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* [Bug c++/109471] New: Missing loop unrolling for small std::vector?
@ 2023-04-11 10:42 stefano.d at posteo dot de
2023-04-11 13:42 ` [Bug tree-optimization/109471] " rguenth at gcc dot gnu.org
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: stefano.d at posteo dot de @ 2023-04-11 10:42 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109471
Bug ID: 109471
Summary: Missing loop unrolling for small std::vector?
Product: gcc
Version: 12.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: stefano.d at posteo dot de
Target Milestone: ---
Hi,
I did some benchmarks where I wanted to bench a switch-case statement against a
small std::vector. In GCC 12.2 the result was as expected: The switch-case
statement was faster than the linear search in std::vector. But when I switched
to clang 13 or above, the std::vector implementation was much faster than the
switch-case statement!
You can the results here:
https://quick-bench.com/q/9DEDS7rQm0MnIFxwZt3A2iD86G0
Please switch here between GCC and clang.
Here an assembly output:
https://godbolt.org/z/j8oenP8x9
Kind regards
Stefano
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/109471] Missing loop unrolling for small std::vector?
2023-04-11 10:42 [Bug c++/109471] New: Missing loop unrolling for small std::vector? stefano.d at posteo dot de
@ 2023-04-11 13:42 ` rguenth at gcc dot gnu.org
2023-04-11 13:47 ` xry111 at gcc dot gnu.org
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: rguenth at gcc dot gnu.org @ 2023-04-11 13:42 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109471
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |missed-optimization
Component|c++ |tree-optimization
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
I suppose both cases could be optimized the same, but we only do limited "IR
interpretation" and only as side-effect of optimizing scalarized code, not
simulated execution traces.
Needs some more investigation.
Can you please attach the source code?
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/109471] Missing loop unrolling for small std::vector?
2023-04-11 10:42 [Bug c++/109471] New: Missing loop unrolling for small std::vector? stefano.d at posteo dot de
2023-04-11 13:42 ` [Bug tree-optimization/109471] " rguenth at gcc dot gnu.org
@ 2023-04-11 13:47 ` xry111 at gcc dot gnu.org
2023-04-11 13:49 ` [Bug tree-optimization/109471] Missing loop unrolling for small std::array? stefano.d at posteo dot de
2023-04-11 13:52 ` stefano.d at posteo dot de
3 siblings, 0 replies; 5+ messages in thread
From: xry111 at gcc dot gnu.org @ 2023-04-11 13:47 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109471
Xi Ruoyao <xry111 at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |xry111 at gcc dot gnu.org
--- Comment #2 from Xi Ruoyao <xry111 at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #1)
> I suppose both cases could be optimized the same, but we only do limited "IR
> interpretation" and only as side-effect of optimizing scalarized code, not
> simulated execution traces.
>
> Needs some more investigation.
>
> Can you please attach the source code?
The code seems available in the godbolt link but it uses std::array, not
std::vector.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/109471] Missing loop unrolling for small std::array?
2023-04-11 10:42 [Bug c++/109471] New: Missing loop unrolling for small std::vector? stefano.d at posteo dot de
2023-04-11 13:42 ` [Bug tree-optimization/109471] " rguenth at gcc dot gnu.org
2023-04-11 13:47 ` xry111 at gcc dot gnu.org
@ 2023-04-11 13:49 ` stefano.d at posteo dot de
2023-04-11 13:52 ` stefano.d at posteo dot de
3 siblings, 0 replies; 5+ messages in thread
From: stefano.d at posteo dot de @ 2023-04-11 13:49 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109471
--- Comment #3 from Stefano <stefano.d at posteo dot de> ---
(In reply to Xi Ruoyao from comment #2)
> The code seems available in the godbolt link but it uses std::array, not
> std::vector.
I'm sorry. I mean std::array of course. :-/
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/109471] Missing loop unrolling for small std::array?
2023-04-11 10:42 [Bug c++/109471] New: Missing loop unrolling for small std::vector? stefano.d at posteo dot de
` (2 preceding siblings ...)
2023-04-11 13:49 ` [Bug tree-optimization/109471] Missing loop unrolling for small std::array? stefano.d at posteo dot de
@ 2023-04-11 13:52 ` stefano.d at posteo dot de
3 siblings, 0 replies; 5+ messages in thread
From: stefano.d at posteo dot de @ 2023-04-11 13:52 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109471
--- Comment #4 from Stefano <stefano.d at posteo dot de> ---
Created attachment 54829
--> https://gcc.gnu.org/bugzilla/attachment.cgi?id=54829&action=edit
source code
^ permalink raw reply [flat|nested] 5+ messages in thread
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2023-04-11 10:42 [Bug c++/109471] New: Missing loop unrolling for small std::vector? stefano.d at posteo dot de
2023-04-11 13:42 ` [Bug tree-optimization/109471] " rguenth at gcc dot gnu.org
2023-04-11 13:47 ` xry111 at gcc dot gnu.org
2023-04-11 13:49 ` [Bug tree-optimization/109471] Missing loop unrolling for small std::array? stefano.d at posteo dot de
2023-04-11 13:52 ` stefano.d at posteo dot de
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