[interpreter] Bytecode register optimizer.

test/cctest/interpreter/bytecode_expectations/ForIn.golden

 #
 # Autogenerated by generate-bytecode-expectations.
 #
 
 ---
 pool type: mixed
 execute: yes
 wrap: yes
 
 ---
@@ skipping 55 matching lines @@
 frame size: 8
 parameter count: 1
 bytecode array length: 45
 bytecodes: [
   /*   30 E> */ B(StackCheck),
   /*   42 S> */ B(LdaConstant), U8(0),
   /*   42 E> */ B(Star), R(1),
   /*   68 S> */ B(JumpIfUndefined), U8(38),
                 B(JumpIfNull), U8(36),
                 B(ToObject),
+                B(ForInPrepare), R(4),
                 B(Star), R(3),
-                B(ForInPrepare), R(4),
                 B(LdaZero),
                 B(Star), R(7),
   /*   63 S> */ B(ForInDone), R(7), R(6),
                 B(JumpIfTrue), U8(23),
                 B(ForInNext), R(3), R(7), R(4), U8(1),
                 B(JumpIfUndefined), U8(10),
                 B(Star), R(0),
   /*   54 E> */ B(StackCheck),
-                B(Ldar), R(0),
                 B(Star), R(2),
+  /*   73 S> */ B(Ldar), R(2),

[Yang, 2016/05/20 08:00:55]

How come we end up with an additional statement position? This will likely
change stepping behavior.

[oth, 2016/05/20 09:01:04]

The older code has peephole optimized out the statement position that is now
visible.

The completely non-optimized code looks like:

   20 E> 0x13f6a12d62b4 @    0 : 5e                StackCheck 
   42 S> 0x13f6a12d62b5 @    1 : 09 00             LdaConstant [0]
   42 E> 0x13f6a12d62b7 @    3 : 17 f9             Star r1
   68 S> 0x13f6a12d62b9 @    5 : 16 f9             Ldar r1
         0x13f6a12d62bb @    7 : 56 28             JumpIfUndefined [40]
(0x13f6a12d62e3 @ 47)
         0x13f6a12d62bd @    9 : 54 26             JumpIfNull [38]
(0x13f6a12d62e3 @ 47)
         0x13f6a12d62bf @   11 : 42                ToObject 
         0x13f6a12d62c0 @   12 : 17 f7             Star r3
         0x13f6a12d62c2 @   14 : 5a f6             ForInPrepare r4-r6
         0x13f6a12d62c4 @   16 : 02                LdaZero 
         0x13f6a12d62c5 @   17 : 17 f3             Star r7
   63 S> 0x13f6a12d62c7 @   19 : 5b f3 f4          ForInDone r7, r6
         0x13f6a12d62ca @   22 : 50 19             JumpIfToBooleanTrue [25]
(0x13f6a12d62e3 @ 47)
         0x13f6a12d62cc @   24 : 5c f7 f3 f6 01    ForInNext r3, r7, r4-r5, [1]
         0x13f6a12d62d1 @   29 : 56 0c             JumpIfUndefined [12]
(0x13f6a12d62dd @ 41)
         0x13f6a12d62d3 @   31 : 17 fa             Star r0
   54 E> 0x13f6a12d62d5 @   33 : 5e                StackCheck 
         0x13f6a12d62d6 @   34 : 16 fa             Ldar r0
         0x13f6a12d62d8 @   36 : 17 f8             Star r2
   73 S> 0x13f6a12d62da @   38 : 16 f8             Ldar r2
   85 S> 0x13f6a12d62dc @   40 : 61                Return 
         0x13f6a12d62dd @   41 : 5d f3             ForInStep r7
         0x13f6a12d62df @   43 : 17 f3             Star r7
         0x13f6a12d62e1 @   45 : 4a e6             Jump [-26] (0x13f6a12d62c7 @
19)
         0x13f6a12d62e3 @   47 : 04                LdaUndefined 
   85 S> 0x13f6a12d62e4 @   48 : 61                Return 

   /*   85 S> */ B(Return),
                 B(ForInStep), R(7),
                 B(Star), R(7),
                 B(Jump), U8(-24),
                 B(LdaUndefined),
   /*   85 S> */ B(Return),
 ]
 constant pool: [
   InstanceType::ONE_BYTE_INTERNALIZED_STRING_TYPE,
 ]
 handlers: [
 ]
 
 ---
 snippet: "
   var x = 0;
   for (var p in [1,2,3]) { x += p; }
 "
 frame size: 9
 parameter count: 1
-bytecode array length: 57
+bytecode array length: 54
 bytecodes: [
   /*   30 E> */ B(StackCheck),
   /*   42 S> */ B(LdaZero),
   /*   42 E> */ B(Star), R(1),
   /*   59 S> */ B(CreateArrayLiteral), U8(0), U8(0), U8(3),
-                B(JumpIfUndefined), U8(47),
-                B(JumpIfNull), U8(45),
+                B(JumpIfUndefined), U8(44),
+                B(JumpIfNull), U8(42),
                 B(ToObject),
+                B(ForInPrepare), R(4),
                 B(Star), R(3),
-                B(ForInPrepare), R(4),
                 B(LdaZero),
                 B(Star), R(7),
   /*   54 S> */ B(ForInDone), R(7), R(6),
-                B(JumpIfTrue), U8(32),
+                B(JumpIfTrue), U8(29),
                 B(ForInNext), R(3), R(7), R(4), U8(1),
-                B(JumpIfUndefined), U8(19),
+                B(JumpIfUndefined), U8(16),
                 B(Star), R(0),
   /*   45 E> */ B(StackCheck),
-                B(Ldar), R(0),
                 B(Star), R(2),
-  /*   70 S> */ B(Ldar), R(1),
-                B(Star), R(8),
-  /*   75 E> */ B(Ldar), R(2),
-                B(Add), R(8),
-  /*   72 E> */ B(Star), R(1),
+  /*   70 S> */ B(Ldar), R(0),
+                B(Add), R(1),
+  /*   72 E> */ B(Mov), R(1), R(8),
+                B(Star), R(1),
                 B(ForInStep), R(7),
                 B(Star), R(7),
-                B(Jump), U8(-33),
+                B(Jump), U8(-30),
                 B(LdaUndefined),
   /*   80 S> */ B(Return),
 ]
 constant pool: [
   InstanceType::FIXED_ARRAY_TYPE,
 ]
 handlers: [
 ]
 
 ---
 snippet: "
   var x = { 'a': 1, 'b': 2 };
   for (x['a'] in [10, 20, 30]) {
     if (x['a'] == 10) continue;
     if (x['a'] == 20) break;
   }
 "
 frame size: 8
 parameter count: 1
-bytecode array length: 94
+bytecode array length: 82
 bytecodes: [
   /*   30 E> */ B(StackCheck),
   /*   42 S> */ B(CreateObjectLiteral), U8(0), U8(0), U8(1),
                 B(Star), R(1),
   /*   42 E> */ B(Star), R(0),
   /*   77 S> */ B(CreateArrayLiteral), U8(1), U8(1), U8(3),
-                B(JumpIfUndefined), U8(79),
-                B(JumpIfNull), U8(77),
+                B(JumpIfUndefined), U8(67),
+                B(JumpIfNull), U8(65),
                 B(ToObject),
+                B(ForInPrepare), R(2),
                 B(Star), R(1),
-                B(ForInPrepare), R(2),
                 B(LdaZero),
                 B(Star), R(5),
   /*   68 S> */ B(ForInDone), R(5), R(4),
-                B(JumpIfTrue), U8(64),
+                B(JumpIfTrue), U8(52),
                 B(ForInNext), R(1), R(5), R(2), U8(9),
-                B(JumpIfUndefined), U8(51),
+                B(JumpIfUndefined), U8(39),
                 B(Star), R(6),
-  /*   67 E> */ B(Ldar), R(0),
-                B(Star), R(7),
-                B(Ldar), R(6),
-                B(StoreICSloppy), R(7), U8(2), U8(7),
+  /*   67 E> */ B(Ldar), R(6),
+                B(StoreICSloppy), R(0), U8(2), U8(7),
   /*   62 E> */ B(StackCheck),
-  /*   95 S> */ B(Ldar), R(0),
-                B(Star), R(6),
-  /*  100 E> */ B(LoadIC), R(6), U8(2), U8(3),
+  /*   95 S> */ B(LoadIC), R(0), U8(2), U8(3),
                 B(Star), R(7),
                 B(LdaSmi), U8(10),
   /*  106 E> */ B(TestEqual), R(7),
                 B(JumpIfFalse), U8(4),
-  /*  113 S> */ B(Jump), U8(20),
-  /*  125 S> */ B(Ldar), R(0),
-                B(Star), R(6),
-  /*  130 E> */ B(LoadIC), R(6), U8(2), U8(5),
+  /*  113 S> */ B(Jump), U8(16),
+  /*  125 S> */ B(LoadIC), R(0), U8(2), U8(5),
                 B(Star), R(7),
                 B(LdaSmi), U8(20),
   /*  136 E> */ B(TestEqual), R(7),
                 B(JumpIfFalse), U8(4),
   /*  143 S> */ B(Jump), U8(8),
                 B(ForInStep), R(5),
                 B(Star), R(5),
-                B(Jump), U8(-65),
+                B(Jump), U8(-53),
                 B(LdaUndefined),
   /*  152 S> */ B(Return),
 ]
 constant pool: [
   InstanceType::FIXED_ARRAY_TYPE,
   InstanceType::FIXED_ARRAY_TYPE,
   InstanceType::ONE_BYTE_INTERNALIZED_STRING_TYPE,
 ]
 handlers: [
 ]
 
 ---
 snippet: "
   var x = [ 10, 11, 12 ] ;
   for (x[0] in [1,2,3]) { return x[3]; }
 "
 frame size: 9
 parameter count: 1
-bytecode array length: 69
+bytecode array length: 61
 bytecodes: [
   /*   30 E> */ B(StackCheck),
   /*   42 S> */ B(CreateArrayLiteral), U8(0), U8(0), U8(3),
   /*   42 E> */ B(Star), R(0),
   /*   72 S> */ B(CreateArrayLiteral), U8(1), U8(1), U8(3),
-                B(JumpIfUndefined), U8(56),
-                B(JumpIfNull), U8(54),
+                B(JumpIfUndefined), U8(48),
+                B(JumpIfNull), U8(46),
                 B(ToObject),
+                B(ForInPrepare), R(2),
                 B(Star), R(1),
-                B(ForInPrepare), R(2),
                 B(LdaZero),
                 B(Star), R(5),
   /*   65 S> */ B(ForInDone), R(5), R(4),
-                B(JumpIfTrue), U8(41),
+                B(JumpIfTrue), U8(33),
                 B(ForInNext), R(1), R(5), R(2), U8(7),
-                B(JumpIfUndefined), U8(28),
+                B(JumpIfUndefined), U8(20),
                 B(Star), R(6),
-  /*   64 E> */ B(Ldar), R(0),
-                B(Star), R(7),
-                B(LdaZero),
+  /*   64 E> */ B(LdaZero),
                 B(Star), R(8),
                 B(Ldar), R(6),
-                B(KeyedStoreICSloppy), R(7), R(8), U8(5),
+                B(KeyedStoreICSloppy), R(0), R(8), U8(5),
   /*   59 E> */ B(StackCheck),
-  /*   83 S> */ B(Ldar), R(0),
-                B(Star), R(6),
-  /*   91 E> */ B(LdaSmi), U8(3),
-                B(KeyedLoadIC), R(6), U8(3),
+  /*   83 S> */ B(LdaSmi), U8(3),
+                B(KeyedLoadIC), R(0), U8(3),
   /*   98 S> */ B(Return),
                 B(ForInStep), R(5),
                 B(Star), R(5),
-                B(Jump), U8(-42),
+                B(Jump), U8(-34),
                 B(LdaUndefined),
   /*   98 S> */ B(Return),
 ]
 constant pool: [
   InstanceType::FIXED_ARRAY_TYPE,
   InstanceType::FIXED_ARRAY_TYPE,
 ]
 handlers: [
 ]