[PATCH v3 5/9] RISC-V: Emit fences according to chosen memory model [PR 100265]

[Christoph Muellner via Gcc-patches]

mem_thread_fence gets the desired memory model as operand.
Let's emit fences according to this value (as defined in section
    "Code Porting and Mapping Guidelines" of the unpriv spec).

    gcc/
        PR 100265
        * config/riscv/sync.md (mem_thread_fence):
          Emit fences according to given operand.
        * config/riscv/sync.md (mem_fence):
          Add INSNs for different fence flavours.
        * config/riscv/sync.md (mem_thread_fence_1):
          Remove.
---
 gcc/config/riscv/sync.md | 41 +++++++++++++++++++++++++++-------------
 1 file changed, 28 insertions(+), 13 deletions(-)

diff --git a/gcc/config/riscv/sync.md b/gcc/config/riscv/sync.md
index 86f4cef6af9..ae80f94f2e0 100644
--- a/gcc/config/riscv/sync.md
+++ b/gcc/config/riscv/sync.md
@@ -34,26 +34,41 @@ (define_code_attr atomic_optab
 ;; Memory barriers.
 
 (define_expand "mem_thread_fence"
-  [(match_operand:SI 0 "const_int_operand" "")] ;; model
+  [(match_operand:SI 0 "const_int_operand")] ;; model
   ""
 {
-  if (INTVAL (operands[0]) != MEMMODEL_RELAXED)
-    {
-      rtx mem = gen_rtx_MEM (BLKmode, gen_rtx_SCRATCH (Pmode));
-      MEM_VOLATILE_P (mem) = 1;
-      emit_insn (gen_mem_thread_fence_1 (mem, operands[0]));
-    }
+  enum memmodel model = memmodel_from_int (INTVAL (operands[0]));
+  if (!(is_mm_relaxed (model)))
+      emit_insn (gen_mem_fence (operands[0]));
   DONE;
 })
 
-;; Until the RISC-V memory model (hence its mapping from C++) is finalized,
-;; conservatively emit a full FENCE.
-(define_insn "mem_thread_fence_1"
+(define_expand "mem_fence"
+  [(set (match_dup 1)
+       (unspec:BLK [(match_dup 1) (match_operand:SI 0 "const_int_operand")]
+                   UNSPEC_MEMORY_BARRIER))]
+  ""
+{
+  operands[1] = gen_rtx_MEM (BLKmode, gen_rtx_SCRATCH (Pmode));
+  MEM_VOLATILE_P (operands[1]) = 1;
+})
+
+(define_insn "*mem_fence"
   [(set (match_operand:BLK 0 "" "")
-       (unspec:BLK [(match_dup 0)] UNSPEC_MEMORY_BARRIER))
-   (match_operand:SI 1 "const_int_operand" "")] ;; model
+       (unspec:BLK [(match_dup 0) (match_operand:SI 1 "const_int_operand")]
+                   UNSPEC_MEMORY_BARRIER))]
   ""
-  "fence\tiorw,iorw")
+{
+  enum memmodel model = memmodel_from_int (INTVAL (operands[1]));
+  if (is_mm_consume (model) || is_mm_acquire (model))
+    return "fence\tr, rw";
+  else if (is_mm_release (model))
+    return "fence\trw, w";
+  else if (is_mm_acq_rel (model))
+    return "fence.tso";
+  else
+    return "fence\trw, rw";
+})
 
 ;; Atomic memory operations.
 
-- 
2.35.3