[cfe-commits] PATCH: wide strings alignment fix in clang

[Craig Topper]

The previous patch no longer applies due to the my unicode string
literal patch that went in last week. I took a stab at a new patch.
Rather than using the different string kinds to get the proper
alignment, I queried ASTContext for the alignment of the type
contained in the StringLiteral. I push the alignment as an argument
down to the functions that actually look up the string in the map. If
we find a match in the map, I max the old alignment and the new
alignment.

~Craig

>> I have been working on a bug in clang dealing with alignment of wide
>> strings. Clang is aligning wide string literals to 1 byte boundary. However,
>> LLVM treats wide strings as 4 byte aligned and generates memory operations
>> accessing 4 bytes at a time. This works fine on architectures that allow
>> unaligned access. But for architectures which don't allow unaligned access,
>> this results in an exception and segfault.
>
> +      unsigned Align = TI.getWCharAlign() / TI.getCharAlign();
>
> This should be dividing by the bit-width of char, not by its alignment.
>
> Also, there are multiple kinds of wide strings ? official wide strings (L),
> and then UTF-16 (u) and UTF-32 (U) wide strings.  It would be good if
> this worked for all of them.  You should also make sure that you never
> *decrease* the alignment of a string, as you might if there were a
> utf32 string literal followed by a utf16 string literal which expanded
> to the same sequence of bytes.
>
> Also, in the future, please give your patch files some sort of sensible
> file extension, preferably ".txt".
>
> John.
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