[crankshaft] do not restore rsi in stub for deferred number conversions

src/crankshaft/mips64/lithium-codegen-mips64.cc

Index: src/crankshaft/mips64/lithium-codegen-mips64.cc
diff --git a/src/crankshaft/mips64/lithium-codegen-mips64.cc b/src/crankshaft/mips64/lithium-codegen-mips64.cc
index c03dd107a4fa32310a038474db246c1d923ce056..c7832b66523c3e3588fd036d5c76ad33850562a5 100644
--- a/src/crankshaft/mips64/lithium-codegen-mips64.cc
+++ b/src/crankshaft/mips64/lithium-codegen-mips64.cc
@@ -4626,13 +4626,10 @@ void LCodeGen::DoDeferredNumberTagIU(LInstruction* instr,
     __ mov(dst, zero_reg);
     // Preserve the value of all registers.
     PushSafepointRegistersScope scope(this);
-
-    // NumberTagI and NumberTagD use the context from the frame, rather than
-    // the environment's HContext or HInlinedContext value.
-    // They only call Runtime::kAllocateHeapNumber.
-    // The corresponding HChange instructions are added in a phase that does
-    // not have easy access to the local context.
-    __ ld(cp, MemOperand(fp, StandardFrameConstants::kContextOffset));
+    // Reset the context register.
+    if (!dst.is(cp)) {
+      __ mov(cp, zero_reg);
+    }
     __ CallRuntimeSaveDoubles(Runtime::kAllocateHeapNumber);
     RecordSafepointWithRegisters(
         instr->pointer_map(), 0, Safepoint::kNoLazyDeopt);
@@ -4685,12 +4682,10 @@ void LCodeGen::DoDeferredNumberTagD(LNumberTagD* instr) {
   __ mov(reg, zero_reg);
 
   PushSafepointRegistersScope scope(this);
-  // NumberTagI and NumberTagD use the context from the frame, rather than
-  // the environment's HContext or HInlinedContext value.
-  // They only call Runtime::kAllocateHeapNumber.
-  // The corresponding HChange instructions are added in a phase that does
-  // not have easy access to the local context.
-  __ ld(cp, MemOperand(fp, StandardFrameConstants::kContextOffset));
+  // Reset the context register.
+  if (!reg.is(cp)) {
+    __ mov(cp, zero_reg);
+  }
   __ CallRuntimeSaveDoubles(Runtime::kAllocateHeapNumber);
   RecordSafepointWithRegisters(
       instr->pointer_map(), 0, Safepoint::kNoLazyDeopt);