[LLVMdev] Unaligned vector memory access for ARM/NEON.

Peter Couperus peter.couperus at st.com
Wed Sep 5 14:42:07 PDT 2012

Hello all,

I am a first time writer here, but am a happy LLVM tinkerer.  It is a 
pleasure to use :).
We have come across some sub-optimal behavior when LLVM lowers loads for 
vectors with small integers, i.e. load <4 x i16>* %a, align 2,
using a sequence of scalar loads rather than a single vld1 on armv7 
linux with NEON.
Looking at the code in svn, it appears the ARM backend is capable of 
lowering these loads as desired, and will if we use an appropriate 
darwin triple.
It appears this was actually enabled relatively recently.
Seemingly, the case where the Subtarget has NEON available should be 
handled the same on Darwin and Linux.
Is this true, or am I missing something?
Do the regulars have an opinion on the best way to handle this?


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