MIPS: Change CmpWeakValue to a more MIPS like GetWeakValue.

This approach saves one instruction by eliminating the use of Subu as a
pseudo-comparison.

BUG=

Review URL: https://codereview.chromium.org/779793004

Cr-Commit-Position: refs/heads/master@{#25662}

src/ic/mips/handler-compiler-mips.cc

@@ -419,8 +419,8 @@ Register PropertyHandlerCompiler::CheckPrototypes(
       __ lw(map_reg, FieldMemOperand(reg, HeapObject::kMapOffset));
       if (depth != 1 || check == CHECK_ALL_MAPS) {
         Handle<WeakCell> cell = Map::WeakCellForMap(current_map);
-        __ CmpWeakValue(scratch2, map_reg, cell);
-        __ Branch(miss, ne, scratch2, Operand(zero_reg));
+        __ GetWeakValue(scratch2, cell);
+        __ Branch(miss, ne, scratch2, Operand(map_reg));
       }
 
       // Check access rights to the global object.  This has to happen after
@@ -453,8 +453,8 @@ Register PropertyHandlerCompiler::CheckPrototypes(
     // Check the holder map.
     __ lw(scratch1, FieldMemOperand(reg, HeapObject::kMapOffset));
     Handle<WeakCell> cell = Map::WeakCellForMap(current_map);
-    __ CmpWeakValue(scratch2, scratch1, cell);
-    __ Branch(miss, ne, scratch2, Operand(zero_reg));
+    __ GetWeakValue(scratch2, cell);
+    __ Branch(miss, ne, scratch2, Operand(scratch1));
   }
 
   // Perform security check for access to the global object.

src/ic/mips64/handler-compiler-mips64.cc

@@ -420,8 +420,8 @@ Register PropertyHandlerCompiler::CheckPrototypes(
       __ ld(map_reg, FieldMemOperand(reg, HeapObject::kMapOffset));
       if (depth != 1 || check == CHECK_ALL_MAPS) {
         Handle<WeakCell> cell = Map::WeakCellForMap(current_map);
-        __ CmpWeakValue(scratch2, map_reg, cell);
-        __ Branch(miss, ne, scratch2, Operand(zero_reg));
+        __ GetWeakValue(scratch2, cell);
+        __ Branch(miss, ne, scratch2, Operand(map_reg));
       }
 
       // Check access rights to the global object.  This has to happen after
@@ -454,8 +454,8 @@ Register PropertyHandlerCompiler::CheckPrototypes(
     // Check the holder map.
     __ ld(scratch1, FieldMemOperand(reg, HeapObject::kMapOffset));
     Handle<WeakCell> cell = Map::WeakCellForMap(current_map);
-    __ CmpWeakValue(scratch2, scratch1, cell);
-    __ Branch(miss, ne, scratch2, Operand(zero_reg));
+    __ GetWeakValue(scratch2, cell);
+    __ Branch(miss, ne, scratch2, Operand(scratch1));
   }
 
   // Perform security check for access to the global object.

src/mips/macro-assembler-mips.cc

@@ -4027,18 +4027,15 @@ void MacroAssembler::CheckMap(Register obj,
 }
 
 
-void MacroAssembler::CmpWeakValue(Register match, Register value,
-                                  Handle<WeakCell> cell) {
-  li(match, Operand(cell));
-  lw(match, FieldMemOperand(match, WeakCell::kValueOffset));
-  Subu(match, value, match);
+void MacroAssembler::GetWeakValue(Register value, Handle<WeakCell> cell) {
+  li(value, Operand(cell));
+  lw(value, FieldMemOperand(value, WeakCell::kValueOffset));
 }
 
 
 void MacroAssembler::LoadWeakValue(Register value, Handle<WeakCell> cell,
                                    Label* miss) {
-  li(value, Operand(cell));
-  lw(value, FieldMemOperand(value, WeakCell::kValueOffset));
+  GetWeakValue(value, cell);
   JumpIfSmi(value, miss);
 }
 

src/mips/macro-assembler-mips.h

@@ -1089,9 +1089,8 @@ class MacroAssembler: public Assembler {
                    Handle<Code> success,
                    SmiCheckType smi_check_type);
 
-  // Compare the given value and the value of the weak cell. Write the result
-  // to the match register.
-  void CmpWeakValue(Register match, Register value, Handle<WeakCell> cell);
+  // Get value of the weak cell.
+  void GetWeakValue(Register value, Handle<WeakCell> cell);
 
   // Load the value of the weak cell in the value register. Branch to the
   // given miss label is the weak cell was cleared.

src/mips64/macro-assembler-mips64.cc

@@ -3994,18 +3994,15 @@ void MacroAssembler::CheckMap(Register obj,
 }
 
 
-void MacroAssembler::CmpWeakValue(Register match, Register value,
-                                  Handle<WeakCell> cell) {
-  li(match, Operand(cell));
-  ld(match, FieldMemOperand(match, WeakCell::kValueOffset));
-  Dsubu(match, value, match);
+void MacroAssembler::GetWeakValue(Register value, Handle<WeakCell> cell) {
+  li(value, Operand(cell));
+  ld(value, FieldMemOperand(value, WeakCell::kValueOffset));
 }
 
 
 void MacroAssembler::LoadWeakValue(Register value, Handle<WeakCell> cell,
                                    Label* miss) {
-  li(value, Operand(cell));
-  ld(value, FieldMemOperand(value, WeakCell::kValueOffset));
+  GetWeakValue(value, cell);
   JumpIfSmi(value, miss);
 }
 

src/mips64/macro-assembler-mips64.h

@@ -1119,9 +1119,8 @@ class MacroAssembler: public Assembler {
                    Handle<Code> success,
                    SmiCheckType smi_check_type);
 
-  // Compare the given value and the value of the weak cell. Write the result
-  // to the match register.
-  void CmpWeakValue(Register match, Register value, Handle<WeakCell> cell);
+  // Get value of the weak cell.
+  void GetWeakValue(Register value, Handle<WeakCell> cell);
 
   // Load the value of the weak cell in the value register. Branch to the
   // given miss label is the weak cell was cleared.