Ensure hole checks take place in switch statement scopes

src/full-codegen/mips/full-codegen-mips.cc

 // Copyright 2012 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.
 
 #if V8_TARGET_ARCH_MIPS
 
 // Note on Mips implementation:
 //
 // The result_register() for mips is the 'v0' register, which is defined
 // by the ABI to contain function return values. However, the first
@@ skipping 1433 matching lines @@
       context()->Plug(v0);
       break;
     }
 
     case VariableLocation::PARAMETER:
     case VariableLocation::LOCAL:
     case VariableLocation::CONTEXT: {
       DCHECK_EQ(NOT_INSIDE_TYPEOF, typeof_mode);
       Comment cmnt(masm_, var->IsContextSlot() ? "[ Context variable"
                                                : "[ Stack variable");
-      if (var->binding_needs_init()) {
-        // var->scope() may be NULL when the proxy is located in eval code and
-        // refers to a potential outside binding. Currently those bindings are
-        // always looked up dynamically, i.e. in that case
-        //     var->location() == LOOKUP.
-        // always holds.
-        DCHECK(var->scope() != NULL);
-
-        // Check if the binding really needs an initialization check. The check
-        // can be skipped in the following situation: we have a LET or CONST
-        // binding in harmony mode, both the Variable and the VariableProxy have
-        // the same declaration scope (i.e. they are both in global code, in the
-        // same function or in the same eval code) and the VariableProxy is in
-        // the source physically located after the initializer of the variable.
-        //
-        // We cannot skip any initialization checks for CONST in non-harmony
-        // mode because const variables may be declared but never initialized:
-        //   if (false) { const x; }; var y = x;
-        //
-        // The condition on the declaration scopes is a conservative check for
-        // nested functions that access a binding and are called before the
-        // binding is initialized:
-        //   function() { f(); let x = 1; function f() { x = 2; } }
-        //
-        bool skip_init_check;
-        if (var->scope()->DeclarationScope() != scope()->DeclarationScope()) {
-          skip_init_check = false;
-        } else if (var->is_this()) {
-          CHECK(info_->has_literal() &&
-                (info_->literal()->kind() & kSubclassConstructor) != 0);
-          // TODO(dslomov): implement 'this' hole check elimination.
-          skip_init_check = false;
+      if (NeedsHoleCheckForLoad(proxy)) {
+        // Let and const need a read barrier.
+        GetVar(v0, var);
+        __ LoadRoot(at, Heap::kTheHoleValueRootIndex);
+        __ subu(at, v0, at);  // Sub as compare: at == 0 on eq.
+        if (var->mode() == LET || var->mode() == CONST) {
+          // Throw a reference error when using an uninitialized let/const
+          // binding in harmony mode.
+          Label done;
+          __ Branch(&done, ne, at, Operand(zero_reg));
+          __ li(a0, Operand(var->name()));
+          __ push(a0);
+          __ CallRuntime(Runtime::kThrowReferenceError, 1);
+          __ bind(&done);
         } else {
-          // Check that we always have valid source position.
-          DCHECK(var->initializer_position() != RelocInfo::kNoPosition);
-          DCHECK(proxy->position() != RelocInfo::kNoPosition);
-          skip_init_check = var->mode() != CONST_LEGACY &&
-              var->initializer_position() < proxy->position();
+          // Uninitialized legacy const bindings are unholed.
+          DCHECK(var->mode() == CONST_LEGACY);
+          __ LoadRoot(a0, Heap::kUndefinedValueRootIndex);
+          __ Movz(v0, a0, at);  // Conditional move: Undefined if TheHole.
         }
-
-        if (!skip_init_check) {
-          // Let and const need a read barrier.
-          GetVar(v0, var);
-          __ LoadRoot(at, Heap::kTheHoleValueRootIndex);
-          __ subu(at, v0, at);  // Sub as compare: at == 0 on eq.
-          if (var->mode() == LET || var->mode() == CONST) {
-            // Throw a reference error when using an uninitialized let/const
-            // binding in harmony mode.
-            Label done;
-            __ Branch(&done, ne, at, Operand(zero_reg));
-            __ li(a0, Operand(var->name()));
-            __ push(a0);
-            __ CallRuntime(Runtime::kThrowReferenceError, 1);
-            __ bind(&done);
-          } else {
-            // Uninitalized const bindings outside of harmony mode are unholed.
-            DCHECK(var->mode() == CONST_LEGACY);
-            __ LoadRoot(a0, Heap::kUndefinedValueRootIndex);
-            __ Movz(v0, a0, at);  // Conditional move: Undefined if TheHole.
-          }
-          context()->Plug(v0);
-          break;
-        }
+        context()->Plug(v0);
+        break;
       }
       context()->Plug(var);
       break;
     }
 
     case VariableLocation::LOOKUP: {
       Comment cmnt(masm_, "[ Lookup variable");
       Label done, slow;
       // Generate code for loading from variables potentially shadowed
       // by eval-introduced variables.
@@ skipping 3817 matching lines @@
          reinterpret_cast<uint32_t>(
              isolate->builtins()->OsrAfterStackCheck()->entry()));
   return OSR_AFTER_STACK_CHECK;
 }
 
 
 }  // namespace internal
 }  // namespace v8
 
 #endif  // V8_TARGET_ARCH_MIPS