[Atomics] code stubs for atomic operations

src/compiler/code-stub-assembler.cc

Index: src/compiler/code-stub-assembler.cc
diff --git a/src/compiler/code-stub-assembler.cc b/src/compiler/code-stub-assembler.cc
index 702b12ad127776cfd0b59cd6ecaf2e5a1e74b580..6bc9c5a1ed46163a1f32c0e18a991d1e2dc2a46e 100644
--- a/src/compiler/code-stub-assembler.cc
+++ b/src/compiler/code-stub-assembler.cc
@@ -78,11 +78,51 @@ Node* CodeStubAssembler::BooleanConstant(bool value) {
 }
 
 
+Node* CodeStubAssembler::Load(MachineType type, Node* base) {
+  return raw_assembler_->Load(type, base);
+}
+
+
+Node* CodeStubAssembler::Load(MachineType type, Node* base, Node* index) {
+  return raw_assembler_->Load(type, base, index);
+}
+
+
 Node* CodeStubAssembler::Parameter(int value) {
   return raw_assembler_->Parameter(value);
 }
 
 
+Node* CodeStubAssembler::StackArg(Node* num_args, int value) {
+  // N = num_args
+  // Arg 0:   [sp + (N + 1) * kPointerSize]
+  // Arg 1:   [sp + N * kPointerSize]
+  // ...
+  // Arg N-1: [sp + kPointerSize]
+  RawMachineAssembler* rma = raw_assembler_.get();
+  return rma->Load(
+      MachineType::AnyTagged(), rma->LoadStackPointer(),
+      rma->Word32Shl(rma->Int32Sub(num_args, rma->Int32Constant(value - 1)),
+                     rma->Int32Constant(kPointerSizeLog2)));
+}
+
+
+Node* CodeStubAssembler::StackArgOrUndefined(Node* num_args, int value) {
+  RawMachineAssembler* rma = raw_assembler_.get();
+  RawMachineLabel ok, not_ok, done;
+  rma->Branch(rma->Int32LessThan(rma->Int32Constant(value - 1), num_args), &ok,
+              &not_ok);
+  rma->Bind(&ok);
+  Node* arg = StackArg(num_args, value);
+  rma->Goto(&done);
+  rma->Bind(&not_ok);
+  Node* undefined = rma->UndefinedConstant();
+  rma->Goto(&done);
+  rma->Bind(&done);
+  return rma->Phi(MachineRepresentation::kTagged, arg, undefined);
+}
+
+
 void CodeStubAssembler::Return(Node* value) {
   return raw_assembler_->Return(value);
 }