Optimized megamorphic stubs

runtime/vm/stub_code_arm64.cc

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_ARM64)
 
 #include "vm/assembler.h"
 #include "vm/code_generator.h"
 #include "vm/compiler.h"
@@ skipping 2083 matching lines @@
   __ LoadFromOffset(left, SP, 1 * kWordSize);
   __ LoadFromOffset(right, SP, 0 * kWordSize);
   GenerateIdenticalWithNumberCheckStub(assembler, left, right);
   __ ret();
 }
 
 
 void StubCode::EmitMegamorphicLookup(Assembler* assembler) {
   __ LoadTaggedClassIdMayBeSmi(R0, R0);
   // R0: class ID of the receiver (smi).
-  __ ldr(R4, FieldAddress(R5, MegamorphicCache::arguments_descriptor_offset()));
   __ ldr(R2, FieldAddress(R5, MegamorphicCache::buckets_offset()));
   __ ldr(R1, FieldAddress(R5, MegamorphicCache::mask_offset()));
   // R2: cache buckets array.
   // R1: mask.
-  __ LoadImmediate(TMP, MegamorphicCache::kSpreadFactor);
-  __ mul(R3, R0, TMP);
+
+  // Compute the table index.
+  ASSERT(MegamorphicCache::kSpreadFactor == 7);
+  // Use lsl and sub to multiply with 7 == 8 - 1.
+  __ LslImmediate(R3, R0, 3);
+  __ sub(R3, R3, Operand(R0));
   // R3: probe.
 
   Label loop, update, load_target_function;
   __ b(&loop);
 
   __ Bind(&update);
   __ add(R3, R3, Operand(Smi::RawValue(1)));
   __ Bind(&loop);
   __ and_(R3, R3, Operand(R1));
   const intptr_t base = Array::data_offset();
   // R3 is smi tagged, but table entries are 16 bytes, so LSL 3.
   __ add(TMP, R2, Operand(R3, LSL, 3));
   __ ldr(R6, FieldAddress(TMP, base));
 
   ASSERT(kIllegalCid == 0);
   __ tst(R6, Operand(R6));
   __ b(&load_target_function, EQ);
   __ CompareRegisters(R6, R0);
   __ b(&update, NE);
 
   __ Bind(&load_target_function);
   // 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.
   __ add(TMP, R2, Operand(R3, LSL, 3));
   __ ldr(R0, FieldAddress(TMP, base + kWordSize));
+  __ ldr(R4, FieldAddress(R5, MegamorphicCache::arguments_descriptor_offset()));
   __ ldr(R1, FieldAddress(R0, Function::entry_point_offset()));
   __ ldr(CODE_REG, FieldAddress(R0, Function::code_offset()));
 }
 
 
 // Called from megamorphic calls.
 //  R0: receiver
 //  R5: MegamorphicCache (preserved)
 // Result:
 //  R1: target entry point
 //  CODE_REG: target Code
 //  R4: arguments descriptor
 void StubCode::GenerateMegamorphicLookupStub(Assembler* assembler) {
-  EmitMegamorphicLookup(assembler);
+  __ LoadTaggedClassIdMayBeSmi(R0, R0);

[Florian Schneider, 2016/07/07 18:20:15]

Maybe make this avoid the null-load like on x64.

+  // R0: class ID of the receiver (smi).
+  __ ldr(R2, FieldAddress(R5, MegamorphicCache::buckets_offset()));
+  __ ldr(R1, FieldAddress(R5, MegamorphicCache::mask_offset()));
+  // R2: cache buckets array.
+  // R1: mask.
+
+  // Compute the table index.
+  ASSERT(MegamorphicCache::kSpreadFactor == 7);
+  // Use lsl and sub to multiply with 7 == 8 - 1.
+  __ LslImmediate(R3, R0, 3);
+  __ sub(R3, R3, Operand(R0));
+  // 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 16 bytes, so LSL 3.
+  __ add(TMP, R2, Operand(R3, LSL, 3));
+  __ ldr(R6, FieldAddress(TMP, base));
+  Label probe_failed;
+  __ CompareRegisters(R6, 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(TMP, base + kWordSize));
+  __ ldr(R4, FieldAddress(R5, 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, R3, Smi::RawValue(1));
+  __ b(&loop);
 }
 
 
 // Called from switchable IC calls.
 //  R0: receiver
 //  R5: ICData (preserved)
 // Result:
 //  R1: target entry point
 //  CODE_REG: target Code object
 //  R4: arguments descriptor
@@ skipping 67 matching lines @@
 }
 
 
 void StubCode::GenerateFrameAwaitingMaterializationStub(Assembler* assembler) {
   __ brk(0);
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM64