tree 2629d42772a7d78ef11789759e5a5b756b9ff835
parent e93f7e595cbcbc995c97942ae343a1382f921f18
author Pedro Lobo <pedro.lobo@tecnico.ulisboa.pt> 1776625099 +0100
committer GitHub <noreply@github.com> 1776625099 +0100
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[ConstantFold] Support byte values in `bitcast` constant folding (#188030)

Add support for constant folding `bitcast` instructions including
`ConstantByte` values. This patch handles bitcasts between byte types
and integer, FP, and other byte types in both directions.

`poison` source bytes are preserved, rather than letting the generic
integer fold refine them to `undef` or zero. This is because some
threading optimizations just compare the result of constant folding
(e.g., https://github.com/llvm/llvm-project/pull/114280).

Folds are skipped for byte `bitcast`s where element counts don't divide
evenly and the source contains `poison` values. Some of these casts can
be folded. However, this is left for a future PR.