MIPS: Fix [runtime] [proxy] implement [[Construct]].

Avoid overwrite of instance type while checking IsCallable() (t2->t3).
Also slightly optimize push of register pair.

TEST=mjsunit/harmony/proxies-construct
BUG=

Review URL: https://codereview.chromium.org/1510493011

Cr-Commit-Position: refs/heads/master@{#32736}

src/mips/builtins-mips.cc

@@ -1762,8 +1762,7 @@ void Builtins::Generate_ConstructProxy(MacroAssembler* masm) {
   // -----------------------------------
 
   // Call into the Runtime for Proxy [[Construct]].
-  __ Push(a1);
-  __ Push(a3);
+  __ Push(a1, a3);
   // Include the pushed new_target, constructor and the receiver.
   __ Addu(a0, a0, Operand(3));
   // Tail-call to the runtime.
@@ -1792,9 +1791,9 @@ void Builtins::Generate_Construct(MacroAssembler* masm) {
           RelocInfo::CODE_TARGET, eq, t2, Operand(JS_FUNCTION_TYPE));
 
   // Check if target has a [[Construct]] internal method.
-  __ lbu(t2, FieldMemOperand(t1, Map::kBitFieldOffset));
-  __ And(t2, t2, Operand(1 << Map::kIsCallable));
-  __ Branch(&non_constructor, eq, t2, Operand(zero_reg));
+  __ lbu(t3, FieldMemOperand(t1, Map::kBitFieldOffset));
+  __ And(t3, t3, Operand(1 << Map::kIsCallable));
+  __ Branch(&non_constructor, eq, t3, Operand(zero_reg));
 
   // Only dispatch to proxies after checking whether they are constructors.
   __ Jump(masm->isolate()->builtins()->ConstructProxy(), RelocInfo::CODE_TARGET,

src/mips64/builtins-mips64.cc

@@ -1753,8 +1753,7 @@ void Builtins::Generate_ConstructProxy(MacroAssembler* masm) {
   // -----------------------------------
 
   // Call into the Runtime for Proxy [[Construct]].
-  __ Push(a1);
-  __ Push(a3);
+  __ Push(a1, a3);
   // Include the pushed new_target, constructor and the receiver.
   __ Daddu(a0, a0, Operand(3));
   // Tail-call to the runtime.
@@ -1783,9 +1782,9 @@ void Builtins::Generate_Construct(MacroAssembler* masm) {
           RelocInfo::CODE_TARGET, eq, t2, Operand(JS_FUNCTION_TYPE));
 
   // Check if target has a [[Construct]] internal method.
-  __ lbu(t2, FieldMemOperand(t1, Map::kBitFieldOffset));
-  __ And(t2, t2, Operand(1 << Map::kIsCallable));
-  __ Branch(&non_constructor, eq, t2, Operand(zero_reg));
+  __ lbu(t3, FieldMemOperand(t1, Map::kBitFieldOffset));
+  __ And(t3, t3, Operand(1 << Map::kIsCallable));
+  __ Branch(&non_constructor, eq, t3, Operand(zero_reg));
 
   // Only dispatch to proxies after checking whether they are constructors.
   __ Jump(masm->isolate()->builtins()->ConstructProxy(), RelocInfo::CODE_TARGET,