[Interpreter] Add a simple dead-code elimination bytecode optimizer.

test/cctest/interpreter/test-source-positions.cc

Index: test/cctest/interpreter/test-source-positions.cc
diff --git a/test/cctest/interpreter/test-source-positions.cc b/test/cctest/interpreter/test-source-positions.cc
index d50bb62b2b31ca9c4de77d112dd27c0020695419..19be47fa8e141192d67258203045158ead5f4e60 100644
--- a/test/cctest/interpreter/test-source-positions.cc
+++ b/test/cctest/interpreter/test-source-positions.cc
@@ -19,11 +19,12 @@ namespace interpreter {
 
 // Flags enabling optimizations that change generated bytecode array.
 // Format is <command-line flag> <flag name> <bit index>
-#define OPTIMIZATION_FLAGS(V)                  \
-  V(FLAG_ignition_reo, kUseReo, 0)             \
-  V(FLAG_ignition_peephole, kUsePeephole, 1)   \
-  V(FLAG_ignition_filter_expression_positions, \
-    kUseUseFilterExpressionPositions, 2)
+#define OPTIMIZATION_FLAGS(V)                                                 \
+  V(FLAG_ignition_reo, kUseReo, 0)                                            \
+  V(FLAG_ignition_peephole, kUsePeephole, 1)                                  \
+  V(FLAG_ignition_filter_expression_positions, kUseFilterExpressionPositions, \
+    2)                                                                        \
+  V(FLAG_ignition_deadcode, kUseDeadCode, 3)
 
 #define DECLARE_BIT(_, Name, BitIndex) static const int Name = 1 << BitIndex;
 OPTIMIZATION_FLAGS(DECLARE_BIT)
@@ -32,17 +33,22 @@ OPTIMIZATION_FLAGS(DECLARE_BIT)
 // Test cases source positions are checked for. Please ensure all
 // combinations of flags are present here. This is done manually
 // because it provides easier to comprehend failure case for humans.
-#define TEST_CASES(V)                                                    \
-  V(UsingReo, kUseReo)                                                   \
-  V(UsingPeephole, kUsePeephole)                                         \
-  V(UsingReoAndPeephole, kUseReo | kUsePeephole)                         \
-  V(UsingUseFilterExpressionPositions, kUseUseFilterExpressionPositions) \
-  V(UsingReoAndUseFilterExpressionPositions,                             \
-    kUseReo | kUseUseFilterExpressionPositions)                          \
-  V(UsingPeepholeAndUseFilterExpressionPositions,                        \
-    kUsePeephole | kUseUseFilterExpressionPositions)                     \
-  V(UsingAllOptimizations,                                               \
-    kUseReo | kUsePeephole | kUseUseFilterExpressionPositions)
+#define TEST_CASES(V)                                              \
+  V(UsingReo, kUseReo)                                             \
+  V(UsingPeephole, kUsePeephole)                                   \
+  V(UsingDeadCode, kUseDeadCode)                                   \
+  V(UsingFilterExpressionPositions, kUseFilterExpressionPositions) \
+  V(UsingReoAndPeephole, kUseReo | kUsePeephole)                   \
+  V(UsingReoAndFilterExpressionPositions,                          \
+    kUseReo | kUseFilterExpressionPositions)                       \
+  V(UsingReoAndDeadCode, kUseReo | kUseDeadCode)                   \
+  V(UsingPeepholeAndFilterExpressionPositions,                     \
+    kUsePeephole | kUseFilterExpressionPositions)                  \
+  V(UsingPeepholeAndDeadCode, kUsePeephole | kUseDeadCode)         \
+  V(UsingFilterExpressionPositionsAndDeadCode,                     \
+    kUseFilterExpressionPositions | kUseDeadCode)                  \

[rmcilroy, 2016/06/21 10:25:19]

Since adding all the combinations quickly becomes exponental, I decided only to
do each individual flag, each pair
of flags and all flags together - I don't think it's worth doing all the other
combinations. WDYT?

[oth, 2016/06/21 11:03:56]

Okay here. I preferred using a counter to sweep through all combinations, but
it's a bit cryptic. The number of cases is still smallish, but agree it could be
overly conservative and doesn't scale.

+  V(UsingAllOptimizations,                                         \
+    kUseReo | kUsePeephole | kUseFilterExpressionPositions | kUseDeadCode)
 
 struct TestCaseData {
   TestCaseData(const char* const script,
@@ -142,9 +148,7 @@ class OptimizedBytecodeSourcePositionTester final {
                                      const char* function_body,
                                      const char* function_decl_params,
                                      const char* function_args);
-  static std::string MakeFunctionName(int optimization_bitmap);
-  static std::string MakeScript(const char* function_name,
-                                const char* function_body,
+  static std::string MakeScript(const char* function_body,
                                 const char* function_decl_params,
                                 const char* function_args);
 
@@ -161,39 +165,30 @@ class OptimizedBytecodeSourcePositionTester final {
 };
 
 // static
-std::string OptimizedBytecodeSourcePositionTester::MakeFunctionName(
-    int optimization_bitmap) {
-  std::ostringstream os;
-  os << "test_function_" << optimization_bitmap;
-  return os.str();
-}
-
-// static
 std::string OptimizedBytecodeSourcePositionTester::MakeScript(
-    const char* function_name, const char* function_body,
-    const char* function_decl_params, const char* function_args) {
+    const char* function_body, const char* function_decl_params,
+    const char* function_args) {
   std::ostringstream os;
-  os << "function " << function_name << "(" << function_decl_params << ") {";
+  os << "function test_function"
+     << "(" << function_decl_params << ") {";
   os << function_body;
   os << "}";
-  os << function_name << "(" << function_args << ");";
+  os << "test_function(" << function_args << ");";
   return os.str();
 }
 
 Handle<BytecodeArray> OptimizedBytecodeSourcePositionTester::MakeBytecode(
     int optimization_bitmap, const char* function_body,
     const char* function_decl_params, const char* function_args) {
-  std::string function_name = MakeFunctionName(optimization_bitmap);

[rmcilroy, 2016/06/21 10:25:19]

It turned out this was the issue with the source positions - if the optimization
bitmap reached double digits it shifted the source positions relative to the
unoptimized case. I've just removed the suffix so both functions are the same.

[oth, 2016/06/21 11:03:56]

Ouch, mea culpa! Sorry!

-  std::string script = MakeScript(function_name.c_str(), function_body,
-                                  function_decl_params, function_args);
+  std::string script =
+      MakeScript(function_body, function_decl_params, function_args);
   SetOptimizationFlags(optimization_bitmap);
   CompileRun(script.c_str());
 
-  Local<Function> api_function =
-      Local<Function>::Cast(CcTest::global()
-                                ->Get(CcTest::isolate()->GetCurrentContext(),
-                                      v8_str(function_name.c_str()))
-                                .ToLocalChecked());
+  Local<Function> api_function = Local<Function>::Cast(
+      CcTest::global()
+          ->Get(CcTest::isolate()->GetCurrentContext(), v8_str("test_function"))
+          .ToLocalChecked());
   Handle<JSFunction> function =
       Handle<JSFunction>::cast(v8::Utils::OpenHandle(*api_function));
   return handle(function->shared()->bytecode_array());