A64: Add support for --deopt-every-n-times for n != 2

src/a64/lithium-codegen-a64.cc

Index: src/a64/lithium-codegen-a64.cc
diff --git a/src/a64/lithium-codegen-a64.cc b/src/a64/lithium-codegen-a64.cc
index eaeb9cee9041b2c621d0af99082553167904fe99..a753990604c94ca1845231b426ef14e45033c257 100644
--- a/src/a64/lithium-codegen-a64.cc
+++ b/src/a64/lithium-codegen-a64.cc
@@ -958,14 +958,25 @@ bool LCodeGen::DeoptimizeHeader(LEnvironment* environment) {
     return false;
   }
 
-  ASSERT(FLAG_deopt_every_n_times < 2);  // Other values not supported on A64.
-  TODO_UNIMPLEMENTED("Support for FLAG_deopt_every_n_times >= 2.");
-  if (FLAG_deopt_every_n_times == 1 &&
-      !info()->IsStub() &&
-      info()->opt_count() == id) {
-    ASSERT(frame_is_built_);
+  if (FLAG_deopt_every_n_times != 0 && !info()->IsStub()) {
+    Label not_zero;
+    ExternalReference count = ExternalReference::stress_deopt_count(isolate());
+
+    __ Push(x0, x1);
+    __ Mov(x0, Operand(count));
+    __ Ldr(w1, MemOperand(x0));
+    __ Subs(x1, x1, 1);
+    __ B(gt, &not_zero);
+    __ Mov(w1, FLAG_deopt_every_n_times);
+    __ Str(w1, MemOperand(x0));
+    __ Pop(x0, x1);
     __ Call(entry, RelocInfo::RUNTIME_ENTRY);

[ulan, 2014/02/10 15:21:40]

This works only if (frame_is_built_ && !info()->saves_caller_doubles()), right?

Instead of duplicating deoptimizing code here and in 
LCodeGen::Deoptimize, wouldn't it be better to pass a condition and labels to
this function? This function then could check the condition and
deopt_every_n_times counter and if we need to deopt it could jump to the
corresponding label.

[jochen (gone - plz use gerrit), 2014/02/10 16:05:59]

Before I added the jump table, we would always use Call(), and arm and x64 have
the same code, so I assume it'll always work
We could do this, but then we can't use the fancy Tbz() etc instructions to test
and branch.

-    return false;
+    __ Unreachable();
+
+    __ Bind(&not_zero);
+    __ Str(w1, MemOperand(x0));
+    __ Pop(x0, x1);
+    return true;
   }
 
   return true;