[VPlan] Manage created blocks directly in VPlan. (NFC) (#120918)

This patch changes the way blocks are managed by VPlan. Previously all
blocks reachable from entry would be cleaned up when a VPlan

[VPlan] Manage created blocks directly in VPlan. (NFC) (#120918)

This patch changes the way blocks are managed by VPlan. Previously all
blocks reachable from entry would be cleaned up when a VPlan is
destroyed. With this patch, each VPlan keeps track of blocks created for
it in a list and this list is then used to delete all blocks in the list
when the VPlan is destroyed. To do so, block creation is funneled
through helpers in directly in VPlan.

The main advantage of doing so is it simplifies CFG transformations, as
those do not have to take care of deleting any blocks, just adjusting
the CFG. This helps to simplify
https://github.com/llvm/llvm-project/pull/108378 and
https://github.com/llvm/llvm-project/pull/106748.

This also simplifies handling of 'immutable' blocks a VPlan holds
references to, which at the moment only include the scalar header block.

PR: https://github.com/llvm/llvm-project/pull/120918

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[VPlan] Always create initial blocks in constructor (NFC).

Update C++ unit tests to use VPlanTestBase to construct initial VPlan,
using a constructor that creates the VP blocks directly in the
const

[VPlan] Always create initial blocks in constructor (NFC).

Update C++ unit tests to use VPlanTestBase to construct initial VPlan,
using a constructor that creates the VP blocks directly in the
constructor.

Split off from and in preparation for
https://github.com/llvm/llvm-project/pull/120918.

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[VPlan] Don't use VPlan ctor taking trip count in most unit tests (NFC).

Update tests to use constructor not passing a trip count VPValue. The
tests don't need that and are simpler as a result.

[VPlan] Remove legacy VPlan() constructors (NFC).

The constructors were retained to reduce the diff during transition.

Remove them now.

[VPlan] Don't leak ScalarHeader BasicBlock in unit tests.

[VPlan] Connect scalar header to VPlan CFG in unit tests.

This ensures the VPIRBasicBlocks are deleted when the VPlan is
destroyed.

Fixes a buildbot failure with ASAN, including
https://lab.llvm.or

[VPlan] Connect scalar header to VPlan CFG in unit tests.

This ensures the VPIRBasicBlocks are deleted when the VPlan is
destroyed.

Fixes a buildbot failure with ASAN, including
https://lab.llvm.org/buildbot/#/builders/52/builds/3368

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[VPlan] Introduce scalar loop header in plan, remove VPLiveOut. (#109975)

Update VPlan to include the scalar loop header. This allows retiring
VPLiveOut, as the remaining live-outs can now be handl

[VPlan] Introduce scalar loop header in plan, remove VPLiveOut. (#109975)

Update VPlan to include the scalar loop header. This allows retiring
VPLiveOut, as the remaining live-outs can now be handled by adding
operands to the wrapped phis in the scalar loop header.

Note that the current version only includes the scalar loop header, no
other loop blocks and also does not wrap it in a region block.

PR: https://github.com/llvm/llvm-project/pull/109975

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[VPlan] Introduce new entry block to VPlan for early SCEV expansion.

This patch adds a new preheader block the VPlan to place SCEV expansions
expansions like the trip count. This preheader block is

[VPlan] Introduce new entry block to VPlan for early SCEV expansion.

This patch adds a new preheader block the VPlan to place SCEV expansions
expansions like the trip count. This preheader block is disconnected
at the moment, as the bypass blocks of the skeleton are not yet modeled
in VPlan.

The preheader block is executed before skeleton creation, so the SCEV
expansion results can be used during skeleton creation. At the moment,
the trip count expression and induction steps are expanded in the new
preheader. The remainder of SCEV expansions will be moved gradually in
the future.

D147965 will update skeleton creation to use the steps expanded in the
pre-header to fix #58811.

Reviewed By: Ayal

Differential Revision: https://reviews.llvm.org/D147964

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[VPlan] Turn Plan entry node into VPBasicBlock (NFCI).

The entry to the plan is the preheader of the vector loop and
guaranteed to be a VPBasicBlock. Make sure this is the case by
adjusting the type

[VPlan] Turn Plan entry node into VPBasicBlock (NFCI).

The entry to the plan is the preheader of the vector loop and
guaranteed to be a VPBasicBlock. Make sure this is the case by
adjusting the type.

Reviewed By: Ayal

Differential Revision: https://reviews.llvm.org/D149005

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[VPlan] Switch default graph traits to be recursive, update VPDomTree.

This updates the GraphTraits specialization for VPBlockBase to recurse
through VPRegionBlocks.

This in turn enables using VPDo

[VPlan] Switch default graph traits to be recursive, update VPDomTree.

This updates the GraphTraits specialization for VPBlockBase to recurse
through VPRegionBlocks.

This in turn enables using VPDominatorTree to query dominance between
any block in a plan. This should enable additional use cases, including
improvements to def-use verification and porting IR-based transforms
that rely on the dominator tree.

Specifically, this change means that for regions, the entry and exit
blocks dominate the successors of the region.

Depends on D140512 and D142162.

Reviewed By: Ayal

Differential Revision: https://reviews.llvm.org/D140513

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[VPlan] Add initial VPDT test. (NFC)