# HG changeset patch
# User rkennke
# Date 1569855260 -7200
#      Mon Sep 30 16:54:20 2019 +0200
# Node ID 964415a05aa7c8ccbd3505e3a0b98f2072158669
# Parent  4107e5a422b6ece5a6d063eb0b8e1a1043857954
8231583: Shenandoah: Fix register clash in SBSA::resolve_forwarding_pointer() borrowing

diff --git a/src/hotspot/cpu/x86/gc/shenandoah/shenandoahBarrierSetAssembler_x86.cpp b/src/hotspot/cpu/x86/gc/shenandoah/shenandoahBarrierSetAssembler_x86.cpp
--- a/src/hotspot/cpu/x86/gc/shenandoah/shenandoahBarrierSetAssembler_x86.cpp
+++ b/src/hotspot/cpu/x86/gc/shenandoah/shenandoahBarrierSetAssembler_x86.cpp
@@ -247,16 +247,16 @@
   __ bind(done);
 }
 
-void ShenandoahBarrierSetAssembler::resolve_forward_pointer(MacroAssembler* masm, Register dst, Register tmp) {
+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, tmp);
+  resolve_forward_pointer_not_null(masm, dst);
   __ bind(is_null);
 }
 
-void ShenandoahBarrierSetAssembler::resolve_forward_pointer_not_null(MacroAssembler* masm, Register dst, Register tmp) {
+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
@@ -267,12 +267,15 @@
   // - 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);
+  // 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()));
@@ -284,9 +287,7 @@
   __ mov(dst, tmp);
   __ bind(done);
 
-  if (borrow_reg) {
-    __ pop(tmp);
-  }
+  __ pop(tmp);
 }
 
 
diff --git a/src/hotspot/cpu/x86/gc/shenandoah/shenandoahBarrierSetAssembler_x86.hpp b/src/hotspot/cpu/x86/gc/shenandoah/shenandoahBarrierSetAssembler_x86.hpp
--- a/src/hotspot/cpu/x86/gc/shenandoah/shenandoahBarrierSetAssembler_x86.hpp
+++ b/src/hotspot/cpu/x86/gc/shenandoah/shenandoahBarrierSetAssembler_x86.hpp
@@ -55,8 +55,8 @@
                                     bool tosca_live,
                                     bool expand_call);
 
-  void resolve_forward_pointer(MacroAssembler* masm, Register dst, Register tmp = noreg);
-  void resolve_forward_pointer_not_null(MacroAssembler* masm, Register dst, Register tmp = noreg);
+  void resolve_forward_pointer(MacroAssembler* masm, Register dst);
+  void resolve_forward_pointer_not_null(MacroAssembler* masm, Register dst);
 
   void load_reference_barrier_not_null(MacroAssembler* masm, Register dst);