A64: Fix CallApiFunctionAndReturn.

src/a64/macro-assembler-a64.cc

Index: src/a64/macro-assembler-a64.cc
diff --git a/src/a64/macro-assembler-a64.cc b/src/a64/macro-assembler-a64.cc
index c55a59fbb8d708ce3f3f7dfa70da5e9589e7c28a..623a54bd2d20edaa36718ec0b4d89df3ec2fd11f 100644
--- a/src/a64/macro-assembler-a64.cc
+++ b/src/a64/macro-assembler-a64.cc
@@ -1347,18 +1347,12 @@ void MacroAssembler::CallApiFunctionAndReturn(
   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.
@@ -1395,7 +1389,7 @@ void MacroAssembler::CallApiFunctionAndReturn(
   // 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);