From: Dave Love <d.love@dl.ac.uk>
To: egcs@cygnus.com
Subject: x86 stack alignment redux
Date: Thu, 13 Nov 1997 09:28:00 -0000 [thread overview]
Message-ID: <rzq3el01z6k.fsf@djlvig.dl.ac.uk> (raw)
It's a while since I tried to get something like this in for the
benefit of people doing double precision fortran calculations, at
least...
With this change, a glibc2-based system such as is now apparently
becoming usable, and -malign-double, g77 users running on GNUish
686-based boxes should no longer suffer an average 50% perfromance hit
because doubles on the stack only get word-aligned (or a smaller hit
on 586). Previous discussion suggested it's a bug if STACK_BOUNDARY
doesn't agree with the initial stack pointer alignment and glibc2
ensures initial double alignment.
This really is important to serious scientific users with high-profile
projects of the sort I understand have just been slagging off g77/gcc
at a high-performance computing meeting here.
1997-11-13 Dave Love <d.love@dl.ac.uk>
* config/i386/linux.h (STACK_BOUNDARY): Define as 64 for glibc2.
* config/i386/gnu.h (STACK_BOUNDARY): Define as 64.
*** config/i386/linux.h 1997/11/02 15:23:02 1.1
--- config/i386/linux.h 1997/11/13 16:45:40
***************
*** 37,42 ****
--- 37,48 ----
#undef DEFAULT_PCC_STRUCT_RETURN
#define DEFAULT_PCC_STRUCT_RETURN 1
+ #ifndef USE_GNULIBC_1
+ #undef STACK_BOUNDARY
+ #define STACK_BOUNDARY 64 /* glibc2's crt ensures this, libc5
+ only gives you 32 */
+ #endif
+
/* This is how to output an element of a case-vector that is relative.
This is only used for PIC code. See comments by the `casesi' insn in
i386.md for an explanation of the expression this outputs. */
*** config/i386/gnu.h 1997/11/13 16:46:29 1.1
--- config/i386/gnu.h 1997/11/13 16:47:18
***************
*** 3,8 ****
--- 3,11 ----
/* This does it mostly for us. */
#include <i386/linux.h>
+ #undef STACK_BOUNDARY
+ #define STACK_BOUNDARY 64 /* glibc2's crt ensures this */
+
#undef CPP_PREDEFINES
#define CPP_PREDEFINES GNU_CPP_PREDEFINES("i386")
next reply other threads:[~1997-11-13 9:28 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
1997-11-13 9:28 Dave Love [this message]
1997-12-11 23:10 ` Jeffrey A Law
1997-12-11 23:40 ` H.J. Lu
1997-12-12 0:18 ` Jeffrey A Law
1997-12-12 7:28 ` H.J. Lu
1997-12-12 10:18 ` Marc Lehmann
1997-12-12 13:04 ` Dave Love
1997-12-14 22:36 ` Jeffrey A Law
1997-12-12 13:04 ` Marc Lehmann
1997-12-14 22:41 ` Jeffrey A Law
1997-12-12 13:04 Mike Stump
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