[interpreter] ToObject never yields null.

We don't need to compare the result of ToObject against null, since
ToObject will always yield a proper receiver (or throw a TypeError).

R=rmcilroy@chromium.org

Review URL: https://codereview.chromium.org/1736233002

Cr-Commit-Position: refs/heads/master@{#34318}

src/interpreter/bytecode-generator.cc

@@ -1099,7 +1099,7 @@ void BytecodeGenerator::VisitForInStatement(ForInStatement* stmt) {
   }
 
   LoopBuilder loop_builder(builder());
-  BytecodeLabel subject_null_label, subject_undefined_label, not_object_label;
+  BytecodeLabel subject_null_label, subject_undefined_label;
 
   // Prepare the state for executing ForIn.
   VisitForAccumulatorValue(stmt->subject());
@@ -1107,7 +1107,6 @@ void BytecodeGenerator::VisitForInStatement(ForInStatement* stmt) {
   builder()->JumpIfNull(&subject_null_label);
   Register receiver = register_allocator()->NewRegister();
   builder()->CastAccumulatorToJSObject();
-  builder()->JumpIfNull(&not_object_label);
   builder()->StoreAccumulatorInRegister(receiver);
 
   register_allocator()->PrepareForConsecutiveAllocations(3);
@@ -1138,7 +1137,6 @@ void BytecodeGenerator::VisitForInStatement(ForInStatement* stmt) {
   builder()->StoreAccumulatorInRegister(index);
   loop_builder.JumpToHeader();
   loop_builder.EndLoop();
-  builder()->Bind(&not_object_label);
   builder()->Bind(&subject_null_label);
   builder()->Bind(&subject_undefined_label);
 }

test/cctest/interpreter/bytecode_expectations/ForIn.golden

@@ -65,15 +65,14 @@ snippet: "
 "
 frame size: 8
 parameter count: 1
-bytecode array length: 46
+bytecode array length: 44
 bytecodes: [
   B(StackCheck),
   B(LdaConstant), U8(0),
   B(Star), R(1),
-  B(JumpIfUndefined), U8(39),
-  B(JumpIfNull), U8(37),
+  B(JumpIfUndefined), U8(37),
+  B(JumpIfNull), U8(35),
   B(ToObject),
-  B(JumpIfNull), U8(34),
   B(Star), R(3),
   B(ForInPrepare), R(4),
   B(LdaZero),
@@ -106,16 +105,15 @@ snippet: "
 "
 frame size: 9
 parameter count: 1
-bytecode array length: 58
+bytecode array length: 56
 bytecodes: [
   B(StackCheck),
   B(LdaZero),
   B(Star), R(1),
   B(CreateArrayLiteral), U8(0), U8(0), U8(3),
-  B(JumpIfUndefined), U8(48),
-  B(JumpIfNull), U8(46),
+  B(JumpIfUndefined), U8(46),
+  B(JumpIfNull), U8(44),
   B(ToObject),
-  B(JumpIfNull), U8(43),
   B(Star), R(3),
   B(ForInPrepare), R(4),
   B(LdaZero),
@@ -155,17 +153,16 @@ snippet: "
 "
 frame size: 8
 parameter count: 1
-bytecode array length: 95
+bytecode array length: 93
 bytecodes: [
   B(StackCheck),
   B(CreateObjectLiteral), U8(0), U8(0), U8(9),
   B(Star), R(1),
   B(Star), R(0),
   B(CreateArrayLiteral), U8(1), U8(1), U8(3),
-  B(JumpIfUndefined), U8(80),
-  B(JumpIfNull), U8(78),
+  B(JumpIfUndefined), U8(78),
+  B(JumpIfNull), U8(76),
   B(ToObject),
-  B(JumpIfNull), U8(75),
   B(Star), R(1),
   B(ForInPrepare), R(2),
   B(LdaZero),
@@ -217,16 +214,15 @@ snippet: "
 "
 frame size: 9
 parameter count: 1
-bytecode array length: 70
+bytecode array length: 68
 bytecodes: [
   B(StackCheck),
   B(CreateArrayLiteral), U8(0), U8(0), U8(3),
   B(Star), R(0),
   B(CreateArrayLiteral), U8(1), U8(1), U8(3),
-  B(JumpIfUndefined), U8(57),
-  B(JumpIfNull), U8(55),
+  B(JumpIfUndefined), U8(55),
+  B(JumpIfNull), U8(53),
   B(ToObject),
-  B(JumpIfNull), U8(52),
   B(Star), R(1),
   B(ForInPrepare), R(2),
   B(LdaZero),

test/cctest/interpreter/bytecode_expectations/WideRegisters.golden

@@ -1125,7 +1125,7 @@ snippet: "
 "
 frame size: 167
 parameter count: 1
-bytecode array length: 111
+bytecode array length: 109
 bytecodes: [
   B(StackCheck),
   B(LdaConstant), U8(0),
@@ -1133,10 +1133,9 @@ bytecodes: [
   B(LdaZero),
   B(Star), R(1),
   B(Ldar), R(0),
-  B(JumpIfUndefined), U8(98),
-  B(JumpIfNull), U8(96),
+  B(JumpIfUndefined), U8(96),
+  B(JumpIfNull), U8(94),
   B(ToObject),
-  B(JumpIfNull), U8(93),
   B(Star), R(125),
   B(MovWide), R16(125), R16(161),
   B(ForInPrepareWide), R16(162),