[InstCombine] Infer nusw + nneg -> nuw for getelementptr (#111144)

If the gep is nusw (usually via inbounds) and the offset is
non-negative, we can infer nuw.

Proof: https://alive2.llvm.org/ce/z

[InstCombine] Infer nusw + nneg -> nuw for getelementptr (#111144)

If the gep is nusw (usually via inbounds) and the offset is
non-negative, we can infer nuw.

Proof: https://alive2.llvm.org/ce/z/ihztLy

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[InstCombine] Remove the canonicalization of `trunc` to `i1` (#84628)

Remove the canonicalization of `trunc` to `i1` according to the
suggestion of
https://github.com/llvm/llvm-project/pull/83829#

[InstCombine] Remove the canonicalization of `trunc` to `i1` (#84628)

Remove the canonicalization of `trunc` to `i1` according to the
suggestion of
https://github.com/llvm/llvm-project/pull/83829#issuecomment-1986801166

https://github.com/llvm/llvm-project/blob/a84e66a92d7b97f68aa3ae7d2c5839f3fb0d291d/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp#L737-L745

Alive2: https://alive2.llvm.org/ce/z/cacYVA

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[InstCombine] Canonicalize constant GEPs to i8 source element type (#68882)

This patch canonicalizes getelementptr instructions with constant
indices to use the `i8` source element type. This makes

[InstCombine] Canonicalize constant GEPs to i8 source element type (#68882)

This patch canonicalizes getelementptr instructions with constant
indices to use the `i8` source element type. This makes it easier for
optimizations to recognize that two GEPs are identical, because they
don't need to see past many different ways to express the same offset.

This is a first step towards
https://discourse.llvm.org/t/rfc-replacing-getelementptr-with-ptradd/68699.
This is limited to constant GEPs only for now, as they have a clear
canonical form, while we're not yet sure how exactly to deal with
variable indices.

The test llvm/test/Transforms/PhaseOrdering/switch_with_geps.ll gives
two representative examples of the kind of optimization improvement we
expect from this change. In the first test SimplifyCFG can now realize
that all switch branches are actually the same. In the second test it
can convert it into simple arithmetic. These are representative of
common optimization failures we see in Rust.

Fixes https://github.com/llvm/llvm-project/issues/69841.

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[InstCombine] Convert test to opaque pointers (NFC)

Slightly adjust the test so it uses non-zero GEP indices, otherwise
these would get folded away with opaque pointers.

[InstCombine] Regenerate test checks (NFC)

[InstCombine] Don't slice up PHIs when pred BB has catchswitch

If an integer PHI has an illegal type (according to the data layout) and
it is only used by `trunc` or `trunc(lshr)` operations, we spl

[InstCombine] Don't slice up PHIs when pred BB has catchswitch

If an integer PHI has an illegal type (according to the data layout) and
it is only used by `trunc` or `trunc(lshr)` operations, we split the PHI
into various instructions in its predecessors:
https://github.com/llvm/llvm-project/blob/6d1543a16797fa07eecea7e542df5b42422fc721/llvm/lib/Transforms/InstCombine/InstCombinePHI.cpp#L1536-L1543

So this can produce code like the following:
Before:
```
pred:
...

bb:
%p = phi i8 [ %somevalue, %pred ], ...
...
%tobool = trunc i8 %p to i1
use %tobool
...
```
In this code, `%p` has an illegal integer type, `i8`, and its only used
in a `trunc` instruction later. In this case this pass puts extraction
code in its predecessors:

After:
```
pred:
...
%t = and i8 %somevalue, 1
%extract = icmp ne i8 %t, 0

bb:
%p.new = phi i1 [ %extract, %pred ], ...
use %p.new instead of %tobool
```

But this doesn't work if `pred` is a `catchswitch` BB because it cannot
have any non-PHI instructions. This CL ensures we bail out in that case.

Fixes https://github.com/llvm/llvm-project/issues/55803.

Reviewed By: dschuff

Differential Revision: https://reviews.llvm.org/D127699

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[NFC] remove 'br undef' from InstCombine test cases
This is UB and allows the compiler to give any result, so these tests weren't meaningful
InstCombine tests are now clean of 'br undef'

[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] Don't combine PHI before catchswitch

This tries to bail out if the PHI is in a `catchswitch` BB in
InstCombine. A PHI cannot be combined into a non-PHI instruction if it
is in a `catch

[InstCombine] Don't combine PHI before catchswitch

This tries to bail out if the PHI is in a `catchswitch` BB in
InstCombine. A PHI cannot be combined into a non-PHI instruction if it
is in a `catchswitch` BB, because `catchswitch` BB cannot have any
non-PHI instruction other than `catchswitch` itself.

The given test case started crashing after D98058.

Reviewed By: lebedev.ri, rnk

Differential Revision: https://reviews.llvm.org/D105309

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