https://gcc.gnu.org/bugzilla/show_bug.cgi?id=105748
Bug ID: 105748
Summary: gcc ignores the pure attribute
Product: gcc
Version: 12.1.0
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: c++
Assignee: unassigned at gcc dot gnu.org
Reporter: yubowen15 at foxmail dot com
Target Milestone: ---
Snippet:
const int g_value() __attribute__((pure));
int bar(int n) {
int s = 0;
for (int i=0; i<n; ++i) {
s += g_value() * i;
}
return s;
}
Expected: call g_value only once
Actual: call g_value n times
The problem can be reproduced in godbolt compiler explorer:
1. command line argument: -O3 -march=skylake-avx512 -std=c++2b
2. gcc failed to do loop-invariant code motion: https://godbolt.org/z/PvWc1xYvr
3. clang successfully performed loop-invariant code motion:
https://godbolt.org/z/aEhMT88jM
