typeLookup: guard on tp_version_tag instead of mro + Box::getattr

For types which don't have Py_TPFLAGS_HAVE_VERSION_TAG set we keep the old behaviour

from_cpython/Include/object.h

@@ -430,7 +430,9 @@ typedef PyObject *(*allocfunc)(PyTypeObject *, Py_ssize_t);
     destructor tp_del;\
                                                                                 \
     /* Type attribute cache version tag. Added in version 2.6 */\
-    unsigned int tp_version_tag;    \
+    /* Pyston change: change uint to 64bit uint
+    unsigned int tp_version_tag; */    \
+    PY_UINT64_T tp_version_tag;        \
 \
     /* Pyston changes: added these fields */ \
 

src/asm_writing/assembler.cpp

@@ -127,6 +127,17 @@ void Assembler::emitInt(int64_t n, int bytes) {
     ASSERT(n == 0 || n == -1, "%ld", n);
 }
 
+void Assembler::emitUInt(uint64_t n, int bytes) {
+    assert(bytes > 0 && bytes <= 8);
+    if (bytes < 8)
+        assert(n < ((1UL << (8 * bytes))));
+
+    for (int i = 0; i < bytes; i++) {
+        emitByte(n & 0xff);
+        n >>= 8;
+    }
+    ASSERT(n == 0, "%lu", n);
+}
 void Assembler::emitRex(uint8_t rex) {
     emitByte(rex | 0x40);
 }
@@ -167,7 +178,7 @@ void Assembler::mov(Immediate val, Register dest, bool force_64bit_load) {
     if (rex)
         emitRex(rex);
     emitByte(0xb8 + dest_idx);
-    emitInt(val.val, force_64bit_load ? 8 : 4);
+    emitUInt(val.val, force_64bit_load ? 8 : 4);
 }
 
 void Assembler::movq(Immediate src, Indirect dest) {

src/asm_writing/assembler.h

@@ -83,6 +83,7 @@ private:
 private:
     void emitByte(uint8_t b);
     void emitInt(int64_t n, int bytes);
+    void emitUInt(uint64_t n, int bytes);
     void emitRex(uint8_t rex);
     void emitModRM(uint8_t mod, uint8_t reg, uint8_t rm);
     void emitSIB(uint8_t scalebits, uint8_t index, uint8_t base);

src/asm_writing/rewriter.cpp

@@ -270,6 +270,11 @@ void Rewriter::assertArgsInPlace() {
 void RewriterVar::addGuard(uint64_t val) {
     STAT_TIMER(t0, "us_timer_rewriter", 10);
 
+    if (isConstant()) {
+        RELEASE_ASSERT(constant_value == val, "added guard which is always false");
+        return;
+    }
+
     RewriterVar* val_var = rewriter->loadConst(val);
     rewriter->addAction([=]() { rewriter->_addGuard(this, val_var); }, { this, val_var }, ActionType::GUARD);
 }

src/runtime/objmodel.cpp

@@ -957,7 +957,9 @@ extern "C" PyObject* _PyType_Lookup(PyTypeObject* type, PyObject* name) noexcept
 #define MCACHE_CACHEABLE_NAME(name) PyString_CheckExact(name) && PyString_GET_SIZE(name) <= MCACHE_MAX_ATTR_SIZE
 
 struct method_cache_entry {
-    unsigned int version;
+    // Pyston change:
+    // unsigned int version;
+    PY_UINT64_T version;
     PyObject* name;  /* reference to exactly a str or None */
     PyObject* value; /* borrowed */
 };
@@ -984,7 +986,13 @@ int assign_version_tag(PyTypeObject* type) noexcept {
     type->tp_version_tag = next_version_tag++;
     /* for stress-testing: next_version_tag &= 0xFF; */
 
-    if (type->tp_version_tag == 0) {
+    if (unlikely(type->tp_version_tag == 0)) {
+        // Pyston change: check for a wrap around because they are not allowed to happen with our 64bit version tag
+        static bool is_wrap_around = false;
+        if (is_wrap_around)
+            abort();
+        is_wrap_around = true;
+
         /* wrap-around or just starting Python - clear the whole
            cache by filling names with references to Py_None.
            Values are also set to NULL for added protection, as they
@@ -1019,7 +1027,9 @@ template <Rewritable rewritable> Box* typeLookup(BoxedClass* cls, BoxedString* a
 
     Box* val = NULL;
 
-    if (rewrite_args) {
+    // CAPI types defined inside external extension normally don't have this flag set while all types inside pyston set
+    // it.
+    if (rewrite_args && !PyType_HasFeature(cls, Py_TPFLAGS_HAVE_VERSION_TAG)) {
         assert(!rewrite_args->isSuccessful());
 
         RewriterVar* obj_saved = rewrite_args->obj;
@@ -1073,16 +1083,20 @@ template <Rewritable rewritable> Box* typeLookup(BoxedClass* cls, BoxedString* a
         assert(cls->tp_mro);
         assert(cls->tp_mro->cls == tuple_cls);
 
+        bool found_cached_entry = false;
         if (MCACHE_CACHEABLE_NAME(attr) && PyType_HasFeature(cls, Py_TPFLAGS_VALID_VERSION_TAG)) {
             if (attr->hash == -1)
                 strHashUnboxed(attr);
 
             /* fast path */
-            unsigned int h = MCACHE_HASH_METHOD(cls, attr);
-            if (method_cache[h].version == cls->tp_version_tag && method_cache[h].name == attr)
-                return method_cache[h].value;
+            auto h = MCACHE_HASH_METHOD(cls, attr);
+            if (method_cache[h].version == cls->tp_version_tag && method_cache[h].name == attr) {
+                val = method_cache[h].value;
+                found_cached_entry = true;
+            }
         }
 
+        if (!found_cached_entry) {
             for (auto b : *static_cast<BoxedTuple*>(cls->tp_mro)) {
                 // object_cls will get checked very often, but it only
                 // has attributes that start with an underscore.
@@ -1099,13 +1113,25 @@ template <Rewritable rewritable> Box* typeLookup(BoxedClass* cls, BoxedString* a
             }
 
             if (MCACHE_CACHEABLE_NAME(attr) && assign_version_tag(cls)) {
-            unsigned int h = MCACHE_HASH_METHOD(cls, attr);
+                auto h = MCACHE_HASH_METHOD(cls, attr);
                 method_cache[h].version = cls->tp_version_tag;
                 method_cache[h].value = val; /* borrowed */
                 Py_INCREF(attr);
                 Py_DECREF(method_cache[h].name);
                 method_cache[h].name = attr;
             }
+        }
+        if (rewrite_args) {
+            RewriterVar* obj_saved = rewrite_args->obj;
+            static_assert(sizeof(BoxedClass::tp_flags) == 8, "addAttrGuard only supports 64bit values");
+            static_assert(sizeof(BoxedClass::tp_version_tag) == 8, "addAttrGuard only supports 64bit values");
+            obj_saved->addAttrGuard(offsetof(BoxedClass, tp_flags), (intptr_t)cls->tp_flags);
+            obj_saved->addAttrGuard(offsetof(BoxedClass, tp_version_tag), (intptr_t)cls->tp_version_tag);
+            if (!val)
+                rewrite_args->setReturn(NULL, ReturnConvention::NO_RETURN);
+            else
+                rewrite_args->setReturn(rewrite_args->rewriter->loadConst((int64_t)val), ReturnConvention::HAS_RETURN);
+        }
         return val;
     }
 }
@@ -2367,7 +2393,7 @@ void setattrGeneric(Box* obj, BoxedString* attr, Box* val, SetattrRewriteArgs* r
         }
 
         // update_slot() calls PyType_Modified() internally so we only have to explicitly call it inside the IC
-        if (rewrite_args)
+        if (rewrite_args && PyType_HasFeature(self, Py_TPFLAGS_HAVE_VERSION_TAG))
             rewrite_args->rewriter->call(true, (void*)PyType_Modified, rewrite_args->obj);
     }
 }