[hydrogen] don't bailout assignments to consts

src/mips/lithium-codegen-mips.cc

Index: src/mips/lithium-codegen-mips.cc
diff --git a/src/mips/lithium-codegen-mips.cc b/src/mips/lithium-codegen-mips.cc
index 71405b6344aedf410dcc52743e2eec2d59f2637a..ca6c7f24fdb621f83bc1ce1006834082e2dc1c48 100644
--- a/src/mips/lithium-codegen-mips.cc
+++ b/src/mips/lithium-codegen-mips.cc
@@ -2161,13 +2161,31 @@ void LCodeGen::DoLoadContextSlot(LLoadContextSlot* instr) {
   Register context = ToRegister(instr->context());
   Register result = ToRegister(instr->result());
   __ lw(result, ContextOperand(context, instr->slot_index()));
+  if (instr->RequiresHoleCheck()) {
+    Label is_not_hole;
+    __ Branch(&is_not_hole, ne, result, Operand(factory()->the_hole_value()));
+
+    __ li(result, Operand(factory()->undefined_value()));
+
+    __ bind(&is_not_hole);
+  }
 }
 
 
 void LCodeGen::DoStoreContextSlot(LStoreContextSlot* instr) {
   Register context = ToRegister(instr->context());
   Register value = ToRegister(instr->value());
+  Register scratch = scratch0();
   MemOperand target = ContextOperand(context, instr->slot_index());
+
+  Label skip_assignment;
+
+  if (instr->RequiresHoleCheck()) {
+    __ lw(scratch, target);
+    __ Branch(&skip_assignment, ne, scratch,
+              Operand(factory()->the_hole_value()));
+  }
+
   __ sw(value, target);
   if (instr->hydrogen()->NeedsWriteBarrier()) {
     HType type = instr->hydrogen()->value()->type();
@@ -2182,6 +2200,8 @@ void LCodeGen::DoStoreContextSlot(LStoreContextSlot* instr) {
                               EMIT_REMEMBERED_SET,
                               check_needed);
   }
+
+  __ bind(&skip_assignment);
 }