[llvm-dev] How to get CLang array alloca alignments to be smaller than 16 bytes?

Joan Lluch via llvm-dev llvm-dev at lists.llvm.org
Sun May 5 11:41:20 PDT 2019

> Are you looking in Clang's source, and that from the same 7.0 version?

Yes, I am, and it’s the same version (7.0.1).

“LargeArrayMinWidth” is only on the following files:


So I still think there’s something else that makes the difference on the x86 target. 

Anyway, I will now investigate other targets as my temporary frontend. It is right that other targets do not create such big alignments.

Thanks for your help.


Tel: 620 28 45 13

> On 5 May 2019, at 20:10, Tim Northover <t.p.northover at gmail.com> wrote:
> On Sun, 5 May 2019 at 18:26, Joan Lluch <joan.lluch at icloud.com> wrote:
>> I appreciate your reply, but I can’t still find any relation with “LargeArrayMinWidth” and x86 target.
> Are you looking in Clang's source, and that from the same 7.0 version?
> If not, you should be. It traces back to 2010; r105500 to be exact:
> https://lists.llvm.org/pipermail/cfe-commits/Week-of-Mon-20100531/030985.html
> For a long while references were in a single file (Targets.cpp), but
> they'd been split up into one file per target before 7.0
> (Targets/XYZ.cpp).
>> I think there should be something else that causes my issue.
> I think that's unlikely.
>> Are you sure there’s nothing else beyond LargeArrayMinWidth that causes this?
> No, but I am sure the LargeArray stuff exists and behaviour I see from
> multiple targets matches what I'd expect from the values I see set in
> the source.
> Cheers.
> Tim.

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