[turbofan] Validate split-edge form

src/compiler/instruction.cc

 // Copyright 2014 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/compiler/common-operator.h"
 #include "src/compiler/graph.h"
 #include "src/compiler/instruction.h"
 #include "src/compiler/schedule.h"
 #include "src/compiler/state-values-utils.h"
 
@@ skipping 597 matching lines @@
   for (BasicBlockVector::const_iterator it = schedule->rpo_order()->begin();
        it != schedule->rpo_order()->end(); ++it, ++rpo_number) {
     DCHECK(!(*blocks)[rpo_number]);
     DCHECK(GetRpo(*it).ToSize() == rpo_number);
     (*blocks)[rpo_number] = InstructionBlockFor(zone, *it);
   }
   ComputeAssemblyOrder(blocks);
   return blocks;
 }
 
+void InstructionSequence::Validate() {
+  // Validate blocks are in edge-split form: no block with multiple successors
+  // has an edge to a block (== a successor) with more than one predecessors.
+  for (const InstructionBlock* block : instruction_blocks()) {
+    if (block->SuccessorCount() > 1) {
+      for (const RpoNumber& successor_id : block->successors()) {
+        const InstructionBlock* successor = InstructionBlockAt(successor_id);
+        // Expect precisely one predecessor: "block".
+        CHECK(successor->PredecessorCount() == 1 &&
+              successor->predecessors()[0] == block->rpo_number());
+      }
+    }
+  }
+}
 
 void InstructionSequence::ComputeAssemblyOrder(InstructionBlocks* blocks) {
   int ao = 0;
   for (auto const block : *blocks) {
     if (!block->IsDeferred()) {
       block->set_ao_number(RpoNumber::FromInt(ao++));
     }
   }
   for (auto const block : *blocks) {
     if (block->IsDeferred()) {
@@ skipping 330 matching lines @@
   }
   for (int i = 0; i < code.InstructionBlockCount(); i++) {
     printable.sequence_->PrintBlock(printable.register_configuration_, i);
   }
   return os;
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8