isuckatcs added inline comments.
================
Comment at: clang/lib/StaticAnalyzer/Checkers/CheckPlacementNew.cpp:157
"Storage provided to placement new is only {0} bytes, "
- "whereas the allocated array type requires more space for "
- "internal needs",
- SizeOfPlaceCI->getValue(), SizeOfTargetCI->getValue()));
+ "whereas the allocated array type might require more space for "
+ "allocation overhead",
----------------
martong wrote:
> NoQ wrote:
> > "might" is not very convincing, it may cause a reaction like "I've no idea
> > what it's talking about and the compiler itself isn't sure, must be false
> > positive". Can we do anything to point the user in the right direction?
> > Say, if this is implementation-defined, are we looking at a portability
> > issue?
> Okay, I see your point. Let's dissect the corresponding sections of the
> standard:
> ```
> new(2, f) T[5] results in a call of operator new[](sizeof(T) * 5 + y, 2, f).
>
> Here, ... and y are non-negative unspecified values representing array
> allocation overhead;
> ```
> The array overhead is an **unspecified value**. What does it mean exactly? My
> understanding is that this means it is implementation defined and the
> implementation is not required to document or guarantee anything. I came to
> this conclusion based on this [[
> https://stackoverflow.com/questions/2397984/undefined-unspecified-and-implementation-defined-behavior
> | stackoverflow question ]].
>
> My interpretation could be wrong, but that does not matter. I think, we
> should just simply display the user what the standard says, and let them
> digest themselves the meaning of "unspecified". I am updating the patch like
> so.
I also looked into this overhead question. In this [[
https://stackoverflow.com/a/8721932 | stackoverflow answer]] someone links the
same defect report that you did, and claims that since it's a defect report, it
has been applied retroactively.
Apparently [[ https://en.cppreference.com/w/cpp/language/new | cppreference ]]
says the same. If you check the defect reports section on the bottom of the
page you can see:
```
The following behavior-changing defect reports were applied retroactively to
previously published C++ standards.
...
DR | Applied to | Behavior as published | Correct behavior
CWG 2382 | C++98 | non-allocating placement array new could require allocation
overhead | such allocation overhead disallowed
```
So in my understanding you don't need to worry about this overhead at all. I
hope this helps.
Repository:
rG LLVM Github Monorepo
CHANGES SINCE LAST ACTION
https://reviews.llvm.org/D129280/new/
https://reviews.llvm.org/D129280
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