Seeing how we can't generate any debug intrinsics any more: delete a
variety of codepaths where they're handled. For the most part these are
plain deletions, in others I've tweaked comments to remain coherent, or
added a type to (what was) type-generic-lambdas.

This isn't all the DbgInfoIntrinsic call sites but it's most of the
simple scenarios.

Co-authored-by: Nikita Popov <github@npopov.com>

CreateVScale took a scaling parameter that had a single use outside of
IRBuilder with all other callers having to create a redundant
ConstantInt. To work round this some code perferred to use
CreateIntrinsic directly.

This patch simplifies CreateVScale to return a call to the llvm.vscale()
intrinsic and nothing more. As well as simplifying the existing call
sites I've also migrated the uses of CreateIntrinsic.

Whilst IRBuilder used CreateVScale's scaling parameter as part of the
implementations of CreateElementCount and CreateTypeSize, I have
follow-on work to switch them to the NUW varaiety and thus they would
stop using CreateVScale's scaling as well. To prepare for this I have
moved the multiplication and constant folding into the implementations
of CreateElementCount and CreateTypeSize.

As a final step I have replaced some callers of CreateVScale with
CreateElementCount where it's clear from the code they wanted the
latter.

try_emplace value-initializes values, so we do not need to pass
nullptr to try_emplace when the value types are raw pointers or
std::unique_ptr<T>.

This could be more relaxed, and look for uses of globals in
the same function but no tests apparently depend on that.

Update getOrCreateVPValueForSCEVExpr to only skip expansion of
SCEVUnknown if the underlying value isn't an instruction. Instructions
may be defined in a loop and using them without expansion may break
LCSSA form. SCEVExpander will take care of preserving LCSSA if needed.

We could also try to pass LoopInfo, but there are some users of the
function where it won't be available and main benefit from skipping
expansion is slightly more concise VPlans.

Note that SCEVExpander is now used to expand SCEVUnknown with floats.
Adjust the check in expandCodeFor to only check the types and casts if
the type of the value is different to the requested type. Otherwise we
crash when trying to expand a float and requesting a float type.

Fixes https://github.com/llvm/llvm-project/issues/121518.

PR: https://github.com/llvm/llvm-project/pull/125235

As part of the "RemoveDIs" project, BasicBlock::iterator now carries a
debug-info bit that's needed when getFirstNonPHI and similar feed into
instruction insertion positions. Call-sites where that's necessary were
updated a year ago; but to ensure some type safety however, we'd like to
have all calls to moveBefore use iterators.

This patch adds a (guaranteed dereferenceable) iterator-taking
moveBefore, and changes a bunch of call-sites where it's obviously safe
to change to use it by just calling getIterator() on an instruction
pointer. A follow-up patch will contain less-obviously-safe changes.

We'll eventually deprecate and remove the instruction-pointer
insertBefore, but not before adding concise documentation of what
considerations are needed (very few).

With the introduction of CmpPredicate in 51a895a (IR: introduce struct
with CmpInst::Predicate and samesign), PatternMatch is one of the first
key pieces of infrastructure that must be updated to match a CmpInst
respecting samesign information. Implement this change to Cmp-matchers.

This is a preparatory step in migrating the codebase over to
CmpPredicate. Since we no functional changes are desired at this stage,
we have chosen not to migrate CmpPredicate::operator==(CmpPredicate)
calls to use CmpPredicate::getMatching(), as that would have visible
impact on tests that are not yet written: instead, we call
CmpPredicate::operator==(Predicate), preserving the old behavior, while
also inserting a few FIXME comments for follow-ups.