On Wed, Feb 26, 2025 at 02:54:43PM +0100, Daniel Sahlberg wrote: > Should have researched a bit more before replying. There was already some > code to do exactly this, but it was removed in r1722879: > > [[[ > stefan2 2016-01-04 15:17:04 > Stop using pointer arithmetics to check for proper alignment because > that is not portable. > > As a result, platforms that don't allow unaligned data access will > suffer a small additional performance hit. > > * subversion/libsvn_subr/eol.c > (svn_eol__find_eol_start): No longer attempt aligned chunky processing > when unaligned access is not supported. > > * subversion/libsvn_subr/utf_validate.c > (first_non_fsm_start_char): Same. > ]]] > > Don't quite understand why but there is probably a reasonable explanation.
It took us a few rounds of testing to keep things working across all platforms when these optimizations went in. As far as I recall, there was run-time fallout on the OpenBSD/sparc64 buildbot (which no longer exists; I don't have sparc64 hardware anymore). Unaligned access will always cause hardware traps on that platform. The above change was probably related to that. With x86 platform behaviour changing all the testing we did back then is being invalidated. The solution with the least amount of effort on our part would be using the simple char * loop implementation everywhere. The maintenance effort required to keep the unaligned-access code path working and safe on all (modern) platforms would likely exceed our current development capabilities. Though of course, if someone wants to do that work, I wouldn't be opposed.
