Changes

[OpenMP] Take elf_common.c as a interface library

For now `elf_common.c` is taken as a common part included into
different plugin implementations directly via
`#include "../../common/elf_common.c"`, which is not a best practice. Since it
is simple enough such that we don't need to create a real library for it, we just
take it as a interface library so that other targets can link it directly. Another
advantage of this method is, we don't need to add the folder into header search
path which can potentially pollute the search path.

VE and AMD platforms have not been tested because I don't have target machines.

Reviewed By: JonChesterfield

Differential Revision: https://reviews.llvm.org/D94443

[RISCV] Add scalable vector vselect ISel patterns

Reviewed By: craig.topper

Differential Revision: https://reviews.llvm.org/D94294

clang: Always pass PowerPC endian information to GNU as

When building a 64-bit big endian PowerPC Linux kernel with a 64-bit
little endian PowerPC target, the 32-bit vDSO errors:

```
$ make ARCH=powerpc CC=clang CROSS_COMPILE=powerpc64le-linux-gnu- \
       pseries_defconfig arch/powerpc/kernel/vdso32/
ld.lld: error: arch/powerpc/kernel/vdso32/sigtramp.o is incompatible with elf32-powerpc
ld.lld: error: arch/powerpc/kernel/vdso32/gettimeofday.o is incompatible with elf32-powerpc
ld.lld: error: arch/powerpc/kernel/vdso32/datapage.o is incompatible with elf32-powerpc
ld.lld: error: arch/powerpc/kernel/vdso32/cacheflush.o is incompatible with elf32-powerpc
ld.lld: error: arch/powerpc/kernel/vdso32/note.o is incompatible with elf32-powerpc
ld.lld: error: arch/powerpc/kernel/vdso32/getcpu.o is incompatible with elf32-powerpc
ld.lld: error: arch/powerpc/kernel/vdso32/vgettimeofday.o is incompatible with elf32-powerpc
...
```

This happens because the endian information is missing from the call to
the assembler, even though it was explicitly passed to clang. See the
below example.

```
$ echo | clang --target=powerpc64le-linux-gnu \
               --prefix=/usr/bin/powerpc64le-linux-gnu- \
               -no-integrated-as -m32 -mbig-endian -### -x c -c -
 ".../clang-12" "-cc1" "-triple" "powerpc-unknown-linux-gnu" ...
...
  "/usr/bin/powerpc64le-linux-gnu-as" "-a32" "-mppc" "-many" "-o" "-.o" "/tmp/--e69e28.s"
```

clang sets the right target with -m32 and -mbig-endian but -mbig-endian
does not make it to the assembler, resulting in a 32-bit little endian
binary. This differs from the little endian targets, which always pass
-mlittle-endian.

```
$ echo | clang --target=powerpc64-linux-gnu \
               --prefix=/usr/bin/powerpc64-linux-gnu- \
               -no-integrated-as -m32 -mlittle-endian -### -x c -c -
 ".../clang-12" "-cc1" "-triple" "powerpcle-unknown-linux-gnu" ...
...
 "/usr/bin/powerpc64-linux-gnu-as" "-a32" "-mppc" "-mlittle-endian" "-many" "-o" "-.o" "/tmp/--405dbd.s"
```

Do the same thing for the big endian targets so that there is no more
error. This matches GCC's behavior, where -mbig and -mlittle are always
passed along to GNU as.

```
$ echo | powerpc64-linux-gcc -### -x c -c -
...
.../powerpc64-linux/bin/as -a64 -mpower4 -many -mbig -o -.o /tmp/ccVn7NAm.s
...

$ echo | powerpc64le-linux-gcc -### -x c -c -
...
.../powerpc64le-linux/bin/as -a64 -mpower8 -many -mlittle -o -.o /tmp/ccPN9ato.s
...
```

Reviewed By: nickdesaulniers, MaskRay

Differential Revision: https://reviews.llvm.org/D94442

Update syntax for tensor and memref types to match parser.

Based on the comments in lib/Parser/TypeParser.cpp on the
parseMemRefType and parseTensorType functions.

Reviewed By: mehdi_amini

Differential Revision: https://reviews.llvm.org/D94262

[RISCV] Use vmv.v.i vd, 0 instead of vmv.v.x vd, x0 for llvm.riscv.vfmv.v.f with 0.0

This matches what we use for integer 0. It's also consistent with
the scalar 'mv' pseudo that uses addi rather than add with x0.

[SimplifyCFG] SwitchToLookupTable(): don't insert a DomTree edge that already exists

SI is the terminator of BB, so the edge we are adding obviously already existed.

Indeed, this change does not have a test coverage change.
This failure has been exposed in an existing test coverage
by a follow-up patch that switches to lazy domtreeupdater mode,
and removes domtree verification from
SimplifyCFGOpt::simplifyOnce()/SimplifyCFGOpt::run(),
IOW it does not appear feasible to add dedicated test coverage here.

[SimplifyCFG] SimplifyBranchOnICmpChain(): don't insert a DomTree edge that already exists

BB was already always branching to EdgeBB, there is no edge to add.

Indeed, this change does not have a test coverage change.
This failure has been exposed in an existing test coverage
by a follow-up patch that switches to lazy domtreeupdater mode,
and removes domtree verification from
SimplifyCFGOpt::simplifyOnce()/SimplifyCFGOpt::run(),
IOW it does not appear feasible to add dedicated test coverage here.

[SimplifyCFG] FoldValueComparisonIntoPredecessors(): don't insert a DomTree edge if it already exists

When we are adding edges to the terminator and potentially turning it
into a switch (if it wasn't already), it is possible that the
case we're adding will share it's destination with one of the
preexisting cases, in which case there is no domtree edge to add.

Indeed, this change does not have a test coverage change.
This failure has been exposed in an existing test coverage
by a follow-up patch that switches to lazy domtreeupdater mode,
and removes domtree verification from
SimplifyCFGOpt::simplifyOnce()/SimplifyCFGOpt::run(),
IOW it does not appear feasible to add dedicated test coverage here.

[NFCI][Utils/Local] removeUnreachableBlocks(): cleanup support for lazy DomTreeUpdater

When DomTreeUpdater is in lazy update mode, the blocks
that were scheduled to be removed, won't be removed
until the updates are flushed, e.g. by asking
DomTreeUpdater for a up-to-date DomTree.

From the function's current code, it is pretty evident
that the support for the lazy mode is an afterthought,
see e.g. how we roll-back NumRemoved statistic..

So instead of considering all the unreachable blocks
as the blocks-to-be-removed, simply additionally skip
all the blocks that are already scheduled to be removed

[SimplifyCFGPass] mergeEmptyReturnBlocks(): skip blocks scheduled for removal as per DomTreeUpdater

Thus supporting lazy DomTreeUpdater mode,
where the domtree updates (and thus block removals)
aren't applied immediately, but are delayed
until last possible moment.

[SimplifyCFGPass] iterativelySimplifyCFG(): support lazy DomTreeUpdater

This boils down to how we deal with early-increment iterator
over function's basic blocks: not only we need to early-increment,
after that we also need to skip all the blocks
that are scheduled for removal, as per DomTreeUpdater.

ADT: Fix pointer comparison UB in SmallVector

The standard requires comparisons of pointers to unrelated storage to
use `std::less`. Split out some helpers that do that and update all the
code that was comparing using `<` and friends (mostly assertions).

Differential Revision: https://reviews.llvm.org/D93777