Optimize string offset setting

I was looking at this code while working on a vector
translator diff and noticed that we're doing some unnecessary
refcounting.

hphp/runtime/base/tv_helpers.cpp

@@ -85,6 +85,34 @@ void tvCastToInt64InPlace(TypedValue* tv, int base /* = 10 */) {
   tv->m_type = KindOfInt64;
 }
 
+int64_t tvCastToInt64(TypedValue* tv, int base /* = 10 */) {
+  if (tv->m_type == KindOfRef) {
+    tv = tv->m_data.pref->tv();
+  }
+
+  switch (tv->m_type) {
+  case KindOfUninit:
+  case KindOfNull:
+    return 0;
+  case KindOfBoolean:
+    assert(tv->m_data.num == 0LL || tv->m_data.num == 1LL);
+    // Fall through
+  case KindOfInt64:
+    return tv->m_data.num;
+  case KindOfDouble:
+    return toInt64(tv->m_data.dbl);
+  case KindOfStaticString:
+  case KindOfString:
+    return tv->m_data.pstr->toInt64(base);
+  case KindOfArray:
+    return tv->m_data.parr->empty() ? 0 : 1;
+  case KindOfObject:
+    return tv->m_data.pobj->o_toInt64();
+  default:
+    not_reached();
+  }
+}
+
 void tvCastToDoubleInPlace(TypedValue* tv) {
   if (tv->m_type == KindOfRef) {
     tvUnbox(tv);
@@ -133,13 +161,36 @@ void tvCastToStringInPlace(TypedValue* tv) {
     tvAsVariant(tv) = tv->m_data.pobj->t___tostring();
     return;
   }
-  default:            assert(false); s = buildStringData(""); break;
+  default:            not_reached();
   }
   tv->m_data.pstr = s;
   tv->m_type = KindOfString;
   tv->m_data.pstr->incRefCount();
 }
 
+StringData* tvCastToString(TypedValue* tv) {
+  if (tv->m_type == KindOfRef) {
+    tv = tv->m_data.pref->tv();
+  }
+
+  StringData* s;
+  switch (tv->m_type) {
+  case KindOfUninit:
+  case KindOfNull:    s = buildStringData(""); break;
+  case KindOfBoolean: s = buildStringData(tv->m_data.num ? "1" : ""); break;
+  case KindOfInt64:   s = buildStringData(tv->m_data.num); break;
+  case KindOfDouble:  s = buildStringData(tv->m_data.dbl); break;
+  case KindOfStaticString:
+  case KindOfString:  s = tv->m_data.pstr; break;
+  case KindOfArray:   return StringData::GetStaticString("Array");
+  case KindOfObject:  return tv->m_data.pobj->t___tostring().detach();
+  default:            not_reached();
+  }
+
+  s->incRefCount();
+  return s;
+}
+
 void tvCastToArrayInPlace(TypedValue* tv) {
   if (tv->m_type == KindOfRef) {
     tvUnbox(tv);

hphp/runtime/base/tv_helpers.h

@@ -447,8 +447,10 @@ inline bool tvIsString(const TypedValue* tv) {
 
 void tvCastToBooleanInPlace(TypedValue* tv);
 void tvCastToInt64InPlace(TypedValue* tv, int base = 10);
+int64_t tvCastToInt64(TypedValue* tv, int base = 10);
 void tvCastToDoubleInPlace(TypedValue* tv);
 void tvCastToStringInPlace(TypedValue* tv);
+StringData* tvCastToString(TypedValue* tv);
 void tvCastToArrayInPlace(TypedValue* tv);
 void tvCastToObjectInPlace(TypedValue* tv);
 

hphp/runtime/vm/member_operations.h

@@ -650,11 +650,10 @@ inline void SetElem(TypedValue* base, TypedValue* key, Cell* value) {
     } else {
       // Convert key to string offset.
       int64_t x;
-      {
-        TypedValue tv;
-        tvDup(key, &tv);
-        tvCastToInt64InPlace(&tv);
-        x = tv.m_data.num;
+      if (LIKELY(key->m_type == KindOfInt64)) {
+        x = key->m_data.num;
+      } else {
+        x = tvCastToInt64(key);
       }
       if (x < 0 || x >= StringData::MaxSize) {
         // Andrei: can't use PRId64 here because of order of inclusion
@@ -673,16 +672,21 @@ inline void SetElem(TypedValue* base, TypedValue* key, Cell* value) {
       // Extract the first character of (string)value.
       char y[2];
       {
-        TypedValue tv;
-        tvDup(value, &tv);
-        tvCastToStringInPlace(&tv);
-        if (tv.m_data.pstr->size() > 0) {
-          y[0] = tv.m_data.pstr->data()[0];
+        StringData* valStr;
+        if (LIKELY(IS_STRING_TYPE(value->m_type))) {
+          valStr = value->m_data.pstr;
+          valStr->incRefCount();
+        } else {
+          valStr = tvCastToString(value);
+        }
+
+        if (valStr->size() > 0) {
+          y[0] = valStr->data()[0];
           y[1] = '\0';
         } else {
           y[0] = '\0';
         }
-        tvRefcountedDecRef(&tv);
+        decRefStr(valStr);
       }
       // Create and save the result.
       if (x >= 0 && x < baseLen && base->m_data.pstr->getCount() <= 1) {