Change Details

X86 codegen uses min-legal-vector-width to decide the proper ABI level. So we should always make sure the attribute reflects the correct vector width when doing argument promotion. Here are failed case: https://godbolt.org/z/zo3hba8xW

X86 codegen uses function attribute `min-legal-vector-width` to select the proper ABI. The intention of the attribute is to reflect user's requirement when they passing or returning vector arguments. So Clang front-end will iterate the vector arguments and set `min-legal-vector-width` to the width of the maximum for both caller and callee. It is assumed any middle end optimizations won't care of the attribute expect inlining and argument promotion. - For inlining, we will propagate the attribute of inlined functions because the inlining functions become the newer caller. - For argument promotion, we check the `min-legal-vector-width` of the caller and callee and refuse to promote when they don't match. The problem comes from the optimizations' combination, as shown by https://godbolt.org/z/zo3hba8xW. The caller `foo` has two callees `bar` and `baz`. When doing argument promotion, both `foo` and `bar` has the same `min-legal-vector-width`. So the argument was promoted to vector. Then the inlining inlines `baz` to `foo` and updates `min-legal-vector-width`, which results in ABI mismatch between `foo` and `bar`. This patch fixes the problem by expanding the concept of `min-legal-vector-width` to indicator of functions arguments. That says, any passes touch functions arguments have to set `min-legal-vector-width` to the value reflects the width of vector arguments. It makes sense to me because any arguments modifications are ABI related and should response for the ABI compatibility.

X86 codegen uses min-legal-vector-width to decide the proper ABI levelfunction attribute `min-legal-vector-width` to select the proper ABI. The intention of the attribute is to reflect user's requirement when they passing or returning vector arguments. So Clang front-end will iterate the vector arguments and set `min-legal-vector-width` to the width of the maximum for both caller and callee. It is assumed any middle end optimizations won't care of the attribute expect inlining and argument promotion. So we should always make sur- For inlining, we will propagate the attribute reflectsof inlined functions because the correct vectorinlining functions become the newer caller. width when doing argument promotion- For argument promotion, we check the `min-legal-vector-width` of the caller and callee and refuse to promote when they don't match. The problem comes from the optimizations' combination, as shown by https://godbolt.org/z/zo3hba8xW. The caller `foo` has two callees `bar` and `baz`. When doing argument promotion, both `foo` and `bar` has the same `min-legal-vector-width`. So the argument was promoted to vector. Then the inlining inlines `baz` to `foo` and updates `min-legal-vector-width`, which results in ABI mismatch between `foo` and `bar`. Here are failed case: https://godbolt.org/z/zo3hba8xWThis patch fixes the problem by expanding the concept of `min-legal-vector-width` to indicator of functions arguments. That says, any passes touch functions arguments have to set `min-legal-vector-width` to the value reflects the width of vector arguments. It makes sense to me because any arguments modifications are ABI related and should response for the ABI compatibility.