On Tue, Jan 14, 2014 at 08:12:41PM +0100, Jakub Jelinek wrote:
> For 4.9, if what you've added is what you want to do for performance
> reasons, then I'd do something like:
Ok, here it is in a form of patch, bootstrapped/regtested on x86_64-linux
and i686-linux, ok for trunk?
2014-01-17 Jakub Jelinek <ja...@redhat.com>
* config/i386/i386.c (ix86_data_alignment): For compatibility with
(incorrect) GCC 4.8 and earlier alignment assumptions ensure we align
decls to at least the GCC 4.8 used alignments.
--- gcc/config/i386/i386.c.jj 2014-01-16 20:22:50.000000000 +0100
+++ gcc/config/i386/i386.c 2014-01-17 11:56:51.183501322 +0100
@@ -26433,6 +26433,15 @@ ix86_constant_alignment (tree exp, int a
int
ix86_data_alignment (tree type, int align, bool opt)
{
+ /* GCC 4.8 and earlier used to incorrectly assume this alignment even
+ for symbols from other compilation units or symbols that don't need
+ to bind locally. In order to preserve some ABI compatibility with
+ those compilers, ensure we don't decrease alignment from what we
+ used to assume. */
+
+ int max_align_compat
+ = optimize_size ? BITS_PER_WORD : MIN (256, MAX_OFILE_ALIGNMENT);
+
/* A data structure, equal or greater than the size of a cache line
(64 bytes in the Pentium 4 and other recent Intel processors, including
processors based on Intel Core microarchitecture) should be aligned
@@ -26447,11 +26456,17 @@ ix86_data_alignment (tree type, int alig
if (opt
&& AGGREGATE_TYPE_P (type)
&& TYPE_SIZE (type)
- && TREE_CODE (TYPE_SIZE (type)) == INTEGER_CST
- && (TREE_INT_CST_LOW (TYPE_SIZE (type)) >= (unsigned) max_align
- || TREE_INT_CST_HIGH (TYPE_SIZE (type)))
- && align < max_align)
- align = max_align;
+ && TREE_CODE (TYPE_SIZE (type)) == INTEGER_CST)
+ {
+ if ((TREE_INT_CST_LOW (TYPE_SIZE (type)) >= (unsigned) max_align_compat
+ || TREE_INT_CST_HIGH (TYPE_SIZE (type)))
+ && align < max_align_compat)
+ align = max_align_compat;
+ if ((TREE_INT_CST_LOW (TYPE_SIZE (type)) >= (unsigned) max_align
+ || TREE_INT_CST_HIGH (TYPE_SIZE (type)))
+ && align < max_align)
+ align = max_align;
+ }
/* x86-64 ABI requires arrays greater than 16 bytes to be aligned
to 16byte boundary. */
Jakub
