Revert of [turbofan] Fix impossible type handling for TypeGuard and...

Revert of [turbofan] Fix impossible type handling for TypeGuard and BooleanNot. (patchset #1 id:1 of https://codereview.chromium.org/2836203004/ )

Reason for revert:
Tentative revert for https://build.chromium.org/p/client.v8/builders/V8%20Linux%20-%20debug/builds/14886

Original issue's description:
> [turbofan] Fix impossible type handling for TypeGuard and BooleanNot.
>
> BUG=chromium:715204
>
> Review-Url: https://codereview.chromium.org/2836203004
> Cr-Commit-Position: refs/heads/master@{#44883}
> Committed: https://chromium.googlesource.com/v8/v8/+/9c47a061cf325addf8bd2ba4b71a4d1ef210c5d6

TBR=bmeurer@chromium.org,jarin@chromium.org
# Skipping CQ checks because original CL landed less than 1 days ago.
NOPRESUBMIT=true
NOTREECHECKS=true
NOTRY=true
BUG=chromium:715204

Review-Url: https://codereview.chromium.org/2842793004
Cr-Commit-Position: refs/heads/master@{#44898}

src/compiler/simplified-lowering.cc

@@ -1531,14 +1531,11 @@ class RepresentationSelector {
             // BooleanNot(x: kRepBit) => Word32Equal(x, #0)
             node->AppendInput(jsgraph_->zone(), jsgraph_->Int32Constant(0));
             NodeProperties::ChangeOp(node, lowering->machine()->Word32Equal());
-          } else if (CanBeTaggedPointer(input_info->representation())) {
+          } else {
+            DCHECK(CanBeTaggedPointer(input_info->representation()));
             // BooleanNot(x: kRepTagged) => WordEqual(x, #false)
             node->AppendInput(jsgraph_->zone(), jsgraph_->FalseConstant());
             NodeProperties::ChangeOp(node, lowering->machine()->WordEqual());
-          } else {
-            DCHECK_EQ(MachineRepresentation::kNone,
-                      input_info->representation());
-            DeferReplacement(node, lowering->jsgraph()->Int32Constant(0));
           }
         } else {
           // No input representation requirement; adapt during lowering.
@@ -2782,13 +2779,8 @@ class RepresentationSelector {
         // We just get rid of the sigma here. In principle, it should be
         // possible to refine the truncation and representation based on
         // the sigma's type.
-
-        // For now, we just handle specially the impossible case.
         MachineRepresentation output =
-            TypeOf(node)->IsInhabited()
-                ? GetOutputInfoForPhi(node, TypeOf(node->InputAt(0)),
-                                      truncation)
-                : MachineRepresentation::kNone;
+            GetOutputInfoForPhi(node, TypeOf(node->InputAt(0)), truncation);
         VisitUnop(node, UseInfo(output, truncation), output);
         if (lower()) DeferReplacement(node, node->InputAt(0));
         return;

test/mjsunit/compiler/regress-715204.js

-// Copyright 2017 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.
-
-var global = true;
-global = false;
-
-function f() {
-  global = 1;
-  return !global;
-}
-
-f();