David Edelsohn wrote: > On Wed, Jul 9, 2014 at 12:06 PM, Ulrich Weigand <uweig...@de.ibm.com> wrote: > > Hello, > > > > running the ABI compatibility test suite against another compiler showed > > strange effects caused by code in ADJUST_FIELD_ALIGN on rs6000: > > > > #define ADJUST_FIELD_ALIGN(FIELD, COMPUTED) \ > > ((TARGET_ALTIVEC && TREE_CODE (TREE_TYPE (FIELD)) == VECTOR_TYPE) \ > > ? 128 \ > > : (TARGET_64BIT \ > > && TARGET_ALIGN_NATURAL == 0 \ > > && TYPE_MODE (strip_array_types (TREE_TYPE (FIELD))) == DFmode) \ > > ? MIN ((COMPUTED), 32) \ > > : (COMPUTED)) > > > > The first test for VECTOR_TYPE if TARGET_ALTIVEC causes the trouble. > > This has been present (in slight variations) ever since Altivec support > > was first merged by Aldy Hernandez back in 2001: > > https://gcc.gnu.org/ml/gcc-cvs/2001-11/msg00148.html > > > > Note that at this time, both ADJUST_FIELD_ALIGN and ROUND_TYPE_ALIGN > > contained that check. The check was later removed from ROUND_TYPE_ALIGN > > in the following patch intended to fix PR 17961: > > https://gcc.gnu.org/ml/gcc-patches/2005-06/msg00920.html > > > > The check has no effect in most usual cases anyway, since Altivec vectors > > already carry a default alignment of 16 bytes. However, the check *does* > > affect non-Altivec vectors created via attribute((vector_size)) with a > > size != 16. When any of those is used as element of a struct, GCC on > > PowerPC will ignore the normal alignment and always force 16 byte alignment. > > (An explicit attribute((aligned)) however, is still respected.) This > > behavior seems to have been unintended. > > > > In off-line discussions, we came to the conclusion that this check > > should have been removed from ADJUST_FIELD_ALIGN at the same time > > as it was removed from ROUND_TYPE_ALIGN. This patch implements this. > > > > Note that the check has been copied over time into the instances of > > ADJUST_FIELD_ALIGN in sysv4.h, linux64.h, and freebsd64.h. For > > consistency, the patch removes the check in all these places. > > > > Tested on powerpc64-linux and powerp64le-linux; built a cross-cc1 > > for powerpc64-freebsd6. > > > > OK for mainline? > > [ It may also be useful to backport to the currently open branches, > > but the bug was already present in many releases that are no longer > > maintained ... ] > > This is okay with me. > > Do you want to explicitly ask rth if he has any further insight?
Sorry, forgot to add rth on CC initially ... Richard, you were involved in the discussion back in 2005 (see gcc-patches link above) and suggested to completely remove the Altivec check from ROUND_TYPE_ALIGN. Do you agree that this check should likewise be removed from the ADJUST_FIELD_ALIGN macro? Bye, Ulrich
