As part of the effort to transition to using Debug Records instead of
Debug intrinsics, some API/argument changes are necessary to achieve the
desired behavior from Debug Records. This particular fix involves
passing iterators instead of instruction pointers to the SetInsertPoint
function. While this is crucial in certain areas, it may be more than
needed in others, but it does not cause any harm.

/llvm-project/polly/lib/CodeGen/LoopGeneratorsKMP.cpp:396:15: error: unused variable 'IdentTy' [-Werror,-Wunused-variable]
  StructType *IdentTy =
              ^
/llvm-project/polly/lib/CodeGen/LoopGeneratorsKMP.cpp:460:15: error: unused variable 'IdentTy' [-Werror,-Wunused-variable]
  StructType *IdentTy =
              ^
2 errors generated.

`llvm::Type::getPointerTo()` is to be deprecated & removed soon.

DominatorTree, LoopInfo, and ScalarEvolution are function-level analyses
that expect to be called only on instructions and basic blocks of the
function they were original created for. When Polly outlined a parallel
loop body into a separate function, it reused the same analyses seemed
to work until new checks to be added in #101198.

This patch creates new analyses for the subfunctions. GenDT, GenLI, and
GenSE now refer to the analyses of the current region of code. Outside
of an outlined function, they refer to the same analysis as used for the
SCoP, but are substituted within an outlined function.

Additionally to the cross-function queries of DT/LI/SE, we must not
create SCEVs that refer to a mix of expressions for old and generated
values. Currently, SCEVs themselves do not "remember" which
ScalarEvolution analysis they were created for, but mixing them is just
as unexpected as using DT/LI across function boundaries. Hence
`SCEVLoopAddRecRewriter` was combined into `ScopExpander`.
`SCEVLoopAddRecRewriter` only replaced induction variables but left
SCEVUnknowns to reference the old function. `SCEVParameterRewriter`
would have done so but its job was effectively superseded by
`ScopExpander`, and now also `SCEVLoopAddRecRewriter`. Some issues
persist put marked with a FIXME in the code. Changing them would
possibly cause this patch to be not NFC anymore.

No longer relevant with opaque pointers.

The IR Verifier requires that every call instruction to an inlineable
function (among other things, its implementation must be visible in the
translation unit) must also have !dbg metadata attached to it. When
parallelizing, Polly emits calls to OpenMP runtime function out of thin
air, or at least not directly derived from a bounded list of previous
instruction. While we could search for instructions in the SCoP that has
some debug info attached to it, there is no guarantee that we find any.
Our solution is to generate a new DILocation that points to line 0 to
represent optimized code.

The OpenMP function implementation is usually not available in the
user's translation unit, but can become visible in an LTO build. For
the bug to appear, libomp must also be built with debug symbols.

IMHO, the IR verifier rule is too strict. Runtime functions can
also be inserted by other optimization passes, such as
LoopIdiomRecognize. When inserting a call to e.g. memset, it uses the
DebugLoc from a StoreInst from the unoptimized code. It is not
required to have !dbg metadata attached either.

Fixes #56692

Identified with modernize-use-nullptr.

Explicitly pass loaded type when creating loads, in preparation
for the deprecation of these APIs.

There are still a couple of uses left.

There's a small number of users of this function, they are all updated.

This updates the C API adding a new method LLVMGetTypeByName2 that takes a context and a name.

Differential Revision: https://reviews.llvm.org/D78793