[PATCH] D79532: [SelectionDAG] Don't promote the alignment of allocas beyond the stack alignment.

[Sander de Smalen via Phabricator via llvm-commits]

sdesmalen accepted this revision.
sdesmalen added a comment.
This revision is now accepted and ready to land.

LGTM!



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Comment at: llvm/lib/CodeGen/SelectionDAG/FunctionLoweringInfo.cpp:150
         Align Alignment =
-            max(MF->getDataLayout().getPrefTypeAlign(Ty), AI->getAlign());
+            std::max(std::min(TyPrefAlign, StackAlign), SpecifiedAlign);
 
----------------
efriedma wrote:
> sdesmalen wrote:
> > The LangRef says:
> > > On every specification that takes a <abi>:<pref>, specifying the <pref> alignment is optional. If omitted, the preceding : should be omitted too and <pref> will be equal to <abi>.
> > 
> > Does this need an assert to ensure that the type's ABI alignment <= StackAlign?
> The use of the preferred alignment here is purely an optimization.  If the IR specifies the alignment it wants, the datalayout rules aren't relevant.
> 
> The alignment of the alloca could end up less than the ABI alignment, and that's fine; if the frontend needed an ABI-aligned alloca, it wouldn't have specified a lower alignment.
Okay I wasn't sure about that, thanks for clarifying.


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  https://reviews.llvm.org/D79532/new/

https://reviews.llvm.org/D79532