From: Christoph Muellner <cmuellner@gcc.gnu.org>
To: gcc-patches@gcc.gnu.org
Cc: Jim Wilson <jimw@sifive.com>, Kito Cheng <kito.cheng@sifive.com>,
Christoph Muellner <cmuellner@gcc.gnu.org>
Subject: [PATCH v2 04/10] RISC-V: Use STORE instead of AMOSWAP for atomic stores [PR 100265]
Date: Wed, 5 May 2021 21:36:45 +0200 [thread overview]
Message-ID: <20210505193651.2075405-5-cmuellner@gcc.gnu.org> (raw)
In-Reply-To: <20210505193651.2075405-1-cmuellner@gcc.gnu.org>
Using AMOSWAP as atomic store does not allow us to do sub-word accesses.
Further, it is not consistent with our atomic_load () implementation.
The benefit of AMOSWAP is that the resulting code sequence will be
smaller (comapred to FENCE+STORE), however, this does not weight
out for the lack of sub-word accesses.
Additionally, HW implementors have claimed that an optimal
implementation AMOSWAP is slightly more expensive than FENCE+STORE.
So let's use STORE instead of AMOSWAP.
gcc/
PR 100265
* config/riscv/sync.md (atomic_store<mode>):
Remove.
---
gcc/config/riscv/sync.md | 11 -----------
1 file changed, 11 deletions(-)
diff --git a/gcc/config/riscv/sync.md b/gcc/config/riscv/sync.md
index aeeb2e854b68..efd49745a8e2 100644
--- a/gcc/config/riscv/sync.md
+++ b/gcc/config/riscv/sync.md
@@ -57,17 +57,6 @@
;; Atomic memory operations.
-;; Implement atomic stores with amoswap. Fall back to fences for atomic loads.
-(define_insn "atomic_store<mode>"
- [(set (match_operand:GPR 0 "memory_operand" "=A")
- (unspec_volatile:GPR
- [(match_operand:GPR 1 "reg_or_0_operand" "rJ")
- (match_operand:SI 2 "const_int_operand")] ;; model
- UNSPEC_ATOMIC_STORE))]
- "TARGET_ATOMIC"
- "amoswap.<amo>%A2 zero,%z1,%0"
- [(set (attr "length") (const_int 8))])
-
(define_insn "atomic_<atomic_optab><mode>"
[(set (match_operand:GPR 0 "memory_operand" "+A")
(unspec_volatile:GPR
--
2.31.1
next prev parent reply other threads:[~2021-05-05 19:37 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-05-05 19:36 [PATCH v2 00/10] [RISC-V] Atomics improvements [PR100265/PR100266] Christoph Muellner
2021-05-05 19:36 ` [PATCH v2 01/10] RISC-V: Simplify memory model code [PR 100265] Christoph Muellner
2021-05-05 19:36 ` [PATCH v2 02/10] RISC-V: Emit proper memory ordering suffixes for AMOs " Christoph Muellner
2021-05-05 19:36 ` [PATCH v2 03/10] RISC-V: Eliminate %F specifier from riscv_print_operand() " Christoph Muellner
2021-05-05 19:36 ` Christoph Muellner [this message]
2021-05-05 19:36 ` [PATCH v2 05/10] RISC-V: Emit fences according to chosen memory model " Christoph Muellner
2021-05-05 19:36 ` [PATCH v2 06/10] RISC-V: Implement atomic_{load,store} " Christoph Muellner
2021-05-05 19:36 ` [PATCH v2 07/10] RISC-V: Model INSNs for LR and SC [PR 100266] Christoph Muellner
2021-05-05 19:36 ` [PATCH v2 08/10] RISC-V: Add s.ext-consuming " Christoph Muellner
2021-05-05 19:36 ` [PATCH v2 09/10] RISC-V: Provide programmatic implementation of CAS " Christoph Muellner
2021-05-06 0:27 ` Jim Wilson
2021-05-05 19:36 ` [PATCH v2 10/10] RISC-V: Introduce predicate "riscv_sync_memory_operand" " Christoph Muellner
2022-10-11 19:06 ` [PATCH v2 00/10] [RISC-V] Atomics improvements [PR100265/PR100266] Vineet Gupta
2022-10-11 19:31 ` Palmer Dabbelt
2022-10-11 20:46 ` Christoph Müllner
2022-10-11 23:31 ` Vineet Gupta
2022-10-12 0:15 ` Palmer Dabbelt
2022-10-12 8:03 ` Christoph Müllner
2022-10-13 23:11 ` Jeff Law
2022-10-12 17:16 ` Andrea Parri
2022-10-20 19:01 ` Andrea Parri
2022-10-29 5:02 ` Jeff Law
2022-10-13 23:04 ` Jeff Law
2022-10-13 22:39 ` Jeff Law
2022-10-13 23:14 ` Palmer Dabbelt
2022-10-14 11:03 ` Christoph Müllner
2022-10-14 20:39 ` Jeff Law
2022-10-14 21:57 ` Palmer Dabbelt
2022-10-15 0:31 ` Palmer Dabbelt
2022-10-14 0:14 ` Vineet Gupta
2022-10-11 23:14 ` Jeff Law
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