8318157: RISC-V: implement ensureMaterializedForStackWalk intrinsic

Backport-of: d6b4aa01a20eb7ecd44602a9fab3e3380bff3d3a

Author: Olga Mikhaltsova

src/hotspot/cpu/riscv/riscv.ad

@@ -2352,6 +2352,11 @@ encode %{
         ciEnv::current()->record_failure("CodeCache is full");
         return;
       }
+    } else if (_method->intrinsic_id() == vmIntrinsicID::_ensureMaterializedForStackWalk) {
+      // The NOP here is purely to ensure that eliding a call to
+      // JVM_EnsureMaterializedForStackWalk doesn't change the code size.
+      __ nop();
+      __ block_comment("call JVM_EnsureMaterializedForStackWalk (elided)");
     } else {
       int method_index = resolved_method_index(cbuf);
       RelocationHolder rspec = _optimized_virtual ? opt_virtual_call_Relocation::spec(method_index)