[PATCH] D77621: ADT: SmallVector size/capacity use word-size integers when elements are small

[Andrew via Phabricator via cfe-commits]

browneee added a comment.

Thanks for the tips, MaskRay.

Yes, I expect this would fix that issue.

smeenai, SizeTypeMax() is intended to return size_t.

---

I see a couple of options for fixing the truncation warning on 32-bit platforms:

1. Add an explicit cast to remove the warning.
  - Disadvantage: the second instantiation still exists even though it is unused.

  static constexpr size_t SizeTypeMax() {
    return static_cast<size_t>(std::numeric_limits<Size_T>::max());
  }



2. Use a std::conditional to swap the type of one instantiation to avoid conflicts.

  In this case I'd probably swap back to using uintptr_t and disable the uint32_t on 32bit.
  - Disadvantage: the second instantiation still exists even though it is unused.

  // Will be unused when instantiated with char.
  // This is to avoid instantiation for uint32_t conflicting with uintptr_t on 32-bit systems.
  template class llvm::SmallVectorBase<std::conditional<sizeof(void *) != 4, uint32_t, char>::type>;     
  template class llvm::SmallVectorBase<uintptr_t>;  



3. Use preprocessor to disable one of the instantiations on 32-bit platforms.

  In this case I'd probably swap back to using uintptr_t and disable the uint32_t on 32bit.
  - Disadvantage: uses preprocessor
  - Disadvantage: potential for portability issues with different platforms lacking certain macros

  #if __SIZEOF_POINTER__ != 4  && !defined(_WIN32) && !defined(__ILP32)
  template class llvm::SmallVectorBase<uint32_t>;     
  #endif    
  template class llvm::SmallVectorBase<uintptr_t>;  

My order of preference would be 1, 2, 3.

Is there another solution I've missed? Thoughts on which is best? @dblaikie


Repository:
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  https://reviews.llvm.org/D77621/new/

https://reviews.llvm.org/D77621