[VectorCombine] Generalise foldBitOpOfBitcasts into foldBitOpOfCastops

[RKSimon]

foldBitOpOfBitcasts (#137322) allows us to fold bitlogic(bitcast(x),bitcast(y)) -> bitcast(bitlogic(x,y)) if x and y are the same type and it doesn't cost anymore.

We can generalise this to work with other matching cast ops (trunc/sext/zext) - similar to how foldShuffleOfCastops works (although much simpler as there's no shuffle mask manipulation to do).

[llvmbot]

Hi!

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[llvmbot]

@llvm/issue-subscribers-good-first-issue

Author: Simon Pilgrim (RKSimon)

foldBitOpOfBitcasts allows us to fold bitlogic(bitcast(x),bitcast(y)) -> bitcast(bitlogic(x,y)) if x and y are the same type and it doesn't cost anymore.

We can generalise this to work with other matching cast ops (trunc/sext/zext) - similar to how foldShuffleOfCastops works (although much simpler as there's no shuffle mask manipulation to do).

[woruyu]

hello, @RKSimon , I'm glad to this!

[rhyadav]

Hi, I would like to contribute to this, thanks @RKSimon