[interpreter] Don't keep postfix result if only visited for effect

Remove TODO to perform same optimization as AstGraphBuilder.
When visiting for effect in a postfix count operation, don't
keep the intermediate result of ToNumber.

BUG=v4:4280
LOG=n

Review-Url: https://codereview.chromium.org/2187823002
Cr-Commit-Position: refs/heads/master@{#38101}

src/interpreter/bytecode-generator.cc

@@ -2782,8 +2782,7 @@ void BytecodeGenerator::VisitCountOperation(CountOperation* expr) {
   Property* property = expr->expression()->AsProperty();
   LhsKind assign_type = Property::GetAssignType(property);
 
-  // TODO(rmcilroy): Set is_postfix to false if visiting for effect.
-  bool is_postfix = expr->is_postfix();
+  bool is_postfix = expr->is_postfix() && !execution_result()->IsEffect();
 
   // Evaluate LHS expression and get old value.
   Register object, home_object, key, old_value, value;

test/cctest/interpreter/bytecode_expectations/AssignmentsInBinaryExpression.golden

@@ -99,7 +99,7 @@ snippet: "
 "
 frame size: 3
 parameter count: 1
-bytecode array length: 28
+bytecode array length: 26
 bytecodes: [
   /*   30 E> */ B(StackCheck),
   /*   42 S> */ B(LdaSmi), U8(55),
@@ -112,8 +112,7 @@ bytecodes: [
                 B(Star), R(0),
   /*   68 E> */ B(Add), R(2),
                 B(Star), R(0),
-  /*   75 S> */ B(ToNumber), R(1),
-                B(Inc),
+  /*   75 S> */ B(Inc),
                 B(Star), R(0),
   /*   80 S> */ B(Nop),
   /*   90 S> */ B(Return),

test/cctest/interpreter/bytecode_expectations/BasicLoops.golden

@@ -679,15 +679,15 @@ snippet: "
     }
   }
 "
-frame size: 7
+frame size: 6
 parameter count: 1
-bytecode array length: 118
+bytecode array length: 116
 bytecodes: [
   /*   30 E> */ B(StackCheck),
   /*   42 S> */ B(LdaZero),
                 B(Star), R(1),
   /*   52 S> */ B(Ldar), R(1),
-                B(JumpIfToBooleanFalse), U8(110),
+                B(JumpIfToBooleanFalse), U8(108),
   /*   45 E> */ B(StackCheck),
                 B(LdaConstant), U8(0),
                 B(Star), R(4),
@@ -714,24 +714,23 @@ bytecodes: [
                 B(JumpIfToBooleanFalse), U8(8),
   /*  113 S> */ B(PopContext), R(3),
                 B(PopContext), R(3),
-                B(Jump), U8(42),
+                B(Jump), U8(40),
   /*  126 S> */ B(LdaContextSlot), R(context), U8(4),
                 B(JumpIfNotHole), U8(11),
                 B(LdaConstant), U8(3),
                 B(Star), R(4),
                 B(CallRuntime), U16(Runtime::kThrowReferenceError), R(4), U8(1),
-                B(ToNumber), R(4),
                 B(Inc),
-                B(Star), R(5),
+                B(Star), R(4),
   /*  127 E> */ B(LdaContextSlot), R(context), U8(4),
                 B(JumpIfNotHole), U8(11),
                 B(LdaConstant), U8(3),
-                B(Star), R(6),
-                B(CallRuntime), U16(Runtime::kThrowReferenceError), R(6), U8(1),
-                B(Ldar), R(5),
+                B(Star), R(5),
+                B(CallRuntime), U16(Runtime::kThrowReferenceError), R(5), U8(1),
+                B(Ldar), R(4),
                 B(StaContextSlot), R(context), U8(4),
                 B(PopContext), R(3),
-                B(Jump), U8(-110),
+                B(Jump), U8(-108),
                 B(LdaUndefined),
   /*  137 S> */ B(Return),
 ]

test/cctest/interpreter/bytecode_expectations/JumpsRequiringConstantWideOperands.golden

@@ -327,9 +327,9 @@ snippet: "
   }
   return 3;
 "
-frame size: 3
+frame size: 2
 parameter count: 1
-bytecode array length: 1409
+bytecode array length: 1407
 bytecodes: [
   /*   30 E> */ B(StackCheck),
   /*   42 S> */ B(LdaConstant), U8(0),
@@ -960,7 +960,7 @@ bytecodes: [
                 B(Star), R(1),
   /* 4108 S> */ B(LdaSmi), U8(3),
   /* 4108 E> */ B(TestLessThan), R(1),
-                B(Wide), B(JumpIfFalse), U16(37),
+                B(Wide), B(JumpIfFalse), U16(35),
   /* 4090 E> */ B(StackCheck),
   /* 4122 S> */ B(LdaSmi), U8(1),
   /* 4128 E> */ B(TestEqual), R(1),
@@ -969,12 +969,11 @@ bytecodes: [
   /* 4146 S> */ B(LdaSmi), U8(2),
   /* 4152 E> */ B(TestEqual), R(1),
                 B(Wide), B(JumpIfFalse), U16(7),
-  /* 4158 S> */ B(Wide), B(Jump), U16(12),
+  /* 4158 S> */ B(Wide), B(Jump), U16(10),
   /* 4114 S> */ B(Ldar), R(1),
-                B(ToNumber), R(2),
                 B(Inc),
                 B(Star), R(1),
-                B(Jump), U8(-40),
+                B(Jump), U8(-38),
   /* 4167 S> */ B(LdaSmi), U8(3),
   /* 4177 S> */ B(Return),
 ]

test/cctest/interpreter/bytecode_expectations/WideRegisters.golden

@@ -893,7 +893,7 @@ snippet: "
 "
 frame size: 158
 parameter count: 1
-bytecode array length: 55
+bytecode array length: 51
 bytecodes: [
   /*   30 E> */ B(StackCheck),
   /* 1503 S> */ B(LdaZero),
@@ -904,17 +904,16 @@ bytecodes: [
                 B(Wide), B(Star), R16(128),
   /* 1538 S> */ B(LdaSmi), U8(64),
   /* 1538 E> */ B(Wide), B(TestLessThan), R16(128),
-                B(JumpIfFalse), U8(32),
+                B(JumpIfFalse), U8(28),
   /* 1518 E> */ B(StackCheck),
   /* 1555 S> */ B(Wide), B(Ldar), R16(128),
   /* 1561 E> */ B(Add), R(1),
                 B(Wide), B(Mov), R16(1), R16(157),
                 B(Star), R(1),
   /* 1548 S> */ B(Wide), B(Ldar), R16(128),
-                B(Wide), B(ToNumber), R16(157),
                 B(Inc),
                 B(Wide), B(Star), R16(128),
-                B(Jump), U8(-36),
+                B(Jump), U8(-32),
   /* 1567 S> */ B(Wide), B(Ldar), R16(128),
   /* 1580 S> */ B(Return),
 ]