Extracts technically do not use scalars, but vectors, but if the operand
is a single scalar we do not need a vector and they should not block
forming single scalars.

Dissolving the hierarchical VPlan CFG and converting abstract to
concrete recipes can expose additional simplification opportunities.

Do a final run of simplifyRecipes before executing the VPlan.

Materialize constant vector trip counts before ::execute, if the trip
count can be computed as Original (TC / (VF * UF)) * (VF * UF). For now
this excludes when the tail is folded or scalar epilogues are required.

This enables removing a number of redundant branches from the middle
block.

For now this is also only done when not vectorizing the epilogue, as the
simplification complicates stitching the 2 plans together.

PR: https://github.com/llvm/llvm-project/pull/142309

Create a IR BB directly for the middle.block, instead of creating the IR
BB during skeleton creation and then replacing the middle VPBB with a
VPIRBB.

This moves another part of skeleton creation to VPlan and simplififes
the code slightly by removing code to disconnect the middle block and
vector preheader + the corresponding DT update.

NFC modulo IR block naming and block creation order, which changes the
IR names for the blocks.

Use createDerivedIV to compute IV end values directly in VPlan, instead
of creating them up-front.

This allows updating IV users outside the loop as follow-up.

Depends on https://github.com/llvm/llvm-project/pull/110004 and
https://github.com/llvm/llvm-project/pull/109975.

PR: https://github.com/llvm/llvm-project/pull/112145

This reverts commit f09b16e2671cbcdf7cb7dc7ed705db092a9deda1.

The crash when building llvm-test-suite with stage2 should have been
fixed by 1091fad31a83d5ab87eb6fa11fe3bdb3f0d152ea.

This reverts commit 0678e2058364ec10b94560d27ec7138dfa003287.
This reverts commit 1091fad31a83d5ab87eb6fa11fe3bdb3f0d152ea.

Causes crashes in llvm-test-suite when using stage 2 clang.

Updated ILV.createInductionResumeValues (now createInductionResumeVPValue)
to directly update the VPIRInstructions wrapping the original phis with the 
created resume values.

This is the first step towards modeling them completely in VPlan.
Subsequent patches will move creation of the resume values completely
into VPlan.

Depends on https://github.com/llvm/llvm-project/pull/109975.

PR: https://github.com/llvm/llvm-project/pull/110577

This an alternative to #69886. The basic problem is that SCEV can look
through trivial LCSSA phis. When the phi node later becomes non-trivial,
we do invalidate it, but this doesn't catch uses that are not covered by
the IR use-def walk, such as those in BECounts.

Fix this by adding a special invalidation method for LCSSA phis, which
will also invalidate all the SCEVUnknowns/SCEVAddRecExprs used by the
LCSSA phi node and defined in the loop.

We should probably also use this invalidation method in other places
that add predecessors to exit blocks, such as loop unrolling and loop
peeling.

Fixes #69097.
Fixes #66616.
Fixes #63970.