NullSafe props, part 1: Runtime

Summary: This diff adds support of NullSafe properties to the runtime (see also {D1875131}).

===Overview===

- Object property AST node support
- Bytecode emitter support
- Bytecode interpreter support
- Bytecode verifier support
- Runtime errors for mutation cases of NullSafe props
- Parse time errors
- JIT support

===Details==

The new `QT` member code is introduced in the `CGetM` instruction:

- QT:<id> - a null-safe version of PT:<id> (a litstr by an immediate id as a prop)

Example:

  $x = null;
  $x?->y;

Generated bytecode:

  Pseudo-main at 0
  maxStackCells: 2
  numLocals: 1
  numIterators: 0
    // line 3
      0: Null
      1: SetL 0
      3: PopC
    // line 4
      4: CGetM <L:0 QT:"y"> # note QT
     20: PopC
     21: Int 1
     30: RetC
  Pseudo-main at 0
  maxStackCells: 2
  numLocals: 1
  numIterators: 0

Runtime/parse checks that forbids several use-cases:

  $x?->y;        // allow
  isset($x?->y); // allow
  empty($x?->y); // allow

  $x?->y = 1;    // disallow
  $x?->y += 1;   // disallow
  $x?->y++;      // disallow
  unset($x?->y); // disallow

  function byRef(&x) {}
  byRef($x?->y); // disallow

Reviewed By: @jdelong

Differential Revision: D1818128

hphp/compiler/analysis/emitter.cpp

@@ -49,7 +49,6 @@
 #include "hphp/compiler/expression/modifier_expression.h"
 #include "hphp/compiler/expression/new_object_expression.h"
 #include "hphp/compiler/expression/object_method_expression.h"
-#include "hphp/compiler/expression/object_property_expression.h"
 #include "hphp/compiler/expression/parameter_expression.h"
 #include "hphp/compiler/expression/qop_expression.h"
 #include "hphp/compiler/expression/scalar_expression.h"
@@ -156,6 +155,7 @@ namespace StackSym {
   static const char S = 0x60; // Static property marker
   static const char M = 0x70; // Non elem/prop/W part of M-vector
   static const char K = 0x80; // Marker for information about a class base
+  static const char Q = 0x90; // NullSafe Property marker
 
   static const char CN = C | N;
   static const char CG = C | G;
@@ -189,6 +189,7 @@ namespace StackSym {
       case StackSym::E: res += "E"; break;
       case StackSym::W: res += "W"; break;
       case StackSym::P: res += "P"; break;
+      case StackSym::Q: res += "Q"; break;
       case StackSym::S: res += "S"; break;
       case StackSym::K: res += "K"; break;
       default: break;
@@ -1983,7 +1984,8 @@ void EmitterVisitor::popEvalStackMMany() {
     char sym = m_evalStack.top();
     char symFlavor = StackSym::GetSymFlavor(sym);
     char marker = StackSym::GetMarker(sym);
-    if (marker == StackSym::E || marker == StackSym::P) {
+    if (marker == StackSym::E || marker == StackSym::P ||
+        marker == StackSym::Q) {
       if (symFlavor != StackSym::C && symFlavor != StackSym::L &&
           symFlavor != StackSym::T && symFlavor != StackSym::I) {
         InvariantViolation(
@@ -4370,6 +4372,16 @@ bool EmitterVisitor::visit(ConstructPtr node) {
       case Expression::KindOfObjectPropertyExpression: {
         ObjectPropertyExpressionPtr op(
           static_pointer_cast<ObjectPropertyExpression>(node));
+        if (op->isNullSafe() &&
+            op->hasAnyContext(
+                Expression::RefValue
+              | Expression::LValue
+              | Expression::DeepReference
+            ) && !op->hasContext(Expression::InvokeArgument)
+        ) {
+          throw IncludeTimeFatalException(op,
+            Strings::NULLSAFE_PROP_WRITE_ERROR);
+        }
         ExpressionPtr obj = op->getObject();
         SimpleVariablePtr sv = dynamic_pointer_cast<SimpleVariable>(obj);
         if (sv && sv->isThis() && sv->hasContext(Expression::ObjectContext)) {
@@ -4387,7 +4399,12 @@ bool EmitterVisitor::visit(ConstructPtr node) {
                                Expression::ObjectContext)) {
           m_tempLoc = op->getLocation();
         }
-        markProp(e);
+        markProp(
+          e,
+          op->isNullSafe()
+            ? PropAccessType::NullSafe
+            : PropAccessType::Normal
+        );
         return true;
       }
 
@@ -4872,7 +4889,8 @@ int EmitterVisitor::scanStackForLocation(int iLast) {
   for (int i = iLast; i >= 0; --i) {
     char marker = StackSym::GetMarker(m_evalStack.get(i));
     if (marker != StackSym::E && marker != StackSym::W &&
-        marker != StackSym::P && marker != StackSym::M) {
+        marker != StackSym::P && marker != StackSym::M &&
+        marker != StackSym::Q) {
       return i;
     }
   }
@@ -4998,6 +5016,10 @@ void EmitterVisitor::buildVectorImm(std::vector<uchar>& vectorImm,
           vectorImm.push_back(MPC);
         }
       } break;
+      case StackSym::Q: {
+        assert(symFlavor == StackSym::T);
+        vectorImm.push_back(MQT);
+      } break;
       case StackSym::S: {
         assert(false);
       }
@@ -5981,7 +6003,7 @@ void EmitterVisitor::markNewElem(Emitter& e) {
   m_evalStack.push(StackSym::W);
 }
 
-void EmitterVisitor::markProp(Emitter& e) {
+void EmitterVisitor::markProp(Emitter& e, PropAccessType propAccessType) {
   if (m_evalStack.empty()) {
     InvariantViolation(
       "Emitter encountered an empty evaluation stack inside "
@@ -5991,7 +6013,13 @@ void EmitterVisitor::markProp(Emitter& e) {
   }
   char sym = m_evalStack.top();
   if (sym == StackSym::C || sym == StackSym::L || sym == StackSym::T) {
-    m_evalStack.set(m_evalStack.size()-1, (sym | StackSym::P));
+    m_evalStack.set(
+      m_evalStack.size()-1,
+      (sym | (propAccessType == PropAccessType::NullSafe
+        ? StackSym::Q
+        : StackSym::P
+      ))
+    );
   } else {
     InvariantViolation(
       "Emitter encountered an unsupported StackSym \"%s\" on "
@@ -6928,7 +6956,7 @@ void EmitterVisitor::emitMemoizeProp(Emitter& e,
     m_evalStack.setKnownCls(m_curFunc->pce()->name(), false);
     m_evalStack.push(StackSym::T);
     m_evalStack.setString(m_curFunc->memoizePropName);
-    markProp(e);
+    markProp(e, PropAccessType::Normal);
   }
 
   assert(numParams <= paramIDs.size());

hphp/compiler/analysis/emitter.h

@@ -24,6 +24,8 @@
 #include "hphp/compiler/statement/trait_prec_statement.h"
 #include "hphp/compiler/statement/trait_alias_statement.h"
 #include "hphp/compiler/statement/typedef_statement.h"
+#include "hphp/compiler/expression/object_property_expression.h"
+#include "hphp/parser/parser.h"
 
 #include "hphp/runtime/vm/func.h"
 #include "hphp/runtime/vm/func-emitter.h"
@@ -717,7 +719,7 @@ class EmitterVisitor {
 
   void markElem(Emitter& e);
   void markNewElem(Emitter& e);
-  void markProp(Emitter& e);
+  void markProp(Emitter& e, PropAccessType propAccessType);
   void markSProp(Emitter& e);
   void markName(Emitter& e);
   void markNameSecond(Emitter& e);

hphp/compiler/analysis/select_rewriters.cpp

@@ -166,7 +166,7 @@ ObjectPropertyExpressionPtr getResultColumn(
   );
   ObjectPropertyExpressionPtr result(
     new ObjectPropertyExpression(expr->getScope(),
-        expr->getLocation(), obj, propName)
+        expr->getLocation(), obj, propName, PropAccessType::Normal)
   );
   return result;
 }

hphp/compiler/expression/object_property_expression.cpp

@@ -23,7 +23,6 @@
 #include "hphp/compiler/analysis/file_scope.h"
 #include "hphp/compiler/analysis/variable_table.h"
 #include "hphp/compiler/option.h"
-#include "hphp/compiler/expression/scalar_expression.h"
 #include "hphp/compiler/expression/simple_variable.h"
 #include "hphp/util/hash.h"
 #include "hphp/parser/hphp.tab.hpp"
@@ -35,7 +34,7 @@ using namespace HPHP;
 
 ObjectPropertyExpression::ObjectPropertyExpression
 (EXPRESSION_CONSTRUCTOR_PARAMETERS,
- ExpressionPtr object, ExpressionPtr property)
+ ExpressionPtr object, ExpressionPtr property, PropAccessType propAccessType)
   : Expression(
       EXPRESSION_CONSTRUCTOR_PARAMETER_VALUES(ObjectPropertyExpression)),
     LocalEffectsContainer(AccessorEffect),
@@ -44,6 +43,7 @@ ObjectPropertyExpression::ObjectPropertyExpression
   m_propSymValid = false;
   m_object->setContext(Expression::ObjectContext);
   m_object->setContext(Expression::AccessContext);
+  m_nullsafe = (propAccessType == PropAccessType::NullSafe);
 }
 
 ExpressionPtr ObjectPropertyExpression::clone() {

hphp/compiler/expression/object_property_expression.h

@@ -18,6 +18,7 @@
 #define incl_HPHP_OBJECT_PROPERTY_EXPRESSION_H_
 
 #include "hphp/compiler/expression/expression.h"
+#include "hphp/parser/parser.h"
 
 namespace HPHP {
 ///////////////////////////////////////////////////////////////////////////////
@@ -31,7 +32,8 @@ class ObjectPropertyExpression : public Expression,
                                  public LocalEffectsContainer {
 public:
   ObjectPropertyExpression(EXPRESSION_CONSTRUCTOR_PARAMETERS,
-                           ExpressionPtr object, ExpressionPtr property);
+                           ExpressionPtr object, ExpressionPtr property,
+                           PropAccessType propAccessType);
 
   DECLARE_EXPRESSION_VIRTUAL_FUNCTIONS;
   DECL_AND_IMPL_LOCAL_EFFECTS_METHODS;
@@ -43,6 +45,7 @@ class ObjectPropertyExpression : public Expression,
 
   ExpressionPtr getObject() { return m_object;}
   ExpressionPtr getProperty() { return m_property;}
+  bool isNullSafe() const { return m_nullsafe; }
 
   bool isTemporary() const;
   bool isNonPrivate(AnalysisResultPtr ar);
@@ -53,6 +56,7 @@ class ObjectPropertyExpression : public Expression,
 
   unsigned m_valid : 1;
   unsigned m_propSymValid : 1;
+  unsigned m_nullsafe : 1;
 
   Symbol *m_propSym;
   ClassScopeRawPtr m_objectClass;