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Re: gcc-4_9 inlines less funcs than gcc-4_8 because of used_as_abstract_origin flag.
- From: Wei Mi <wmi at google dot com>
- To: Richard Biener <richard dot guenther at gmail dot com>
- Cc: Jan Hubicka <hubicka at ucw dot cz>, GCC Development <gcc at gcc dot gnu dot org>, David Li <davidxl at google dot com>, Teresa Johnson <tejohnson at google dot com>, Dehao Chen <dehao at google dot com>
- Date: Wed, 19 Nov 2014 09:08:45 -0800
- Subject: Re: gcc-4_9 inlines less funcs than gcc-4_8 because of used_as_abstract_origin flag.
- Authentication-results: sourceware.org; auth=none
- References: <CA+4CFy7eHnH_cbOv8SON2grM-Wb7nJrSNba-FvDJYi3oaXEQrw at mail dot gmail dot com> <56D04223-99D3-46B1-97D5-07A1731723AE at gmail dot com> <CAFiYyc2Sdf5FASTVVCW7gTN6fUJbUtF=d4STppFkekg3hTJPTQ at mail dot gmail dot com>
Submit a bug here:
On Wed, Nov 19, 2014 at 2:18 AM, Richard Biener
> On Wed, Nov 19, 2014 at 8:21 AM, Richard Biener
> <email@example.com> wrote:
>> On November 19, 2014 8:13:09 AM CET, Wei Mi <firstname.lastname@example.org> wrote:
>>>We see an inline problem as below caused by r201408
>>>foo is func splitted, so its body changes to
>>>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.
>>> \ /
>>>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
>> 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.