[turbofan] add non fixed slot constraint to register allocator

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 668216141f7e1ff82fa2586e6a822ec2abb54abc..279cbcb805c0e5935e3a2226f1a50ff0d74009d3 100644
--- a/src/compiler/instruction-selector-impl.h
+++ b/src/compiler/instruction-selector-impl.h
@@ -75,6 +75,11 @@ class OperandGenerator {
                                         GetVReg(node)));
   }
 
+  InstructionOperand UseUniqueSlot(Node* node) {
+    return Use(node, UnallocatedOperand(UnallocatedOperand::MUST_HAVE_SLOT,
+                                        GetVReg(node)));
+  }
+
   // Use register or operand for the node. If a register is chosen, it won't
   // alias any temporary or output registers.
   InstructionOperand UseUnique(Node* node) {