[all-commits] [llvm/llvm-project] edff73: [LLVMABI] Fix build for GCC < 8 (#190974)

[Mészáros Gergely via All-commits]

  Branch: refs/heads/main
  Home:   https://github.com/llvm/llvm-project
  Commit: edff73e19e4448541086431b325df75de62817ba
      https://github.com/llvm/llvm-project/commit/edff73e19e4448541086431b325df75de62817ba
  Author: Mészáros Gergely <gergely.meszaros at intel.com>
  Date:   2026-04-09 (Thu, 09 Apr 2026)

  Changed paths:
    M llvm/include/llvm/ABI/FunctionInfo.h

  Log Message:
  -----------
  [LLVMABI] Fix build for GCC < 8 (#190974)

`llvm::abi::ArgInfo::get*` functions return `llvm::abi::ArgInfo` by
value, so we need the type to be copyable. It is not though, because of
the non trivially copyable member `MaybeAlign` (`std::optional<Align>`)
in a union, which deletes the implicit copy/move constructors and
assignment operators.
For modern GCC versions and for clang this does not present as a problem
due to named return value optimization (NRVO). It is however not a bug
in old GCC versions, because NRVO is not guaranteed. Similary
`std::optional`
could be trivially copyable, but that is also not guaranteed by the
standard.

Instead of depending on these details of the C++ implementation, move
the `MaybeAlign` member out of the union, and make it a separate member
of `abi::ArgInfo`. We lose the expressiveness from the type system that
`IndirectAttrInfo` always has a defined alignment, but we can get that
back in practice by placing asserts in the code that uses it. Therefore
`llvm::abi::ArgInfo` can still maintain this invariant.

Fixes: #190972



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