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* [Bug tree-optimization/112819] New: rearrange branches to improve code generation
@ 2023-12-02 1:10 pinskia at gcc dot gnu.org
2023-12-04 6:57 ` [Bug tree-optimization/112819] " rguenth at gcc dot gnu.org
0 siblings, 1 reply; 2+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-12-02 1:10 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112819
Bug ID: 112819
Summary: rearrange branches to improve code generation
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Keywords: missed-optimization
Severity: enhancement
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: pinskia at gcc dot gnu.org
Target Milestone: ---
Take:
```
bool src(char *a, int l) {
if(l < 1) {
return false;
}
if(*a != 'a') {
return false;
}
if(l < 2) {
return false;
}
return true;
}
bool tgt(char *a, int l) {
if(l < 1) {
return false;
}
if(l < 2) {
return false;
}
if(*a != 'a') {
return false;
}
return true;
}
```
You would expect these 2 to produce both the same code but only tgt produces
decent code. That is because we can merge `l < 1` with `l < 2` into just `l <
2` (or `l <= 1`).
This might be an reassociation problem or something else.
^ permalink raw reply [flat|nested] 2+ messages in thread
* [Bug tree-optimization/112819] rearrange branches to improve code generation
2023-12-02 1:10 [Bug tree-optimization/112819] New: rearrange branches to improve code generation pinskia at gcc dot gnu.org
@ 2023-12-04 6:57 ` rguenth at gcc dot gnu.org
0 siblings, 0 replies; 2+ messages in thread
From: rguenth at gcc dot gnu.org @ 2023-12-04 6:57 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112819
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|UNCONFIRMED |NEW
CC| |fkastl at suse dot cz,
| |hubicka at gcc dot gnu.org,
| |rguenth at gcc dot gnu.org
Last reconfirmed| |2023-12-04
Ever confirmed|0 |1
--- Comment #1 from Richard Biener <rguenth at gcc dot gnu.org> ---
We don't "re-associate" branches. But we might want to turn if-to-switch
into sth that does (relaxing the restriction on the ifs testing the same var).
We should have a PHI node with incoming vals predicated by the ifs, free to
re-order otherwise.
The *a deref might impose some limitations for re-ordering, but we can always
handle it last in this case.
Might be also interesting to order branches which are predictable earlier.
Related to switch-conversion/if-to-switch IMHO.
^ permalink raw reply [flat|nested] 2+ messages in thread
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2023-12-02 1:10 [Bug tree-optimization/112819] New: rearrange branches to improve code generation pinskia at gcc dot gnu.org
2023-12-04 6:57 ` [Bug tree-optimization/112819] " rguenth at gcc dot gnu.org
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