From: Richard Sandiford <richard.sandiford@arm.com>
To: Jeff Law <law@redhat.com>
Cc: gcc-patches@gcc.gnu.org
Subject: Re: [08/23] Add an alternative splay tree implementation
Date: Thu, 17 Dec 2020 00:29:53 +0000 [thread overview]
Message-ID: <mptk0thqnpa.fsf@arm.com> (raw)
In-Reply-To: <3068cea8-2188-83b4-0a8a-e27665e245af@redhat.com> (Jeff Law's message of "Wed, 2 Dec 2020 13:36:17 -0700")
Jeff Law <law@redhat.com> writes:
> On 11/13/20 1:15 AM, Richard Sandiford via Gcc-patches wrote:
>> We already have two splay tree implementations: the old C one in
>> libiberty and a templated reimplementation of it in typed-splay-tree.h.
>> However, they have some drawbacks:
>>
>> - They hard-code the assumption that nodes should have both a key and
>> a value, which isn't always true.
>>
>> - They use the two-phase method of lookup, and so nodes need to store
>> a temporary back pointer. We can avoid that overhead by using the
>> top-down method (as e.g. the bitmap tree code already does).
>>
>> - The tree node has to own the key and the value. For some use cases
>> it's more convenient to embed the tree links in the value instead.
>>
>> Also, a later patch wants to use splay trees to represent an
>> adaptive total order: the splay tree itself records whether node N1
>> is less than node N2, and (in the worst case) comparing nodes is
>> a splay operation.
>>
>> This patch therefore adds an alternative implementation. The main
>> features are:
>>
>> - Nodes can optionally point back to their parents.
>>
>> - An Accessors class abstracts accessing child nodes and (where
>> applicable) parent nodes, so that the information can be embedded
>> in larger data structures.
>>
>> - There is no fixed comparison function at the class level. Instead,
>> individual functions that do comparisons take a comparison function
>> argument.
>>
>> - There are two styles of comparison function, optimised for different
>> use cases. (See the comments in the patch for details.)
>>
>> - It's possible to do some operations directly on a given node,
>> without knowing whether it's the root. This includes the comparison
>> use case described above.
>>
>> This of course has its own set of drawbacks. It's really providing
>> splay utility functions rather than a true ADT, and so is more low-level
>> than the existing routines. It's mostly geared for cases in which the
>> client code wants to participate in the splay operations to some extent.
>>
>> gcc/
>> * Makefile.in (OBJS): Add splay-tree-utils.o.
>> * system.h: Include <array> when INCLUDE_ARRAY is defined.
>> * selftest.h (splay_tree_cc_tests): Declare.
>> * selftest-run-tests.c (selftest::run_tests): Run splay_tree_cc_tests.
>> * splay-tree-utils.h: New file.
>> * splay-tree-utils.tcc: Likewise.
>> * splay-tree-utils.cc: Likewise.
> I must admit, I'm not a fan of adding another splay tree. Though I
> suspect the one in libiberty will be there forever since there could
> well be clients outside our source base.
>
> The typed_splay_tree implementation however is internal to GCC and only
> has a couple users (the JIT and fixit hints). Is there any chance we
> could convert those two users to the new one? Your cover hints that's
> not the case, but I'm going to explicitly ask :-)
Yeah, I agree it's not great to have three versions. I had a look at
converting the uses of typed_splay_tree, and all of them seem to be a
natural fit for the new scheme. In particular, although typed_splay_tree
maps keys to values, in practice the keys are already part of the values.
However, I think a natural conversion would need a couple of new helpers
for “get or insert” type operations. Would it be OK to wait until GCC 12
stage 1 for that?
Thanks,
Richard
next prev parent reply other threads:[~2020-12-17 0:29 UTC|newest]
Thread overview: 88+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-11-13 8:10 [00/23] Make fwprop use an on-the-side RTL SSA representation Richard Sandiford
2020-11-13 8:11 ` [01/23] vec: Silence clang warning Richard Sandiford
2020-11-25 19:58 ` Jeff Law
2020-11-13 8:12 ` [02/23] rtlanal: Remove noop_move_p REG_EQUAL condition Richard Sandiford
2020-11-25 20:00 ` Jeff Law
2020-11-13 8:12 ` [03/23] reginfo: Add a global_reg_set Richard Sandiford
2020-11-25 20:01 ` Jeff Law
2020-11-13 8:13 ` [04/23] Move iterator_range to a new iterator-utils.h file Richard Sandiford
2020-11-25 20:02 ` Jeff Law
2020-11-13 8:13 ` [05/23] Add more iterator utilities Richard Sandiford
2020-11-25 20:12 ` Jeff Law
2020-11-13 8:14 ` [06/23] Add an RAII class for managing obstacks Richard Sandiford
2020-11-25 20:15 ` Jeff Law
2020-11-13 8:14 ` [07/23] Add a class that multiplexes two pointer types Richard Sandiford
2020-11-25 20:23 ` Jeff Law
2020-11-26 16:15 ` Richard Sandiford
2020-11-30 1:28 ` Jeff Law
2020-11-25 23:33 ` Martin Sebor
2020-11-26 17:06 ` Richard Sandiford
2020-11-27 18:12 ` Richard Sandiford
2020-11-28 0:17 ` Martin Sebor
2020-12-17 0:17 ` Richard Sandiford
2020-12-17 14:21 ` Tom Tromey
2020-12-17 15:38 ` Richard Sandiford
2020-12-17 15:44 ` Nathan Sidwell
2021-01-04 15:32 ` Jeff Law
2020-11-13 8:15 ` [08/23] Add an alternative splay tree implementation Richard Sandiford
2020-12-02 20:36 ` Jeff Law
2020-12-17 0:29 ` Richard Sandiford [this message]
2021-01-04 15:27 ` Jeff Law
2021-01-01 8:25 ` Andreas Schwab
2021-01-04 14:53 ` Richard Sandiford
2021-01-04 15:02 ` Andreas Schwab
2021-01-04 15:42 ` Richard Sandiford
2021-01-05 12:13 ` Richard Biener
2020-11-13 8:15 ` [09/23] Add a cut-down version of std::span (array_slice) Richard Sandiford
2020-11-30 19:56 ` Jeff Law
2022-08-03 15:13 ` Martin Jambor
2022-08-03 15:31 ` Richard Sandiford
2022-08-10 16:03 ` Martin Jambor
2022-08-11 6:58 ` Richard Biener
2022-08-16 7:59 ` Richard Sandiford
2020-11-13 8:16 ` [10/23] Tweak the way that is_a is implemented Richard Sandiford
2020-12-02 5:15 ` Jeff Law
2020-11-13 8:16 ` [11/23] Split update_cfg_for_uncondjump out of combine Richard Sandiford
2020-11-30 6:14 ` Jeff Law
2020-11-13 8:17 ` [12/23] Export print-rtl.c:print_insn_with_notes Richard Sandiford
2020-11-25 20:24 ` Jeff Law
2020-11-13 8:18 ` [13/23] recog: Split out a register_asm_p function Richard Sandiford
2020-11-25 20:24 ` Jeff Law
2020-11-13 8:18 ` [14/23] simplify-rtx: Put simplify routines into a class Richard Sandiford
2020-11-30 19:54 ` Jeff Law
2020-11-13 8:19 ` [15/23] recog: Add a validate_change_xveclen function Richard Sandiford
2020-11-30 20:03 ` Jeff Law
2020-11-13 8:19 ` [16/23] recog: Add a way of temporarily undoing changes Richard Sandiford
2020-11-25 20:27 ` Jeff Law
2020-12-17 0:22 ` Richard Sandiford
2020-11-13 8:20 ` [17/23] recog: Add a class for propagating into insns Richard Sandiford
2020-12-03 22:32 ` Jeff Law
2020-11-13 8:20 ` [18/23] recog: Add an RAII class for undoing insn changes Richard Sandiford
2020-11-25 20:27 ` Jeff Law
2020-11-13 8:20 ` [19/23] rtlanal: Add some new helper classes Richard Sandiford
2020-12-13 17:30 ` Jeff Law
2020-12-14 16:37 ` Richard Sandiford
2020-12-14 20:02 ` Jeff Law
2020-11-13 8:21 ` [20/23] rtlanal: Add simple_regno_set Richard Sandiford
2020-11-25 20:31 ` Jeff Law
2020-12-17 0:47 ` Richard Sandiford
2021-01-04 15:28 ` Jeff Law
2020-11-13 8:22 ` [21/23] doc: Add documentation for rtl-ssa Richard Sandiford
2020-11-30 6:26 ` Jeff Law
2020-11-13 8:23 ` [PATCH 22/23] Add rtl-ssa Richard Sandiford
2020-12-16 3:31 ` Jeff Law
2020-12-17 0:33 ` Richard Sandiford
2020-12-19 20:01 ` Jeff Law
2020-11-13 8:24 ` [PATCH 23/23] fwprop: Rewrite to use RTL SSA Richard Sandiford
2020-12-16 3:52 ` Jeff Law
2020-12-17 0:34 ` Richard Sandiford
2020-11-25 19:58 ` [00/23] Make fwprop use an on-the-side RTL SSA representation Jeff Law
2020-11-26 16:03 ` Richard Sandiford
2020-11-27 15:56 ` Michael Matz
2020-11-27 16:31 ` Richard Sandiford
2020-11-30 21:13 ` Jeff Law
2020-12-01 0:03 ` Michael Matz
2020-12-01 10:15 ` Richard Sandiford
2020-12-02 0:25 ` Jeff Law
2020-11-30 6:45 ` Jeff Law
2020-11-30 14:12 ` Richard Sandiford
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