Recognize special comparisons via pattern matching on the hydrogen graph, 2nd attempt.

src/hydrogen.cc

 // Copyright 2011 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 5771 matching lines @@
 Representation HGraphBuilder::ToRepresentation(TypeInfo info) {
   if (info.IsSmi()) return Representation::Integer32();
   if (info.IsInteger32()) return Representation::Integer32();
   if (info.IsDouble()) return Representation::Double();
   if (info.IsNumber()) return Representation::Double();
   return Representation::Tagged();
 }
 
 
 void HGraphBuilder::HandleLiteralCompareTypeof(CompareOperation* expr,
-                                               Expression* sub_expr,
+                                               HTypeof* typeof_expr,
                                                Handle<String> check) {
-  CHECK_ALIVE(VisitForTypeOf(sub_expr));
-  HValue* value = Pop();
+  // Note: The HTypeof itself is removed during canonicalization, if possible.
+  HValue* value = typeof_expr->value();
   HTypeofIsAndBranch* instr = new(zone()) HTypeofIsAndBranch(value, check);
   instr->set_position(expr->position());
-  return ast_context()->ReturnControl(instr, expr->id());
+  ast_context()->ReturnControl(instr, expr->id());

[Kevin Millikin (Chromium), 2011/10/19 07:24:41]

I like the "return".  This function is (sort of) assumed to be called in tail
position as part of translating an expression, so the return (sort of) enforces
that.

[Sven Panne, 2011/10/19 07:33:32]

Done. Personally I like returning void, too, it is just like any other type
IMHO. :-) But I had discussions about this in other places in the past, so I
removed it during my various attempts to get this function right. Now it has
made its glorious comeback...

 }
 
 
-bool HGraphBuilder::TryLiteralCompare(CompareOperation* expr) {
-  Expression *sub_expr;
-  Handle<String> check;
-  if (expr->IsLiteralCompareTypeof(&sub_expr, &check)) {
-    HandleLiteralCompareTypeof(expr, sub_expr, check);
+static bool MatchLiteralCompareNil(HValue* left,
+                                   Token::Value op,
+                                   HValue* right,
+                                   Handle<Object> nil,
+                                   HValue** expr) {
+  if (left->IsConstant() &&
+      HConstant::cast(left)->handle().is_identical_to(nil) &&
+      Token::IsEqualityOp(op)) {
+    *expr = right;
     return true;
   }
+  return false;
+}
 
-  if (expr->IsLiteralCompareUndefined(&sub_expr)) {
-    HandleLiteralCompareNil(expr, sub_expr, kUndefinedValue);
+
+static bool MatchLiteralCompareTypeof(HValue* left,
+                                      Token::Value op,
+                                      HValue* right,
+                                      HTypeof** typeof_expr,
+                                      Handle<String>* check) {
+  if (left->IsTypeof() &&
+      Token::IsEqualityOp(op) &&
+      right->IsConstant() &&
+      HConstant::cast(right)->HasStringValue()) {
+    *typeof_expr = HTypeof::cast(left);
+    *check = Handle<String>::cast(HConstant::cast(right)->handle());
     return true;
   }
+  return false;
+}
 
-  if (expr->IsLiteralCompareNull(&sub_expr)) {
-    HandleLiteralCompareNil(expr, sub_expr, kNullValue);
-    return true;
-  }
 
-  return false;
+static bool IsLiteralCompareTypeof(HValue* left,
+                                   Token::Value op,
+                                   HValue* right,
+                                   HTypeof** typeof_expr,
+                                   Handle<String>* check) {
+  return MatchLiteralCompareTypeof(left, op, right, typeof_expr, check) ||
+      MatchLiteralCompareTypeof(right, op, left, typeof_expr, check);
+}
+
+
+static bool IsLiteralCompareNil(HValue* left,
+                                Token::Value op,
+                                HValue* right,
+                                Handle<Object> nil,
+                                HValue** expr) {
+  return MatchLiteralCompareNil(left, op, right, nil, expr) ||
+      MatchLiteralCompareNil(right, op, left, nil, expr);
 }
 
 
 void HGraphBuilder::VisitCompareOperation(CompareOperation* expr) {
   ASSERT(!HasStackOverflow());
   ASSERT(current_block() != NULL);
   ASSERT(current_block()->HasPredecessor());
   if (IsClassOfTest(expr)) {
     CallRuntime* call = expr->left()->AsCallRuntime();
     ASSERT(call->arguments()->length() == 1);
     CHECK_ALIVE(VisitForValue(call->arguments()->at(0)));
     HValue* value = Pop();
     Literal* literal = expr->right()->AsLiteral();
     Handle<String> rhs = Handle<String>::cast(literal->handle());
     HClassOfTestAndBranch* instr =
         new(zone()) HClassOfTestAndBranch(value, rhs);
     instr->set_position(expr->position());
     return ast_context()->ReturnControl(instr, expr->id());
   }
 
-  // Check for special cases that compare against literals.
-  if (TryLiteralCompare(expr)) return;
-
   TypeInfo type_info = oracle()->CompareType(expr);
   // Check if this expression was ever executed according to type feedback.
+  // Note that for the special typeof/null/undefined cases we get unknown here.
   if (type_info.IsUninitialized()) {
     AddInstruction(new(zone()) HSoftDeoptimize);
     current_block()->MarkAsDeoptimizing();
     type_info = TypeInfo::Unknown();
   }
 
   CHECK_ALIVE(VisitForValue(expr->left()));
   CHECK_ALIVE(VisitForValue(expr->right()));
 
   HValue* context = environment()->LookupContext();
   HValue* right = Pop();
   HValue* left = Pop();
   Token::Value op = expr->op();
 
+  HTypeof* typeof_expr = NULL;
+  Handle<String> check;
+  if (IsLiteralCompareTypeof(left, op, right, &typeof_expr, &check)) {
+    return HandleLiteralCompareTypeof(expr, typeof_expr, check);
+  }
+  HValue* sub_expr = NULL;
+  Factory* f = graph()->isolate()->factory();
+  if (IsLiteralCompareNil(left, op, right, f->undefined_value(), &sub_expr)) {
+    return HandleLiteralCompareNil(expr, sub_expr, kUndefinedValue);
+  }
+  if (IsLiteralCompareNil(left, op, right, f->null_value(), &sub_expr)) {
+    return HandleLiteralCompareNil(expr, sub_expr, kNullValue);
+  }
+
   if (op == Token::INSTANCEOF) {
     // Check to see if the rhs of the instanceof is a global function not
     // residing in new space. If it is we assume that the function will stay the
     // same.
     Handle<JSFunction> target = Handle<JSFunction>::null();
     VariableProxy* proxy = expr->right()->AsVariableProxy();
     bool global_function = (proxy != NULL) && proxy->var()->IsUnallocated();
     if (global_function &&
         info()->has_global_object() &&
         !info()->global_object()->IsAccessCheckNeeded()) {
@@ skipping 68 matching lines @@
           new(zone()) HCompareIDAndBranch(left, right, op);
       result->set_position(expr->position());
       result->SetInputRepresentation(r);
       return ast_context()->ReturnControl(result, expr->id());
     }
   }
 }
 
 
 void HGraphBuilder::HandleLiteralCompareNil(CompareOperation* expr,
-                                            Expression* sub_expr,
+                                            HValue* value,
                                             NilValue nil) {
   ASSERT(!HasStackOverflow());
   ASSERT(current_block() != NULL);
   ASSERT(current_block()->HasPredecessor());
-  CHECK_ALIVE(VisitForValue(sub_expr));
-  HValue* value = Pop();
   EqualityKind kind =
       expr->op() == Token::EQ_STRICT ? kStrictEquality : kNonStrictEquality;
   HIsNilAndBranch* instr = new(zone()) HIsNilAndBranch(value, kind, nil);
   instr->set_position(expr->position());
   return ast_context()->ReturnControl(instr, expr->id());
 }
 
 
 void HGraphBuilder::VisitThisFunction(ThisFunction* expr) {
   ASSERT(!HasStackOverflow());
@@ skipping 972 matching lines @@
     }
   }
 
 #ifdef DEBUG
   if (graph_ != NULL) graph_->Verify(false);  // No full verify.
   if (allocator_ != NULL) allocator_->Verify();
 #endif
 }
 
 } }  // namespace v8::internal