X86 uses implicit widening and BLEND/MOV shuffles in these cases - otherwise we still treat it as a SK_PermuteTwoSrc

The memory value and mask value types might legalise differently - e.g. a v64i32 might split into 4 x v16i32 / 8 x v8i32 but the mask might legalize as 1 x v64i8 / 2 x v32i8 etc.

If the legalised value type has been split, then we must ensure we compute the cost for the entire mask value type and let getShuffleCost handle any legalisation, not assume that only a single trailing split mask will require widening.

A shuffle will take two input vectors and a mask, to produce a new
vector of size <MaskElts x SrcEltTy>. Historically it has been assumed
that the SrcTy and the DstTy are the same for getShuffleCost, with that
being relaxed in recent years. If the Tp passed to getShuffleCost is the
SrcTy, then the DstTy can be calculated from the Mask elts and the src
elt size, but the Mask is not always provided and the Tp is not reliably
always the SrcTy. This has led to situations notably in the SLP
vectorizer but also in the generic cost routines where assumption about
how vectors will be legalized are built into the generic cost routines -
for example whether they will widen or promote, with the cost modelling
assuming they will widen but the default lowering to promote for integer
vectors.

This patch attempts to start improving that - it originally tried to
alter more of the cost model but that too quickly became too many
changes at once, so this patch just plumbs in a DstTy to getShuffleCost
so that DstTy and SrcTy can be reliably distinguished. The callers of
getShuffleCost have been updated to try and include a DstTy that is more
accurate. Otherwise it tries to be fairly non-functional, keeping the
SrcTy used as the primary type used in shuffle cost routines, only using
DstTy where it was in the past (for InsertSubVector for example).

Some asserts have been added that help to check for consistent values
when a Mask and a DstTy are provided to getShuffleCost. Some of them
took a while to get right, and some non-mask calls might still be
incorrect. Hopefully this will provide a useful base to build more
shuffles that alter size.

Increase specificity by using the correct unit sizes. KBytes is an
abbreviation for kB, 1000 bytes, and the hardware industry as well as
several operating systems have now switched to using 1000 byte kBs.

If this change is acceptable, sometimes GitHub mangles merges to use the
original email of the account. $dayjob asks contributions have my work
email. Thanks!

If the lower 32-bits of a i64 value are known to be zero, then icmp
lowering will shift+truncate down to a i32 allowing the immediate to be
embedded.

There's a lot more that could be done here to match icmp lowering, but
this PR just focuses on known regressions.

Fixes #142513
Fixes #62145

This does not alter much at the moment, but allows const pointers to be
passed as Op0 and Op1, simplifying later patches

`ad9909d "[SLP]Fix perfect diamond match with extractelements in scalars" `
changed SLPVectorizer getScalarizationOverhead() to call
TTI.getVectorInstrCost() instead of TTI.getScalarizationOverhead() in some
cases. This was due to X86 specific handlings in these (overridden) methods,
and unfortunately the general preference of TTI.getScalarizationOverhead()
was dropped. If VL is available it should always be preferred to use
getScalarizationOverhead(), and this is indeed the case for SystemZ which
has a special insertion instruction that can insert two GPR64s.

Then ` 33af951 "[SLP]Synchronize cost of gather/buildvector nodes with
codegen"` reworked SLPVectorizer getGatherCost() which together with
ad9909d caused the SystemZ test vec-elt-insertion.ll to fail.

This patch restores the SystemZ test and reverts the change in SLPVectorizer
getScalarizationOverhead() so that TTI.getScalarizationOverhead() is always
called again. The ForPoisonSrc argument is now passed on to the TTI method
so that X86 can handle this as required.

Fixes: #135346

InstructionCost is already an optional value, containing an Invalid
state that can be checked with isValid(). There is little point in
returning another optional from getValue(). Most uses do not make use of
it being a std::optional, dereferencing the value directly (either
isValid has been checked previously or the Cost is assumed to be valid).
The one case that does in AMDGPU used value_or which has been replaced
by a isValid() check.

These are not diagnosed because implementations hide the methods of the base class rather than overriding them.
This works as long as a hiding function is callable with the same arguments as the same function from the base class.

Pull Request: https://github.com/llvm/llvm-project/pull/136655

Making `TargetTransformInfo::Model::Impl` `const` makes sure all
interface methods are `const`, in `BasicTTIImpl`, its bases, and in all
derived classes.

Pull Request: https://github.com/llvm/llvm-project/pull/136598