MIPS64: Fix VirtualObject field offset calculation on Big-endian architectures

src/compiler/escape-analysis.cc

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "src/compiler/escape-analysis.h"
 
 #include <limits>
 
 #include "src/base/flags.h"
 #include "src/bootstrapper.h"
@@ skipping 1323 matching lines @@
   if (IsEquivalentPhi(left, right)) {
     return true;
   }
   return false;
 }
 
 namespace {
 
 int OffsetForFieldAccess(Node* node) {
   FieldAccess access = FieldAccessOf(node->op());
+#if V8_TARGET_LITTLE_ENDIAN
   DCHECK_EQ(access.offset % kPointerSize, 0);
+#else
+  DCHECK_EQ((access.offset +
+             (1 << ElementSizeLog2Of(access.machine_type.representation()))) %
+                kPointerSize,
+            0);
+#endif
   return access.offset / kPointerSize;
 }
 
 int OffsetForElementAccess(Node* node, int index) {
   ElementAccess access = ElementAccessOf(node->op());
   DCHECK_GE(ElementSizeLog2Of(access.machine_type.representation()),
             kPointerSizeLog2);
   DCHECK_EQ(access.header_size % kPointerSize, 0);
   return access.header_size / kPointerSize + index;
 }
@@ skipping 45 matching lines @@
     if (!object->IsTracked()) return;
     int offset = OffsetForFieldAccess(node);
     if (static_cast<size_t>(offset) >= object->field_count()) return;
     Node* value = object->GetField(offset);
     if (value) {
       value = ResolveReplacement(value);
     }
     // Record that the load has this alias.
     UpdateReplacement(state, node, value);
   } else if (from->opcode() == IrOpcode::kPhi &&
              FieldAccessOf(node->op()).offset % kPointerSize == 0) {

[Michael Starzinger, 2016/11/03 14:29:55]

It seems this implies that the above predicate fails "more often" on big endian
as well. I think this predicate and the above assert should be kept in sync. Can
we hoist out the modulus computation into a {OffsetCanBePointerCoerced(int)} or
similar so that we can use it in the DCHECK above as well as here?

[ivica.bogosavljevic, 2016/11/03 15:47:30]

This is certainly true, but no tests are failing because of this. I will update
the code according to your remarks and rerun the tests.

     int offset = OffsetForFieldAccess(node);
     // Only binary phis are supported for now.
     ProcessLoadFromPhi(offset, from, node, state);
   } else {
     UpdateReplacement(state, node, nullptr);
   }
 }
 
 void EscapeAnalysis::ProcessLoadElement(Node* node) {
   DCHECK_EQ(node->opcode(), IrOpcode::kLoadElement);
@@ skipping 215 matching lines @@
     }
   }
   return false;
 }
 
 Graph* EscapeAnalysis::graph() const { return status_analysis_->graph(); }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8