WIP Atomics

src/compiler/js-builtin-reducer.cc

Index: src/compiler/js-builtin-reducer.cc
diff --git a/src/compiler/js-builtin-reducer.cc b/src/compiler/js-builtin-reducer.cc
index 12b0e2f6cc97d38eb8986ec3f8a19b923ba008a3..9fe7d40a33b9c691df198e65492d01bfdc3b691b 100644
--- a/src/compiler/js-builtin-reducer.cc
+++ b/src/compiler/js-builtin-reducer.cc
@@ -2,6 +2,7 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+#include "src/compiler/access-builder.h"
 #include "src/compiler/diamond.h"
 #include "src/compiler/js-builtin-reducer.h"
 #include "src/compiler/js-graph.h"
@@ -152,6 +153,85 @@ Reduction JSBuiltinReducer::ReduceMathFround(Node* node) {
 }
 
 
+Reduction JSBuiltinReducer::ReduceAtomicsLoad(Node* node) {
+  JSCallReduction r(node);
+  if (r.GetJSCallArity() == 2) {
+    // TODO(binji): copy-pasta from JSTypedLowering::ReduceJSLoadProperty
+    Node* base = r.GetJSCallInput(0);
+    Node* index = r.GetJSCallInput(1);
+    Type* index_type = NodeProperties::GetBounds(index).upper;
+    HeapObjectMatcher<Object> mbase(base);
+    if (mbase.HasValue() && mbase.Value().handle()->IsJSTypedArray()) {
+      Handle<JSTypedArray> array =
+          Handle<JSTypedArray>::cast(mbase.Value().handle());
+      if (array->is_shared()) {
+        bool const is_external = true;
+        ElementAccess const access =
+            AccessBuilder::ForTypedArrayElement(array->type(), is_external);
+        size_t const k = ElementSizeLog2Of(access.machine_type);
+        double const byte_length = array->byte_length()->Number();
+        DCHECK(IsExternalArrayElementsKind(array->map()->elements_kind()));
+        Handle<ExternalArray> elements =
+            Handle<ExternalArray>::cast(handle(array->elements()));
+        Node* buffer = jsgraph()->PointerConstant(elements->external_pointer());
+        Node* effect = NodeProperties::GetEffectInput(node);
+        Node* control = NodeProperties::GetControlInput(node);
+
+        // TODO(binji): reuse from js-typed-lowering.cc?
+        Type* shifted_int32_range = Type::Range(
+            kMinInt / (1 << k), kMaxInt / (1 << k), graph()->zone());
+        if (index_type->Is(shifted_int32_range) && byte_length <= kMaxInt) {
+          // Check if we can avoid the bounds check.
+          if (index_type->Min() >= 0 &&
+              index_type->Max() < array->length()->Number()) {
+            Node* load =
+                graph()->NewNode(simplified()->LoadElementAtomic(access),
+                                 buffer, index, effect, control);
+            NodeProperties::ReplaceWithValue(node, load, load);
+            return Changed(node);
+          }
+        }
+
+        // Copy-pasta from SimplifiedLowering::DoLoadBuffer
+        Node* offset =
+            graph()->NewNode(machine()->Word32Shl(), index,
+                             jsgraph()->Int32Constant(static_cast<int>(k)));
+        Node* length = jsgraph()->Constant(byte_length);
+        Node* check =
+            graph()->NewNode(machine()->Uint32LessThan(), offset, length);
+        Node* branch = graph()->NewNode(common()->Branch(BranchHint::kTrue),
+                                        check, control);
+
+        Node* if_true = graph()->NewNode(common()->IfTrue(), branch);
+        Node* etrue = graph()->NewNode(simplified()->LoadElementAtomic(access),
+                                       buffer, index, effect, if_true);
+        Node* vtrue = etrue;
+
+        Node* if_false = graph()->NewNode(common()->IfFalse(), branch);
+        Node* efalse = effect;
+        Node* vfalse = jsgraph()->UndefinedConstant();
+        Node* merge = graph()->NewNode(common()->Merge(2), if_true, if_false);
+        Node* ephi =
+            graph()->NewNode(common()->EffectPhi(2), etrue, efalse, merge);
+
+        // Replace effect uses of {node} with the {ephi}.
+        NodeProperties::ReplaceWithValue(node, node, ephi);
+
+        // Turn the {node} into a Phi.
+        node->set_op(common()->Phi(kMachAnyTagged, 2));
+        node->ReplaceInput(0, vtrue);
+        node->ReplaceInput(1, vfalse);
+        node->ReplaceInput(2, merge);
+        node->TrimInputCount(3);
+        return Changed(node);
+      }
+    }
+  }
+
+  return NoChange();
+}
+
+
 Reduction JSBuiltinReducer::Reduce(Node* node) {
   JSCallReduction r(node);
 
@@ -164,6 +244,8 @@ Reduction JSBuiltinReducer::Reduce(Node* node) {
       return ReplaceWithPureReduction(node, ReduceMathImul(node));
     case kMathFround:
       return ReplaceWithPureReduction(node, ReduceMathFround(node));
+    case kAtomicsLoad:
+      return ReduceAtomicsLoad(node);
     default:
       break;
   }