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[X86] Emit a reg-reg copy for fast isel of vector bitcasts.
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Authored by craig.topper on Jun 24 2020, 6:02 PM.

Details

Summary

Previously we just update a map and moved on. But it possible
we cached known bits information with the vreg that can be used by
another basic block. If the other basic block has a different view
of the VT these known bits won't make sense.

By emitting a copy we ensure we have different vregs before and
after the bitcast. This prevents the known bits from being used
with the wrong type.

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Event Timeline

craig.topper created this revision.Jun 24 2020, 6:02 PM
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Add comment to the X86FastISel.cpp

echristo accepted this revision.Jun 24 2020, 6:40 PM

I think this is the right solution, we need to emit the instruction either way and then hopefully we won't fall out, but if we do we're not leaving mistaken state.

-eric

This revision is now accepted and ready to land.Jun 24 2020, 6:40 PM
This revision was automatically updated to reflect the committed changes.