Optimized megamorphic stubs

runtime/vm/stub_code_arm.cc

Index: runtime/vm/stub_code_arm.cc
diff --git a/runtime/vm/stub_code_arm.cc b/runtime/vm/stub_code_arm.cc
index 9a7429b5d0e51ba1241a16bf655bcf3d39599345..69eb048b4970d052c7e46eebd56721dc32ba746d 100644
--- a/runtime/vm/stub_code_arm.cc
+++ b/runtime/vm/stub_code_arm.cc
@@ -2051,13 +2051,15 @@ void StubCode::GenerateOptimizedIdenticalWithNumberCheckStub(
 void StubCode::EmitMegamorphicLookup(Assembler* assembler) {
   __ LoadTaggedClassIdMayBeSmi(R0, R0);
   // R0: receiver cid as Smi.
-  __ ldr(R4, FieldAddress(R9, MegamorphicCache::arguments_descriptor_offset()));
   __ ldr(R2, FieldAddress(R9, MegamorphicCache::buckets_offset()));
   __ ldr(R1, FieldAddress(R9, MegamorphicCache::mask_offset()));
   // R2: cache buckets array.
   // R1: mask.
-  __ LoadImmediate(IP, MegamorphicCache::kSpreadFactor);
-  __ mul(R3, R0, IP);
+
+  // Compute the table index.
+  ASSERT(MegamorphicCache::kSpreadFactor == 7);
+  // Use reverse substract to multiply with 7 == 8 - 1.
+  __ rsb(R3, R0, Operand(R0, LSL, 3));
   // R3: probe.
 
   Label loop, update, load_target_function;
@@ -2085,6 +2087,7 @@ void StubCode::EmitMegamorphicLookup(Assembler* assembler) {
   // be invoked as a normal Dart function.
   __ add(IP, R2, Operand(R3, LSL, 2));
   __ ldr(R0, FieldAddress(IP, base + kWordSize));
+  __ ldr(R4, FieldAddress(R9, MegamorphicCache::arguments_descriptor_offset()));
   __ ldr(R1, FieldAddress(R0, Function::entry_point_offset()));
   __ ldr(CODE_REG, FieldAddress(R0, Function::code_offset()));
 }
@@ -2098,8 +2101,51 @@ void StubCode::EmitMegamorphicLookup(Assembler* assembler) {
 //  CODE_REG: target Code
 //  R4: arguments descriptor
 void StubCode::GenerateMegamorphicLookupStub(Assembler* assembler) {
-  EmitMegamorphicLookup(assembler);
+  __ LoadTaggedClassIdMayBeSmi(R0, R0);
+  // R0: receiver cid as Smi.
+  __ ldr(R2, FieldAddress(R9, MegamorphicCache::buckets_offset()));
+  __ ldr(R1, FieldAddress(R9, MegamorphicCache::mask_offset()));
+  // R2: cache buckets array.
+  // R1: mask.
+
+  // Compute the table index.
+  ASSERT(MegamorphicCache::kSpreadFactor == 7);
+  // Use reverse substract to multiply with 7 == 8 - 1.
+  __ rsb(R3, R0, Operand(R0, LSL, 3));
+  // R3: probe.
+  Label loop;
+  __ Bind(&loop);
+  __ and_(R3, R3, Operand(R1));
+
+  const intptr_t base = Array::data_offset();
+  // R3 is smi tagged, but table entries are two words, so LSL 2.
+  Label probe_failed;
+  __ add(IP, R2, Operand(R3, LSL, 2));
+  __ ldr(R6, FieldAddress(IP, base));
+  __ cmp(R6, Operand(R0));
+  __ b(&probe_failed, NE);
+
+  Label load_target;
+  __ Bind(&load_target);
+  // Call the target found in the cache.  For a class id match, this is a
+  // proper target for the given name and arguments descriptor.  If the
+  // illegal class id was found, the target is a cache miss handler that can
+  // be invoked as a normal Dart function.
+  __ ldr(R0, FieldAddress(IP, base + kWordSize));
+  __ ldr(R4, FieldAddress(R9, MegamorphicCache::arguments_descriptor_offset()));
+  __ ldr(R1, FieldAddress(R0, Function::entry_point_offset()));
+  __ ldr(CODE_REG, FieldAddress(R0, Function::code_offset()));
   __ Ret();
+
+  // Probe failed, check if it is a miss.
+  __ Bind(&probe_failed);
+  ASSERT(kIllegalCid == 0);
+  __ tst(R6, Operand(R6));
+  __ b(&load_target, EQ);  // branch if miss.
+
+  // Try next extry in the table.
+  __ AddImmediate(R3, Smi::RawValue(1));
+  __ b(&loop);
 }