[LLVM][IR] Use splat syntax when printing Constant[Data]Vector. (#112548)

[InstCombine] Remove some of the complexity-based canonicalization (#91185)

The idea behind this canonicalization is that it allows us to handle less
patterns, because we know that some will be can

[InstCombine] Remove some of the complexity-based canonicalization (#91185)

The idea behind this canonicalization is that it allows us to handle less
patterns, because we know that some will be canonicalized away. This is
indeed very useful to e.g. know that constants are always on the right.

However, this is only useful if the canonicalization is actually
reliable. This is the case for constants, but not for arguments: Moving
these to the right makes it look like the "more complex" expression is
guaranteed to be on the left, but this is not actually the case in
practice. It fails as soon as you replace the argument with another
instruction.

The end result is that it looks like things correctly work in tests,
while they actually don't. We use the "thwart complexity-based
canonicalization" trick to handle this in tests, but it's often a
challenge for new contributors to get this right, and based on the
regressions this PR originally exposed, we clearly don't get this right
in many cases.

For this reason, I think that it's better to remove this complexity
canonicalization. It will make it much easier to write tests for
commuted cases and make sure that they are handled.

show more ...

Use `analyzeKnownBitsFromAndXorOr` in `SimplifyDemandedUseBits` for and/xor/or

There are extra patterns that have for these three logic operations
that aren't covered in `SimplifyDemandedUseBits`. T

Use `analyzeKnownBitsFromAndXorOr` in `SimplifyDemandedUseBits` for and/xor/or

There are extra patterns that have for these three logic operations
that aren't covered in `SimplifyDemandedUseBits`. To avoid duplicating
the code, just use `analyzeKnownBitsFromAndXorOr` in
`SimplifyDemandedUseBits` to get full coverage.

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D142429

show more ...

[ValueTracking] Add KnownBits patterns `xor(x, x - 1)` and `and(x, -x)` for knowing upper bits to be zero

These two BMI pattern will clear the upper bits of result past the
first set bit. So if we k

[ValueTracking] Add KnownBits patterns `xor(x, x - 1)` and `and(x, -x)` for knowing upper bits to be zero

These two BMI pattern will clear the upper bits of result past the
first set bit. So if we know a single bit in `x` is set, we know that
`results[bitwidth - 1, log2(x) + 1] = 0`.

Alive2:
blsmsk: https://alive2.llvm.org/ce/z/a397BS
blsi: https://alive2.llvm.org/ce/z/tsbQhC

Differential Revision: https://reviews.llvm.org/D142271

show more ...

[ValueTracking] Add tests for known bits after common BMI pattern (blsmsk/blsi); NFC

Differential Revision: https://reviews.llvm.org/D142270