[turbofan] Fix assert caused by bogus merging of out-of-scope CodeAssembler variables

Previously, CodeAssembler Variables declared in an explicit C++ scope would
continue to be merged into future labels beyond that scope, causing
asserts. This CL ensures that Variables are properly ignored when they go out of
scope.

Review-Url: https://codereview.chromium.org/2035683002
Cr-Commit-Position: refs/heads/master@{#36690}

src/compiler/code-assembler.cc

@@ -600,10 +600,12 @@ class CodeAssembler::Variable::Impl : public ZoneObject {
 
 CodeAssembler::Variable::Variable(CodeAssembler* assembler,
                                   MachineRepresentation rep)
-    : impl_(new (assembler->zone()) Impl(rep)) {
-  assembler->variables_.push_back(impl_);
+    : impl_(new (assembler->zone()) Impl(rep)), assembler_(assembler) {
+  assembler->variables_.insert(impl_);
 }
 
+CodeAssembler::Variable::~Variable() { assembler_->variables_.erase(impl_); }
+
 void CodeAssembler::Variable::Bind(Node* value) { impl_->value_ = value; }
 
 Node* CodeAssembler::Variable::value() const {

src/compiler/code-assembler.h

@@ -166,6 +166,7 @@ class CodeAssembler {
   class Variable {
    public:
     explicit Variable(CodeAssembler* assembler, MachineRepresentation rep);
+    ~Variable();
     void Bind(Node* value);
     Node* value() const;
     MachineRepresentation rep() const;
@@ -175,6 +176,7 @@ class CodeAssembler {
     friend class CodeAssembler;
     class Impl;
     Impl* impl_;
+    CodeAssembler* assembler_;
   };
 
   enum AllocationFlag : uint8_t {
@@ -362,7 +364,7 @@ class CodeAssembler {
   Code::Flags flags_;
   const char* name_;
   bool code_generated_;
-  ZoneVector<Variable::Impl*> variables_;
+  ZoneSet<Variable::Impl*> variables_;
 
   DISALLOW_COPY_AND_ASSIGN(CodeAssembler);
 };

test/cctest/test-code-stub-assembler.cc

@@ -1090,5 +1090,34 @@ TEST(DeferredCodePhiHints) {
   CHECK(!m.GenerateCode().is_null());
 }
 
+TEST(TestOutOfScopeVariable) {
+  typedef CodeStubAssembler::Label Label;
+  typedef CodeStubAssembler::Variable Variable;
+  Isolate* isolate(CcTest::InitIsolateOnce());
+  VoidDescriptor descriptor(isolate);
+  CodeStubAssemblerTester m(isolate, descriptor);
+  Label block1(&m);
+  Label block2(&m);
+  Label block3(&m);
+  Label block4(&m);
+  m.Branch(m.WordEqual(m.Parameter(0), m.IntPtrConstant(0)), &block1, &block4);
+  m.Bind(&block4);
+  {
+    Variable var_object(&m, MachineRepresentation::kTagged);
+    m.Branch(m.WordEqual(m.Parameter(0), m.IntPtrConstant(0)), &block2,
+             &block3);
+
+    m.Bind(&block2);
+    var_object.Bind(m.IntPtrConstant(55));
+    m.Goto(&block1);
+
+    m.Bind(&block3);
+    var_object.Bind(m.IntPtrConstant(66));
+    m.Goto(&block1);
+  }
+  m.Bind(&block1);
+  CHECK(!m.GenerateCode().is_null());
+}
+
 }  // namespace internal
 }  // namespace v8