| Issue |
175160
|
| Summary |
[DAG] SelectionDAG::ComputeNumSignBits - add ISD::ABDS handling
|
| Labels |
good first issue,
llvm:SelectionDAG
|
| Assignees |
|
| Reporter |
RKSimon
|
We can probably handle this best by thinking in terms of the `abds(lhs, rhs) -> sub(smax(lhs,rhs), smin(lhs,rhs))` expansion:
numsignbits = max(sub(min(numsignbits(lhs),numsignbits(rhs)),1),1)
Although I'm sure there will be special cases that can improve on that.
Test coverage probably easiest to add to aarch64 which has neon support for ABDS instructions - either in codegen tests or via AArch64SelectionDAGTest.cpp
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