[turbofan] Improve representation selection for Smi checking.

src/compiler/simplified-lowering.cc

Index: src/compiler/simplified-lowering.cc
diff --git a/src/compiler/simplified-lowering.cc b/src/compiler/simplified-lowering.cc
index fc7dcf8f939344dba37a79bb1d7eaf4a45611763..a531b27ec87a63408961611d6ccf874d4d53ef39 100644
--- a/src/compiler/simplified-lowering.cc
+++ b/src/compiler/simplified-lowering.cc
@@ -2126,6 +2126,15 @@ class RepresentationSelector {
         }
         return;
       }
+      case IrOpcode::kCheckHeapObject: {
+        if (InputCannotBe(node, Type::SignedSmall())) {
+          VisitUnop(node, UseInfo::AnyTagged(), MachineRepresentation::kTagged);
+          if (lower()) DeferReplacement(node, node->InputAt(0));
+        } else {
+          VisitUnop(node, UseInfo::AnyTagged(), MachineRepresentation::kTagged);
+        }
+        return;
+      }
       case IrOpcode::kCheckIf: {
         ProcessInput(node, 0, UseInfo::Bool());
         ProcessRemainingInputs(node, 1);
@@ -2151,28 +2160,20 @@ class RepresentationSelector {
         }
         return;
       }
-      case IrOpcode::kCheckString: {
-        if (InputIs(node, Type::String())) {
-          VisitUnop(node, UseInfo::AnyTagged(), MachineRepresentation::kTagged);
-          if (lower()) DeferReplacement(node, node->InputAt(0));
+      case IrOpcode::kCheckSmi: {
+        if (SmiValuesAre32Bits() && truncation.IsUsedAsWord32()) {
+          VisitUnop(node, UseInfo::CheckedSignedSmallAsWord32(),
+                    MachineRepresentation::kWord32);
         } else {
-          VisitUnop(node, UseInfo::AnyTagged(), MachineRepresentation::kTagged);
+          VisitUnop(node, UseInfo::CheckedSignedSmallAsTaggedSigned(),
+                    MachineRepresentation::kTaggedSigned);
         }
+        if (lower()) DeferReplacement(node, node->InputAt(0));
         return;
       }
-      case IrOpcode::kCheckTaggedPointer: {
-        if (InputCannotBe(node, Type::SignedSmall())) {
-          VisitUnop(node, UseInfo::AnyTagged(), MachineRepresentation::kTagged);
-          if (lower()) DeferReplacement(node, node->InputAt(0));
-        } else {
+      case IrOpcode::kCheckString: {
+        if (InputIs(node, Type::String())) {
           VisitUnop(node, UseInfo::AnyTagged(), MachineRepresentation::kTagged);
-        }
-        return;
-      }
-      case IrOpcode::kCheckTaggedSigned: {
-        if (SmiValuesAre32Bits() && truncation.IsUsedAsWord32()) {
-          VisitUnop(node, UseInfo::CheckedSignedSmallAsWord32(),
-                    MachineRepresentation::kWord32);
           if (lower()) DeferReplacement(node, node->InputAt(0));
         } else {
           VisitUnop(node, UseInfo::AnyTagged(), MachineRepresentation::kTagged);