From: Mike Stump <mikestump@comcast.net>
To: gcc-patches <gcc-patches@gcc.gnu.org>
Subject: arm memcpy of aligned data
Date: Thu, 28 May 2015 21:36:00 -0000 [thread overview]
Message-ID: <9FF08D9A-529E-4FDE-9193-4BD81EDD89E3@comcast.net> (raw)
[-- Attachment #1: Type: text/plain, Size: 2010 bytes --]
So, the arm memcpy code of aligned data isn’t as good as it can be.
void *memcpy(void *dest, const void *src, unsigned int n);
void foo(char *dst, int i) {
memcpy (dst, &i, sizeof (i));
}
generates horrible code, but, it we are willing to notice the src or the destination are aligned, we can do much better:
$ ./cc1 -fschedule-fusion -fdump-tree-all-all -da -march=armv7ve -mcpu=cortex-m4 -fomit-frame-pointer -quiet -O2 /tmp/t.c -o t.s
$ cat t.s
[ … ]
foo:
@ args = 0, pretend = 0, frame = 4
@ frame_needed = 0, uses_anonymous_args = 0
@ link register save eliminated.
sub sp, sp, #4
str r1, [r0] @ unaligned
add sp, sp, #4
Index: gcc/config/arm/arm.c
===================================================================
--- gcc/config/arm/arm.c (revision 223842)
+++ gcc/config/arm/arm.c (working copy)
@@ -14376,7 +14376,10 @@ arm_block_move_unaligned_straight (rtx d
srcoffset + j * UNITS_PER_WORD - src_autoinc);
mem = adjust_automodify_address (srcbase, SImode, addr,
srcoffset + j * UNITS_PER_WORD);
- emit_insn (gen_unaligned_loadsi (regs[j], mem));
+ if (src_aligned)
+ emit_move_insn (regs[j], mem);
+ else
+ emit_insn (gen_unaligned_loadsi (regs[j], mem));
}
srcoffset += words * UNITS_PER_WORD;
}
@@ -14395,7 +14398,10 @@ arm_block_move_unaligned_straight (rtx d
dstoffset + j * UNITS_PER_WORD - dst_autoinc);
mem = adjust_automodify_address (dstbase, SImode, addr,
dstoffset + j * UNITS_PER_WORD);
- emit_insn (gen_unaligned_storesi (mem, regs[j]));
+ if (dst_aligned)
+ emit_move_insn (mem, regs[j]);
+ else
+ emit_insn (gen_unaligned_storesi (mem, regs[j]));
}
dstoffset += words * UNITS_PER_WORD;
}
Ok?
Can someone spin this through an arm test suite run for me, I was doing this by inspection and cross compile on a system with no arm bits. Bonus points if you can check it in with the test case above marked up as appropriate.
[-- Attachment #2: arm.diffs.txt --]
[-- Type: text/plain, Size: 1081 bytes --]
Index: gcc/config/arm/arm.c
===================================================================
--- gcc/config/arm/arm.c (revision 223842)
+++ gcc/config/arm/arm.c (working copy)
@@ -14376,7 +14376,10 @@ arm_block_move_unaligned_straight (rtx d
srcoffset + j * UNITS_PER_WORD - src_autoinc);
mem = adjust_automodify_address (srcbase, SImode, addr,
srcoffset + j * UNITS_PER_WORD);
- emit_insn (gen_unaligned_loadsi (regs[j], mem));
+ if (src_aligned)
+ emit_move_insn (regs[j], mem);
+ else
+ emit_insn (gen_unaligned_loadsi (regs[j], mem));
}
srcoffset += words * UNITS_PER_WORD;
}
@@ -14395,7 +14398,10 @@ arm_block_move_unaligned_straight (rtx d
dstoffset + j * UNITS_PER_WORD - dst_autoinc);
mem = adjust_automodify_address (dstbase, SImode, addr,
dstoffset + j * UNITS_PER_WORD);
- emit_insn (gen_unaligned_storesi (mem, regs[j]));
+ if (dst_aligned)
+ emit_move_insn (mem, regs[j]);
+ else
+ emit_insn (gen_unaligned_storesi (mem, regs[j]));
}
dstoffset += words * UNITS_PER_WORD;
}
next reply other threads:[~2015-05-28 21:16 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-05-28 21:36 Mike Stump [this message]
2015-05-29 8:22 ` Oleg Endo
2015-05-29 10:15 ` Kyrill Tkachov
2015-05-29 10:40 ` Kyrill Tkachov
2015-06-15 14:41 ` Kyrill Tkachov
2015-06-15 15:25 ` Richard Earnshaw
2015-08-16 19:24 ` Mike Stump
2015-08-17 10:01 ` Kyrill Tkachov
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=9FF08D9A-529E-4FDE-9193-4BD81EDD89E3@comcast.net \
--to=mikestump@comcast.net \
--cc=gcc-patches@gcc.gnu.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for read-only IMAP folder(s) and NNTP newsgroup(s).