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* [Bug tree-optimization/114539] New: `__builtin_add_overflow(unsigned, b, &r); r < b` where b is a CST is not optimized to using the overflow
@ 2024-04-01 2:45 pinskia at gcc dot gnu.org
2024-04-01 2:47 ` [Bug tree-optimization/114539] " pinskia at gcc dot gnu.org
0 siblings, 1 reply; 2+ messages in thread
From: pinskia at gcc dot gnu.org @ 2024-04-01 2:45 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114539
Bug ID: 114539
Summary: `__builtin_add_overflow(unsigned, b, &r); r < b`
where b is a CST is not optimized to using the
overflow
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 f(unsigned v, unsigned tt)
{
unsigned r;
unsigned t = __builtin_add_overflow(v, tt, &r);
return (r < tt) == t;
}
bool f1(unsigned v, unsigned tt)
{
tt = 3;
unsigned r;
unsigned t = __builtin_add_overflow(v, tt, &r);
return (r < tt) == t;
}
```
f is able to be optimized to 1 but f1 is not due to the `r < 3` being Canonical
form being `r <= 2` (or in the case of 1, `r == 0`).
I found this while looking into PR 114538 if we change things slightly.
^ permalink raw reply [flat|nested] 2+ messages in thread
* [Bug tree-optimization/114539] `__builtin_add_overflow(unsigned, b, &r); r < b` where b is a CST is not optimized to using the overflow
2024-04-01 2:45 [Bug tree-optimization/114539] New: `__builtin_add_overflow(unsigned, b, &r); r < b` where b is a CST is not optimized to using the overflow pinskia at gcc dot gnu.org
@ 2024-04-01 2:47 ` pinskia at gcc dot gnu.org
0 siblings, 0 replies; 2+ messages in thread
From: pinskia at gcc dot gnu.org @ 2024-04-01 2:47 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114539
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Assignee|unassigned at gcc dot gnu.org |pinskia at gcc dot gnu.org
Status|UNCONFIRMED |ASSIGNED
See Also| |https://gcc.gnu.org/bugzill
| |a/show_bug.cgi?id=114538
Last reconfirmed| |2024-04-01
Ever confirmed|0 |1
--- Comment #1 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
This is the current pattern that matches the non-CST case:
```
/* Testing for overflow is unnecessary if we already know the result. */
/* A - B > A */
(for cmp (gt le)
out (ne eq)
(simplify
(cmp:c (realpart (IFN_SUB_OVERFLOW@2 @0 @1)) @0)
(if (TYPE_UNSIGNED (TREE_TYPE (@0))
&& types_match (TREE_TYPE (@0), TREE_TYPE (@1)))
(out (imagpart @2) { build_zero_cst (TREE_TYPE (@0)); }))))
/* A + B < A */
(for cmp (lt ge)
out (ne eq)
(simplify
(cmp:c (realpart (IFN_ADD_OVERFLOW:c@2 @0 @1)) @0)
(if (TYPE_UNSIGNED (TREE_TYPE (@0))
&& types_match (TREE_TYPE (@0), TREE_TYPE (@1)))
(out (imagpart @2) { build_zero_cst (TREE_TYPE (@0)); }))))
```
Mine for GCC 15.
^ permalink raw reply [flat|nested] 2+ messages in thread
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2024-04-01 2:45 [Bug tree-optimization/114539] New: `__builtin_add_overflow(unsigned, b, &r); r < b` where b is a CST is not optimized to using the overflow pinskia at gcc dot gnu.org
2024-04-01 2:47 ` [Bug tree-optimization/114539] " pinskia at gcc dot gnu.org
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