alexfh wrote:
There's one more questionable effect of this commit (together with the fix in
#89567). Some of our code started triggering "loop not unrolled" warnings. A
reduced example is at https://godbolt.org/z/jG4xsGY7s
```
#include <cstddef>
#include <bit>
template <bool Flag>
int FailToBuild(int n) {
constexpr int N = 100;
auto init = [=]() { return Flag ? n : 0UL; };
auto cond = [=](size_t ix) { return Flag ? ix != 0 : ix < 10; };
auto iter = [=](size_t ix) {
return Flag ? ix & ~(1ULL << std::countr_zero(ix)) : ix + 1;
};
#pragma unroll Flag ? 1 : N
for (size_t ix = init(); cond(ix); ix = iter(ix)) {
n *= n;
}
return n;
}
int foo(int n) {
return FailToBuild<true>(n);
}
int bar(int n) {
return FailToBuild<false>(n);
}
```
`clang -std=c++20 -O3` started generating the following warning on this code
after the commit:
```
<source>:13:3: warning: loop not unrolled: the optimizer was unable to perform
the requested transformation; the transformation might be disabled or specified
as part of an unsupported transformation ordering
[-Wpass-failed=transform-warning]
13 | for (size_t ix = init(); cond(ix); ix = iter(ix)) {
```
It doesn't seem the generated code has actually changed, thus, the question is
whether these are legit warnings that used to be missed, or vice versa?
https://github.com/llvm/llvm-project/pull/88666
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