[turbofan] Handle dead diamonds in scheduling and add a test.

src/compiler/scheduler.cc

Index: src/compiler/scheduler.cc
diff --git a/src/compiler/scheduler.cc b/src/compiler/scheduler.cc
index 80ce8b17112da8404f14fd5ed5db0a2c3f49eacf..8be33fc4a25507a3fe5a7844497a33062a3e4446 100644
--- a/src/compiler/scheduler.cc
+++ b/src/compiler/scheduler.cc
@@ -1538,6 +1538,8 @@ class ScheduleLateNodeVisitor {
   }
 
   BasicBlock* GetBlockForUse(Edge edge) {
+    // TODO(titzer): ignore uses from dead nodes (not visited in PrepareUses()).
+    // Dead uses only occur if the graph is not trimmed before scheduling.
     Node* use = edge.from();
     if (IrOpcode::IsPhiOpcode(use->opcode())) {
       // If the use is from a coupled (i.e. floating) phi, compute the common
@@ -1545,7 +1547,6 @@ class ScheduleLateNodeVisitor {
       if (scheduler_->GetPlacement(use) == Scheduler::kCoupled) {
         TRACE("  inspecting uses of coupled #%d:%s\n", use->id(),
               use->op()->mnemonic());
-        DCHECK_EQ(edge.to(), NodeProperties::GetControlInput(use));

[Michael Starzinger, 2016/04/04 17:07:43]

After the above TODO is being addressed, we really should bring back this
assertion again. Can you move the TODO here and just comment out the DCHECK for
now? Also the TODO should mention to re-enable this DCHECK.

         return GetCommonDominatorOfUses(use);
       }
       // If the use is from a fixed (i.e. non-floating) phi, we use the