PPC/s390: Reland [in-place weak refs] Add in-place weak references & migrate one WeakCell to it.

Port 88062a2c

Original Commit Message:

    Implement in-place weak reference handling in GC.

    Turn FeedbackVector::optimized_code_or_smi into an in-place weak reference (this
    is the only in-place weak reference at this point).

    (See bug for design doc.)

R=marja@chromium.org, joransiu@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=v8:7308
LOG=N

Change-Id: I00c6aa7c08524b7769d3428d0c18ce334f35a722
Reviewed-on: https://chromium-review.googlesource.com/949368Reviewed-by: Joran Siu <joransiu@ca.ibm.com>
Commit-Queue: Junliang Yan <jyan@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#51747}

src/builtins/ppc/builtins-ppc.cc

@@ -751,7 +751,7 @@ static void MaybeTailCallOptimizedCodeSlot(MacroAssembler* masm,
   DCHECK(
       !AreAliased(feedback_vector, r3, r4, r6, scratch1, scratch2, scratch3));
 
-  Label optimized_code_slot_is_cell, fallthrough;
+  Label optimized_code_slot_is_weak_ref, fallthrough;
 
   Register closure = r4;
   Register optimized_code_entry = scratch1;
@@ -761,9 +761,9 @@ static void MaybeTailCallOptimizedCodeSlot(MacroAssembler* masm,
       FieldMemOperand(feedback_vector, FeedbackVector::kOptimizedCodeOffset));
 
   // Check if the code entry is a Smi. If yes, we interpret it as an
-  // optimisation marker. Otherwise, interpret is as a weak cell to a code
+  // optimisation marker. Otherwise, interpret it as a weak reference to a code
   // object.
-  __ JumpIfNotSmi(optimized_code_entry, &optimized_code_slot_is_cell);
+  __ JumpIfNotSmi(optimized_code_entry, &optimized_code_slot_is_weak_ref);
 
   {
     // Optimized code slot is a Smi optimization marker.
@@ -798,12 +798,10 @@ static void MaybeTailCallOptimizedCodeSlot(MacroAssembler* masm,
   }
 
   {
-    // Optimized code slot is a WeakCell.
-    __ bind(&optimized_code_slot_is_cell);
+    // Optimized code slot is a weak reference.
+    __ bind(&optimized_code_slot_is_weak_ref);
 
-    __ LoadP(optimized_code_entry,
-             FieldMemOperand(optimized_code_entry, WeakCell::kValueOffset));
-    __ JumpIfSmi(optimized_code_entry, &fallthrough);
+    __ LoadWeakValue(optimized_code_entry, optimized_code_entry, &fallthrough);
 
     // Check if the optimized code is marked for deopt. If it is, call the
     // runtime to clear it.

src/builtins/s390/builtins-s390.cc

@@ -754,7 +754,7 @@ static void MaybeTailCallOptimizedCodeSlot(MacroAssembler* masm,
   DCHECK(
       !AreAliased(feedback_vector, r2, r3, r5, scratch1, scratch2, scratch3));
 
-  Label optimized_code_slot_is_cell, fallthrough;
+  Label optimized_code_slot_is_weak_ref, fallthrough;
 
   Register closure = r3;
   Register optimized_code_entry = scratch1;
@@ -764,9 +764,9 @@ static void MaybeTailCallOptimizedCodeSlot(MacroAssembler* masm,
       FieldMemOperand(feedback_vector, FeedbackVector::kOptimizedCodeOffset));
 
   // Check if the code entry is a Smi. If yes, we interpret it as an
-  // optimisation marker. Otherwise, interpret is as a weak cell to a code
+  // optimisation marker. Otherwise, interpret it as a weak reference to a code
   // object.
-  __ JumpIfNotSmi(optimized_code_entry, &optimized_code_slot_is_cell);
+  __ JumpIfNotSmi(optimized_code_entry, &optimized_code_slot_is_weak_ref);
 
   {
     // Optimized code slot is a Smi optimization marker.
@@ -801,12 +801,10 @@ static void MaybeTailCallOptimizedCodeSlot(MacroAssembler* masm,
   }
 
   {
-    // Optimized code slot is a WeakCell.
-    __ bind(&optimized_code_slot_is_cell);
+    // Optimized code slot is a weak reference.
+    __ bind(&optimized_code_slot_is_weak_ref);
 
-    __ LoadP(optimized_code_entry,
-             FieldMemOperand(optimized_code_entry, WeakCell::kValueOffset));
-    __ JumpIfSmi(optimized_code_entry, &fallthrough);
+    __ LoadWeakValue(optimized_code_entry, optimized_code_entry, &fallthrough);
 
     // Check if the optimized code is marked for deopt. If it is, call the
     // runtime to clear it.

src/ppc/macro-assembler-ppc.cc

@@ -1632,6 +1632,15 @@ void MacroAssembler::JumpToInstructionStream(const InstructionStream* stream) {
   Jump(kOffHeapTrampolineRegister);
 }
 
+void MacroAssembler::LoadWeakValue(Register out, Register in,
+                                   Label* target_if_cleared) {
+  cmpi(in, Operand(kClearedWeakHeapObject));
+  beq(target_if_cleared);
+
+  mov(r0, Operand(~kWeakHeapObjectMask));
+  and_(out, in, r0);
+}
+
 void MacroAssembler::IncrementCounter(StatsCounter* counter, int value,
                                       Register scratch1, Register scratch2) {
   DCHECK_GT(value, 0);

src/ppc/macro-assembler-ppc.h

@@ -935,6 +935,10 @@ class MacroAssembler : public TurboAssembler {
   // Generates a trampoline to jump to the off-heap instruction stream.
   void JumpToInstructionStream(const InstructionStream* stream);
 
+  // ---------------------------------------------------------------------------
+  // In-place weak references.
+  void LoadWeakValue(Register out, Register in, Label* target_if_cleared);
+
   // ---------------------------------------------------------------------------
   // StatsCounter support
 

src/s390/macro-assembler-s390.cc

@@ -1544,6 +1544,14 @@ void MacroAssembler::JumpToInstructionStream(const InstructionStream* stream) {
   Jump(kOffHeapTrampolineRegister);
 }
 
+void MacroAssembler::LoadWeakValue(Register out, Register in,
+                                   Label* target_if_cleared) {
+  CmpP(in, Operand(kClearedWeakHeapObject));
+  beq(target_if_cleared);
+
+  AndP(out, in, Operand(~kWeakHeapObjectMask));
+}
+
 void MacroAssembler::IncrementCounter(StatsCounter* counter, int value,
                                       Register scratch1, Register scratch2) {
   DCHECK(value > 0 && is_int8(value));

src/s390/macro-assembler-s390.h

@@ -1108,6 +1108,10 @@ class MacroAssembler : public TurboAssembler {
   void TryDoubleToInt32Exact(Register result, DoubleRegister double_input,
                              Register scratch, DoubleRegister double_scratch);
 
+  // ---------------------------------------------------------------------------
+  // In-place weak references.
+  void LoadWeakValue(Register out, Register in, Label* target_if_cleared);
+
   // ---------------------------------------------------------------------------
   // StatsCounter support