Optimising ARM DMBs

[Reinoud Elhorst]

I just recently joined, and this will be my first patch. It finds places in
ARM machine code where 2 dmbs follow one another, and eliminates one of
them. In some cases this can result in considerable (30%) speedups, as I
will argue in my talk at EuroLLVM next week.

I discussed the patch off-list with several people, but am more than happy
to get some more feedback.

Thanks,


Reinoud

M       lib/Target/ARM/ARM.h
A       lib/Target/ARM/ARMOptimizeBarriersPass.cpp
M       lib/Target/ARM/ARMTargetMachine.cpp
M       lib/Target/ARM/CMakeLists.txt
A       test/CodeGen/ARM/optimize-dmbs-v7.ll
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