Bjorn Pettersson c2fbc701aa [SelectionDAG] Let ComputeKnownSignBits handle (shl (ext X), C) (#97695) ...

Add simple support for looking through ZEXT/ANYEXT/SEXT when doing
ComputeKnownSignBits for SHL. This is valid for the case when all
extended bits are shifted out, because then the number of sign bits
can be found by analysing the EXT operand.

A future improvement could be to pass along the "shifted left by"
information in the recursive calls to ComputeKnownSignBits. Allowing
us to handle this more generically.

2024-07-05 22:37:26 +02:00

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