[turbofan] CheckBounds with Unsigned32 inputs is also supported.

If the first input to CheckBounds is already an Unsigned32, then
we can just truncate both inputs to word32 and lower the bounds
check.

R=jarin@chromium.org

Review-Url: https://codereview.chromium.org/2138753002
Cr-Commit-Position: refs/heads/master@{#37643}

src/compiler/simplified-lowering.cc

@@ -1810,8 +1810,14 @@ class RepresentationSelector {
       }
 
       case IrOpcode::kCheckBounds: {
+        if (TypeOf(node->InputAt(0))->Is(Type::Unsigned32())) {
+          VisitBinop(node, UseInfo::TruncatingWord32(),
+                     MachineRepresentation::kWord32);
+        } else {
           VisitBinop(node, UseInfo::CheckedSigned32AsWord32(),
-                   UseInfo::TruncatingWord32(), MachineRepresentation::kWord32);
+                     UseInfo::TruncatingWord32(),
+                     MachineRepresentation::kWord32);
+        }
         return;
       }
       case IrOpcode::kCheckIf: {