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[IR] Add zext nneg flag #67982

Merged
merged 3 commits into from
Oct 30, 2023
Merged

[IR] Add zext nneg flag #67982

merged 3 commits into from
Oct 30, 2023

Commits on Oct 18, 2023

  1. [IR] Add zext nneg flag 

    Add an nneg flag to the zext instruction, which specifies that the
argument is non-negative. Otherwise, the result is a poison value.

The primary use-case for the flag is to preserve information when
sext gets replaced with zext due to range-based canonicalization.
The nneg flag allows us to convert the zext back into an sext
later. This is useful for some optimizations (e.g. a signed icmp
can fold with sext but not zext), as well as some targets (e.g.
RISCV prefers sext over zext).

Co-authored-by: Nikita Popov <npopov@redhat.com>
    @karouzakisp @nikic
    karouzakisp and nikic committed Oct 18, 2023
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  2. Add additional description to overview

    @nikic
    nikic committed Oct 18, 2023
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  3. Rename NonNegInstruction -> PossiblyNonNegInst

    @nikic
    nikic committed Oct 18, 2023
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