[Atomics] Remove Atomics code stubs; use TF ops

src/compiler/arm/code-generator-arm.cc

Index: src/compiler/arm/code-generator-arm.cc
diff --git a/src/compiler/arm/code-generator-arm.cc b/src/compiler/arm/code-generator-arm.cc
index ecbee760b9ee8470c0a85fd3d5290268c2d6b6a1..9ac862c6175104054676e95fc1075b053a745065 100644
--- a/src/compiler/arm/code-generator-arm.cc
+++ b/src/compiler/arm/code-generator-arm.cc
@@ -388,6 +388,13 @@ Condition FlagsConditionToCondition(FlagsCondition condition) {
     DCHECK_EQ(LeaveCC, i.OutputSBit());           \
   } while (0)
 
+#define ASSEMBLE_ATOMIC_LOAD_INTEGER(asm_instr)                       \
+  do {                                                                \
+    __ asm_instr(i.OutputRegister(),                                  \
+                 MemOperand(i.InputRegister(0), i.InputRegister(1))); \
+    __ dmb(ISH);                                                      \
+  } while (0)
+
 void CodeGenerator::AssembleDeconstructFrame() {
   __ LeaveFrame(StackFrame::MANUAL);
 }
@@ -1250,6 +1257,22 @@ void CodeGenerator::AssembleArchInstruction(Instruction* instr) {
     case kCheckedStoreWord64:
       UNREACHABLE();  // currently unsupported checked int64 load/store.
       break;
+
+    case kAtomicLoadInt8:
+      ASSEMBLE_ATOMIC_LOAD_INTEGER(ldrsb);
+      break;
+    case kAtomicLoadUint8:
+      ASSEMBLE_ATOMIC_LOAD_INTEGER(ldrb);
+      break;
+    case kAtomicLoadInt16:
+      ASSEMBLE_ATOMIC_LOAD_INTEGER(ldrsh);
+      break;
+    case kAtomicLoadUint16:
+      ASSEMBLE_ATOMIC_LOAD_INTEGER(ldrh);
+      break;
+    case kAtomicLoadWord32:
+      ASSEMBLE_ATOMIC_LOAD_INTEGER(ldr);
+      break;
   }
 }  // NOLINT(readability/fn_size)