Drop incorrect cache_slot optimization for typed properties

For a particular assignment, a non-coerced constant assignment
value will remain valid. However, opcache merges cache slots for
all identical property references, which means that this
optimization also disables property type checks for all other
operands on the property that occur in the same functions.

This could be addressed by blocking cache slot merging in opcache,
but I prefer dropping it entirely instead. It does not seem
important enough to warrant doing that.

Author: nikic

Zend/tests/type_declarations/typed_properties_cache_slot_opt.phpt

@@ -0,0 +1,30 @@
+--TEST--
+Demonstrate that cache_slot optimization is illegal due to cache_slot merging
+--FILE--
+<?php
+
+class Test {
+    public int $prop;
+
+    public function method() {
+        // Opcache merges cache slots for both assignments.
+        $this->prop = 1;
+        try {
+            $this->prop = "foobar";
+        } catch (TypeError $e) {
+            echo $e->getMessage(), "\n";
+        }
+        var_dump($this->prop);
+    }
+}
+
+$test = new Test;
+$test->method();
+$test->method();
+
+?>
+--EXPECT--
+Typed property Test::$prop must be int, string used
+int(1)
+Typed property Test::$prop must be int, string used
+int(1)

Zend/zend_vm_def.h

@@ -2480,18 +2480,7 @@ ZEND_VM_C_LABEL(assign_object):
 				zend_property_info *prop_info = (zend_property_info*) CACHED_PTR_EX(cache_slot + 2);
 
 				if (UNEXPECTED(prop_info != NULL)) {
-					zend_uchar orig_type = IS_UNDEF;
-
-					if (OP_DATA_TYPE == IS_CONST) {
-						orig_type = Z_TYPE_P(value);
-					}
-
 					value = zend_assign_to_typed_prop(prop_info, property_val, value EXECUTE_DATA_CC);
-
-					/* will remain valid, thus no need to check prop_info in future here */
-					if (OP_DATA_TYPE == IS_CONST && Z_TYPE_P(value) == orig_type) {
-						CACHE_PTR_EX(cache_slot + 2, NULL);
-					}
 					ZEND_VM_C_GOTO(free_and_exit_assign_obj);
 				} else {
 ZEND_VM_C_LABEL(fast_assign_obj):