[turbofan] support small immediates

src/compiler/instruction-selector-impl.h

Index: src/compiler/instruction-selector-impl.h
diff --git a/src/compiler/instruction-selector-impl.h b/src/compiler/instruction-selector-impl.h
index 657167ee7dc388fbe1b8c917dabfc691d204b441..79d3c5783858e65121f239bb69aa2c546ed264be 100644
--- a/src/compiler/instruction-selector-impl.h
+++ b/src/compiler/instruction-selector-impl.h
@@ -119,8 +119,7 @@ class OperandGenerator {
   }
 
   InstructionOperand UseImmediate(Node* node) {
-    int index = sequence()->AddImmediate(ToConstant(node));
-    return ImmediateOperand(index);
+    return sequence()->AddImmediate(ToConstant(node));
   }
 
   InstructionOperand UseLocation(Node* node, LinkageLocation location,
@@ -149,8 +148,7 @@ class OperandGenerator {
   }
 
   InstructionOperand TempImmediate(int32_t imm) {
-    int index = sequence()->AddImmediate(Constant(imm));
-    return ImmediateOperand(index);
+    return sequence()->AddImmediate(Constant(imm));
   }
 
   InstructionOperand TempLocation(LinkageLocation location, MachineType type) {
@@ -159,9 +157,8 @@ class OperandGenerator {
   }
 
   InstructionOperand Label(BasicBlock* block) {
-    int index = sequence()->AddImmediate(
+    return sequence()->AddImmediate(
         Constant(RpoNumber::FromInt(block->rpo_number())));
-    return ImmediateOperand(index);
   }
 
  protected: