src/hotspot/cpu/x86/gc/shenandoah/shenandoahBarrierSetAssembler_x86.cpp

rev 56437 : 8231583: Shenandoah: Fix register clash in SBSA::resolve_forwarding_pointer() borrowing

*** 245,280 ****
    if(tosca_live) __ pop(rax);
  
    __ bind(done);
  }
  
! void ShenandoahBarrierSetAssembler::resolve_forward_pointer(MacroAssembler* masm, Register dst, Register tmp) {
    assert(ShenandoahCASBarrier, "should be enabled");
    Label is_null;
    __ testptr(dst, dst);
    __ jcc(Assembler::zero, is_null);
!   resolve_forward_pointer_not_null(masm, dst, tmp);
    __ bind(is_null);
  }
  
! void ShenandoahBarrierSetAssembler::resolve_forward_pointer_not_null(MacroAssembler* masm, Register dst, Register tmp) {
    assert(ShenandoahCASBarrier || ShenandoahLoadRefBarrier, "should be enabled");
    // The below loads the mark word, checks if the lowest two bits are
    // set, and if so, clear the lowest two bits and copy the result
    // to dst. Otherwise it leaves dst alone.
    // Implementing this is surprisingly awkward. I do it here by:
    // - Inverting the mark word
    // - Test lowest two bits == 0
    // - If so, set the lowest two bits
    // - Invert the result back, and copy to dst
  
-   bool borrow_reg = (tmp == noreg);
-   if (borrow_reg) {
      // No free registers available. Make one useful.
      tmp = LP64_ONLY(rscratch1) NOT_LP64(rdx);
!     __ push(tmp);
    }
  
    Label done;
    __ movptr(tmp, Address(dst, oopDesc::mark_offset_in_bytes()));
    __ notptr(tmp);
    __ testb(tmp, markWord::marked_value);
--- 245,283 ----
    if(tosca_live) __ pop(rax);
  
    __ bind(done);
  }
  
! void ShenandoahBarrierSetAssembler::resolve_forward_pointer(MacroAssembler* masm, Register dst) {
    assert(ShenandoahCASBarrier, "should be enabled");
    Label is_null;
    __ testptr(dst, dst);
    __ jcc(Assembler::zero, is_null);
!   resolve_forward_pointer_not_null(masm, dst);
    __ bind(is_null);
  }
  
! void ShenandoahBarrierSetAssembler::resolve_forward_pointer_not_null(MacroAssembler* masm, Register dst) {
    assert(ShenandoahCASBarrier || ShenandoahLoadRefBarrier, "should be enabled");
    // The below loads the mark word, checks if the lowest two bits are
    // set, and if so, clear the lowest two bits and copy the result
    // to dst. Otherwise it leaves dst alone.
    // Implementing this is surprisingly awkward. I do it here by:
    // - Inverting the mark word
    // - Test lowest two bits == 0
    // - If so, set the lowest two bits
    // - Invert the result back, and copy to dst
  
    // No free registers available. Make one useful.
+   Register tmp = rscratch1;
    tmp = LP64_ONLY(rscratch1) NOT_LP64(rdx);
!   if (tmp == dst) {
!     tmp = LP64_ONLY(rscratch2) NOT_LP64(rcx);
    }
+   __ push(tmp);
+ 
+   assert_different_registers(dst, tmp);
  
    Label done;
    __ movptr(tmp, Address(dst, oopDesc::mark_offset_in_bytes()));
    __ notptr(tmp);
    __ testb(tmp, markWord::marked_value);
*** 282,294 ****
    __ orptr(tmp, markWord::marked_value);
    __ notptr(tmp);
    __ mov(dst, tmp);
    __ bind(done);
  
-   if (borrow_reg) {
      __ pop(tmp);
-   }
  }
  
  
  void ShenandoahBarrierSetAssembler::load_reference_barrier_not_null(MacroAssembler* masm, Register dst) {
    assert(ShenandoahLoadRefBarrier, "Should be enabled");
--- 285,295 ----