[Bug target/36135] GCC creates suboptimal ASM : suboptimal Adressing-Modes used
--- Comment #7 from pinskia at gcc dot gnu dot org 2008-06-13 14:34 --- >Andrew, do you plan to fix this issue? Personally no. Mostly because IV-opts is hard to understand. Also it is not the m68k back-end doing the optimization rather loop.c did it. See PR 31849. *** This bug has been marked as a duplicate of 31849 *** -- pinskia at gcc dot gnu dot org changed: What|Removed |Added Status|UNCONFIRMED |RESOLVED Resolution||DUPLICATE http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36135
[Bug target/36135] GCC creates suboptimal ASM : suboptimal Adressing-Modes used
--- Comment #6 from gunnar at greyhound-data dot com 2008-06-13 13:34
---
(In reply to comment #4)
> This comes down to IV-OPTs not understanding {post,pre}_{dec,inc} at all.
> There is another bug about this somewhere I think for arm. PowerPC has the
> same issue too ...
>
Hi Andrew,
I want to make clear that the 68K backend used to be able to do this
optimization in the GCC 2.9 times. Later with 3.4 or 4.x this optmization did
not work anymore and the code became worth.
Does this make sense in your opinion?
Cheers
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36135
[Bug target/36135] GCC creates suboptimal ASM : suboptimal Adressing-Modes used
--- Comment #5 from gunnar at greyhound-data dot com 2008-06-13 09:31
---
(In reply to comment #4)
> This comes down to IV-OPTs not understanding {post,pre}_{dec,inc} at all.
> There is another bug about this somewhere I think for arm. PowerPC has the
> same issue too ...
>
If this effects so many platforms this sounds like an important issue to me.
Maybe someone should increase the priority and severity of the issue in this
case?
Andrew, do you plan to fix this issue?
Cheers
Gunnar
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36135
[Bug target/36135] GCC creates suboptimal ASM : suboptimal Adressing-Modes used
--- Comment #4 from pinskia at gcc dot gnu dot org 2008-06-12 14:38 ---
This comes down to IV-OPTs not understanding {post,pre}_{dec,inc} at all.
There is another bug about this somewhere I think for arm. PowerPC has the
same issue too ...
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36135
[Bug target/36135] GCC creates suboptimal ASM : suboptimal Adressing-Modes used
--- Comment #3 from gunnar at greyhound-data dot com 2008-06-12 14:34
---
Andreas,
What is your opinion to this?
GCC 2.9 used to combine the move with increment in the combine step to
something like this:
***
(insn 32 30 33 (set (reg/v:SI 32)
(mem:SI (post_inc:SI (reg/v:SI 34)) 0)) 42 {movsi+1} (nil)
(expr_list:REG_INC (reg/v:SI 34)
(nil)))
***
So problem is that now GCC seems not to be able to do this anymore by itself
With GCC 4.4 the output is:
**
(insn 34 33 35 4 example2.c:11 (set (reg/v:SI 54 [ value ])
(mem:SI (reg/v/f:SI 52 [ src ]) [2 S4 A16])) 37 {*movsi_cf} (nil))
(insn 35 34 36 4 example2.c:12 (set (reg/v:SI 53 [ value2 ])
(mem:SI (plus:SI (reg/v/f:SI 52 [ src ])
(const_int 4 [0x4])) [2 S4 A16])) 37 {*movsi_cf} (nil))
(insn 36 35 38 4 example2.c:5 (set (reg/v/f:SI 52 [ src ])
(plus:SI (reg/v/f:SI 52 [ src ])
(const_int 8 [0x8]))) 133 {*addsi3_5200} (nil))
(insn 38 36 40 4 example2.c:10 (set (reg/v:SI 50 [ size.21 ])
(plus:SI (reg/v:SI 50 [ size.21 ])
(const_int -1 [0x]))) 133 {*addsi3_5200} (nil))
***
Any ideas about this?
Kind regards
Gunnar von Boehn
--
gunnar at greyhound-data dot com changed:
What|Removed |Added
CC||schwab at suse dot de
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36135
[Bug target/36135] GCC creates suboptimal ASM : suboptimal Adressing-Modes used
--- Comment #2 from gunnar at greyhound-data dot com 2008-05-28 16:23 --- (In reply to comment #1) > It would have been nice to check at least gcc 4.3 (or better current trunk). > I have verified this for you with the most current GCC source. Verified with gcc version 4.4.0 20080523 (experimental) (GCC) The problem that GCC uses bad addressing modes is still persistent. Code generated by GCC 4.4 copy_32x4: link.w %fp,#-12 movem.l #3076,(%sp) move.l 16(%fp),%d2 lsr.l #4,%d2 move.l 8(%fp),%a3 move.l 12(%fp),%a2 jra .L6 .L7: move.l (%a2),%a1 subq.l #1,%d2 move.l 4(%a2),%d0 move.l 8(%a2),%d1 move.l 12(%a2),%a0 add.l #16,%a2 move.l %a1,(%a3) move.l %d0,4(%a3) move.l %d1,8(%a3) move.l %a0,12(%a3) add.l #16,%a3 .L6: tst.l %d2 jne .L7 movem.l (%sp),#3076 unlk %fp rts -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36135
[Bug target/36135] GCC creates suboptimal ASM : suboptimal Adressing-Modes used
--- Comment #1 from rguenth at gcc dot gnu dot org 2008-05-07 19:33 --- It would have been nice to check at least gcc 4.3 (or better current trunk). -- rguenth at gcc dot gnu dot org changed: What|Removed |Added Severity|normal |enhancement Keywords||missed-optimization http://gcc.gnu.org/bugzilla/show_bug.cgi?id=36135
