[PATCH] D125802: Fix std::has_unique_object_representations for _BitInt types with padding bits

[Erich Keane via Phabricator via cfe-commits]

erichkeane added a comment.

I think I agree with the justification here, though am a touch confused in the test.  I'm also a touch concerned that we have getSubobjectSizeInBits returning a 'rounded up to power of 2' bit  happening here.  The bitfield case returns non-powers-of-two, but the _BitInt case does not.



================
Comment at: clang/lib/AST/ASTContext.cpp:2697
   int64_t FieldSizeInBits =
       Context.toBits(Context.getTypeSizeInChars(Field->getType()));
   if (Field->isBitField()) {
----------------
This answer ends up being wrong in the case of _BitInt, consider _BitInt(7).  Its field-size would be 7, yet this would result in 8.  I'm not sure of the fallout of this though.


================
Comment at: clang/test/SemaCXX/has_unique_object_reps_bitint.cpp:7
+static_assert(__has_unique_object_representations(_BitInt(sizeof(int) * 8u)));
+static_assert(sizeof(_BitInt(24)) != 4 || !__has_unique_object_representations(_BitInt(24)));
+
----------------
Whats going on here?  I don't particularly get the condition.


Repository:
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https://reviews.llvm.org/D125802