8344387: RISC-V: C2: Improve encoding of LoadNKlass for compact headers

Reviewed-by: fyang, luhenry

Author: Hamlin Li

src/hotspot/cpu/riscv/c2_MacroAssembler_riscv.cpp

@@ -3124,13 +3124,3 @@ void C2_MacroAssembler::extract_fp_v(FloatRegister dst, VectorRegister src, Basi
     vfmv_f_s(dst, tmp);
   }
 }
-
-void C2_MacroAssembler::load_narrow_klass_compact_c2(Register dst, Address src) {
-  // The incoming address is pointing into obj-start + klass_offset_in_bytes. We need to extract
-  // obj-start, so that we can load from the object's mark-word instead. Usually the address
-  // comes as obj-start in obj and klass_offset_in_bytes in disp.
-  assert(UseCompactObjectHeaders, "must");
-  int offset = oopDesc::mark_offset_in_bytes() - oopDesc::klass_offset_in_bytes();
-  ld(dst, Address(src.base(), src.offset() + offset));
-  srli(dst, dst, markWord::klass_shift);
-}

src/hotspot/cpu/riscv/c2_MacroAssembler_riscv.hpp

@@ -281,6 +281,4 @@
   void extract_v(Register dst, VectorRegister src, BasicType bt, int idx, VectorRegister tmp);
   void extract_fp_v(FloatRegister dst, VectorRegister src, BasicType bt, int idx, VectorRegister tmp);
 
-  void load_narrow_klass_compact_c2(Register dst, Address src);
-
 #endif // CPU_RISCV_C2_MACROASSEMBLER_RISCV_HPP

src/hotspot/cpu/riscv/riscv.ad

@@ -4814,10 +4814,14 @@ instruct loadNKlassCompactHeaders(iRegNNoSp dst, memory mem)
   match(Set dst (LoadNKlass mem));
 
   ins_cost(LOAD_COST);
-  format %{ "load_narrow_klass_compact $dst, $mem\t# compressed class ptr, #@loadNKlassCompactHeaders" %}
+  format %{
+    "lwu  $dst, $mem\t# compressed klass ptr, shifted\n\t"
+    "srli $dst, $dst, markWord::klass_shift_at_offset"
+  %}
 
   ins_encode %{
-    __ load_narrow_klass_compact_c2(as_Register($dst$$reg), Address(as_Register($mem$$base), $mem$$disp));
+    __ lwu(as_Register($dst$$reg), Address(as_Register($mem$$base), $mem$$disp));
+    __ srli(as_Register($dst$$reg), as_Register($dst$$reg), (unsigned) markWord::klass_shift_at_offset);
   %}
 
   ins_pipe(iload_reg_mem);