[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.

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[PatternMatch] Do not accept undef elements in m_AllOnes() and friends (#88217)

Change all the cstval_pred_ty based PatternMatch helpers (things like
m_AllOnes and m_Zero) to only allow poison elem

[PatternMatch] Do not accept undef elements in m_AllOnes() and friends (#88217)

Change all the cstval_pred_ty based PatternMatch helpers (things like
m_AllOnes and m_Zero) to only allow poison elements inside vector
splats, not undef elements.

Historically, we used to represent non-demanded elements in vectors
using undef. Nowadays, we use poison instead. As such, I believe that
support for undef in vector splats is no longer useful.

At the same time, while poison splat elements are pretty much always
safe to ignore, this is not generally the case for undef elements. We
have existing miscompiles in our tests due to this (see the
masked-merge-*.ll tests changed here) and it's easy to miss such cases
in the future, now that we write tests using poison instead of undef
elements.

I think overall, keeping support for undef elements no longer makes
sense, and we should drop it. Once this is done consistently, I think we
may also consider allowing poison in m_APInt by default, as doing that
change is much less risky than doing the same with undef.

This change involves a substantial amount of test changes. For most
tests, I've just replaced undef with poison, as I don't think there is
value in retaining both. For some tests (where the distinction between
undef and poison is important), I've duplicated tests.

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[InstCombine] Infer shift flags with unknown shamt (#72535)

Alive2: https://alive2.llvm.org/ce/z/82Wr3q

Related patch:
https://github.com/llvm/llvm-project/commit/2dd52b4527667837cc525aa48435ab5

[InstCombine] Infer shift flags with unknown shamt (#72535)

Alive2: https://alive2.llvm.org/ce/z/82Wr3q

Related patch:
https://github.com/llvm/llvm-project/commit/2dd52b4527667837cc525aa48435ab5cbfa30a0b

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[test] Use -passes=instcombine instead of -instcombine in lots of tests. NFC

Another step moving away from the deprecated syntax of specifying
pass pipeline in opt.

Differential Revision: https://r

[test] Use -passes=instcombine instead of -instcombine in lots of tests. NFC

Another step moving away from the deprecated syntax of specifying
pass pipeline in opt.

Differential Revision: https://reviews.llvm.org/D119081

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[InstCombine] use redirect of input file in regression tests; NFC

This is a repeat of 1880092722 from 2009. We should have less risk
of hitting bugs at this point because we auto-generate positive C

[InstCombine] use redirect of input file in regression tests; NFC

This is a repeat of 1880092722 from 2009. We should have less risk
of hitting bugs at this point because we auto-generate positive CHECK
lines only, but this makes things consistent.

Copying the original commit msg:
"Change tests from "opt %s" to "opt < %s" so that opt doesn't see the
input filename so that opt doesn't print the input filename in the
output so that grep lines in the tests don't unintentionally match
strings in the input filename."

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[NFC][InstCombine] More tests for "Dropping pointless masking before left shift" (PR42563)

While we already fold that pattern if the sum of shift amounts is not
smaller than bitwidth, there's painfu

[NFC][InstCombine] More tests for "Dropping pointless masking before left shift" (PR42563)

While we already fold that pattern if the sum of shift amounts is not
smaller than bitwidth, there's painfully obvious generalization:
https://rise4fun.com/Alive/F5R
I.e. the "sub of shift amounts" tells us how many bits will be left
in the output. If it's less than bitwidth, we simply need to
apply a mask, which is constant.

llvm-svn: 372170

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[InstCombine] Dropping redundant masking before left-shift [1/5] (PR42563)

Summary:
If we have some pattern that leaves only some low bits set, and then performs
left-shift of those bits, if none of

[InstCombine] Dropping redundant masking before left-shift [1/5] (PR42563)

Summary:
If we have some pattern that leaves only some low bits set, and then performs
left-shift of those bits, if none of the bits that are left after the final
shift are modified by the mask, we can omit the mask.

There are many variants to this pattern:
b. `(x & (~(-1 << maskNbits))) << shiftNbits`
All these patterns can be simplified to just:
`x << ShiftShAmt`
iff:
b. `(MaskShAmt+ShiftShAmt) u>= bitwidth(x)`

alive proof:
b: https://rise4fun.com/Alive/y8M

For now let's start with patterns where both shift amounts are variable,
with trivial constant "offset" between them, since i believe this is
both simplest to handle and i think this is most common.
But again, there are likely other variants where we could use
ValueTracking/ConstantRange to handle more cases.

https://bugs.llvm.org/show_bug.cgi?id=42563

Differential Revision: https://reviews.llvm.org/D64514

llvm-svn: 366536

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[NFC][InstCombine] Comb through just-added "omit mask before left-shift" tests once more

llvm-svn: 365694

[NFC][InstCombine] Fixup some tests in just-added "omit mask before left-shift" tests

llvm-svn: 365663

[NFC][InstCombine] Redundant masking before left-shift (PR42563)

alive proofs:
a,b: https://rise4fun.com/Alive/4zsf
c,d,e,f: https://rise4fun.com/Alive/RC49

Indeed, not all of these patterns ar

[NFC][InstCombine] Redundant masking before left-shift (PR42563)

alive proofs:
a,b: https://rise4fun.com/Alive/4zsf
c,d,e,f: https://rise4fun.com/Alive/RC49

Indeed, not all of these patterns are canonical.
But since this fold will only produce a single instruction
i'm really interested in handling even uncanonical patterns.

Other than these 6 patterns, i can't think of any other
reasonable variants right now, although i'm sure they exist.

For now let's start with patterns where both shift amounts are variable,
with trivial constant "offset" between them, since i believe this is
both simplest to handle and i think this is most common.
But again, there are likely other variants where we could use
ValueTracking/ConstantRange to handle more cases.

https://bugs.llvm.org/show_bug.cgi?id=42563

llvm-svn: 365641

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