[PATCH] D11815: Pass subtarget feature "force-align-stack"

[hfinkel@anl.gov via cfe-commits]

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

In http://reviews.llvm.org/D11815#243031, @hfinkel wrote:

> In http://reviews.llvm.org/D11815#242616, @ahatanak wrote:
>
> > Hal, do you have any thoughts on the points Vasileios brought up? Currently, many of the targets don't guarantee that the realigned stack is at least as aligned as the default alignment required by the ABI. Is this the behavior end-users expect when they use -mstackrealign on the command line?
>
>
> I don't think this is expected behavior, and sounds like a bug.


To be more specific, my understanding of the use case (which is the use case for this I've come across myself), is that you need to compile code for a system that does not actually provide the stack alignment that LLVM believes should be guaranteed by the current target ABI. This can happen if the alignment guarantee has changed in the past, and you need to run on the older systems.

Also, on PowerPC, for example, the current LLVM implementation might relaign to using a lower-than-target-ABI alignment when we force realignment, but this should just be a noop.

In any case, this now LGTM.

> 

> 

> > Fixing this is beyond the initial scope of this patch and probably should be done in a separate patch, but I want to make sure the patch I'll end up committing won't make it harder to fix this problem.

> 

> 

> Agreed. I don't see how this makes it harder.



http://reviews.llvm.org/D11815