[turbofan] Support virtual register redirection in instruction selector.

src/compiler/instruction.cc

Index: src/compiler/instruction.cc
diff --git a/src/compiler/instruction.cc b/src/compiler/instruction.cc
index 2f37075f9b786eea8c06c314633ee59aac590a6c..0df7ca0316ec3881783d07aaea0f48c7d2948688 100644
--- a/src/compiler/instruction.cc
+++ b/src/compiler/instruction.cc
@@ -568,6 +568,10 @@ void PhiInstruction::SetInput(size_t offset, int virtual_register) {
   operands_[offset] = virtual_register;
 }
 
+void PhiInstruction::RenameInput(size_t offset, int virtual_register) {
+  DCHECK_NE(InstructionOperand::kInvalidVirtualRegister, operands_[offset]);
+  operands_[offset] = virtual_register;
+}
 
 InstructionBlock::InstructionBlock(Zone* zone, RpoNumber rpo_number,
                                    RpoNumber loop_header, RpoNumber loop_end,