From 89c8638deb9ccb1f1e1a90f18f2e6b984b70fbe8 Mon Sep 17 00:00:00 2001
From: Xi Ruoyao <xry111@xry111.site>
Date: Sat, 1 Mar 2025 11:46:51 +0800
Subject: LoongArch: Implement 16-byte atomic load with LSX

If the vector is naturally aligned, it cannot cross cache lines so the
LSX load is guaranteed to be atomic.  Thus we can use LSX to do the
lock-free atomic load, instead of using a lock.

gcc/ChangeLog:

	* config/loongarch/sync.md (atomic_loadti_lsx): New define_insn.
	(atomic_loadti): New define_expand.
---
 gcc/config/loongarch/sync.md | 41 +++++++++++++++++++++++++++++++++++++++++
 1 file changed, 41 insertions(+)

(limited to 'gcc')

diff --git a/gcc/config/loongarch/sync.md b/gcc/config/loongarch/sync.md
index f1ab132..b0d3c85 100644
--- a/gcc/config/loongarch/sync.md
+++ b/gcc/config/loongarch/sync.md
@@ -135,6 +135,47 @@
 }
   [(set (attr "length") (const_int 12))])
 
+(define_insn "atomic_loadti_lsx"
+  [(set (match_operand:V2DI 0 "register_operand" "=f")
+	(unspec_volatile:V2DI
+          [(match_operand:TI 1 "memory_operand" "m")
+	   (match_operand:SI 2 "const_int_operand")] ;; model
+	  UNSPEC_ATOMIC_LOAD))]
+  "ISA_HAS_LSX && TARGET_64BIT"
+{
+  enum memmodel model = memmodel_base (INTVAL (operands[2]));
+
+  switch (model)
+    {
+    case MEMMODEL_SEQ_CST:
+      output_asm_insn ("dbar\t0x11", operands);
+      /* fall through */
+    case MEMMODEL_ACQUIRE:
+    case MEMMODEL_RELAXED:
+      return "vld\t%w0,%1\\n\\t%G2";
+
+    default:
+      gcc_unreachable ();
+    }
+}
+  [(set (attr "length") (const_int 12))])
+
+(define_expand "atomic_loadti"
+  [(match_operand:TI 0 "register_operand" "=r")
+   (match_operand:TI 1 "memory_operand"   "m")
+   (match_operand:SI 2 "const_int_operand")]
+  "ISA_HAS_LSX && TARGET_64BIT"
+{
+  rtx vr = gen_reg_rtx (V2DImode);
+
+  emit_insn (gen_atomic_loadti_lsx (vr, operands[1], operands[2]));
+  for (int i = 0; i < 2; i++)
+    emit_insn (
+      gen_lsx_vpickve2gr_d (loongarch_subword (operands[0], i), vr,
+			    GEN_INT (i)));
+  DONE;
+})
+
 ;; Implement atomic stores with amoswap.  Fall back to fences for atomic loads.
 (define_insn "atomic_store<mode>"
   [(set (match_operand:QHWD 0 "memory_operand" "=m")
-- 
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