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List: gcc-patches
Subject: Re: [PATCH] middle-end/108500 - replace recursive domtree DFS traversal
From: Richard Biener via Gcc-patches <gcc-patches () gcc ! gnu ! org>
Date: 2023-01-31 18:20:37
Message-ID: 90BD28AC-CE2D-4002-B4B1-F8510BCD681A () suse ! de
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> Am 31.01.2023 um 16:59 schrieb Jakub Jelinek via Gcc-patches <gcc-patches@gcc.gnu.org>:
>
> On Tue, Jan 31, 2023 at 03:45:43PM +0100, Richard Biener wrote:
>> The following replaces the recursive DFS traversal of the dominator
>> tree in assign_dfs_numbers with a tree traversal using the fact
>> that we have recorded parents.
>>
>> Bootstrapped and tested on x86_64-unknown-linux-gnu.
>>
>> This makes r13-5325 somewhat obsolete, though not computing the
>> DFS numbers at all is beneficial in the cases where we perform
>> immediate CFG manipulations.
>>
>> OK for trunk and later branch(es)?
>>
>> Thanks,
>> Richard.
>>
>> PR middle-end/108500
>> * dominance.cc (assign_dfs_numbers): Replace recursive DFS
>> with tree traversal algorithm.
>
> LGTM.
>
>> diff --git a/gcc/dominance.cc b/gcc/dominance.cc
>> index 099b8fd3f24..34fabe40c18 100644
>> --- a/gcc/dominance.cc
>> +++ b/gcc/dominance.cc
>> @@ -639,18 +639,25 @@ dom_info::calc_idoms ()
>> static void
>> assign_dfs_numbers (struct et_node *node, int *num)
>> {
>> - struct et_node *son;
>> -
>> - node->dfs_num_in = (*num)++;
>> -
>> - if (node->son)
>> + et_node *n = node;
>> + while (1)
>> {
>> - assign_dfs_numbers (node->son, num);
>> - for (son = node->son->right; son != node->son; son = son->right)
>> - assign_dfs_numbers (son, num);
>> + n->dfs_num_in = (*num)++;
>> + if (n->son)
>> + n = n->son;
>> + else
>> + {
>> + while (!n->right || n->right == n->father->son)
>
> Am I right that we could replace !n->right with n == node here too
> (i.e. only node can have NULL father and in that case also NULL
> left/right?
Yes.
> Though !n->right might result in better code because
> we need to load it anyway for the second comparison.
>
>> + {
>> + n->dfs_num_out = (*num)++;
>> + if (n == node)
>> + return;
>> + n = n->father;
>> + }
>> + n->dfs_num_out = (*num)++;
>> + n = n->right;
>> + }
>> }
>> -
>> - node->dfs_num_out = (*num)++;
>> }
>>
>
> Jakub
>
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