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but the bug was already present in many releases that are no longer
maintained ... ]
Bye,
Ulrich
Index: gcc/config/rs6000/freebsd64.h
===================================================================
--- gcc/config/rs6000/freebsd64.h (revision 212147)
+++ gcc/config/rs6000/freebsd64.h (working copy)
@@ -365,13 +365,10 @@
#define DBX_REGISTER_NUMBER(REGNO) rs6000_dbx_register_number (REGNO)
/* PowerPC64 Linux word-aligns FP doubles when -malign-power is given. */
-#undef ADJUST_FIELD_ALIGN
#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) \
+ ((TARGET_64BIT \
+ && TARGET_ALIGN_NATURAL == 0 \
+ && TYPE_MODE (strip_array_types (TREE_TYPE (FIELD))) == DFmode) \
? MIN ((COMPUTED), 32) \
: (COMPUTED))
Index: gcc/config/rs6000/linux64.h
===================================================================
--- gcc/config/rs6000/linux64.h (revision 212147)
+++ gcc/config/rs6000/linux64.h (working copy)
@@ -244,13 +244,10 @@
do { if (TARGET_64BIT) output_profile_hook (LABEL); } while (0)
/* PowerPC64 Linux word-aligns FP doubles when -malign-power is given. */
-#undef ADJUST_FIELD_ALIGN
#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) \
+ ((TARGET_64BIT \
+ && TARGET_ALIGN_NATURAL == 0 \
+ && TYPE_MODE (strip_array_types (TREE_TYPE (FIELD))) == DFmode) \
? MIN ((COMPUTED), 32) \
: (COMPUTED))
Index: gcc/config/rs6000/sysv4.h
===================================================================
--- gcc/config/rs6000/sysv4.h (revision 212147)
+++ gcc/config/rs6000/sysv4.h (working copy)
@@ -289,12 +289,6 @@
#define ABI_STACK_BOUNDARY \
((TARGET_EABI && !TARGET_ALTIVEC && !TARGET_ALTIVEC_ABI) ? 64 : 128)
-/* An expression for the alignment of a structure field FIELD if the
- alignment computed in the usual way is COMPUTED. */
-#define ADJUST_FIELD_ALIGN(FIELD, COMPUTED) \
- ((TARGET_ALTIVEC && TREE_CODE (TREE_TYPE (FIELD)) == VECTOR_TYPE) \
- ? 128 : COMPUTED)
-
#undef BIGGEST_FIELD_ALIGNMENT
/* Use ELF style section commands. */
--
Dr. Ulrich Weigand
GNU/Linux compilers and toolchain
ulrich.weig...@de.ibm.com
