Optimizations to IC stub for unoptimized code performance on x64.

runtime/vm/stub_code_x64.cc

Index: runtime/vm/stub_code_x64.cc
diff --git a/runtime/vm/stub_code_x64.cc b/runtime/vm/stub_code_x64.cc
index b3b18da03bced6a40ab816a2f32e0ad70fb3dc79..c1d5b96e7662d544177c8e5f0799439fc8df2cd2 100644
--- a/runtime/vm/stub_code_x64.cc
+++ b/runtime/vm/stub_code_x64.cc
@@ -1308,12 +1308,8 @@ static void EmitFastSmiOp(Assembler* assembler,
 
   if (FLAG_optimization_counter_threshold >= 0) {
     const intptr_t count_offset = ICData::CountIndexFor(num_args) * kWordSize;
-    // Update counter.
-    __ movq(R8, Address(R13, count_offset));
-    __ addq(R8, Immediate(Smi::RawValue(1)));
-    __ movq(R9, Immediate(Smi::RawValue(Smi::kMaxValue)));
-    __ cmovnoq(R9, R8);
-    __ StoreIntoSmiField(Address(R13, count_offset), R9);
+    // Update counter, ignore overflow.
+    __ addq(Address(R13, count_offset), Immediate(Smi::RawValue(1)));
   }
 
   __ ret();
@@ -1336,7 +1332,7 @@ void StubCode::GenerateNArgsCheckInlineCacheStub(
     const RuntimeEntry& handle_ic_miss,
     Token::Kind kind,
     bool optimized) {
-  ASSERT(num_args > 0);
+  ASSERT(num_args == 1 || num_args == 2);
 #if defined(DEBUG)
   {
     Label ok;
@@ -1371,58 +1367,61 @@ void StubCode::GenerateNArgsCheckInlineCacheStub(
   // Load arguments descriptor into R10.
   __ movq(R10, FieldAddress(RBX, ICData::arguments_descriptor_offset()));
   // Loop that checks if there is an IC data match.
-  Label loop, update, test, found;
+  Label loop, found, miss;
   // RBX: IC data object (preserved).
   __ movq(R13, FieldAddress(RBX, ICData::ic_data_offset()));
   // R13: ic_data_array with check entries: classes and target functions.
   __ leaq(R13, FieldAddress(R13, Array::data_offset()));
   // R13: points directly to the first ic data array element.
 
-  // Get the receiver's class ID (first read number of arguments from
-  // arguments descriptor array and then access the receiver from the stack).
-  __ movq(RAX, FieldAddress(R10, ArgumentsDescriptor::count_offset()));
-  __ movq(R9, Address(RSP, RAX, TIMES_4, 0));  // RAX (argument count) is Smi.
+  // Get argument descriptor into RCX.
+  __ movq(RCX, FieldAddress(R10, ArgumentsDescriptor::count_offset()));
+  // Load first argument into R9.
+  __ movq(R9, Address(RSP, RCX, TIMES_4, 0));
   __ LoadTaggedClassIdMayBeSmi(RAX, R9);
-  // RAX: receiver's class ID as smi.
-  __ movq(R9, Address(R13, 0));  // First class ID (Smi) to check.
-  __ jmp(&test);
+  // RAX: first argument class ID as Smi.
+  if (num_args == 2) {
+    // Load second argument into R9.
+    __ movq(R9, Address(RSP, RCX, TIMES_4, -kWordSize));
+    __ LoadTaggedClassIdMayBeSmi(RCX, R9);
+    // RCX: second argument class ID (smi).
+  }
 
   __ Comment("ICData loop");
+
+  // We unroll the generic one that is generated once more than the others.
+  bool optimize = kind == Token::kILLEGAL;
+  const intptr_t target_offset = ICData::TargetIndexFor(num_args) * kWordSize;
+  const intptr_t count_offset = ICData::CountIndexFor(num_args) * kWordSize;
+
   __ Bind(&loop);
-  for (int i = 0; i < num_args; i++) {
-    if (i > 0) {
-      // If not the first, load the next argument's class ID.
-      __ movq(RAX, FieldAddress(R10, ArgumentsDescriptor::count_offset()));
-      __ movq(R9, Address(RSP, RAX, TIMES_4, -i * kWordSize));
-      __ LoadTaggedClassIdMayBeSmi(RAX, R9);
-      // RAX: next argument class ID (smi).
-      __ movq(R9, Address(R13, i * kWordSize));
-      // R9: next class ID to check (smi).
-    }
+  for (int unroll = optimize ? 4 : 2; unroll >= 0; unroll--) {
+    Label update;
+    __ movq(R9, Address(R13, 0));
     __ cmpq(RAX, R9);  // Class id match?
-    if (i < (num_args - 1)) {
+    if (num_args == 2) {
       __ j(NOT_EQUAL, &update);  // Continue.
-    } else {
-      // Last check, all checks before matched.
-      __ j(EQUAL, &found);  // Break.
+      __ movq(R9, Address(R13, kWordSize));
+      // R9: next class ID to check (smi).
+      __ cmpq(RCX, R9);  // Class id match?
     }
-  }
-  __ Bind(&update);
-  // Reload receiver class ID.  It has not been destroyed when num_args == 1.
-  if (num_args > 1) {
-    __ movq(RAX, FieldAddress(R10, ArgumentsDescriptor::count_offset()));
-    __ movq(R9, Address(RSP, RAX, TIMES_4, 0));
-    __ LoadTaggedClassIdMayBeSmi(RAX, R9);
-  }
+    __ j(EQUAL, &found);  // Break.
 
-  const intptr_t entry_size = ICData::TestEntryLengthFor(num_args) * kWordSize;
-  __ addq(R13, Immediate(entry_size));  // Next entry.
-  __ movq(R9, Address(R13, 0));         // Next class ID.
+    __ Bind(&update);
 
-  __ Bind(&test);
-  __ cmpq(R9, Immediate(Smi::RawValue(kIllegalCid)));  // Done?
-  __ j(NOT_EQUAL, &loop, Assembler::kNearJump);
+    const intptr_t entry_size =
+        ICData::TestEntryLengthFor(num_args) * kWordSize;
+    __ addq(R13, Immediate(entry_size));  // Next entry.
+
+    __ cmpq(R9, Immediate(Smi::RawValue(kIllegalCid)));  // Done?
+    if (unroll == 0) {
+      __ j(NOT_EQUAL, &loop);
+    } else {
+      __ j(EQUAL, &miss);
+    }
+  }
 
+  __ Bind(&miss);
   __ Comment("IC miss");
   // Compute address of arguments (first read number of arguments from
   // arguments descriptor array and then compute address on the stack).
@@ -1457,24 +1456,17 @@ void StubCode::GenerateNArgsCheckInlineCacheStub(
 
   __ Bind(&found);
   // R13: Pointer to an IC data check group.
-  const intptr_t target_offset = ICData::TargetIndexFor(num_args) * kWordSize;
-  const intptr_t count_offset = ICData::CountIndexFor(num_args) * kWordSize;
   __ movq(RAX, Address(R13, target_offset));
 
   if (FLAG_optimization_counter_threshold >= 0) {
-    // Update counter.
     __ Comment("Update caller's counter");
-    __ movq(R8, Address(R13, count_offset));
-    __ addq(R8, Immediate(Smi::RawValue(1)));
-    __ movq(R9, Immediate(Smi::RawValue(Smi::kMaxValue)));
-    __ cmovnoq(R9, R8);
-    __ StoreIntoSmiField(Address(R13, count_offset), R9);
+    // Ignore overflow.
+    __ addq(Address(R13, count_offset), Immediate(Smi::RawValue(1)));
   }
 
   __ Comment("Call target");
   __ Bind(&call_target_function);
   // RAX: Target function.
-  Label is_compiled;
   __ movq(CODE_REG, FieldAddress(RAX, Function::code_offset()));
   __ movq(RCX, FieldAddress(RAX, Function::entry_point_offset()));
   __ jmp(RCX);
@@ -1611,12 +1603,8 @@ void StubCode::GenerateZeroArgsUnoptimizedStaticCallStub(Assembler* assembler) {
   const intptr_t count_offset = ICData::CountIndexFor(0) * kWordSize;
 
   if (FLAG_optimization_counter_threshold >= 0) {
-    // Increment count for this call.
-    __ movq(R8, Address(R12, count_offset));
-    __ addq(R8, Immediate(Smi::RawValue(1)));
-    __ movq(R13, Immediate(Smi::RawValue(Smi::kMaxValue)));
-    __ cmovnoq(R13, R8);
-    __ StoreIntoSmiField(Address(R12, count_offset), R13);
+    // Increment count for this call, ignore overflow.
+    __ addq(Address(R12, count_offset), Immediate(Smi::RawValue(1)));
   }
 
   // Load arguments descriptor into R10.