[Interpreter] Removes unnecessary jumps and dead code from If and loops.

test/cctest/interpreter/test-bytecode-generator.cc

 // Copyright 2015 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/v8.h"
 
 #include "src/compiler.h"
 #include "src/interpreter/bytecode-array-iterator.h"
 #include "src/interpreter/bytecode-generator.h"
 #include "src/interpreter/interpreter.h"
@@ skipping 1236 matching lines @@
 TEST(IfConditions) {
   InitializedHandleScope handle_scope;
   BytecodeGeneratorHelper helper;
 
   Handle<Object> unused = helper.factory()->undefined_value();
 
   ExpectedSnippet<Handle<Object>> snippets[] = {
       {"function f() { if (0) { return 1; } else { return -1; } } f()",
        0,
        1,
-       14,
-       {B(LdaZero),             //
-        B(ToBoolean),           //
-        B(JumpIfFalse), U8(7),  //
-        B(LdaSmi8), U8(1),      //
-        B(Return),              //
-        B(Jump), U8(5),         //
-        B(LdaSmi8), U8(-1),     //
-        B(Return),              //
-        B(LdaUndefined),        //
-        B(Return)},             //
+       5,
+       {B(LdaSmi8), U8(-1),  //
+        B(Return),           //
+        B(LdaUndefined),     //

[oth, 2015/10/30 09:46:19]

It looks like our logic for detecting when to emit return hasn't worked here.
Can you a todo here to avoid emitting the second return.

[mythria, 2015/10/30 15:07:47]

I am not sure if it is easy to eliminate return here. We have to do inter block
optimization here. The earlier return was in a different block. 

[oth, 2015/10/30 15:31:34]

Yes.

+        B(Return)},          //
        0,
        {unused, unused, unused, unused, unused, unused}},
       {"function f() { if ('lucky') { return 1; } else { return -1; } } f();",
        0,
        1,
-       15,
-       {B(LdaConstant), U8(0),  //
-        B(ToBoolean),           //
-        B(JumpIfFalse), U8(7),  //
-        B(LdaSmi8), U8(1),      //
-        B(Return),              //
-        B(Jump), U8(5),         //
-        B(LdaSmi8), U8(-1),     //
-        B(Return),              //
-        B(LdaUndefined),        //
-        B(Return)},             //
-       1,
-       {helper.factory()->NewStringFromStaticChars("lucky"), unused, unused,
-        unused, unused, unused}},
+       5,
+       {B(LdaSmi8), U8(1),  //
+        B(Return),          //
+        B(LdaUndefined),    //
+        B(Return)},         //
+       0,
+       {unused, unused, unused, unused, unused, unused}},
       {"function f() { if (false) { return 1; } else { return -1; } } f();",
        0,
        1,
-       13,
-       {B(LdaFalse),            //
-        B(JumpIfFalse), U8(7),  //
-        B(LdaSmi8), U8(1),      //
-        B(Return),              //
-        B(Jump), U8(5),         //
-        B(LdaSmi8), U8(-1),     //
-        B(Return),              //
-        B(LdaUndefined),        //
-        B(Return)},             //
+       5,
+       {B(LdaSmi8), U8(-1),  //
+        B(Return),           //
+        B(LdaUndefined),     //
+        B(Return)},          //
+       0,
+       {unused, unused, unused, unused, unused, unused}},
+      {"function f() { if (false) { return 1; } } f();",
+       0,
+       1,
+       2,
+       {B(LdaUndefined), B(Return)},
        0,
        {unused, unused, unused, unused, unused, unused}},
       {"function f(a) { if (a <= 0) { return 200; } else { return -200; } }"
        "f(99);",
        0,
        2,
        15,
        {B(LdaZero),                       //
         B(TestLessThanOrEqual), A(1, 2),  //
         B(JumpIfFalse), U8(7),            //
@@ skipping 258 matching lines @@
        "  if (i < 0) continue;"
        "  if (i == 3) break;"
        "  if (i == 4) break;"
        "  if (i == 10) continue;"
        "  if (i == 5) break;"
        "  i = i + 1;"
        "}"
        "return i;",
        1 * kPointerSize,
        1,
-       56,
+       53,
        {
-           B(LdaZero),              //
-           B(Star), R(0),           //
-           B(Jump), U8(47),         //
-           B(LdaZero),              //
-           B(TestLessThan), R(0),   //
-           B(JumpIfFalse), U8(4),   //
-           B(Jump), U8(40),         //
-           B(LdaSmi8), U8(3),       //
-           B(TestEqual), R(0),      //
-           B(JumpIfFalse), U8(4),   //
-           B(Jump), U8(35),         //
-           B(LdaSmi8), U8(4),       //
-           B(TestEqual), R(0),      //
-           B(JumpIfFalse), U8(4),   //
-           B(Jump), U8(27),         //
-           B(LdaSmi8), U8(10),      //
-           B(TestEqual), R(0),      //
-           B(JumpIfFalse), U8(4),   //
-           B(Jump), U8(16),         //
-           B(LdaSmi8), U8(5),       //
-           B(TestEqual), R(0),      //
-           B(JumpIfFalse), U8(4),   //
-           B(Jump), U8(11),         //
-           B(LdaSmi8), U8(1),       //
-           B(Add), R(0),            //
-           B(Star), R(0),           //
-           B(LdaTrue),              //
-           B(JumpIfTrue), U8(-46),  //
-           B(Ldar), R(0),           //
-           B(Return),               //
+           B(LdaZero),             //
+           B(Star), R(0),          //
+           B(LdaZero),             //
+           B(TestLessThan), R(0),  //
+           B(JumpIfFalse), U8(4),  //
+           B(Jump), U8(40),        //
+           B(LdaSmi8), U8(3),      //
+           B(TestEqual), R(0),     //
+           B(JumpIfFalse), U8(4),  //
+           B(Jump), U8(34),        //
+           B(LdaSmi8), U8(4),      //
+           B(TestEqual), R(0),     //
+           B(JumpIfFalse), U8(4),  //
+           B(Jump), U8(26),        //
+           B(LdaSmi8), U8(10),     //
+           B(TestEqual), R(0),     //
+           B(JumpIfFalse), U8(4),  //
+           B(Jump), U8(16),        //
+           B(LdaSmi8), U8(5),      //
+           B(TestEqual), R(0),     //
+           B(JumpIfFalse), U8(4),  //
+           B(Jump), U8(10),        //
+           B(LdaSmi8), U8(1),      //
+           B(Add), R(0),           //
+           B(Star), R(0),          //
+           B(Jump), U8(-45),       //
+           B(Ldar), R(0),          //
+           B(Return),              //
        },
        0},
       {"var x = 0; var y = 1;"
        "do {"
        "  y = y * 10;"
        "  if (x == 5) break;"
        "  if (x == 6) continue;"
        "  x = x + 1;"
        "} while (x < 10);"
        "return y;",
@@ skipping 82 matching lines @@
        "  while (i < 3) {"
        "    if (i == 2) break;"
        "    i = i + 1;"
        "  }"
        "  i = i + 1;"
        "  break;"
        "}"
        "return i;",
        1 * kPointerSize,
        1,
-       41,
+       38,
        {
            B(LdaZero),              //
            B(Star), R(0),           //
-           B(Jump), U8(32),         //
            B(Jump), U8(16),         //
            B(LdaSmi8), U8(2),       //
            B(TestEqual), R(0),      //
            B(JumpIfFalse), U8(4),   //
            B(Jump), U8(14),         //
            B(LdaSmi8), U8(1),       //
            B(Add), R(0),            //
            B(Star), R(0),           //
            B(LdaSmi8), U8(3),       //
            B(TestLessThan), R(0),   //
            B(JumpIfTrue), U8(-18),  //
            B(LdaSmi8), U8(1),       //
            B(Add), R(0),            //
            B(Star), R(0),           //
-           B(Jump), U8(5),          //
-           B(LdaTrue),              //
-           B(JumpIfTrue), U8(-31),  //
+           B(Jump), U8(4),          //
+           B(Jump), U8(-30),        //
            B(Ldar), R(0),           //
            B(Return),               //
        },
        0},
+      {"var x = 0; var y = 1;"
+       "do {"
+       "  y = y * 10;"
+       "  if (x == 5) break;"
+       "  x = x + 1;"
+       "  if (x == 6) continue;"
+       "} while (false);"
+       "return y;",
+       2 * kPointerSize,
+       1,
+       38,
+       {
+           B(LdaZero),             //
+           B(Star), R(0),          //
+           B(LdaSmi8), U8(1),      //
+           B(Star), R(1),          //
+           B(LdaSmi8), U8(10),     //
+           B(Mul), R(1),           //
+           B(Star), R(1),          //
+           B(LdaSmi8), U8(5),      //
+           B(TestEqual), R(0),     //
+           B(JumpIfFalse), U8(4),  //
+           B(Jump), U8(16),        //
+           B(LdaSmi8), U8(1),      //
+           B(Add), R(0),           //
+           B(Star), R(0),          //
+           B(LdaSmi8), U8(6),      //
+           B(TestEqual), R(0),     //
+           B(JumpIfFalse), U8(4),  //
+           B(Jump), U8(2),         //
+           B(Ldar), R(1),          //
+           B(Return),              //
+       },
+       0},
+      {"var x = 0; var y = 1;"
+       "do {"
+       "  y = y * 10;"
+       "  if (x == 5) break;"
+       "  x = x + 1;"
+       "  if (x == 6) continue;"
+       "} while (true);"
+       "return y;",
+       2 * kPointerSize,
+       1,
+       40,
+       {
+           B(LdaZero),             //
+           B(Star), R(0),          //
+           B(LdaSmi8), U8(1),      //
+           B(Star), R(1),          //
+           B(LdaSmi8), U8(10),     //
+           B(Mul), R(1),           //
+           B(Star), R(1),          //
+           B(LdaSmi8), U8(5),      //
+           B(TestEqual), R(0),     //
+           B(JumpIfFalse), U8(4),  //
+           B(Jump), U8(18),        //
+           B(LdaSmi8), U8(1),      //
+           B(Add), R(0),           //
+           B(Star), R(0),          //
+           B(LdaSmi8), U8(6),      //
+           B(TestEqual), R(0),     //
+           B(JumpIfFalse), U8(4),  //
+           B(Jump), U8(2),         //
+           B(Jump), U8(-28),       //
+           B(Ldar), R(1),          //
+           B(Return),              //
+       },
+       0},
+      {"var x = 0;"
+       "while(false) {"
+       "  x = x + 1;"
+       "};"
+       "return x;",
+       1 * kPointerSize,
+       1,
+       6,
+       {
+           B(LdaZero),     //
+           B(Star), R(0),  //
+           B(Ldar), R(0),  //
+           B(Return),      //
+       },
+       0},
+      {"var x = 0;"
+       "for( var i = 0; false; i++) {"
+       "  x = x + 1;"
+       "};"
+       "return x;",
+       2 * kPointerSize,
+       1,
+       9,
+       {
+           B(LdaZero),     //
+           B(Star), R(0),  //
+           B(LdaZero),     //
+           B(Star), R(1),  //
+           B(Ldar), R(0),  //
+           B(Return),      //
+       },
+       0},
+      {"var x = 0;"
+       "for( var i = 0; true; ++i) {"
+       "  x = x + 1;"
+       "  if (x == 20) break;"
+       "};"
+       "return x;",
+       2 * kPointerSize,
+       1,
+       31,
+       {
+           B(LdaZero),             //
+           B(Star), R(0),          //
+           B(LdaZero),             //
+           B(Star), R(1),          //
+           B(LdaSmi8), U8(1),      //
+           B(Add), R(0),           //
+           B(Star), R(0),          //
+           B(LdaSmi8), U8(20),     //
+           B(TestEqual), R(0),     //
+           B(JumpIfFalse), U8(4),  //
+           B(Jump), U8(10),        //
+           B(Ldar), R(1),          //
+           B(ToNumber),            //
+           B(Inc),                 //
+           B(Star), R(1),          //
+           B(Jump), U8(-20),       //
+           B(Ldar), R(0),          //
+           B(Return),              //
+       },
+       0},
   };
 
   for (size_t i = 0; i < arraysize(snippets); i++) {
     Handle<BytecodeArray> bytecode_array =
         helper.MakeBytecodeForFunctionBody(snippets[i].code_snippet);
     CheckBytecodeArrayEqual(snippets[i], bytecode_array);
   }
 }
 
 
@@ skipping 1081 matching lines @@
        3,
        {
            B(LdaConstant), U8(0),  //
            B(Throw),               //
        },
        1,
        {"Error"}},
       {"if ('test') { throw 'Error'; };",
        0,
        1,
-       10,
+       5,
        {
            B(LdaConstant), U8(0),  //
-           B(ToBoolean),           //
-           B(JumpIfFalse), U8(5),  //
-           B(LdaConstant), U8(1),  //
            B(Throw),               //
            B(LdaUndefined),        //
            B(Return),              //
        },
-       2,
-       {"test", "Error"}},
+       1,
+       {"Error"}},
   };
 
   for (size_t i = 0; i < arraysize(snippets); i++) {
     Handle<BytecodeArray> bytecode_array =
         helper.MakeBytecodeForFunctionBody(snippets[i].code_snippet);
     CheckBytecodeArrayEqual(snippets[i], bytecode_array);
   }
 }
 
 
@@ skipping 997 matching lines @@
   for (size_t i = 0; i < arraysize(snippets); i++) {
     Handle<BytecodeArray> bytecode_array =
         helper.MakeBytecodeForFunctionBody(snippets[i].code_snippet);
     CheckBytecodeArrayEqual(snippets[i], bytecode_array);
   }
 }
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8