 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
Btw - please make sure to open a bug so this issue doesn't get lost. Thanks, Richard. > Richard. > >>Thanks, >>Wei. > >