[llvm] [BPF] Select atomic_fetch_add for i64 monotonic atomicrmw with used result (PR #210371)

[Gustas Janušonis via llvm-commits]

https://github.com/LeGusto created https://github.com/llvm/llvm-project/pull/210371

A monotonic atomicrmw add on i64 for BPF would always convert to a non-FETCH instruction, even if the return value is used. Fixed by splitting the monotonic i64 add mapping depending on the outcome of binop_no_use / binop_has_use, which was already being used for and/or/xor i64 ops.

Fixes #210280

Assisted-by: Claude (Anthropic)

>From 6a2c3189ce2a7d4fcd9b27deb104f18f7774e480 Mon Sep 17 00:00:00 2001
From: LeGusto <janusonis.gustas at gmail.com>
Date: Fri, 17 Jul 2026 19:41:59 +0300
Subject: [PATCH] [BPF] Select atomic_fetch_add for i64 monotonic atomicrmw
 with used result

A monotonic atomicrmw add on i64 for BPF would always convert to a non-FETCH instruction, even if the return value is used. Fixed by splitting the monotonic i64 add mapping depending on the outcome of binop_no_use / binop_has_use, which was already being used for and/or/xor i64 ops.

Fixes #210280

Assisted-by: Claude (Anthropic)
---
 llvm/lib/Target/BPF/BPFInstrInfo.td           | 23 +++++++++++--------
 llvm/test/CodeGen/BPF/atomics_mem_order_v3.ll |  2 +-
 2 files changed, 14 insertions(+), 11 deletions(-)

diff --git a/llvm/lib/Target/BPF/BPFInstrInfo.td b/llvm/lib/Target/BPF/BPFInstrInfo.td
index c86b45ee93cc6..9f821954c254b 100644
--- a/llvm/lib/Target/BPF/BPFInstrInfo.td
+++ b/llvm/lib/Target/BPF/BPFInstrInfo.td
@@ -1047,16 +1047,6 @@ let Predicates = [BPFHasALU32] in {
                 ] in {
       def : Pat<(P[0] ADDRri:$addr, GPR32:$val), (P[1]  ADDRri:$addr, (NEG_32 GPR32:$val))>;
     }
-
-    foreach P = [// add
-                 [atomic_load_add_i64_monotonic,  XADDD],
-                 [atomic_load_add_i64_acquire,   XFADDD],
-                 [atomic_load_add_i64_release,   XFADDD],
-                 [atomic_load_add_i64_acq_rel,   XFADDD],
-                 [atomic_load_add_i64_seq_cst,   XFADDD],
-                ] in {
-      def : Pat<(P[0] ADDRri:$addr, GPR:$val), (P[1]  ADDRri:$addr, GPR:$val)>;
-    }
 }
 
 foreach P = [[atomic_load_sub_i64_monotonic,  XADDD],
@@ -1086,6 +1076,19 @@ def atomic_load_ # op # _i64_monotonic_hu:
     binop_has_use<!cast<SDPatternOperator>("atomic_load_"#op# _i64_monotonic)>;
 }
 
+let Predicates = [BPFHasALU32] in {
+  foreach P = [// add
+              [atomic_load_add_i64_monotonic_nu, XADDD],
+              [atomic_load_add_i64_monotonic_hu, XFADDD],
+              [atomic_load_add_i64_acquire,   XFADDD],
+              [atomic_load_add_i64_release,   XFADDD],
+              [atomic_load_add_i64_acq_rel,   XFADDD],
+              [atomic_load_add_i64_seq_cst,   XFADDD],
+            ] in {
+    def : Pat<(P[0] ADDRri:$addr, GPR:$val), (P[1]  ADDRri:$addr, GPR:$val)>;
+  }
+}
+
 foreach P = [// and
              [atomic_load_and_i64_monotonic_nu, XANDD],
              [atomic_load_and_i64_monotonic_hu, XFANDD],
diff --git a/llvm/test/CodeGen/BPF/atomics_mem_order_v3.ll b/llvm/test/CodeGen/BPF/atomics_mem_order_v3.ll
index 76475ac124986..ed6cd7f215d37 100644
--- a/llvm/test/CodeGen/BPF/atomics_mem_order_v3.ll
+++ b/llvm/test/CodeGen/BPF/atomics_mem_order_v3.ll
@@ -261,7 +261,7 @@ define dso_local i64 @test_fetch_add_64_ret(ptr nocapture noundef %i) local_unna
 ; CHECK-NEXT:  # %bb.0: # %entry
 ; CHECK-NEXT:    r2 = 10
 ; CHECK-NEXT:    r3 = 10
-; CHECK-NEXT:    lock *(u64 *)(r1 + 0) += r3
+; CHECK-NEXT:    r3 = atomic_fetch_add((u64 *)(r1 + 0), r3)
 ; CHECK-NEXT:    r0 = 10
 ; CHECK-NEXT:    r0 = atomic_fetch_add((u64 *)(r1 + 0), r0)
 ; CHECK-NEXT:    r0 += r3