[PATCH] D67545: [clang-tidy] Added DefaultOperatorNewCheck.

[Roman Lebedev via Phabricator via cfe-commits]

lebedev.ri added inline comments.


================
Comment at: clang-tools-extra/clang-tidy/cert/DefaultOperatorNewCheck.cpp:51
+  // The alignment used by default 'operator new' (in bits).
+  const unsigned DefaultAlignment = Context.getTargetInfo().getNewAlign();
+
----------------
martong wrote:
> martong wrote:
> > What is the difference between "default" and "fundamental" alignment? Are they the same? Can they differ in any architecture?
> > 
> > https://wiki.sei.cmu.edu/confluence/display/cplusplus/MEM57-CPP.+Avoid+using+default+operator+new+for+over-aligned+types
> > Here there is no wording of "default alignment" only "fundamental alignment" is mentioned. Based on this I'd call this as `FundamentalAligment`.
> > What is the difference between "default" and "fundamental" alignment? Are they the same?
> 
> `fundamental alignment` of any type is the alignment of std::max_align_t. I.e. `alignof(std::max_align_t)`. 
> See C++17 6.11.2.
> 
> On the other hand, default alignment is the value in `__STDCPP_DEFAULT_NEW_ALIGNMENT__` which may be predefined with `fnew-alignment`
> See https://www.bfilipek.com/2019/08/newnew-align.html
> 
> These values can differ: https://wandbox.org/permlink/yIwjiNMw9KyXEQan
> 
> Thus, I think we should use the fundamental alignment here, not the default alignment. 
> So, `getNewAlign()` does not seem right to me.
> @aaron.ballman What do you think?
> Thus, I think we should use the fundamental alignment here, not the default alignment.

I have the exact opposite view.
If as per `getNewAlign()` the alignment would be okay, why should we not trust it?


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https://reviews.llvm.org/D67545