Eliminatable CheckMaps replaced with if(true) or if(false).

src/hydrogen.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 95 matching lines @@
 Isolate* HBasicBlock::isolate() const {
   return graph_->isolate();
 }
 
 
 void HBasicBlock::MarkUnreachable() {
   is_reachable_ = false;
 }
 
 
+void HBasicBlock::MarkSuccEdgeUnreachable(int succ) {
+  ASSERT(IsFinished());
+  HBasicBlock* succ_block = end()->SuccessorAt(succ);
+
+  ASSERT(succ_block->predecessors()->length() == 1);
+  succ_block->MarkUnreachable();
+}
+
+
 void HBasicBlock::AttachLoopInformation() {
   ASSERT(!IsLoopHeader());
   loop_information_ = new(zone()) HLoopInformation(this, zone());
 }
 
 
 void HBasicBlock::DetachLoopInformation() {
   ASSERT(IsLoopHeader());
   loop_information_ = NULL;
 }
@@ skipping 180 matching lines @@
   const HBasicBlock* current = this;
   int result  = (current->IsLoopHeader()) ? 1 : 0;
   while (current->parent_loop_header() != NULL) {
     current = current->parent_loop_header();
     result++;
   }
   return result;
 }
 
 
+void HBasicBlock::ReplaceControlWithGotoSuccessor(int succ) {
+  ASSERT(IsFinished());

[titzer, 2014/01/13 17:26:56]

I think you should go ahead and implement the general case (i.e. more than 2
successors).

[Igor Sheludko, 2014/01/14 10:41:36]

It seems that there are no instructions with more than two successors.

+  ASSERT(end()->SuccessorCount() == 2);  // Only this case is supported yet.
+  ASSERT(succ < end()->SuccessorCount());
+
+  // Replace control instruction with if(true) or if(false).
+  HConstant* value = (succ == 0)
+      ? graph()->GetConstantTrue()
+      : graph()->GetConstantFalse();
+
+  HBranch* new_branch = HBranch::New(
+      zone(),
+      NULL,
+      value,
+      ToBooleanStub::Types(ToBooleanStub::BOOLEAN),
+      end()->SuccessorAt(0),
+      end()->SuccessorAt(1));
+
+  int unreachable_succ = 1 - succ;
+
+  MarkSuccEdgeUnreachable(unreachable_succ);

[titzer, 2014/01/13 17:26:56]

You should go through all the "other" successors, and if they have only one
predecessor (namely this one), then mark them as unreachable. Normally they
wouldn't, since we are careful to have edge-split form, but check anyway.

[Igor Sheludko, 2014/01/14 10:41:36]

Normally they
MarkSuccEdgeUnreachable() contains an ASSERT checking that we deal with the
edge-split form.

+
+  end()->DeleteAndReplaceWith(end()->ActualValue());
+  new_branch->InsertAfter(last());
+  end_ = new_branch;
+}
+
+
 void HBasicBlock::PostProcessLoopHeader(IterationStatement* stmt) {
   ASSERT(IsLoopHeader());
 
   SetJoinId(stmt->EntryId());
   if (predecessors()->length() == 1) {
     // This is a degenerated loop.
     DetachLoopInformation();
     return;
   }
 
@@ skipping 10646 matching lines @@
   if (ShouldProduceTraceOutput()) {
     isolate()->GetHTracer()->TraceHydrogen(name(), graph_);
   }
 
 #ifdef DEBUG
   graph_->Verify(false);  // No full verify.
 #endif
 }
 
 } }  // namespace v8::internal