From: Christoph Muellner <cmuellner@gcc.gnu.org>
To: gcc-patches@gcc.gnu.org, Kito Cheng <kito.cheng@sifive.com>,
Jim Wilson <jim.wilson.gcc@gmail.com>,
Andrew Waterman <andrew@sifive.com>,
Philipp Tomsich <philipp.tomsich@vrull.eu>,
Christoph Muellner <christoph.muellner@vrull.eu>,
Aaron Durbin <adurbin@rivosinc.com>,
Patrick O'Neill <patrick@rivosinc.com>,
Vineet Gupta <vineetg@rivosinc.com>
Subject: [PATCH v3 8/9] RISC-V: Add s.ext-consuming INSNs for LR and SC [PR 100266]
Date: Fri, 27 May 2022 08:07:22 +0200 [thread overview]
Message-ID: <20220527060723.235095-9-cmuellner@gcc.gnu.org> (raw)
In-Reply-To: <20220527060723.235095-1-cmuellner@gcc.gnu.org>
The current model of the LR and SC INSNs requires a sign-extension
to use the generated SImode value for conditional branches, which
only operate on XLEN registers.
However, the sign-extension is actually not required in both cases,
therefore this patch introduces additional INSNs that consume
the sign-extension.
Rationale:
The sign-extension of the loaded value of a LR.W is specified as
sign-extended. Therefore, a sign-extension is not required.
The sign-extension of the success value a SC.W is specified as
non-zero. As sign-extended non-zero value remains non-zero,
therefore the sign-extension is not required.
gcc/
PR 100266
* config/riscv/sync.md (riscv_load_reserved): New.
* config/riscv/sync.md (riscv_store_conditional): New.
---
gcc/config/riscv/sync.md | 34 ++++++++++++++++++++++++++++++++++
1 file changed, 34 insertions(+)
diff --git a/gcc/config/riscv/sync.md b/gcc/config/riscv/sync.md
index 3494683947e..66548bf891b 100644
--- a/gcc/config/riscv/sync.md
+++ b/gcc/config/riscv/sync.md
@@ -125,6 +125,21 @@ (define_insn "@riscv_load_reserved<mode>"
"lr.<amo>%A2 %0, %1"
)
+;; This pattern allows to consume a sign-extension of the loaded value.
+;; This is legal, because the specification of LR.W defines the loaded
+;; value to be sign-extended.
+
+(define_insn "riscv_load_reserved"
+ [(set (match_operand:DI 0 "register_operand" "=r")
+ (sign_extend:DI
+ (unspec_volatile:SI
+ [(match_operand:SI 1 "memory_operand" "A")
+ (match_operand:SI 2 "const_int_operand")] ;; model
+ UNSPEC_LOAD_RESERVED)))]
+ "TARGET_ATOMIC && TARGET_64BIT"
+ "lr.w%A2 %0, %1"
+)
+
(define_insn "@riscv_store_conditional<mode>"
[(set (match_operand:GPR 0 "register_operand" "=&r")
(unspec_volatile:GPR [(const_int 0)] UNSPEC_STORE_CONDITIONAL))
@@ -137,6 +152,25 @@ (define_insn "@riscv_store_conditional<mode>"
"sc.<amo>%A3 %0, %z2, %1"
)
+;; This pattern allows to consume a sign-extension of the success
+;; value of SC.W, which can then be used for instructions which
+;; require values of XLEN-size (e.g. conditional branches).
+;; This is legal, because any non-zero value remains non-zero
+;; after sign-extension.
+
+(define_insn "riscv_store_conditional"
+ [(set (match_operand:DI 0 "register_operand" "=&r")
+ (sign_extend:DI
+ (unspec_volatile:SI [(const_int 0)] UNSPEC_STORE_CONDITIONAL)))
+ (set (match_operand:SI 1 "memory_operand" "=A")
+ (unspec_volatile:SI
+ [(match_operand:SI 2 "reg_or_0_operand" "rJ")
+ (match_operand:SI 3 "const_int_operand")] ;; model
+ UNSPEC_STORE_CONDITIONAL))]
+ "TARGET_ATOMIC && TARGET_64BIT"
+ "sc.w%A3 %0, %z2, %1"
+)
+
(define_insn "atomic_<atomic_optab><mode>"
[(set (match_operand:GPR 0 "memory_operand" "+A")
(unspec_volatile:GPR
--
2.35.3
next prev parent reply other threads:[~2022-05-27 6:07 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-27 6:07 [PATCH v3 0/9] [RISC-V] Atomics improvements Christoph Muellner
2022-05-27 6:07 ` [PATCH v3 1/9] RISC-V: Simplify memory model code [PR 100265] Christoph Muellner
2022-05-27 6:07 ` [PATCH v3 2/9] RISC-V: Emit proper memory ordering suffixes for AMOs " Christoph Muellner
2022-05-27 6:07 ` [PATCH v3 3/9] RISC-V: Eliminate %F specifier from riscv_print_operand() " Christoph Muellner
2022-05-27 6:07 ` [PATCH v3 4/9] RISC-V: Use STORE instead of AMOSWAP for atomic stores " Christoph Muellner
2022-05-27 6:07 ` [PATCH v3 5/9] RISC-V: Emit fences according to chosen memory model " Christoph Muellner
2022-05-27 6:07 ` [PATCH v3 6/9] RISC-V: Implement atomic_{load,store} " Christoph Muellner
2022-05-27 6:07 ` [PATCH v3 7/9] RISC-V: Model INSNs for LR and SC [PR 100266] Christoph Muellner
2022-05-27 6:07 ` Christoph Muellner [this message]
2022-05-27 6:07 ` [PATCH v3 9/9] RISC-V: Introduce predicate "riscv_sync_memory_operand" " Christoph Muellner
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