[PATCH] Check for all known bits on ret in InstCombine

[Chandler Carruth]

On Tue, Jul 22, 2014 at 12:48 PM, Hal Finkel <hfinkel at anl.gov> wrote:

> > I'm defining dead as an SSA subgraph where the only sinks (uses which
> > have "side-effects" or otherwise can't be removed) are the
> > assumptions. I think this is sufficiently conservative to remove
> > assumptions from true dead code regions and prevent them from
> > keeping control flow alive without sacrificing optimization
> > opportunities.
>
> But we should already kill them in unreachable blocks.
>

Probably. It also should handle the case where we if-convert prior to
discovering the block was dead, and thus have a dead SSA subgraph without
dead control flow.
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