suppress warnings for probable NULL dererefences

compile.c

@@ -4774,6 +4774,7 @@ compile_massign_lhs(rb_iseq_t *iseq, LINK_ANCHOR *const pre, LINK_ANCHOR *const
 
         LINK_ELEMENT *insn_element = LAST_ELEMENT(pre);
         iobj = (INSN *)get_prev_insn((INSN *)insn_element); /* send insn */
+	ASSUME(iobj);
         ELEM_REMOVE(LAST_ELEMENT(pre));
         ELEM_REMOVE((LINK_ELEMENT *)iobj);
         pre->last = iobj->link.prev;

encoding.c

@@ -496,6 +496,7 @@ set_base_encoding(struct enc_table *enc_table, int index, rb_encoding *base)
 {
     rb_encoding *enc = enc_table->list[index].enc;
 
+    ASSUME(enc);
     enc_table->list[index].base = base;
     if (ENC_DUMMY_P(base)) ENC_SET_DUMMY((rb_raw_encoding *)enc);
     return enc;
@@ -758,7 +759,9 @@ rb_encdb_alias(const char *alias, const char *orig)
 void
 rb_encdb_set_unicode(int index)
 {
-    ((rb_raw_encoding *)rb_enc_from_index(index))->flags |= ONIGENC_FLAG_UNICODE;
+    rb_raw_encoding *enc = (rb_raw_encoding *)rb_enc_from_index(index);
+    ASSUME(enc);
+    enc->flags |= ONIGENC_FLAG_UNICODE;
 }
 
 static void

vm.c

@@ -1653,6 +1653,7 @@ rb_vm_cref_replace_with_duplicated_cref(void)
     const rb_execution_context_t *ec = GET_EC();
     const rb_control_frame_t *cfp = rb_vm_get_ruby_level_next_cfp(ec, ec->cfp);
     rb_cref_t *cref = vm_cref_replace_with_duplicated_cref(cfp->ep);
+    ASSUME(cref);
     return cref;
 }
 

vm_core.h

@@ -1367,6 +1367,7 @@ vm_assert_env(VALUE obj)
 }
 #endif
 
+RBIMPL_ATTR_NONNULL((1))
 static inline VALUE
 VM_ENV_ENVVAL(const VALUE *ep)
 {
@@ -1376,6 +1377,7 @@ VM_ENV_ENVVAL(const VALUE *ep)
     return envval;
 }
 
+RBIMPL_ATTR_NONNULL((1))
 static inline const rb_env_t *
 VM_ENV_ENVVAL_PTR(const VALUE *ep)
 {