[VectorCombine] foldBitOpOfCastops - failure to handle bitop(castop(x), constant_y) -> castop(bitop(x, invcast(constant_y)))

[RKSimon]

foldBitOpOfCastops currently just folds bitop(castop(x), castop(y)) -> castop(bitop(x, y))

But we often have operands that have already constant folded the castop away which prevents the fold from proceeding.

The most obvious are not patterns:

  %x.cast = bitcast <4 x i32> %x to <2 x i64>
  %not = xor <2 x i64>%x.cast, splat (i64 -1)

-->

  %not.cast = <4 x i32> %x, splat (i32 -1)
  %not = bitcast <4 x i32> %not.cast to <2 x i64>

Any other bitcasted constants would be easy to handle as well.

But other casts that can be easily inverted (truncations, in range sext/zext etc.) could be handled as well.

[llvmbot]

Hi!

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[llvmbot]

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

Author: Simon Pilgrim (RKSimon)

foldBitOpOfCastops currently just folds `bitop(castop(x), castop(y)) -> castop(bitop(x, y))`

But we often have operands that have already constant folded the castop away which prevents the fold from proceeding.

The most obvious are not patterns:

  %x.cast = bitcast <4 x i32> %x to <2 x i64>
  %not = xor <2 x i64>%x.cast, splat (i64 -1)

-->

  %not.cast = <4 x i32> %x, splat (i32 -1)
  %not = bitcast <4 x i32> %not.cast to <2 x i64>

Any other bitcasted constants would be easy to handle as well.

But other casts that can be easily inverted (truncations, in range sext/zext etc.) could be handled as well.

[RKSimon]

CC @vortex73 who handled #66513

[XChy]

@vortex73, would you like to work on this? If not, I want to take this one.

[vortex73]

@vortex73, would you like to work on this? If not, I want to take this one.

Sure, you can go ahead :)