Remove support for the mul constant expression, which has previously
already been marked as undesirable. This removes the APIs to create mul
expressions and updates tests to stop using mul expressions.

Part of:
https://discourse.llvm.org/t/rfc-remove-most-constant-expressions/63179

The check lines in this test were clearly not generated by UTC.

The output for many of these slightly changed (mainly due to
switch indentation), so mass-regenerate them.

This is a follow-up to b71edfaa4ec3c998aadb35255ce2f60bba2940b0
since I forgot the lit.local.cfg files in that one.

Reformatting is done with `black`.

If you end up having problems merging this commit because you
have made changes to a python file, the best way to handle that
is to run git checkout --ours <yourfile> and then reformat it
with black.

If you run into any problems, post to discourse about it and
we will try to help.

RFC Thread below:

https://discourse.llvm.org/t/rfc-document-and-standardize-python-code-style

Reviewed By: barannikov88, kwk

Differential Revision: https://reviews.llvm.org/D150762

There was an alias between 'simplifycfg' and 'simplify-cfg' in the
PassRegistry. That was the original reason for this patch, which
effectively removes the alias.

This patch also replaces all occurrances of 'simplify-cfg'
by 'simplifycfg'. Reason for choosing that form for the name is
that it matches the DEBUG_TYPE for the pass, and the legacy PM name
and also how it is spelled out in other passes such as
'loop-simplifycfg', and in other options such as
'simplifycfg-merge-cond-stores'.

I for some reason the name should be changed to 'simplify-cfg' in
the future, then I think such a renaming should be more widely done
and not only impacting the PassRegistry.

Reviewed By: aeubanks

Differential Revision: https://reviews.llvm.org/D105627

This relands commit 99108c791de0285ee726a10e8274772b18cee73c (D95026) which was
reverted by 8d5a981a135a0f0ae0a10c59b7c8093aae1c28de because the underlying
problem (https://llvm.org/pr49495) is fixed.

This reverts commit 99108c791de0285ee726a10e8274772b18cee73c.
Clang is miscompiling LLVM with this change, a stage-2 build hits
multiple failures.

As a repro, I built clang in a stage1 directory and used it this way:

cmake -G Ninja ../llvm \
  -DCMAKE_CXX_COMPILER=`pwd`/../build-stage1/bin/clang++ \
  -DCMAKE_C_COMPILER=`pwd`/../build-stage1/bin/clang \
  -DLLVM_TARGETS_TO_BUILD="X86;NVPTX;AMDGPU" \
  -DLLVM_ENABLE_PROJECTS=mlir \
  -DLLVM_BUILD_EXAMPLES=ON \
  -DCMAKE_BUILD_TYPE=Release \
  -DLLVM_ENABLE_ASSERTIONS=On
ninja check-mlir

This patch makes FoldBranchToCommonDest merge branch conditions into `select i1` rather than `and/or i1` when it is called by SimplifyCFG.
It is known that merging conditions into and/or is poison-unsafe, and this is towards making things *more* correct by removing possible miscompilations.
Currently, InstCombine simply consumes these selects into and/or of i1 (which is also unsafe), so the visible effect would be very small. The unsafe select -> and/or transformation will be removed in the future.
There has been efforts for updating optimizations to support the select form as well, and they are linked to D93065.

The safe transformation is fired when it is called by SimplifyCFG only. This is done by setting the new `PoisonSafe` argument as true.
Another place that calls FoldBranchToCommonDest is LoopSimplify. `PoisonSafe` flag is set to false in this case because enabling it has a nontrivial impact in performance because SCEV is more conservative with select form and InductiveRangeCheckElimination isn't aware of select form of and/or i1.

Reviewed By: nikic

Differential Revision: https://reviews.llvm.org/D95026