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* [Bug rtl-optimization/42612] post-increment addressing not used
[not found] <bug-42612-4@http.gcc.gnu.org/bugzilla/>
@ 2012-08-23 14:16 ` olegendo at gcc dot gnu.org
2015-05-22 13:57 ` olegendo at gcc dot gnu.org
` (2 subsequent siblings)
3 siblings, 0 replies; 8+ messages in thread
From: olegendo at gcc dot gnu.org @ 2012-08-23 14:16 UTC (permalink / raw)
To: gcc-bugs
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42612
Oleg Endo <olegendo at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |olegendo at gcc dot gnu.org
Known to fail| |
--- Comment #4 from Oleg Endo <olegendo at gcc dot gnu.org> 2012-08-23 14:15:47 UTC ---
I haven't checked this on ARM but on SH there's a similar problem. See PR
50749.
As far as I understand it, it is a problem of the auto-inc-dec pass, which is
unable to find related addresses due to prior optimizations
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug rtl-optimization/42612] post-increment addressing not used
[not found] <bug-42612-4@http.gcc.gnu.org/bugzilla/>
2012-08-23 14:16 ` [Bug rtl-optimization/42612] post-increment addressing not used olegendo at gcc dot gnu.org
@ 2015-05-22 13:57 ` olegendo at gcc dot gnu.org
2022-07-12 5:21 ` bd at mail dot ru
2022-07-12 5:39 ` pinskia at gcc dot gnu.org
3 siblings, 0 replies; 8+ messages in thread
From: olegendo at gcc dot gnu.org @ 2015-05-22 13:57 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=42612
--- Comment #5 from Oleg Endo <olegendo at gcc dot gnu.org> ---
There is a GSoC 2015 project which will try to address the AMS problem.
https://www.google-melange.com/gsoc/project/details/google/gsoc2015/erikvarga/5693417237512192
It will be initially for SH. If it works out, it can be generalized so that
other targets can benefit from it, too.
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug rtl-optimization/42612] post-increment addressing not used
[not found] <bug-42612-4@http.gcc.gnu.org/bugzilla/>
2012-08-23 14:16 ` [Bug rtl-optimization/42612] post-increment addressing not used olegendo at gcc dot gnu.org
2015-05-22 13:57 ` olegendo at gcc dot gnu.org
@ 2022-07-12 5:21 ` bd at mail dot ru
2022-07-12 5:39 ` pinskia at gcc dot gnu.org
3 siblings, 0 replies; 8+ messages in thread
From: bd at mail dot ru @ 2022-07-12 5:21 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=42612
Dmitry Baksheev <bd at mail dot ru> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |bd at mail dot ru
--- Comment #6 from Dmitry Baksheev <bd at mail dot ru> ---
Please consider fixing this issue. Here is another example where not using
post-increment for loops produces suboptimal code on AArch64. The code is 4x
slower than LLVM-generated code for dot-product function:
double dotprod(std::size_t n,
const double* __restrict__ a,
const double* __restrict__ b)
{
double ans = 0;
#if __clang__
#pragma clang loop vectorize(assume_safety)
#else
#pragma GCC ivdep
#endif
for (std::size_t i = 0; i < n; ++i) {
ans += a[i] * b[i];
}
return ans;
}
Compile with: $(CXX) -march=armv8.2-a -O3 dp.cpp
GCC-generated loop does not have post-increment loads:
.L3:
ldr d2, [x1, x3, lsl 3]
ldr d1, [x2, x3, lsl 3]
add x3, x3, 1
fmadd d0, d2, d1, d0
cmp x0, x3
bne .L3
Clang emits this:
.LBB0_4:
ldr d1, [x10], #8
ldr d2, [x8], #8
subs x9, x9, #1
fmadd d0, d1, d2, d0
b.ne .LBB0_4
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug rtl-optimization/42612] post-increment addressing not used
[not found] <bug-42612-4@http.gcc.gnu.org/bugzilla/>
` (2 preceding siblings ...)
2022-07-12 5:21 ` bd at mail dot ru
@ 2022-07-12 5:39 ` pinskia at gcc dot gnu.org
3 siblings, 0 replies; 8+ messages in thread
From: pinskia at gcc dot gnu.org @ 2022-07-12 5:39 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=42612
--- Comment #7 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Dmitry Baksheev from comment #6)
> Please consider fixing this issue. Here is another example where not using
> post-increment for loops produces suboptimal code on AArch64. The code is 4x
> slower than LLVM-generated code for dot-product function:
>
> double dotprod(std::size_t n,
> const double* __restrict__ a,
> const double* __restrict__ b)
> {
> double ans = 0;
> #if __clang__
> #pragma clang loop vectorize(assume_safety)
> #else
> #pragma GCC ivdep
> #endif
> for (std::size_t i = 0; i < n; ++i) {
> ans += a[i] * b[i];
> }
> return ans;
> }
>
>
> Compile with: $(CXX) -march=armv8.2-a -O3 dp.cpp
>
> GCC-generated loop does not have post-increment loads:
> .L3:
>
> ldr d2, [x1, x3, lsl 3]
>
> ldr d1, [x2, x3, lsl 3]
>
> add x3, x3, 1
>
> fmadd d0, d2, d1, d0
>
> cmp x0, x3
>
> bne .L3
>
> Clang emits this:
> .LBB0_4:
> ldr d1, [x10], #8
>
> ldr d2, [x8], #8
>
> subs x9, x9, #1
> fmadd d0, d1, d2, d0
>
> b.ne .LBB0_4
I suspect that is a different issue. And I suspect it is a target cost issue
which depends on the core really. Because some cores the separate add is
better.
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug rtl-optimization/42612] post-increment addressing not used
2010-01-04 16:02 [Bug c/42612] New: [4.4/4.5] " jon at beniston dot com
` (2 preceding siblings ...)
2010-01-05 11:43 ` bonzini at gnu dot org
@ 2010-01-05 12:13 ` jon at beniston dot com
3 siblings, 0 replies; 8+ messages in thread
From: jon at beniston dot com @ 2010-01-05 12:13 UTC (permalink / raw)
To: gcc-bugs
------- Comment #3 from jon at beniston dot com 2010-01-05 12:13 -------
GCC 4.1.2 seems to produce the same code.
mov r2, #0
mov r3, r0
strb r2, [r3], #1
strb r2, [r0, #1]
add r0, r3, #2
@ lr needed for prologue
strb r2, [r3, #1]
bx lr
.size func, .-func
.ident "GCC: (GNU) 4.1.2"
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42612
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug rtl-optimization/42612] post-increment addressing not used
2010-01-04 16:02 [Bug c/42612] New: [4.4/4.5] " jon at beniston dot com
2010-01-04 16:11 ` [Bug rtl-optimization/42612] " rguenth at gcc dot gnu dot org
2010-01-04 18:53 ` steven at gcc dot gnu dot org
@ 2010-01-05 11:43 ` bonzini at gnu dot org
2010-01-05 12:13 ` jon at beniston dot com
3 siblings, 0 replies; 8+ messages in thread
From: bonzini at gnu dot org @ 2010-01-05 11:43 UTC (permalink / raw)
To: gcc-bugs
------- Comment #2 from bonzini at gnu dot org 2010-01-05 11:43 -------
Combine is doing what it knows best (forming complicated instructions,
addressing modes in this case); to do this it is already damaging the nice
shape of the code after the tree optimizers, and synthesizing things like x+2.
I wonder more about what the RTL looks like before auto-inc-dec, and whether it
is missing something because it must be taught some trick...
Is this a regression from pre-DF (that would be 4.2)?
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42612
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug rtl-optimization/42612] post-increment addressing not used
2010-01-04 16:02 [Bug c/42612] New: [4.4/4.5] " jon at beniston dot com
2010-01-04 16:11 ` [Bug rtl-optimization/42612] " rguenth at gcc dot gnu dot org
@ 2010-01-04 18:53 ` steven at gcc dot gnu dot org
2010-01-05 11:43 ` bonzini at gnu dot org
2010-01-05 12:13 ` jon at beniston dot com
3 siblings, 0 replies; 8+ messages in thread
From: steven at gcc dot gnu dot org @ 2010-01-04 18:53 UTC (permalink / raw)
To: gcc-bugs
------- Comment #1 from steven at gcc dot gnu dot org 2010-01-04 18:53 -------
>From the tree optimizers we go to expand with the following code (from
PR42612.c.139t.optimized):
;; Function func (func)
func (char * p)
{
<bb 2>:
*p_1(D) = 0;
p_2 = p_1(D) + 1;
*p_2 = 0;
p_3 = p_2 + 1;
*p_3 = 0;
p_4 = p_3 + 1;
return p_4;
}
The code remains in this form until combine, which changes the code as follows
(left is PR42612.c.174r.dce, right is PR42612.c.175r.combine, dumped with
-fdump-rtl-all-slim):
4 NOTE_INSN_BASIC_BLOCK 4 NOTE_INSN_BASIC_BLOCK
2 r137:SI=r0:SI 2 r137:SI=r0:SI
REG_DEAD: r0:SI REG_DEAD: r0:SI
3 NOTE_INSN_FUNCTION_BEG 3 NOTE_INSN_FUNCTION_BEG
6 r138:SI=0x0 6 r138:SI=0x0
28 r133:SI=r137:SI 28 r133:SI=r137:SI
8 [r133:SI++]=r138:SI#0 8 [r133:SI++]=r138:SI#0
REG_INC: r133:SI REG_INC: r133:SI
REG_EQUAL: 0x0 REG_EQUAL: 0x0
12 [r137:SI+0x1]=r138:SI#0 12 [r137:SI+0x1]=r138:SI#0
REG_DEAD: r137:SI REG_DEAD: r137:SI
REG_EQUAL: 0x0 REG_EQUAL: 0x0
13 r134:SI=r133:SI+0x1 | 13 NOTE_INSN_DELETED
16 [r133:SI+0x1]=r138:SI#0 16 [r133:SI+0x1]=r138:SI#0
REG_DEAD: r138:SI REG_DEAD: r138:SI
REG_DEAD: r133:SI <
REG_EQUAL: 0x0 REG_EQUAL: 0x0
17 r144:SI=r134:SI+0x1 | 17 NOTE_INSN_DELETED
REG_DEAD: r134:SI | 22 r0:SI=r133:SI+0x2
22 r0:SI=r144:SI | REG_DEAD: r133:SI
REG_DEAD: r144:SI <
25 use r0:SI 25 use r0:SI
Paolo, you know combine best. Is there a way, you think, to teach combine about
post-increment addressing?
--
steven at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |bonzini at gnu dot org
Status|UNCONFIRMED |NEW
Ever Confirmed|0 |1
Last reconfirmed|0000-00-00 00:00:00 |2010-01-04 18:53:12
date| |
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42612
^ permalink raw reply [flat|nested] 8+ messages in thread
* [Bug rtl-optimization/42612] post-increment addressing not used
2010-01-04 16:02 [Bug c/42612] New: [4.4/4.5] " jon at beniston dot com
@ 2010-01-04 16:11 ` rguenth at gcc dot gnu dot org
2010-01-04 18:53 ` steven at gcc dot gnu dot org
` (2 subsequent siblings)
3 siblings, 0 replies; 8+ messages in thread
From: rguenth at gcc dot gnu dot org @ 2010-01-04 16:11 UTC (permalink / raw)
To: gcc-bugs
--
rguenth at gcc dot gnu dot org changed:
What |Removed |Added
----------------------------------------------------------------------------
Severity|normal |enhancement
Component|c |rtl-optimization
Keywords| |missed-optimization
Known to fail| |4.4.2 4.5.0
Summary|[4.4/4.5] post-increment |post-increment addressing
|addressing not used |not used
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=42612
^ permalink raw reply [flat|nested] 8+ messages in thread
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[not found] <bug-42612-4@http.gcc.gnu.org/bugzilla/>
2012-08-23 14:16 ` [Bug rtl-optimization/42612] post-increment addressing not used olegendo at gcc dot gnu.org
2015-05-22 13:57 ` olegendo at gcc dot gnu.org
2022-07-12 5:21 ` bd at mail dot ru
2022-07-12 5:39 ` pinskia at gcc dot gnu.org
2010-01-04 16:02 [Bug c/42612] New: [4.4/4.5] " jon at beniston dot com
2010-01-04 16:11 ` [Bug rtl-optimization/42612] " rguenth at gcc dot gnu dot org
2010-01-04 18:53 ` steven at gcc dot gnu dot org
2010-01-05 11:43 ` bonzini at gnu dot org
2010-01-05 12:13 ` jon at beniston dot com
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