[PATCH v3 6/9] RISC-V: Implement atomic_{load,store} [PR 100265]

[Christoph Muellner via Gcc-patches]

A recent commit introduced a mechanism to emit proper fences
for RISC-V. Additionally, we already have emit_move_insn ().
Let's reuse this code and provide atomic_load<mode> and
atomic_store<mode> for RISC-V (as defined in section
"Code Porting and Mapping Guidelines" of the unpriv spec).
Note, that this works also for sub-word atomics.

    gcc/
        PR 100265
        * config/riscv/sync.md (atomic_load<mode>): New.
        * config/riscv/sync.md (atomic_store<mode>): New.
---
 gcc/config/riscv/sync.md | 41 ++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

diff --git a/gcc/config/riscv/sync.md b/gcc/config/riscv/sync.md
index ae80f94f2e0..9eb0dde9086 100644
--- a/gcc/config/riscv/sync.md
+++ b/gcc/config/riscv/sync.md
@@ -23,6 +23,7 @@ (define_c_enum "unspec" [
   UNSPEC_COMPARE_AND_SWAP
   UNSPEC_SYNC_OLD_OP
   UNSPEC_SYNC_EXCHANGE
+  UNSPEC_ATOMIC_LOAD
   UNSPEC_ATOMIC_STORE
   UNSPEC_MEMORY_BARRIER
 ])
@@ -72,6 +73,46 @@ (define_insn "*mem_fence"
 
 ;; Atomic memory operations.
 
+(define_expand "atomic_load<mode>"
+  [(set (match_operand:ANYI 0 "register_operand" "=r")
+    (unspec_volatile:ANYI
+      [(match_operand:ANYI 1 "memory_operand" "A")
+       (match_operand:SI 2 "const_int_operand")]      ;; model
+      UNSPEC_ATOMIC_LOAD))]
+  ""
+  {
+    rtx target = operands[0];
+    rtx mem = operands[1];
+    enum memmodel model = memmodel_from_int (INTVAL (operands[2]));
+
+    if (is_mm_seq_cst (model))
+      emit_insn (gen_mem_fence (GEN_INT (MEMMODEL_SEQ_CST)));
+    emit_move_insn (target, mem);
+    if (is_mm_acquire (model) || is_mm_seq_cst (model))
+      emit_insn (gen_mem_fence (GEN_INT (MEMMODEL_ACQUIRE)));
+
+    DONE;
+})
+
+(define_expand "atomic_store<mode>"
+  [(set (match_operand:ANYI 0 "memory_operand" "=A")
+    (unspec_volatile:ANYI
+      [(match_operand:ANYI 1 "reg_or_0_operand" "rJ")
+       (match_operand:SI 2 "const_int_operand")]      ;; model
+      UNSPEC_ATOMIC_STORE))]
+  ""
+  {
+    rtx mem = operands[0];
+    rtx val = operands[1];
+    enum memmodel model = memmodel_from_int (INTVAL (operands[2]));
+
+    if (is_mm_release (model) || is_mm_seq_cst (model))
+      emit_insn (gen_mem_fence (GEN_INT (MEMMODEL_RELEASE)));
+    emit_move_insn (mem, val);
+
+    DONE;
+})
+
 (define_insn "atomic_<atomic_optab><mode>"
   [(set (match_operand:GPR 0 "memory_operand" "+A")
        (unspec_volatile:GPR
-- 
2.35.3