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* [Bug tree-optimization/111718] New: Missed optimization of '(a+a)/a'
@ 2023-10-07 11:05 652023330028 at smail dot nju.edu.cn
2023-10-07 15:46 ` [Bug tree-optimization/111718] " vanyacpp at gmail dot com
` (3 more replies)
0 siblings, 4 replies; 5+ messages in thread
From: 652023330028 at smail dot nju.edu.cn @ 2023-10-07 11:05 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111718
Bug ID: 111718
Summary: Missed optimization of '(a+a)/a'
Product: gcc
Version: 14.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: tree-optimization
Assignee: unassigned at gcc dot gnu.org
Reporter: 652023330028 at smail dot nju.edu.cn
Target Milestone: ---
Hello, we found some optimizations (regarding Arithmetic optimization) that GCC
may have missed. We would greatly appreicate if you can take a look and let us
know what you think.
Given the following code:
https://godbolt.org/z/5de17zvz9
unsigned n1,n2;
void func1(unsigned a){
if(a>10&&a<20){
n1=a+a;
n2=(a+a)/a;
}
}
We note that `(a+a)/a` should be optimized to `2`, but gcc-trunk -O3 does not:
func1(unsigned int):
lea eax, [rdi-11]
cmp eax, 8
ja .L1
lea eax, [rdi+rdi]
xor edx, edx
mov DWORD PTR n1[rip], eax
div edi
mov DWORD PTR n2[rip], eax
.L1:
ret
Thank you very much for your time and effort! We look forward to hearing from
you.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/111718] Missed optimization of '(a+a)/a'
2023-10-07 11:05 [Bug tree-optimization/111718] New: Missed optimization of '(a+a)/a' 652023330028 at smail dot nju.edu.cn
@ 2023-10-07 15:46 ` vanyacpp at gmail dot com
2023-10-08 3:03 ` 652023330028 at smail dot nju.edu.cn
` (2 subsequent siblings)
3 siblings, 0 replies; 5+ messages in thread
From: vanyacpp at gmail dot com @ 2023-10-07 15:46 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111718
Ivan Sorokin <vanyacpp at gmail dot com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |vanyacpp at gmail dot com
--- Comment #1 from Ivan Sorokin <vanyacpp at gmail dot com> ---
GCC does the optimization if the return from the function is replaced with
__builtin_unreachable:
unsigned n1, n2;
void func1(unsigned a)
{
if (a <= 10 || a >= 20)
__builtin_unreachable();
n1 = a + a;
n2 = (a + a)/a;
}
func1(unsigned int):
mov DWORD PTR n2[rip], 2
add edi, edi
mov DWORD PTR n1[rip], edi
ret
https://godbolt.org/z/Tjsz6neTs
Perhaps this issue has the same underlying cause as the PR80015.
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/111718] Missed optimization of '(a+a)/a'
2023-10-07 11:05 [Bug tree-optimization/111718] New: Missed optimization of '(a+a)/a' 652023330028 at smail dot nju.edu.cn
2023-10-07 15:46 ` [Bug tree-optimization/111718] " vanyacpp at gmail dot com
@ 2023-10-08 3:03 ` 652023330028 at smail dot nju.edu.cn
2023-10-08 3:52 ` pinskia at gcc dot gnu.org
2023-10-08 4:00 ` pinskia at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: 652023330028 at smail dot nju.edu.cn @ 2023-10-08 3:03 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111718
--- Comment #2 from Yi <652023330028 at smail dot nju.edu.cn> ---
We noticed one change between gcc-13.2 and the current gcc-trunk:
https://godbolt.org/z/j5Mnvno9n
In the following code, gcc-13.2 does not yet have the ability to optimize as
expected, but on gcc-trunk, it does.
unsigned n1,n2;
void func1(unsigned a){
if(a<=10 || a>=20)
return;
n2=(a+a)/a;
}
Maybe this change will help solve this issue?
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/111718] Missed optimization of '(a+a)/a'
2023-10-07 11:05 [Bug tree-optimization/111718] New: Missed optimization of '(a+a)/a' 652023330028 at smail dot nju.edu.cn
2023-10-07 15:46 ` [Bug tree-optimization/111718] " vanyacpp at gmail dot com
2023-10-08 3:03 ` 652023330028 at smail dot nju.edu.cn
@ 2023-10-08 3:52 ` pinskia at gcc dot gnu.org
2023-10-08 4:00 ` pinskia at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-10-08 3:52 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111718
--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
For comment #2 from EVRP:
Folding statement: _3 = _2 / a_5(D);
Applying pattern match.pd:934, gimple-match-4.cc:2021
gimple_simplified to _3 = 2;
Which corresponds to the match pattern:
/* Simplify (t * 2) / 2) -> t. */
(for div (trunc_div ceil_div floor_div round_div exact_div)
(simplify
(div (mult:c @0 @1) @1)
(if (ANY_INTEGRAL_TYPE_P (type))
(if (TYPE_OVERFLOW_UNDEFINED (type))
@0
#if GIMPLE
(with {value_range vr0, vr1;}
(if (INTEGRAL_TYPE_P (type)
&& get_range_query (cfun)->range_of_expr (vr0, @0)
&& get_range_query (cfun)->range_of_expr (vr1, @1)
&& range_op_handler (MULT_EXPR).overflow_free_p (vr0, vr1))
@0))
#endif
))))
^ permalink raw reply [flat|nested] 5+ messages in thread
* [Bug tree-optimization/111718] Missed optimization of '(a+a)/a'
2023-10-07 11:05 [Bug tree-optimization/111718] New: Missed optimization of '(a+a)/a' 652023330028 at smail dot nju.edu.cn
` (2 preceding siblings ...)
2023-10-08 3:52 ` pinskia at gcc dot gnu.org
@ 2023-10-08 4:00 ` pinskia at gcc dot gnu.org
3 siblings, 0 replies; 5+ messages in thread
From: pinskia at gcc dot gnu.org @ 2023-10-08 4:00 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=111718
Andrew Pinski <pinskia at gcc dot gnu.org> changed:
What |Removed |Added
----------------------------------------------------------------------------
Severity|normal |enhancement
Ever confirmed|0 |1
Status|UNCONFIRMED |NEW
Keywords| |missed-optimization
Last reconfirmed| |2023-10-08
--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
(In reply to Andrew Pinski from comment #3)
> For comment #2 from EVRP:
> Folding statement: _3 = _2 / a_5(D);
> Applying pattern match.pd:934, gimple-match-4.cc:2021
> gimple_simplified to _3 = 2;
>
> Which corresponds to the match pattern:
> /* Simplify (t * 2) / 2) -> t. */
> (for div (trunc_div ceil_div floor_div round_div exact_div)
> (simplify
> (div (mult:c @0 @1) @1)
> (if (ANY_INTEGRAL_TYPE_P (type))
> (if (TYPE_OVERFLOW_UNDEFINED (type))
> @0
> #if GIMPLE
> (with {value_range vr0, vr1;}
> (if (INTEGRAL_TYPE_P (type)
> && get_range_query (cfun)->range_of_expr (vr0, @0)
> && get_range_query (cfun)->range_of_expr (vr1, @1)
> && range_op_handler (MULT_EXPR).overflow_free_p (vr0, vr1))
> @0))
> #endif
> ))))
Which was improved on the trunk by r14-4082-g55b22a6f630e (and then by
r14-4191-gd946fc1c71bd). I don't know why the original testcase is not causing
the above pattern to match though, maybe because a*2 is used twice ...
^ permalink raw reply [flat|nested] 5+ messages in thread
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2023-10-07 11:05 [Bug tree-optimization/111718] New: Missed optimization of '(a+a)/a' 652023330028 at smail dot nju.edu.cn
2023-10-07 15:46 ` [Bug tree-optimization/111718] " vanyacpp at gmail dot com
2023-10-08 3:03 ` 652023330028 at smail dot nju.edu.cn
2023-10-08 3:52 ` pinskia at gcc dot gnu.org
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