[PATCH] Retain alignment requirements for load->selects modified by DAGCombine

[Hal Finkel]

----- Original Message -----
> From: "Louis Gerbarg" <lgg at apple.com>
> To: llvm-commits at cs.uiuc.edu
> Sent: Wednesday, July 30, 2014 12:40:02 PM
> Subject: [PATCH] Retain alignment requirements for load->selects modified by	DAGCombine
> 
> 
> 
> This patch fixes an issue where we can generate aligned loads for
> unaligned data. It is a latent bug that has been around for years,
> but we have started tripping it recently with the introduction of
> more aggressive vectorization, etc. On x86 this manifests as
> generating a movapd when we should have used a movupd, which then
> results in a segfault if the data does not happened to be aligned.
> The problem is in platform independent codegen, so this may manifest
> on other architectures as well. I suspect on PPC this may result in
> some subtle data corruption bugs since altivec loads will take an
> unaligned address without faulting and just ignore the low bits.

Indeed.

LGTM, thanks!

 -Hal

> 
> Tests included.
> 
> Louis
> 
> 
> 
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> 

-- 
Hal Finkel
Assistant Computational Scientist
Leadership Computing Facility
Argonne National Laboratory