Faster code for megamorphic calls fo get:hashCode for Smi and OneByteString

runtime/vm/flow_graph_compiler_mips.cc

Index: runtime/vm/flow_graph_compiler_mips.cc
diff --git a/runtime/vm/flow_graph_compiler_mips.cc b/runtime/vm/flow_graph_compiler_mips.cc
index 8e3bd7b227b2526bf2d3fe8f2cb86c12e1b4c71d..9fa5d9f31afd4d1d932ee5ba1c059f930732ef44 100644
--- a/runtime/vm/flow_graph_compiler_mips.cc
+++ b/runtime/vm/flow_graph_compiler_mips.cc
@@ -1327,7 +1327,28 @@ void FlowGraphCompiler::EmitMegamorphicInstanceCall(
       MegamorphicCacheTable::Lookup(isolate(), name, arguments_descriptor));
 
   __ Comment("MegamorphicCall");
+  // Load receiver into T0,
   __ lw(T0, Address(SP, (argument_count - 1) * kWordSize));
+  Label done;
+  if (name.raw() == Symbols::hashCode().raw()) {
+    Label try_onebytestring, megamorphic_call;
+    __ Comment("Inlined get:hashCode for Smi and OneByteString");
+    __ andi(CMPRES1, T0, Immediate(kSmiTagMask));
+    __ bne(CMPRES1, ZR, &try_onebytestring);  // Not Smi.
+    __ mov(V0, T0);
+    __ b(&done);
+
+    __ Bind(&try_onebytestring);
+    __ LoadClassId(CMPRES1, T0);  // Class ID check.
+    __ BranchNotEqual(
+        CMPRES1, Immediate(kOneByteStringCid), &megamorphic_call);
+
+    __ lw(V0, FieldAddress(T0, String::hash_offset()));
+    __ bne(V0, ZR, &done);
+
+    __ Bind(&megamorphic_call);
+    __ Comment("Slow case: megamorphic call");
+  }
   __ LoadObject(S5, cache);
   if (FLAG_use_megamorphic_stub) {
     __ BranchLink(*StubCode::MegamorphicLookup_entry());
@@ -1336,6 +1357,7 @@ void FlowGraphCompiler::EmitMegamorphicInstanceCall(
   }
   __ jalr(T1);
 
+  __ Bind(&done);
   RecordSafepoint(locs, slow_path_argument_count);
   const intptr_t deopt_id_after = Thread::ToDeoptAfter(deopt_id);
   if (FLAG_precompiled_mode) {