https://gcc.gnu.org/bugzilla/show_bug.cgi?id=77718
--- Comment #4 from Bernd Schmidt <bernds at gcc dot gnu.org> ---
So something like this maybe?
Index: builtins.c
===================================================================
--- builtins.c (revision 240511)
+++ builtins.c (working copy)
@@ -3707,11 +3707,13 @@ expand_builtin_memcmp (tree exp, rtx tar
by_pieces_constfn constfn = NULL;
- const char *src_str = c_getstr (arg1);
- if (src_str == NULL)
- src_str = c_getstr (arg2);
- else
- std::swap (arg1_rtx, arg2_rtx);
+ const char *src_str = c_getstr (arg2);
+ if (result_eq && src_str == NULL)
+ {
+ src_str = c_getstr (arg1);
+ if (src_str != NULL)
+ std::swap (arg1_rtx, arg2_rtx);
+ }
/* If SRC is a string constant and block move would be done
by pieces, we can avoid loading the string from memory
