We already do this when both sides are a GEP, but not if only one is.
This ensures that the offset arithmetic is not duplicated.

This checks for the interaction with #145474.

More closely match improveShuffleKindFromMask's shuffle ordering by
trying to match a SK_InsertSubvector shuffles patterns before SK_Select
- both can match many of the same patterns, but its much easier to
recognise when a SK_InsertSubvector can be converted to SK_Select than
vice-versa.

Another step towards #145335 - which I'm hoping will allow us to
generalise improveShuffleKindFromMask and remove getInstructionCost's
shuffle matching entirely.

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

Currently, LLVM fails to convert certain pblendvb intrinsics into select
instructions when the blend mask is derived from complex boolean logic
operations. This occurs even when the mask is ultimately based on
sign-extended comparison results, preventing further optimization
opportunities.

Fixes #66513

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Co-authored-by: Simon Pilgrim <llvm-dev@redking.me.uk>

This put the onus on the caller to ensure the result type is big enough.
In the unlikely event a cropped result is required then explicitly
truncate a safe value.

As detailed on #144489 - confirm the vectorisation of scalar FMUL+ADDSUB/FMADDSUB on various targets

Patch fixes cost estimation for the extractelements from non-power-of-2
vectors, defined as subvector extracts. In this case the subvector size
might be not adjusted to a whole register size, need to get the minimum
between whole vector size and the actual difference to prevent compiler
crash.

Fixes #143513