DenseSet, SmallPtrSet, SmallSet, SetVector, and StringSet recently
gained C++23-style insert_range.  This patch replaces:

  Dest.insert(Src.begin(), Src.end());

with:

  Dest.insert_range(Src);

This patch does not touch custom begin like succ_begin for now.

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).

As noted in the comments, findBBsToSinkInto is
   O(UseBBs.size() * ColdLoopBBs.size())

A very large function with a huge loop was incurring a high compile time
in this code. The size of the ColdLoopBBs set was over 14K. There is a
limit on the size of the UseBBs set, but not the ColdLoopBBs (and adding
a limit for the latter actually slowed down some later passes).

This change exits the loop early once we detect that there is no further
refinement possible for the BBsToSinkInto set. This is possible because
the ColdLoopBBs set is sorted in ascending magnitude of frequency.

This cut down the LoopSinkPass time by around 33% (78s to just over
50s).

This pass isn't used anywhere and thus has no test coverage. For these
reasons, remove it.

The `BlockFrequency` class abstracts `uint64_t` frequency values. Use it
more consistently in various APIs and disable implicit conversion to
make usage more consistent and explicit.

- Use `BlockFrequency Freq` parameter for `setBlockFreq`,
`getProfileCountFromFreq` and `setBlockFreqAndScale` functions.
- Return `BlockFrequency` in `getEntryFreq()` functions.
- While on it change some `const BlockFrequency& Freq` parameters to
plain `BlockFreqency Freq`.
- Mark `BlockFrequency(uint64_t)` constructor as explicit.
- Add missing `BlockFrequency::operator!=`.
- Remove `uint64_t BlockFreqency::getMaxFrequency()`.
- Add `BlockFrequency BlockFrequency::max()` function.

This was trigerred by the debug check when comp(a, a) was called.
On line 216 it's checked that LoopBlockNumber should contain
all if there are more than 1. NFC for end users

Differential Revision: https://reviews.llvm.org/D157954

This change allows sinking defs from loop preheader with PHI-use into loop body. Loop sink can now see through PHI-use and select incoming blocks of value being used as candidate sink destination.

It makes loop sink more effective so more LICM can be undone if proven unprofitable with profile info. It addresses the motivating case in D87551, without resorting to profile guided LICM which breaks canonicalization.

This is the 2nd attempt after D152772.

This reverts commit 54711a6a5872d5f97da4c0a1bd7e58d0546ca701.

The commit is causing a clang crash: https://reviews.llvm.org/D152772#4437254

This change allows sinking defs from loop preheader with PHI-use into loop body. Loop sink can now see through PHI-use and select incoming blocks of value being used as candidate sink destination.

It makes loop sink more effective so more LICM can be undone if proven unprofitable with profile info. It addresses the motivating case in D87551, without resorting to profile guided LICM which breaks canonicalization.

Differential Revision: https://reviews.llvm.org/D152772

Nowadays MSSA is required for LICM/LoopSink, so drop the checks
for whether its available or not.