| Issue |
90119
|
| Summary |
LLVM does not eliminate or hoist redundant bounds checks for std::vector and std::string
|
| Labels |
missed-optimization,
hardening
|
| Assignees |
|
| Reporter |
ldionne
|
Given the following code:
```c++
#include <vector>
#include <span>
#include <string>
template <class T>
void use(T const&);
template <class Container>
void f(Container container) {
for (int i = 0; i != container.size(); ++i) {
use(container[i]);
}
}
template void f(std::string);
template void f(std::vector<int>);
template void f(std::span<int>);
```
Godbolt: https://godbolt.org/z/x8fdv8s63
When we compile with hardening enabled, there is a bounds check inside `operator[]`. That check is basically equivalent to `index < size()`. However, it doesn't get elided even though the loop condition should guarantee that the condition always holds. It seems to be elided when iterating over a `span`, but not a `string` or a `vector`, which makes me think the optimizer could be improved.
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