Revert "[turbofan] re-wire Unreachable to the graph end at EffectPhi's"

This reverts commit 2c0b1f6e.

Reason for revert: Seems to cause GC stress failures blocking LKGR:
https://ci.chromium.org/p/v8/builders/ci/V8%20Linux%20-%20gc%20stress/22453
https://ci.chromium.org/p/v8/builders/ci/V8%20Mac64%20GC%20Stress/7318

Original change's description:
> [turbofan] re-wire Unreachable to the graph end at EffectPhi's
> 
> This avoids the EffectControlLinearizer stumbling upon unreachable
> code.
> 
> Bug: chromium:958718
> Change-Id: I135c17813741e48e878a4624370eee1e06081031
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1605737
> Reviewed-by: Jaroslav Sevcik <jarin@chromium.org>
> Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#61434}

TBR=jarin@chromium.org,tebbi@chromium.org

Change-Id: I85cf33f06617b15cdd435e2699ace99e532d26e2
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Bug: chromium:958718
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1607655Reviewed-by: Maya Lekova <mslekova@chromium.org>
Commit-Queue: Maya Lekova <mslekova@chromium.org>
Cr-Commit-Position: refs/heads/master@{#61436}

src/compiler/dead-code-elimination.cc

@@ -61,7 +61,7 @@ Reduction DeadCodeElimination::Reduce(Node* node) {
     case IrOpcode::kPhi:
       return ReducePhi(node);
     case IrOpcode::kEffectPhi:
-      return ReduceEffectPhi(node);
+      return PropagateDeadControl(node);
     case IrOpcode::kDeoptimize:
     case IrOpcode::kReturn:
     case IrOpcode::kTerminate:
@@ -109,6 +109,7 @@ Reduction DeadCodeElimination::ReduceEnd(Node* node) {
   return NoChange();
 }
 
+
 Reduction DeadCodeElimination::ReduceLoopOrMerge(Node* node) {
   DCHECK(IrOpcode::IsMergeOpcode(node->opcode()));
   Node::Inputs inputs = node->inputs();
@@ -232,36 +233,6 @@ Reduction DeadCodeElimination::ReducePhi(Node* node) {
   return NoChange();
 }
 
-Reduction DeadCodeElimination::ReduceEffectPhi(Node* node) {
-  DCHECK_EQ(IrOpcode::kEffectPhi, node->opcode());
-  Reduction reduction = PropagateDeadControl(node);
-  if (reduction.Changed()) return reduction;
-
-  Node* merge = NodeProperties::GetControlInput(node);
-  DCHECK(merge->opcode() == IrOpcode::kMerge ||
-         merge->opcode() == IrOpcode::kLoop);
-  int input_count = node->op()->EffectInputCount();
-  for (int i = 0; i < input_count; ++i) {
-    Node* effect = NodeProperties::GetEffectInput(node, i);
-    if (effect->opcode() == IrOpcode::kUnreachable) {
-      // If Unreachable hits an effect phi, we can re-connect the effect chain
-      // to the graph end and delete the corresponding inputs from the merge and
-      // phi nodes.
-      Node* control = NodeProperties::GetControlInput(merge, i);
-      Node* throw_node = graph_->NewNode(common_->Throw(), effect, control);
-      NodeProperties::MergeControlToEnd(graph_, common_, throw_node);
-      // Only remove the value uses of the Unreachable node, since other Throw
-      // nodes might already have the Unreachable node as an input.
-      ReplaceWithValue(effect, dead_, effect);
-      NodeProperties::ReplaceEffectInput(node, dead_, i);
-      NodeProperties::ReplaceControlInput(merge, dead_, i);
-      Revisit(merge);
-      reduction = Changed(node);
-    }
-  }
-  return reduction;
-}
-
 Reduction DeadCodeElimination::ReducePureNode(Node* node) {
   DCHECK_EQ(0, node->op()->EffectInputCount());
   if (node->opcode() == IrOpcode::kDeadValue) return NoChange();

src/compiler/dead-code-elimination.h

@@ -53,7 +53,6 @@ class V8_EXPORT_PRIVATE DeadCodeElimination final
   Reduction ReduceLoopExit(Node* node);
   Reduction ReduceNode(Node* node);
   Reduction ReducePhi(Node* node);
-  Reduction ReduceEffectPhi(Node* node);
   Reduction ReducePureNode(Node* node);
   Reduction ReduceUnreachableOrIfException(Node* node);
   Reduction ReduceEffectNode(Node* node);