[PATCH v2 08/10] RISC-V: Add s.ext-consuming INSNs for LR and SC [PR 100266]

[Christoph Muellner <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 edff6520b87e..49b860da8ef0 100644
--- a/gcc/config/riscv/sync.md
+++ b/gcc/config/riscv/sync.md
@@ -125,6 +125,21 @@
   "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 @@
   "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
-- 
2.31.1