[turbofan] Slightly improve truncations for CheckBounds.

src/compiler/simplified-lowering.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/simplified-lowering.h"
 
 #include <limits>
 
 #include "src/address-map.h"
 #include "src/base/bits.h"
@@ skipping 2277 matching lines @@
         ProcessInput(node, 0, UseInfo::AnyTagged());
         ProcessInput(node, 1, UseInfo::AnyTagged());
         ProcessInput(node, 2, UseInfo::TaggedSigned());
         SetOutput(node, MachineRepresentation::kTaggedSigned);
         return;
       }
 
       case IrOpcode::kCheckBounds: {
         Type* index_type = TypeOf(node->InputAt(0));
         Type* length_type = TypeOf(node->InputAt(1));
-        if (index_type->Is(Type::Unsigned32())) {
+        if (index_type->Is(Type::Integral32OrMinusZero())) {
+          // Map -0 to 0, and the values in the [-2^31,-1] range to the
+          // [2^31,2^32-1] range, which will be considered out-of-bounds
+          // as well, because the {length_type} is limited to Unsigned31.
           VisitBinop(node, UseInfo::TruncatingWord32(),
                      MachineRepresentation::kWord32);
-          if (lower() && index_type->Max() < length_type->Min()) {
-            // The bounds check is redundant if we already know that
-            // the index is within the bounds of [0.0, length[.
-            DeferReplacement(node, node->InputAt(0));
+          if (lower()) {
+            if (index_type->Min() >= 0.0 &&
+                index_type->Max() < length_type->Min()) {
+              // The bounds check is redundant if we already know that
+              // the index is within the bounds of [0.0, length[.
+              DeferReplacement(node, node->InputAt(0));
+            }
           }
         } else {
           VisitBinop(node, UseInfo::CheckedSigned32AsWord32(kIdentifyZeros),
                      UseInfo::TruncatingWord32(),
                      MachineRepresentation::kWord32);
         }
         return;
       }
       case IrOpcode::kCheckHeapObject: {
         if (InputCannotBe(node, Type::SignedSmall())) {
@@ skipping 1296 matching lines @@
         isolate(), graph()->zone(), callable.descriptor(), 0, flags,
         Operator::kNoProperties);
     to_number_operator_.set(common()->Call(desc));
   }
   return to_number_operator_.get();
 }
 
 }  // namespace compiler
 }  // namespace internal
 }  // namespace v8