Reland of [ignition/turbo] Perform liveness analysis on the bytecodes

src/interpreter/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/interpreter/bytecode-generator.h"
 
 #include "src/ast/compile-time-value.h"
 #include "src/ast/scopes.h"
 #include "src/code-stubs.h"
 #include "src/compilation-info.h"
@@ skipping 704 matching lines @@
         .CompareOperation(Token::Value::EQ_STRICT, index)
         .JumpIfTrue(&(targets[i]));
   }
   BuildAbort(BailoutReason::kInvalidJumpTableIndex);
 }
 
 void BytecodeGenerator::VisitIterationHeader(IterationStatement* stmt,
                                              LoopBuilder* loop_builder) {
   // Recall that stmt->yield_count() is always zero inside ordinary
   // (i.e. non-generator) functions.
+  if (stmt->yield_count() == 0) {
+    loop_builder->LoopHeader();
+  } else {
+    // Collect all labels for generator resume points within the loop (if any)
+    // so
+    // that they can be bound to the loop header below. Also create fresh labels
+    // for these resume points, to be used inside the loop.
+    ZoneVector<BytecodeLabel> resume_points_in_loop(zone());
+    size_t first_yield = stmt->first_yield_id();
+    DCHECK_LE(first_yield + stmt->yield_count(),
+              generator_resume_points_.size());
+    for (size_t id = first_yield; id < first_yield + stmt->yield_count();
+         id++) {
+      auto& label = generator_resume_points_[id];
+      resume_points_in_loop.push_back(label);
+      generator_resume_points_[id] = BytecodeLabel();
+    }
 
-  // Collect all labels for generator resume points within the loop (if any) so
-  // that they can be bound to the loop header below. Also create fresh labels
-  // for these resume points, to be used inside the loop.
-  ZoneVector<BytecodeLabel> resume_points_in_loop(zone());
-  size_t first_yield = stmt->first_yield_id();
-  DCHECK_LE(first_yield + stmt->yield_count(), generator_resume_points_.size());
-  for (size_t id = first_yield; id < first_yield + stmt->yield_count(); id++) {
-    auto& label = generator_resume_points_[id];
-    resume_points_in_loop.push_back(label);
-    generator_resume_points_[id] = BytecodeLabel();
-  }
+    loop_builder->LoopHeader(&resume_points_in_loop);

[rmcilroy, 2016/11/28 10:00:31]

Why did you need to change this code here?

[Leszek Swirski, 2016/11/28 11:07:22]

Oh, this was a drive-by fix -- I had changed LoopBuilder::LoopHeader to allow
nullptr so that I could use it in tests, and I noticed that we could
fast-path/clarify the non-generator case here and avoid initialising a
ZoneVector and risk allocating anything on the zone (afaik in most
implementations vectors are constructed without an initial allocation, but it
doesn't hurt to be careful).

 
-  loop_builder->LoopHeader(&resume_points_in_loop);
-
-  if (stmt->yield_count() > 0) {
     // If we are not resuming, fall through to loop body.
     // If we are resuming, perform state dispatch.
     BytecodeLabel not_resuming;
     builder()
         ->LoadLiteral(Smi::FromInt(JSGeneratorObject::kGeneratorExecuting))
         .CompareOperation(Token::Value::EQ, generator_state_)
         .JumpIfTrue(&not_resuming);
     BuildIndexedJump(generator_state_, first_yield,
         stmt->yield_count(), generator_resume_points_);
     builder()->Bind(&not_resuming);
@@ skipping 2445 matching lines @@
 }
 
 Runtime::FunctionId BytecodeGenerator::StoreKeyedToSuperRuntimeId() {
   return is_strict(language_mode()) ? Runtime::kStoreKeyedToSuper_Strict
                                     : Runtime::kStoreKeyedToSuper_Sloppy;
 }
 
 }  // namespace interpreter
 }  // namespace internal
 }  // namespace v8