Having FindFirstIV tests in if-reduction.ll is misleading, and
iv-select-cmp.ll is already too large.

Don't use the order of incoming values of IR phis when creating 
VPBlendRecipes. Instead, simply use the incoming operands and
blocks from the VPWidenPHIRecipe.

Note that this changes the order of the incoming operands/masks for some
blends.

PR: https://github.com/llvm/llvm-project/pull/139475

This reverts commit 8dd160f4767f971572eac065c8650d9202ff5bf9.

The recommit contains an adjustment to planContainsAdditionalSimplifications,
which considers changes to the original predicate for compares.

Original commit message:

Add simplification to fold negation into a compare, if the negation is
the only user of the compare. This removes a number of redundant
negations.

Alive2 Proofs for FPCMP test changes:  https://alive2.llvm.org/ce/z/WGDz9U

PR: https://github.com/llvm/llvm-project/pull/129430

After unrolling, there may be additional simplifications that can be
applied. One example is removing SCALAR-STEPS for the first part where
only the first lane is demanded.

This removes redundant adds of 0 from a large number of tests (~200),
many which I am still working on updating.

In preparation for removing redundant WideIV steps added in
https://github.com/llvm/llvm-project/pull/119284.

PR: https://github.com/llvm/llvm-project/pull/123655

Reverts llvm/llvm-project#129430

this seems to have introduced a divergence between legacy and
VPlan-based cost model

https://lab.llvm.org/buildbot/#/builders/30/builds/17159

Add simplification to fold negation into a compare, if the negation is
the only user of the compare. This removes a number of redundant
negations.

Alive2 Proofs for FPCMP test changes:  https://alive2.llvm.org/ce/z/WGDz9U

PR: https://github.com/llvm/llvm-project/pull/129430

This PR removes the old `nocapture` attribute, replacing it with the new
`captures` attribute introduced in #116990. This change is
intended to be essentially NFC, replacing existing uses of `nocapture`
with `captures(none)` without adding any new analysis capabilities.
Making use of non-`none` values is left for a followup.

Some notes:
* `nocapture` will be upgraded to `captures(none)` by the bitcode
   reader.
* `nocapture` will also be upgraded by the textual IR reader. This is to
   make it easier to use old IR files and somewhat reduce the test churn in
   this PR.
* Helper APIs like `doesNotCapture()` will check for `captures(none)`.
* MLIR import will convert `captures(none)` into an `llvm.nocapture`
   attribute. The representation in the LLVM IR dialect should be updated
   separately.

Use SCEV to check if the minimum iteration check (TC < Step) is known to
be false.

This is a first step towards addressing
https://github.com/llvm/llvm-project/issues/111098. To catch the exact
case from the issue, we need to do extra work to make sure the wrap
flags on the shl are preserved and used by SCEV.

Note that skeleton creation will be gradually moved to VPlan and this
simplification should be done as VPlan transform eventually. The current
plan is to move skeleton creation to VPlan starting from parts closest
to the parts already created by VPlan, starting with induction resume
value creation (started with
https://github.com/llvm/llvm-project/pull/110577), then memory and SCEV
checks and finally minimum iteration checks.

PR: https://github.com/llvm/llvm-project/pull/111310

Add noalias, where applicable, to eliminate unnecessary memory check,
and regen with UTC.