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[NFC][InstCombine] Add FIXME's for getLogBase2() / visitUDivOperand()

Authored by lebedev.ri on Aug 12 2020, 11:59 AM.

Description

[NFC][InstCombine] Add FIXME's for getLogBase2() / visitUDivOperand()

These are not correctness issues.

In visitUDivOperand(), if the (potential) divisor is undef, then udiv is
already UB, so it is not incorrect to keep undef as shift amount.

But, that is suboptimal.
We could instead simply drop that select, picking the other operand.

Afterwards, getLogBase2() could assert that there is no undef in divisor.

Details

Committed
lebedev.riAug 12 2020, 12:06 PM
Parents
rG12d93a27e7b7: [InstCombine] Sanitize undef vector constant to 1 in X*(2^C) with X << C…
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