[PATCH] D86310: [X86] Align i128 to 16 bytes in x86-64 datalayout

[Craig Topper via Phabricator via cfe-commits]

craig.topper added a comment.

In D86310#2231136 <https://reviews.llvm.org/D86310#2231136>, @efriedma wrote:

> I'm afraid the AutoUpgrade component of this isn't compatible with existing IR without some additional work.  I'm most concerned about cases like the following:
>
>   #pragma pack(8)
>   struct X { __int128 x; }; // Not a packed struct in IR because the native alignment is 8
>   struct Y { long long x; struct X y; }; // 24 bytes before autoupgrade, 32 bytes after
>   struct Y x;
>
>
>
> ------
>
> On a related note, we need to add "Fn8" to the x86 datalayout at some point.

I kind of feared that old IR was going to be a problem. Any thoughts on how to fix it? Do we need to visit every alloca/load/store/etc that don't have explicit alignment and force them to the old alignment?  Alternatively, could we skip the autoupgrade and weaken the compatible layout check somehow?


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