https://gcc.gnu.org/bugzilla/show_bug.cgi?id=66509
--- Comment #10 from Jack Howarth <howarth.at.gcc at gmail dot com> --- The clang developers suggest the test... filds (%ebp) which is compilable with the clang-based assembler at both -m32 and -m64. http://lists.cs.uiuc.edu/pipermail/cfe-dev/2015-June/043463.html fists (%ebp) also appears to work for the second part of the test.