[PATCH] D24426: DebugInfo: Pass non-zero alignment to DIBuilder only if aligment was forced

[David Blaikie via cfe-commits]

On Mon, Sep 12, 2016 at 5:00 PM Paul Robinson <paul.robinson at sony.com>
wrote:

> probinson added a subscriber: probinson.
>
> ================
> Comment at: lib/CodeGen/CGDebugInfo.cpp:3691
> @@ -3635,1 +3690,3 @@
> +  if (D->hasAttr<AlignedAttr>())
> +    AlignInBits = D->getMaxAlignment();
>    StringRef DeclName, LinkageName;
> ----------------
> dblaikie wrote:
> > is max alignment the right thing here? Should it be min alignment?
> > (is alignment in bits the desired thing across all of this too? It
> looked like in the backend patch there was some division by CHAR_BITS, etc?)
> I should think bits is the right choice here; seems more the province of
> the backend to convert it into the appropriate addressable units (commonly
> but not universally chars).
>

The alternative thinking is that we've a generally sense we want to make
more of this type information opaque to LLVM - so I'm somewhat inclined to
make the frontend do the work of choosing what to emit and the backend just
being as simple as possible.

Hmm, seems like the DWARF spec details I can find:
http://www.dwarfstd.org/ShowIssue.php?issue=140528.1 don't really specify
what the value of DW_AT_alignment is, it's sort of assumed, by the looks of
it? I'm assuming it's bytes, the same as the byte_size attribute.




>
>
> https://reviews.llvm.org/D24426
>
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