A64: Fix CallApiFunctionAndReturn.

src/a64/macro-assembler-a64.cc

 // Copyright 2013 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1329 matching lines @@
 
   ASSERT(function_address.is(x1) || function_address.is(x2));
 
   Label profiler_disabled;
   Label end_profiler_check;
   bool* is_profiling_flag = isolate()->cpu_profiler()->is_profiling_address();
   STATIC_ASSERT(sizeof(*is_profiling_flag) == 1);
   Mov(x10, reinterpret_cast<uintptr_t>(is_profiling_flag));
   Ldrb(w10, MemOperand(x10));
   Cbz(w10, &profiler_disabled);
+  Mov(x3, Operand(thunk_ref));

[ulan, 2014/02/10 20:21:23]

I took this from the ARM port.

[jbramley, 2014/02/11 10:45:25]

Ah, I must have overlooked it in the merge.

Out of curiosity, what is the common case here? If the profiler is usually
turned on, this might be faster:

Cmp(w10, 0);
Csel(x3, function_address, Operand(thunk_ref), eq);

It's smaller by one instruction (and doesn't branch), but if the profiler is
disabled we waste a few cycles loading the ExternalReference.

[dcarney, 2014/02/11 15:19:29]

the profiler is almost always disabled
after cleanup, the code to enable profiling will be deferred to the end of this
function on most architectures

+  B(&end_profiler_check);
 
-  // Additional parameter is the address of the actual callback.
-  Mov(function_address, Operand(thunk_ref));
-  if (!function_address.Is(x3)) {
-    B(&end_profiler_check);
-    Bind(&profiler_disabled);
-    Mov(x3, function_address);
-    Bind(&end_profiler_check);
-  } else {
-    Bind(&profiler_disabled);
-    Bind(&end_profiler_check);
-  }
+  Bind(&profiler_disabled);
+  Mov(x3, function_address);
+  Bind(&end_profiler_check);
 
   // Save the callee-save registers we are going to use.
   // TODO(all): Is this necessary? ARM doesn't do it.
   STATIC_ASSERT(kCallApiFunctionSpillSpace == 4);
   Poke(x19, (spill_offset + 0) * kXRegSizeInBytes);
   Poke(x20, (spill_offset + 1) * kXRegSizeInBytes);
   Poke(x21, (spill_offset + 2) * kXRegSizeInBytes);
   Poke(x22, (spill_offset + 3) * kXRegSizeInBytes);
 
   // Allocate HandleScope in callee-save registers.
@@ skipping 16 matching lines @@
     PushSafepointRegisters();
     Mov(x0, Operand(ExternalReference::isolate_address(isolate())));
     CallCFunction(ExternalReference::log_enter_external_function(isolate()), 1);
     PopSafepointRegisters();
   }
 
   // Native call returns to the DirectCEntry stub which redirects to the
   // return address pushed on stack (could have moved after GC).
   // DirectCEntry stub itself is generated early and never moves.
   DirectCEntryStub stub;
-  stub.GenerateCall(this, function_address);
+  stub.GenerateCall(this, x3);
 
   if (FLAG_log_timer_events) {
     FrameScope frame(this, StackFrame::MANUAL);
     PushSafepointRegisters();
     Mov(x0, Operand(ExternalReference::isolate_address(isolate())));
     CallCFunction(ExternalReference::log_leave_external_function(isolate()), 1);
     PopSafepointRegisters();
   }
 
   Label promote_scheduled_exception;
@@ skipping 3393 matching lines @@
   }
 }
 
 
 #undef __
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TARGET_ARCH_A64