From: Jeff Law <law@redhat.com>
To: gcc-patches@gcc.gnu.org, richard.sandiford@arm.com
Subject: Re: [07/23] Add a class that multiplexes two pointer types
Date: Sun, 29 Nov 2020 18:28:24 -0700 [thread overview]
Message-ID: <12a11043-2bf2-8cf5-8e21-60fcd4eab031@redhat.com> (raw)
In-Reply-To: <mptft4wgkm3.fsf@arm.com>
On 11/26/20 9:15 AM, Richard Sandiford wrote:
> Jeff Law <law@redhat.com> writes:
>> On 11/13/20 1:14 AM, Richard Sandiford via Gcc-patches wrote:
>>> This patch adds a pointer_mux<T1, T2> class that provides similar
>>> functionality to:
>>>
>>> union { T1 *a; T2 *b; };
>>> ...
>>> bool is_b_rather_than_a;
>>>
>>> except that the is_b_rather_than_a tag is stored in the low bit
>>> of the pointer. See the comments in the patch for a comparison
>>> between the two approaches and why this one can be more efficient.
>>>
>>> I've tried to microoptimise the class a fair bit, since a later
>>> patch uses it extensively in order to keep the sizes of data
>>> structures down.
>>>
>>> gcc/
>>> * mux-utils.h: New file.
>> Do we have any potentially bootstrappable targets where we can't
>> guarantee pointer alignment of at least 16 bits? I see what look like
>> suitable asserts, and presumably if we trigger them, then we're going to
>> need to rethink this and fall back to a separate bit?
> Like you say, the asserts should trap that if it happens. I think the
> fix would be to increase the alignment of the data types involved (which
> we can now do in a standard way -- probably wouldn't have been possible
> before the switch to C++11, at least not without using extensions).
Yea, I keep forgetting about some of the facilities C++ can provide us now.
Seems like we've got a good backup plan. So this is OK by me.
jeff
next prev parent reply other threads:[~2020-11-30 1:28 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 [this message]
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
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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