[PATCH] D102018: [WebAssembly] Use functions instead of macros for const SIMD intrinsics

[Thomas Lively via Phabricator via cfe-commits]

tlively added a comment.

In D102018#2743818 <https://reviews.llvm.org/D102018#2743818>, @aheejin wrote:

> So what prevented us from using functions when we were using `_Static_assert` and why is it now possible to use functions?

>From inside a function, the parameter never looks like a constant because the function body does not know how the function will be used. Since the static_asserts would have been statements on the function body, they would not have been able to assert that the arguments to the function were constant. We were using macros to copy the static_asserts to each call site so they could see the actual arguments. In contrast, it looks like the diagnose_if attribute is evaluated separately for each call site and is able to see the actual arguments.

>> The remaining macro intrinsics cannot be made into functions until the builtin
>> functions they are implemented with can be replaced with normal code patterns
>> because the builtin functions themselves require that their arguments are
>> constants.
>
> Why can't we also use `__REQUIRE_CONSTANT` there? Can't we call `__REQUIRE_CONSTANT` before we call builtins within intrinsic functions?

The new __REQUIRE_CONSTANT would be able to enforce that the intrinsic is only called with constant arguments, but that information is not propagated to the builtin call in the intrinsic's body. From the builtin's point of view inside the function body, its arguments are function parameters, so they may not be constant. One fix for this would have been to remove the part of the builtin definitions that requires the arguments to be constants, but that seemed more hacky than just keeping the original macros for a little bit longer.


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https://reviews.llvm.org/D102018