[LLVMdev] IR extension proposal: bitset constants (original) (raw)

Peter Collingbourne peter at pcc.me.uk
Tue Feb 3 16:13:33 PST 2015

On Tue, Feb 03, 2015 at 04:03:45PM -0800, Sean Silva wrote:

One other thing: if this can be used for control-flow integrity, I assume it has to have good knowledge of the available indirect call targets. Could we also use this information for devirtualization?

I would expect so. If a bitset contains only one element, we should be able to teach the lowering pass to simply test that the given pointer is equal to that element (i.e. the only valid vptr). If the later IR branches to a trapping block if that condition is false, it should be possible for the optimizer to deduce that the condition is true in any code that is dominated by the branch, and from that do devirtualization.

Thanks,

Peter

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