Use Func::m_funcBody to avoid SrcDB lookups

hphp/runtime/vm/bytecode.cpp

@@ -1850,9 +1850,11 @@ void VMExecutionContext::syncGdbState() {
 }
 
 void VMExecutionContext::enterVMWork(ActRec* enterFnAr) {
+  TCA start = nullptr;
   if (enterFnAr) {
     EventHook::FunctionEnter(enterFnAr, EventHook::NormalFunc);
     INST_HOOK_FENTRY(enterFnAr->m_func->fullName());
+    start = enterFnAr->m_func->getFuncBody();
   }
   Stats::inc(Stats::VMEnter);
   if (RuntimeOption::EvalJit &&
@@ -1862,7 +1864,7 @@ void VMExecutionContext::enterVMWork(ActRec* enterFnAr) {
       LIKELY(!DEBUGGER_FORCE_INTR)) {
     Transl::SrcKey sk(Transl::curFunc(), m_pc);
     (void) curUnit()->offsetOf(m_pc); /* assert */
-    tx64->enterTC(sk);
+    tx64->enterTC(sk, start);
   } else {
     dispatch();
   }

hphp/runtime/vm/translator/translator-x64.cpp

@@ -3278,7 +3278,7 @@ void enterTCHelper(Cell* vm_sp,
                    void* targetCacheBase) asm ("__enterTCHelper");
 
 void
-TranslatorX64::enterTC(SrcKey sk) {
+TranslatorX64::enterTC(SrcKey sk, TCA start) {
   using namespace TargetCache;
 
   if (debug) {
@@ -3289,7 +3289,7 @@ TranslatorX64::enterTC(SrcKey sk) {
   TReqInfo info;
   info.requestNum = -1;
   info.saved_rStashedAr = 0;
-  TCA start = getTranslation(sk, true);
+  if (UNLIKELY(!start)) start = getTranslation(sk, true);
   for (;;) {
     assert(sizeof(Cell) == 16);
     assert(((uintptr_t)vmsp() & (sizeof(Cell) - 1)) == 0);
@@ -3308,7 +3308,8 @@ TranslatorX64::enterTC(SrcKey sk) {
       sk = SrcKey(curFunc(), newPc);
       start = getTranslation(sk, true);
     }
-    assert(isValidCodeAddress(start));
+    assert(start == (TCA)HPHP::VM::Transl::funcBodyHelperThunk ||
+           isValidCodeAddress(start));
     assert(!s_writeLease.amOwner());
     curFunc()->validate();
     INC_TPC(enter_tc);

hphp/runtime/vm/translator/translator-x64.h

@@ -991,7 +991,7 @@ public:
    * a given nested invocation of the intepreter (calling back into it
    * as necessary for blocks that need to be interpreted).
    */
-  void enterTC(SrcKey sk);
+  void enterTC(SrcKey sk, TCA start);
 
   TranslatorX64();
   virtual ~TranslatorX64();