[interpreter] Elide OSR polling from fake loops.

This makes sure we are not inserting {OsrPoll} instructions for any
statements that are not actually loops and have no back edges. Without
back edges the {BytecodeGraphBuilder} is unable to deduce loop ranges
and hence cannot construct a graph for OSR entry.

R=neis@chromium.org
TEST=mjsunit/regress/regress-5252
BUG=v8:5252

Review-Url: https://codereview.chromium.org/2200733002
Cr-Commit-Position: refs/heads/master@{#38233}

src/interpreter/bytecode-generator.cc

@@ -1052,13 +1052,14 @@ void BytecodeGenerator::VisitIterationBody(IterationStatement* stmt,
 
 void BytecodeGenerator::VisitDoWhileStatement(DoWhileStatement* stmt) {
   LoopBuilder loop_builder(builder());
-  VisitIterationHeader(stmt, &loop_builder);
   if (stmt->cond()->ToBooleanIsFalse()) {
     VisitIterationBody(stmt, &loop_builder);
   } else if (stmt->cond()->ToBooleanIsTrue()) {
+    VisitIterationHeader(stmt, &loop_builder);
     VisitIterationBody(stmt, &loop_builder);
     loop_builder.JumpToHeader();
   } else {
+    VisitIterationHeader(stmt, &loop_builder);
     VisitIterationBody(stmt, &loop_builder);
     builder()->SetExpressionAsStatementPosition(stmt->cond());
     VisitForAccumulatorValue(stmt->cond());

src/interpreter/control-flow-builders.cc

@@ -102,11 +102,21 @@ void LoopBuilder::LoopHeader(ZoneVector<BytecodeLabel>* additional_labels) {
   }
 }
 
+void LoopBuilder::JumpToHeader() {
+  // Loop must have closed form, i.e. all loop elements are within the loop,
+  // the loop header precedes the body and next elements in the loop.
+  DCHECK(loop_header_.is_bound());
+  builder()->Jump(&loop_header_);
+}
 
-void LoopBuilder::EndLoop() {
+void LoopBuilder::JumpToHeaderIfTrue() {
   // Loop must have closed form, i.e. all loop elements are within the loop,
   // the loop header precedes the body and next elements in the loop.
   DCHECK(loop_header_.is_bound());
+  builder()->JumpIfTrue(&loop_header_);
+}
+
+void LoopBuilder::EndLoop() {
   builder()->Bind(&loop_end_);
   SetBreakTarget(loop_end_);
 }

src/interpreter/control-flow-builders.h

@@ -89,8 +89,8 @@ class LoopBuilder final : public BreakableControlFlowBuilder {
   ~LoopBuilder();
 
   void LoopHeader(ZoneVector<BytecodeLabel>* additional_labels);
-  void JumpToHeader() { builder()->Jump(&loop_header_); }
-  void JumpToHeaderIfTrue() { builder()->JumpIfTrue(&loop_header_); }
+  void JumpToHeader();
+  void JumpToHeaderIfTrue();
   void SetContinueTarget();
   void EndLoop();
 

test/cctest/interpreter/bytecode_expectations/RemoveRedundantLdar.golden

@@ -51,13 +51,13 @@ snippet: "
 "
 frame size: 1
 parameter count: 1
-bytecode array length: 23
+bytecode array length: 22
 bytecodes: [
   /*   30 E> */ B(StackCheck),
   /*   45 S> */ B(LdaSmi), U8(1),
                 B(Star), R(0),
   /*   48 E> */ B(StackCheck),
-  /*   55 S> */ B(Ldar), R(0),
+  /*   55 S> */ B(Nop),
   /*   69 E> */ B(Add), R(0),
                 B(Star), R(0),
   /*   77 S> */ B(LdaSmi), U8(10),

test/mjsunit/regress/regress-5252.js

+// Copyright 2016 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.
+
+// Flags: --allow-natives-syntax --ignition --ignition-osr --turbo-from-bytecode
+
+(function TestNonLoopyLoop() {
+  function f() {
+    do {
+      %OptimizeOsr();
+      return 23;
+    } while(false)
+  }
+  assertEquals(23, f());
+  assertEquals(23, f());
+})();
+
+(function TestNonLoopyGenerator() {
+  function* g() {
+    do {
+      %OptimizeOsr();
+      yield 23;
+      yield 42;
+    } while(false)
+    return 999;
+  }
+  var gen = g();
+  assertEquals({ value:23, done:false }, gen.next());
+  assertEquals({ value:42, done:false }, gen.next());
+  assertEquals({ value:999, done:true }, gen.next());
+})();