openrisc: always use unaligned-struct header

openrisc is the only architecture using the linux/unaligned/*memmove
infrastructure. There is a comment saying that this version is more
efficient, but this was added in 2011 before the openrisc gcc port
was merged upstream.

I checked a couple of files to see what the actual difference is with
the mainline gcc (9.4 and 11.1), and found that the generic header
seems to produce better code now, regardless of the gcc version.

Specifically, the be_memmove leads to allocating a stack slot and
copying the data one byte at a time, then reading the whole word
from the stack:

00000000 <test_get_unaligned_memmove>:
   0:	9c 21 ff f4 	l.addi r1,r1,-12
   4:	d4 01 10 04 	l.sw 4(r1),r2
   8:	8e 63 00 00 	l.lbz r19,0(r3)
   c:	9c 41 00 0c 	l.addi r2,r1,12
  10:	8e 23 00 01 	l.lbz r17,1(r3)
  14:	db e2 9f f4 	l.sb -12(r2),r19
  18:	db e2 8f f5 	l.sb -11(r2),r17
  1c:	8e 63 00 02 	l.lbz r19,2(r3)
  20:	8e 23 00 03 	l.lbz r17,3(r3)
  24:	d4 01 48 08 	l.sw 8(r1),r9
  28:	db e2 9f f6 	l.sb -10(r2),r19
  2c:	db e2 8f f7 	l.sb -9(r2),r17
  30:	85 62 ff f4 	l.lwz r11,-12(r2)
  34:	85 21 00 08 	l.lwz r9,8(r1)
  38:	84 41 00 04 	l.lwz r2,4(r1)
  3c:	44 00 48 00 	l.jr r9
  40:	9c 21 00 0c 	l.addi r1,r1,12

while the be_struct version reads each byte into a register
and does a shift to the right position:

00000000 <test_get_unaligned_struct>:
   0:	9c 21 ff f8 	l.addi r1,r1,-8
   4:	8e 63 00 00 	l.lbz r19,0(r3)
   8:	aa 20 00 18 	l.ori r17,r0,0x18
   c:	e2 73 88 08 	l.sll r19,r19,r17
  10:	8d 63 00 01 	l.lbz r11,1(r3)
  14:	aa 20 00 10 	l.ori r17,r0,0x10
  18:	e1 6b 88 08 	l.sll r11,r11,r17
  1c:	e1 6b 98 04 	l.or r11,r11,r19
  20:	8e 23 00 02 	l.lbz r17,2(r3)
  24:	aa 60 00 08 	l.ori r19,r0,0x8
  28:	e2 31 98 08 	l.sll r17,r17,r19
  2c:	d4 01 10 00 	l.sw 0(r1),r2
  30:	d4 01 48 04 	l.sw 4(r1),r9
  34:	9c 41 00 08 	l.addi r2,r1,8
  38:	e2 31 58 04 	l.or r17,r17,r11
  3c:	8d 63 00 03 	l.lbz r11,3(r3)
  40:	e1 6b 88 04 	l.or r11,r11,r17
  44:	84 41 00 00 	l.lwz r2,0(r1)
  48:	85 21 00 04 	l.lwz r9,4(r1)
  4c:	44 00 48 00 	l.jr r9
  50:	9c 21 00 08 	l.addi r1,r1,8

According to Stafford Horne, the new version should in fact perform
better.

In the trivial example, the struct version is a few instructions longer,
but building a whole kernel shows an overall reduction in code size,
presumably because it now has to manage fewer stack slots:

   text	   data	    bss	    dec	    hex	filename
4792010	 181480	  82324	5055814	 4d2546	vmlinux-unaligned-memmove
4790642	 181480	  82324	5054446	 4d1fee	vmlinux-unaligned-struct

Remove the memmove version completely and let openrisc use the same
code as everyone else, as a simplification.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Stafford Horne <shorne@gmail.com>

0 files changed, 0 insertions, 0 deletions