[compiler] Drop the CompareNilIC.

src/crankshaft/hydrogen.cc

 // Copyright 2013 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/crankshaft/hydrogen.h"
 
 #include <sstream>
 
 #include "src/allocation-site-scopes.h"
 #include "src/ast/ast-numbering.h"
@@ skipping 3162 matching lines @@
   // And the result of the length
   HValue* length = AddLoadArrayLength(boilerplate, kind);
   Add<HStoreNamedField>(result, HObjectAccess::ForArrayLength(kind), length);
 
   BuildCopyElements(boilerplate_elements, kind, elements,
                     kind, length, NULL);
   return result;
 }
 
 
-void HGraphBuilder::BuildCompareNil(HValue* value, Type* type,
-                                    HIfContinuation* continuation,
-                                    MapEmbedding map_embedding) {
-  IfBuilder if_nil(this);
-
-  if (type->Maybe(Type::Undetectable())) {
-    if_nil.If<HIsUndetectableAndBranch>(value);
-  } else {
-    bool maybe_null = type->Maybe(Type::Null());
-    if (maybe_null) {
-      if_nil.If<HCompareObjectEqAndBranch>(value, graph()->GetConstantNull());
-    }
-
-    if (type->Maybe(Type::Undefined())) {
-      if (maybe_null) if_nil.Or();
-      if_nil.If<HCompareObjectEqAndBranch>(value,
-                                           graph()->GetConstantUndefined());
-    }
-
-    if_nil.Then();
-    if_nil.Else();
-
-    if (type->NumClasses() == 1) {
-      BuildCheckHeapObject(value);
-      // For ICs, the map checked below is a sentinel map that gets replaced by
-      // the monomorphic map when the code is used as a template to generate a
-      // new IC. For optimized functions, there is no sentinel map, the map
-      // emitted below is the actual monomorphic map.
-      if (map_embedding == kEmbedMapsViaWeakCells) {
-        HValue* cell =
-            Add<HConstant>(Map::WeakCellForMap(type->Classes().Current()));
-        HValue* expected_map = Add<HLoadNamedField>(
-            cell, nullptr, HObjectAccess::ForWeakCellValue());
-        HValue* map =
-            Add<HLoadNamedField>(value, nullptr, HObjectAccess::ForMap());
-        IfBuilder map_check(this);
-        map_check.IfNot<HCompareObjectEqAndBranch>(expected_map, map);
-        map_check.ThenDeopt(Deoptimizer::kUnknownMap);
-        map_check.End();
-      } else {
-        DCHECK(map_embedding == kEmbedMapsDirectly);
-        Add<HCheckMaps>(value, type->Classes().Current());
-      }
-    } else {
-      if_nil.Deopt(Deoptimizer::kTooManyUndetectableTypes);
-    }
-  }
-
-  if_nil.CaptureContinuation(continuation);
-}
-
-
 void HGraphBuilder::BuildCreateAllocationMemento(
     HValue* previous_object,
     HValue* previous_object_size,
     HValue* allocation_site) {
   DCHECK(allocation_site != NULL);
   HInnerAllocatedObject* allocation_memento = Add<HInnerAllocatedObject>(
       previous_object, previous_object_size, HType::HeapObject());
   AddStoreMapConstant(
       allocation_memento, isolate()->factory()->allocation_memento_map());
   Add<HStoreNamedField>(
@@ skipping 8480 matching lines @@
         result->SetOperandPositions(zone(), left_position, right_position);
       }
       return result;
     }
   }
 }
 
 
 void HOptimizedGraphBuilder::HandleLiteralCompareNil(CompareOperation* expr,
                                                      Expression* sub_expr,
                                                      NilValue nil) {

[Toon Verwaest, 2016/02/23 20:03:19]

As a next step I guess we should just drop this entire function, and just check
whether it's an abstract equality check with either side evaluated to an
undetectable HConstant. In that case we do an HIsUndetectable on the other side.
That removes some hacky code from the ast.

[Benedikt Meurer, 2016/02/24 05:39:19]

Fullcodegen still uses the Ast functionality, and we need to make sure that we
get the environment right, i.e. FCG doesn't push the nil value onto the
expression stack (although since we don't eager deopt from the nil comparison
anymore after this CL, this shouldn't matter).

   DCHECK(!HasStackOverflow());
   DCHECK(current_block() != NULL);
   DCHECK(current_block()->HasPredecessor());
   DCHECK(expr->op() == Token::EQ || expr->op() == Token::EQ_STRICT);
   if (!top_info()->is_tracking_positions()) SetSourcePosition(expr->position());
   CHECK_ALIVE(VisitForValue(sub_expr));
   HValue* value = Pop();
+  HControlInstruction* instr;
   if (expr->op() == Token::EQ_STRICT) {
     HConstant* nil_constant = nil == kNullValue
         ? graph()->GetConstantNull()
         : graph()->GetConstantUndefined();
-    HCompareObjectEqAndBranch* instr =
-        New<HCompareObjectEqAndBranch>(value, nil_constant);
-    return ast_context()->ReturnControl(instr, expr->id());
+    instr = New<HCompareObjectEqAndBranch>(value, nil_constant);
   } else {
     DCHECK_EQ(Token::EQ, expr->op());
-    Type* type = expr->combined_type()->Is(Type::None())
-                     ? Type::Any()
-                     : expr->combined_type();
-    HIfContinuation continuation;
-    BuildCompareNil(value, type, &continuation);
-    return ast_context()->ReturnContinuation(&continuation, expr->id());
+    instr = New<HIsUndetectableAndBranch>(value);
   }
+  return ast_context()->ReturnControl(instr, expr->id());
 }
 
 
 void HOptimizedGraphBuilder::VisitSpread(Spread* expr) { UNREACHABLE(); }
 
 
 void HOptimizedGraphBuilder::VisitEmptyParentheses(EmptyParentheses* expr) {
   UNREACHABLE();
 }
 
@@ skipping 1756 matching lines @@
     isolate()->GetHTracer()->TraceHydrogen(name(), graph_);
   }
 
 #ifdef DEBUG
   graph_->Verify(false);  // No full verify.
 #endif
 }
 
 }  // namespace internal
 }  // namespace v8