bpo-40998: Address compiler warnings found by ubsan (GH-20929)

Signed-off-by: Christian Heimes <christian@python.org>

Automerge-Triggered-By: GH:tiran
(cherry picked from commit 07f2ade)

Co-authored-by: Christian Heimes <christian@python.org>

Misc/NEWS.d/next/Build/2020-06-17-09-05-02.bpo-40998.sgqmg9.rst

@@ -0,0 +1,2 @@
+Addressed three compiler warnings found by undefined behavior sanitizer
+(ubsan).

Objects/unicodeobject.c

@@ -847,7 +847,11 @@ xmlcharrefreplace(_PyBytesWriter *writer, char *str,
 
     /* generate replacement */
     for (i = collstart; i < collend; ++i) {
-        str += sprintf(str, "&#%d;", PyUnicode_READ(kind, data, i));
+        size = sprintf(str, "&#%d;", PyUnicode_READ(kind, data, i));
+        if (size < 0) {
+            return NULL;
+        }
+        str += size;
     }
     return str;
 }

Parser/pegen/parse_string.c

@@ -74,6 +74,9 @@ decode_unicode_with_escapes(Parser *parser, const char *s, size_t len, Token *t)
         return NULL;
     }
     p = buf = PyBytes_AsString(u);
+    if (p == NULL) {
+        return NULL;
+    }
     end = s + len;
     while (s < end) {
         if (*s == '\\') {

Python/pylifecycle.c

@@ -1353,7 +1353,6 @@ Py_FinalizeEx(void)
 
     /* Get current thread state and interpreter pointer */
     PyThreadState *tstate = _PyRuntimeState_GetThreadState(runtime);
-    PyInterpreterState *interp = tstate->interp;
 
     // Wrap up existing "threading"-module-created, non-daemon threads.
     wait_for_thread_shutdown(tstate);
@@ -1376,13 +1375,13 @@ Py_FinalizeEx(void)
     /* Copy the core config, PyInterpreterState_Delete() free
        the core config memory */
 #ifdef Py_REF_DEBUG
-    int show_ref_count = interp->config.show_ref_count;
+    int show_ref_count = tstate->interp->config.show_ref_count;
 #endif
 #ifdef Py_TRACE_REFS
-    int dump_refs = interp->config.dump_refs;
+    int dump_refs = tstate->interp->config.dump_refs;
 #endif
 #ifdef WITH_PYMALLOC
-    int malloc_stats = interp->config.malloc_stats;
+    int malloc_stats = tstate->interp->config.malloc_stats;
 #endif
 
     /* Remaining daemon threads will automatically exit