hazohelet added a comment.
In D155064#4651306 <https://reviews.llvm.org/D155064#4651306>, @hans wrote:
> We saw a new warning in Chromium after this, and I wasn't sure if that's
> intentional:
>
> #include <limits>
>
> template <typename T> float foo(T input) {
> if (sizeof(T) > 2) {
> return 42;
> } else {
> constexpr float inverseMax = 1.0f / std::numeric_limits<T>::max();
> return input * inverseMax;
> }
> }
>
> float f() {
> return foo(1);
> }
> $ build/bin/clang -c /tmp/a.cc
> /tmp/a.cc:7:41: warning: implicit conversion from 'int' to 'float' changes
> value from 2147483647 to 2147483648 [-Wimplicit-const-int-float-conversion]
> 7 | constexpr float inverseMax = 1.0f /
> std::numeric_limits<T>::max();
> | ~
> ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> /tmp/a.cc:13:10: note: in instantiation of function template specialization
> 'foo<int>' requested here
> 13 | return foo(1);
> | ^
> 1 warning generated.
>
> Note that the branch with the conversion can be determined to not be taken
> based on the template argument.
>
> Using `if constexpr` suppresses the warning, but I'm not sure if that should
> really be necessary?
>
> (Our tracking bug is https://crbug.com/1487142)
It's unintended, but the cause is that I started using `Sema::Diag` instead of
`Sema::DiagRuntimeBehavior`, in narrowing check for constexpr variable
initializers, and thus lost the reachability analysis. It will be a simple fix,
but would involve some adaptations to `Sema::DiagIfReachable`. I'll fix it
after other concerns are resolved.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D155064/new/
https://reviews.llvm.org/D155064
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