https://gcc.gnu.org/bugzilla/show_bug.cgi?id=112905
Bug ID: 112905
Summary: [missed optimization] fail to reduce a loop that
increments two locations of the same buffer
Product: gcc
Version: 13.2.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: AceSrc at outlook dot com
Target Milestone: ---
Previously, I posted a question in Stackoverflow about loop optimization
(https://stackoverflow.com/questions/77618348/why-does-gcc-fail-to-reduce-a-loop-that-increments-two-locations-of-the-same-buf),
and the answer suggests me to post a [missed optimization] report here.
The question is about GCC does not optimize the following C++ codes into
`counter[A] += n; counter[B] += n;`. In contrast, GCC optimizes the loop into
`counter[A] += n` if `++counter[B]` is deleted.
```
unsigned int getid();
void foo(unsigned int *counter, unsigned int n) {
unsigned int A = getid();
unsigned int B = getid();
for (unsigned int i = 0; i < n; i++) {
++counter[A];
++counter[B];
}
}
```
LLVM has the same behavior.
