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[SelectionDAG] Let ComputeKnownSignBits handle (shl (ext X), C) #97695

Merged
merged 2 commits into from
Jul 5, 2024
Merged

[SelectionDAG] Let ComputeKnownSignBits handle (shl (ext X), C) #97695

merged 2 commits into from
Jul 5, 2024

Commits on Jul 5, 2024

  1. [CodeGen] Pre-commit test case related to ComputeNumSignBits for SHL (l… 

    …lvm#97695)

Adding test cases aiming at showing possibility to look through
ZERO_EXTEND/ANY_EXTEND when computing number of sign bits for an
SHL node. If all extended bits are shifted out we can analyze the
operand that is extended.
    @bjope
    bjope committed Jul 5, 2024
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  2. [SelectionDAG] Let ComputeKnownSignBits handle (shl (ext X), C) (llvm… 

    …#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.
    @bjope
    bjope committed Jul 5, 2024
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