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* [Bug tree-optimization/97856] New: Missed optimization: repeated call
@ 2020-11-16 17:40 miguel.ojeda.sandonis at gmail dot com
2020-11-17 7:12 ` [Bug rtl-optimization/97856] " rguenth at gcc dot gnu.org
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: miguel.ojeda.sandonis at gmail dot com @ 2020-11-16 17:40 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97856
Bug ID: 97856
Summary: Missed optimization: repeated call
Product: gcc
Version: unknown
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: miguel.ojeda.sandonis at gmail dot com
Target Milestone: ---
For code such as:
void f(int);
void g(int v) {
switch (v) {
case 1: f(1);
case 2: f(2);
case 3: f(3);
default: f(4);
}
}
GCC generates for e.g. x86_64:
g(int):
subq $8, %rsp
cmpl $2, %edi
je .L2
cmpl $3, %edi
je .L3
cmpl $1, %edi
je .L13
movl $4, %edi
addq $8, %rsp
jmp f(int)
.L13:
call f(int)
.L2:
movl $2, %edi
call f(int)
.L3:
movl $3, %edi
call f(int)
movl $4, %edi
addq $8, %rsp
jmp f(int)
Repeating the `f(4);` call can be avoided by reordering the cases, reducing
code size.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug rtl-optimization/97856] Missed optimization: repeated call
2020-11-16 17:40 [Bug tree-optimization/97856] New: Missed optimization: repeated call miguel.ojeda.sandonis at gmail dot com
@ 2020-11-17 7:12 ` rguenth at gcc dot gnu.org
2021-09-01 4:41 ` pinskia at gcc dot gnu.org
2021-09-01 4:41 ` pinskia at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: rguenth at gcc dot gnu.org @ 2020-11-17 7:12 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97856
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Keywords| |missed-optimization
Version|unknown |11.0
Component|tree-optimization |rtl-optimization
Ever confirmed|0 |1
CC| |hubicka at gcc dot gnu.org
Status|UNCONFIRMED |NEW
Last reconfirmed| |2020-11-17
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
Confirmed. basic-block reordering decides to duplicate the block:
Redirecting fallthru edge 7->8 to 9
Duplicated bb 8 (created bb 9)
Final order:
2 3 4 8 5 6 7 9
Reordered sequence:
2 bb 2
3 bb 3
4 bb 4
5 bb 8
6 bb 5
7 bb 6
8 bb 7
9 duplicate of 8
since we decide to put the default: handling on the fallthru edge of the
condition chain we duplicate it to the tail as well. IIRC expansion
always does it this way and BB reorder simply avoids one jump. With -Os
we flip the last jump and avoid the duplication.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug rtl-optimization/97856] Missed optimization: repeated call
2020-11-16 17:40 [Bug tree-optimization/97856] New: Missed optimization: repeated call miguel.ojeda.sandonis at gmail dot com
2020-11-17 7:12 ` [Bug rtl-optimization/97856] " rguenth at gcc dot gnu.org
@ 2021-09-01 4:41 ` pinskia at gcc dot gnu.org
2021-09-01 4:41 ` pinskia at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-09-01 4:41 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97856
--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Richard Biener from comment #1)
> Confirmed. basic-block reordering decides to duplicate the block:
Yes there are a few other bugs where we like to duplicate the return block I
have seen too.
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug rtl-optimization/97856] Missed optimization: repeated call
2020-11-16 17:40 [Bug tree-optimization/97856] New: Missed optimization: repeated call miguel.ojeda.sandonis at gmail dot com
2020-11-17 7:12 ` [Bug rtl-optimization/97856] " rguenth at gcc dot gnu.org
2021-09-01 4:41 ` pinskia at gcc dot gnu.org
@ 2021-09-01 4:41 ` pinskia at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: pinskia at gcc dot gnu.org @ 2021-09-01 4:41 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97856
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Severity|normal |enhancement
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2021-09-01 4:41 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
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2020-11-16 17:40 [Bug tree-optimization/97856] New: Missed optimization: repeated call miguel.ojeda.sandonis at gmail dot com
2020-11-17 7:12 ` [Bug rtl-optimization/97856] " rguenth at gcc dot gnu.org
2021-09-01 4:41 ` pinskia at gcc dot gnu.org
2021-09-01 4:41 ` pinskia at gcc dot gnu.org
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