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src/hotspot/cpu/x86/c2_MacroAssembler_x86.cpp

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@@ -6177,5 +6177,27 @@
    } else {
      assert(bt == T_FLOAT, "");
      vpermps(dst, shuffle, src, vlen_enc);
    }
  }
+ 
+ #ifdef _LP64
+ void C2_MacroAssembler::load_nklass_compact_c2(Register dst, Register obj, Register index, Address::ScaleFactor scale, int disp) {
+   C2LoadNKlassStub* stub = new (Compile::current()->comp_arena()) C2LoadNKlassStub(dst);
+   Compile::current()->output()->add_stub(stub);
+ 
+   // Note: Don't clobber obj anywhere in that method!
+ 
+   // 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. However, sometimes C2
+   // emits code that pre-computes obj-start + klass_offset_in_bytes into a register, and
+   // then passes that register as obj and 0 in disp. The following code extracts the base
+   // and offset to load the mark-word.
+   int offset = oopDesc::mark_offset_in_bytes() + disp - oopDesc::klass_offset_in_bytes();
+   movq(dst, Address(obj, index, scale, offset));
+   testb(dst, markWord::monitor_value);
+   jcc(Assembler::notZero, stub->entry());
+   bind(stub->continuation());
+   shrq(dst, markWord::klass_shift);
+ }
+ #endif
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