| Issue |
127486
|
| Summary |
GlobalISel should have G_POISON
|
| Labels |
good first issue,
llvm:globalisel
|
| Assignees |
|
| Reporter |
arsenm
|
Currently GlobalISel has G_IMPLICIT_DEF, which acts like `undef`. This is used to lower both `poison` and `undef` from the IR. To mirror the semantics of the IR, we need a separate representation of poison. We should introduce G_POISON to enable better optimizations, particularly when legalization introduces padding vector elements.
This change would mostly be finding all the places G_IMPLICIT_DEF is handled, and equivalently handling G_POISON. We should then migrate vector widening and other transforms to introduce poison instead of undef.
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