riscv64: [codegen] Implement VisitNop

Test: m test-art-host-gtest
Bug: 283082089
Change-Id: I0e9bb075cd05769fd013a95ae6f084dbd0a91063
diff --git a/compiler/optimizing/code_generator_riscv64.cc b/compiler/optimizing/code_generator_riscv64.cc
index e4160bd..cda31f7 100644
--- a/compiler/optimizing/code_generator_riscv64.cc
+++ b/compiler/optimizing/code_generator_riscv64.cc
@@ -2488,13 +2488,11 @@
 }
 
 void LocationsBuilderRISCV64::VisitNop(HNop* instruction) {
-  UNUSED(instruction);
-  LOG(FATAL) << "Unimplemented";
+  new (GetGraph()->GetAllocator()) LocationSummary(instruction);
 }
 
-void InstructionCodeGeneratorRISCV64::VisitNop(HNop* instruction) {
-  UNUSED(instruction);
-  LOG(FATAL) << "Unimplemented";
+void InstructionCodeGeneratorRISCV64::VisitNop([[maybe_unused]] HNop* instruction) {
+  // The environment recording already happened in CodeGenerator::Compile.
 }
 
 void LocationsBuilderRISCV64::VisitNot(HNot* instruction) {