Add LoadTaggedClassIdMayBeSmi to assembly and improve performance of inline cache stubs.

runtime/vm/stub_code_arm.cc

Index: runtime/vm/stub_code_arm.cc
===================================================================
--- runtime/vm/stub_code_arm.cc	(revision 37007)
+++ runtime/vm/stub_code_arm.cc	(working copy)
@@ -1283,7 +1283,7 @@
   // Preserve return address, since LR is needed for subroutine call.
   __ mov(R8, Operand(LR));
   // Loop that checks if there is an IC data match.
-  Label loop, update, test, found, get_class_id_as_smi;
+  Label loop, update, test, found;
   // R5: IC data object (preserved).
   __ ldr(R6, FieldAddress(R5, ICData::ic_data_offset()));
   // R6: ic_data_array with check entries: classes and target functions.
@@ -1295,7 +1295,7 @@
   __ ldr(R7, FieldAddress(R4, ArgumentsDescriptor::count_offset()));
   __ sub(R7, R7, Operand(Smi::RawValue(1)));
   __ ldr(R0, Address(SP, R7, LSL, 1));  // R7 (argument_count - 1) is smi.
-  __ bl(&get_class_id_as_smi);
+  __ LoadTaggedClassIdMayBeSmi(R0, R0);
   // R7: argument_count - 1 (smi).
   // R0: receiver's class ID (smi).
   __ ldr(R1, Address(R6, 0));  // First class id (smi) to check.
@@ -1307,7 +1307,7 @@
       // If not the first, load the next argument's class ID.
       __ AddImmediate(R0, R7, Smi::RawValue(-i));
       __ ldr(R0, Address(SP, R0, LSL, 1));
-      __ bl(&get_class_id_as_smi);
+      __ LoadTaggedClassIdMayBeSmi(R0, R0);
       // R0: next argument class ID (smi).
       __ LoadFromOffset(kWord, R1, R6, i * kWordSize);
       // R1: next class ID to check (smi).
@@ -1325,7 +1325,7 @@
   // Reload receiver class ID.  It has not been destroyed when num_args == 1.
   if (num_args > 1) {
     __ ldr(R0, Address(SP, R7, LSL, 1));
-    __ bl(&get_class_id_as_smi);
+    __ LoadTaggedClassIdMayBeSmi(R0, R0);
   }
 
   const intptr_t entry_size = ICData::TestEntryLengthFor(num_args) * kWordSize;
@@ -1385,17 +1385,6 @@
   __ ldr(R2, FieldAddress(R0, Function::instructions_offset()));
   __ AddImmediate(R2, Instructions::HeaderSize() - kHeapObjectTag);
   __ bx(R2);
-
-  // Instance in R0, return its class-id in R0 as Smi.
-  __ Bind(&get_class_id_as_smi);
-
-  // Test if Smi -> load Smi class for comparison.
-  __ tst(R0, Operand(kSmiTagMask));
-  __ mov(R0, Operand(Smi::RawValue(kSmiCid)), EQ);
-  __ bx(LR, EQ);
-  __ LoadClassId(R0, R0);
-  __ SmiTag(R0);
-  __ bx(LR);
 }