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* [Bug tree-optimization/114651] New: Missed optimization: (c - y) + ((a - c) - (b - y)) => a-b
@ 2024-04-09 6:13 652023330028 at smail dot nju.edu.cn
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From: 652023330028 at smail dot nju.edu.cn @ 2024-04-09 6:13 UTC (permalink / raw)
To: gcc-bugs
https://gcc.gnu.org/bugzilla/show_bug.cgi?id=114651
Bug ID: 114651
Summary: Missed optimization: (c - y) + ((a - c) - (b - y)) =>
a-b
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 noticed that the computation of 'z' in the following code can be
optimized to 'a-b'.
https://godbolt.org/z/hKT8YT6MW
int x, y, z;
void func(int a, int b, int c){
x = b;
y = c + a / b;
z = (c - y) + ((a - c) - (b - y));
}
But GCC -O3 (-fwrapv):
_1 = a_10(D) / b_8(D);
_2 = _1 + c_11(D);
y = _2;
# DEBUG BEGIN_STMT
_4 = a_10(D) - c_11(D);
_17 = _4 - b_8(D);
_6 = _2 + _17;
_3 = _6 - _1;
z = _3;
Expected code:
_1 = a_7(D) / b_8(D);
_2 = _1 + c_9(D);
y = _2;
# DEBUG BEGIN_STMT
_17 = a_7(D) - b_8(D);
z = _17;
Thank you very much for your time and effort! We look forward to hearing from
you.
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2024-04-09 6:13 [Bug tree-optimization/114651] New: Missed optimization: (c - y) + ((a - c) - (b - y)) => a-b 652023330028 at smail dot nju.edu.cn
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