[PATCH] D91512: [AArch64][Isel] Avoid implicit zext for SIGN_EXTEND_INREG (TRUNCATE)

[Eli Friedman via Phabricator via llvm-commits]

efriedma added a comment.

In D91512#2999435 <https://reviews.llvm.org/D91512#2999435>, @jaykang10 wrote:

> I wonder we can extend this check to other basic blocks.
>
> For example, if the `trunc` is in other basic block, there could be `CopyFromReg` instead of `trunc` in current basic block. Can we detect the `trunc` in this case please?

Ideally, I think we should kill off isDef32, and run a pass after isel to clean up redundant extension operations.  That would have fewer bugs, and we'd get cross-block optimization for free.


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