This reverts commit c858bf620c3ab2a4db53e84b9365b553c3ad1aa6 as it casuse optimization crash on -O2, see https://github.com/llvm/llvm-project/pull/120721#issuecomment-2563192057

This re-lands the reverted #92418 

When the VF is small enough so that dividing the VF by the scaling
factor results in 1, the reduction phi execution thinks the VF is scalar
and sets the reduction's output as a scalar value, tripping assertions
expecting a vector value. The latest commit in this PR fixes that by
using `State.VF` in the scalar check, rather than the divided VF.

---------

Co-authored-by: Nicholas Guy <nicholas.guy@arm.com>

Use VPlan-based type analysis to retrieve type of phi node. Also adds
missing type inference for ResumePhi and ComputeReductionResult opcodes.

This reverts commit 060d62b48aeb5080ffcae1dc56e41a06c6f56701.

It looks like this is triggering an assertion when build llvm-test-suite
on ARM64 macOS.

Reproducer from MultiSource/Benchmarks/Ptrdist/bc/number.c

    target datalayout = "e-m:o-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-n32:64-S128-Fn32"
    target triple = "arm64-apple-macosx15.0.0"

    define void @test(i64 %idx.neg, i8 %0) #0 {
    entry:
      br label %while.body

    while.body:                                       ; preds = %while.body, %entry
      %n1ptr.0.idx131 = phi i64 [ %n1ptr.0.add, %while.body ], [ %idx.neg, %entry ]
      %n2ptr.0.idx130 = phi i64 [ %n2ptr.0.add, %while.body ], [ 0, %entry ]
      %sum.1129 = phi i64 [ %add99, %while.body ], [ 0, %entry ]
      %n1ptr.0.add = add i64 %n1ptr.0.idx131, 1
      %conv = sext i8 %0 to i64
      %n2ptr.0.add = add i64 %n2ptr.0.idx130, 1
      %1 = load i8, ptr null, align 1
      %conv97 = sext i8 %1 to i64
      %mul = mul i64 %conv97, %conv
      %add99 = add i64 %mul, %sum.1129
      %cmp94 = icmp ugt i64 %n1ptr.0.idx131, 0
      %cmp95 = icmp ne i64 %n2ptr.0.idx130, -1
      %2 = and i1 %cmp94, %cmp95
      br i1 %2, label %while.body, label %while.end.loopexit

    while.end.loopexit:                               ; preds = %while.body
      %add99.lcssa = phi i64 [ %add99, %while.body ]
      ret void
    }

    attributes #0 = { "target-cpu"="apple-m1" }

> opt -p loop-vectorize
Assertion failed: ((VF.isScalar() || V->getType()->isVectorTy()) && "scalar values must be stored as (0, 0)"), function set, file VPlan.h, line 284.

Following on from https://github.com/llvm/llvm-project/pull/94499, this
patch adds support to the Loop Vectorizer to emit the partial reduction
intrinsics where they may be beneficial for the target.

---------

Co-authored-by: Samuel Tebbs <samuel.tebbs@arm.com>

Introduce a general recipe to generate a scalar phi. Lower
VPCanonicalIVPHIRecipe and VPEVLBasedIVRecipe to VPScalarIVPHIrecipe
before plan execution, avoiding the need for duplicated ::execute
implementations. There are other cases that could benefit, including
in-loop reduction phis and pointer induction phis.

Builds on a similar idea as
https://github.com/llvm/llvm-project/pull/82270.

PR: https://github.com/llvm/llvm-project/pull/114305

Refactors VPVectorPointerRecipe to use the VF VPValue to obtain the
runtime VF, similar to #95305.

Since only reverse vector pointers require the runtime VF, the patch
sets VPUnrollPart::PartOpIndex to 1 for vector pointers and 2 for
reverse vector pointers. As a result, the generation of reverse vector
pointers is moved into a separate recipe.

Use VPWidenIntrinsicRecipe
(https://github.com/llvm/llvm-project/pull/110486)
to create vp.select intrinsics. This potentially offers an alternative
to duplicating EVL recipes for all existing recipes.

There are some recipes that will need duplicates (at least at the
moment), due to extra code-gen needs (e.g. widening loads and stores).
But in cases the intrinsic can directly be used, creating the widened
intrinsic directly would reduce the need to duplicate some recipes.


PR: https://github.com/llvm/llvm-project/pull/110489