chh added inline comments.
================
Comment at: lib/AST/RecordLayoutBuilder.cpp:1887
+ // greater than the one after packing.
+ if (Packed && UnpackedAlignment <= Alignment)
Diag(D->getLocation(), diag::warn_unnecessary_packed)
----------------
With this change, UnpackedSize is unused and caused a warning about
unused-but-set-variable. Please use it or remove the variable.
I think UnpackedSizeInBits should be used somehow in the condition, because bit
fields can be affected by the packed attribute. Please add a few unit test
cases with bit fields. For example, the following cases showed that S21 is
affected by packed, but got a wrong "unnecessary" warning after this change.
```
struct S21 {
unsigned char a:6;
unsigned char b:6;
} __attribute__((packed, aligned(1)));
struct S22 {
unsigned char a:6;
unsigned char b:6;
} __attribute__((aligned(1)));
struct S23 {
unsigned char a:6;
unsigned char b:6;
};
```
Warnings:
```
padding size of 'S21' with 4 bits to alignment boundary
packed attribute is unnecessary for 'S21'
padding struct 'S22' with 2 bits to align 'b'
padding size of 'S22' with 2 bits to alignment boundary
padding struct 'S23' with 2 bits to align 'b'
padding size of 'S23' with 2 bits to alignment boundary
```
https://reviews.llvm.org/D34114
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