From: Patrick O'Neill <patrick@rivosinc.com>
To: Jeff Law <jeffreyalaw@gmail.com>, gcc-patches@gcc.gnu.org
Cc: palmer@rivosinc.com, kito.cheng@gmail.com, david.abd@gmail.com
Subject: Re: [PATCH v5] RISCV: Inline subword atomic ops
Date: Tue, 18 Apr 2023 13:48:13 -0700 [thread overview]
Message-ID: <c8ee3d1b-d511-8d12-6be2-39cfa44c7649@rivosinc.com> (raw)
In-Reply-To: <dcab135e-dc8a-f610-dd0b-c38bab6e292b@gmail.com>
On 4/18/23 09:59, Jeff Law wrote:
> On 4/18/23 08:28, Patrick O'Neill wrote:
> ...
>> + rtx addr = force_reg (Pmode, XEXP (mem, 0));
>> +
>> + rtx aligned_addr = gen_reg_rtx (Pmode);
>> + emit_move_insn (aligned_addr, gen_rtx_AND (Pmode, addr,
>> + gen_int_mode (-4, Pmode)));
> So rather than -4 as a magic number, GET_MODE_MASK would be better.
> That may result in needing to rewrap this code. I'd bring the
> gen_rtx_AND down on a new line, aligned with aligned_addr.
IIUC GET_MODE_MASK generates masks like 0xFF for QI (for example). It
doesn't have the granularity to generate 0x3 (which we can NOT to get
-4). I searched the GCC internals docs but couldn't find a function that
does address alignment masks.
> Presumably using SImode is intentional here rather than wanting to use
> word_mode which would be SImode for rv32 and DImode for rv64? I'm
> going to work based on that assumption, but if it isn't there's more
> work to do to generalize this code.
It's been a year but IIRC it was just simpler to implement (and to me it
didn't make sense to use 64 bits for a subword op).
Is there a benefit in using 64 bit instructions when computing subwords?
>> +
>> +(define_expand "atomic_fetch_nand<mode>"
>> + [(set (match_operand:SHORT 0 "register_operand" "=&r")
>> + (match_operand:SHORT 1 "memory_operand" "+A"))
>> + (set (match_dup 1)
>> + (unspec_volatile:SHORT
>> + [(not:SHORT (and:SHORT (match_dup 1)
>> + (match_operand:SHORT 2 "reg_or_0_operand" "rJ")))
>> + (match_operand:SI 3 "const_int_operand")] ;; model
>> + UNSPEC_SYNC_OLD_OP_SUBWORD))]
>> + "TARGET_ATOMIC && TARGET_INLINE_SUBWORD_ATOMIC"
> Just a note, constraints aren't necessary for a define_expand. They
> don't hurt anything though. They do document expectations, but then
> you have to maintain them over time. I'm OK leaving them, mostly
> wanted to make sure you're aware they aren't strictly necessary for a
> define_expand.
I wasn't aware, thanks for pointing it out! - you're referring to the
"TARGET_ATOMIC && TARGET_INLINE_SUBWORD_ATOMIC", (not the register
constraints) right?
> ...
Thanks for reviewing!
Patrick
next prev parent reply other threads:[~2023-04-18 20:48 UTC|newest]
Thread overview: 24+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-21 21:58 [PATCH v4] RISC-V: Add support for inlining subword atomic operations Palmer Dabbelt
2022-09-02 10:08 ` Kito Cheng
2022-10-28 16:55 ` David Abdurachmanov
2022-11-16 3:53 ` Jeff Law
2023-04-18 14:28 ` [PATCH v5] RISCV: Inline subword atomic ops Patrick O'Neill
2023-04-18 15:06 ` Andreas Schwab
2023-04-18 16:39 ` [PATCH v6] " Patrick O'Neill
2023-04-18 20:17 ` Palmer Dabbelt
2023-04-18 21:41 ` [PATCH v7] " Patrick O'Neill
2023-04-24 17:20 ` Patrick O'Neill
2023-04-25 5:52 ` Jeff Law
2023-04-25 15:20 ` Patrick O'Neill
2023-04-26 2:27 ` Jeff Law
2023-04-26 17:01 ` [committed] " Patrick O'Neill
2023-05-02 20:34 ` Patrick O'Neill
2023-05-03 6:32 ` Jeff Law
2023-05-03 9:49 ` Richard Biener
2023-05-03 14:14 ` Palmer Dabbelt
2023-05-03 15:13 ` Jeff Law
2023-05-03 15:33 ` Palmer Dabbelt
2023-05-03 16:13 ` Patrick O'Neill
2023-04-18 16:59 ` [PATCH v5] " Jeff Law
2023-04-18 20:48 ` Patrick O'Neill [this message]
2023-04-18 21:04 ` Jeff Law
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=c8ee3d1b-d511-8d12-6be2-39cfa44c7649@rivosinc.com \
--to=patrick@rivosinc.com \
--cc=david.abd@gmail.com \
--cc=gcc-patches@gcc.gnu.org \
--cc=jeffreyalaw@gmail.com \
--cc=kito.cheng@gmail.com \
--cc=palmer@rivosinc.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).