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* [Bug middle-end/109370] New: Missed optimization for std::optional branchless unwrapping
@ 2023-04-01 16:52 andre.schackier at gmail dot com
2023-04-01 16:53 ` [Bug middle-end/109370] " pinskia at gcc dot gnu.org
` (2 more replies)
0 siblings, 3 replies; 4+ messages in thread
From: andre.schackier at gmail dot com @ 2023-04-01 16:52 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109370
Bug ID: 109370
Summary: Missed optimization for std::optional branchless
unwrapping
Product: gcc
Version: 12.2.1
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: middle-end
Assignee: unassigned at gcc dot gnu.org
Reporter: andre.schackier at gmail dot com
Target Milestone: ---
Given the following source code godbolt: https://godbolt.org/z/vW6ebqafK
#include <optional>
int f(std::optional<int>&& o) {
if (!o) return -1;
return *o;
}
gcc with '-O3' generates:
f(std::optional<int>&&):
cmp BYTE PTR [rdi+4], 0
je .L3
mov eax, DWORD PTR [rdi]
ret
.L3:
mov eax, -1
ret
while clang generates:
f(std::optional<int>&&): # @f(std::optional<int>&&)
xor eax, eax
cmp byte ptr [rdi + 4], 1
sbb eax, eax
or eax, dword ptr [rdi]
ret
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug middle-end/109370] Missed optimization for std::optional branchless unwrapping
2023-04-01 16:52 [Bug middle-end/109370] New: Missed optimization for std::optional branchless unwrapping andre.schackier at gmail dot com
@ 2023-04-01 16:53 ` pinskia at gcc dot gnu.org
2023-04-01 16:59 ` pinskia at gcc dot gnu.org
2023-04-11 11:59 ` [Bug rtl-optimization/109370] " rguenth at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-04-01 16:53 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109370
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Severity|normal |enhancement
Keywords| |missed-optimization
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug middle-end/109370] Missed optimization for std::optional branchless unwrapping
2023-04-01 16:52 [Bug middle-end/109370] New: Missed optimization for std::optional branchless unwrapping andre.schackier at gmail dot com
2023-04-01 16:53 ` [Bug middle-end/109370] " pinskia at gcc dot gnu.org
@ 2023-04-01 16:59 ` pinskia at gcc dot gnu.org
2023-04-11 11:59 ` [Bug rtl-optimization/109370] " rguenth at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-04-01 16:59 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109370
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
I am not so sure this is worse.
Also I find LLVM code generataion depdedent on if the argument is a pointer vs
a reference (rvalue or normal):
```
struct a
{
int b;
bool c;
};
int f(struct a &o) {
if (!o.c) return -1;
return o.b;
}
int f(struct a *o) {
if (!o->c) return -1;
return o->b;
}
```
^ permalink raw reply [flat|nested] 4+ messages in thread
* [Bug rtl-optimization/109370] Missed optimization for std::optional branchless unwrapping
2023-04-01 16:52 [Bug middle-end/109370] New: Missed optimization for std::optional branchless unwrapping andre.schackier at gmail dot com
2023-04-01 16:53 ` [Bug middle-end/109370] " pinskia at gcc dot gnu.org
2023-04-01 16:59 ` pinskia at gcc dot gnu.org
@ 2023-04-11 11:59 ` rguenth at gcc dot gnu.org
2 siblings, 0 replies; 4+ messages in thread
From: rguenth at gcc dot gnu.org @ 2023-04-11 11:59 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=109370
Richard Biener <rguenth at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Component|middle-end |rtl-optimization
--- Comment #2 from Richard Biener <rguenth at gcc dot gnu.org> ---
Note we would need to know that dereferencing 'o' is OK (not sure if RTL knows
this), and this if-conversion is certainly RTL territorry because of costing.
On x86 I'd expect the branchy version to be faster.
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2023-04-11 11:59 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2023-04-01 16:52 [Bug middle-end/109370] New: Missed optimization for std::optional branchless unwrapping andre.schackier at gmail dot com
2023-04-01 16:53 ` [Bug middle-end/109370] " pinskia at gcc dot gnu.org
2023-04-01 16:59 ` pinskia at gcc dot gnu.org
2023-04-11 11:59 ` [Bug rtl-optimization/109370] " rguenth at gcc dot gnu.org
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