[X86] combineX86ShuffleChain - prefer combining to X86ISD::SHUF128 if PERMQ operands are splittable

[RKSimon]

If the 512-bit unary shuffle is a concatenation of 128/256-bit subvectors then we're better off using a X86ISD::SHUF128 node so we can fold the concatenation into the shuffle as well.

[llvm-ci]

LLVM Buildbot has detected a new failure on builder lldb-x86_64-debian running on lldb-x86_64-debian while building llvm at step 6 "test".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/162/builds/19291

Here is the relevant piece of the build log for the reference

Step 6 (test) failure: build (failure)
...
XFAIL: lldb-api :: functionalities/thread/multi_break/TestMultipleBreakpoints.py (307 of 2804)
PASS: lldb-api :: python_api/file_handle/TestFileHandle.py (308 of 2804)
PASS: lldb-api :: commands/frame/var/TestFrameVar.py (309 of 2804)
PASS: lldb-api :: commands/command/backticks/TestBackticksInAlias.py (310 of 2804)
PASS: lldb-shell :: Expr/TestIRMemoryMap.test (311 of 2804)
PASS: lldb-api :: functionalities/vtable/TestVTableValue.py (312 of 2804)
PASS: lldb-api :: functionalities/data-formatter/data-formatter-disabling/TestDataFormatterDisabling.py (313 of 2804)
PASS: lldb-api :: functionalities/thread/concurrent_events/TestConcurrentTwoWatchpointsOneDelayBreakpoint.py (314 of 2804)
PASS: lldb-api :: functionalities/data-formatter/data-formatter-advanced/TestDataFormatterAdv.py (315 of 2804)
UNRESOLVED: lldb-api :: driver/batch_mode/TestBatchMode.py (316 of 2804)
******************** TEST 'lldb-api :: driver/batch_mode/TestBatchMode.py' FAILED ********************
Script:
--
/usr/bin/python3 /home/worker/2.0.1/lldb-x86_64-debian/llvm-project/lldb/test/API/dotest.py -u CXXFLAGS -u CFLAGS --env LLVM_LIBS_DIR=/home/worker/2.0.1/lldb-x86_64-debian/build/./lib --env LLVM_INCLUDE_DIR=/home/worker/2.0.1/lldb-x86_64-debian/build/include --env LLVM_TOOLS_DIR=/home/worker/2.0.1/lldb-x86_64-debian/build/./bin --arch x86_64 --build-dir /home/worker/2.0.1/lldb-x86_64-debian/build/lldb-test-build.noindex --lldb-module-cache-dir /home/worker/2.0.1/lldb-x86_64-debian/build/lldb-test-build.noindex/module-cache-lldb/lldb-api --clang-module-cache-dir /home/worker/2.0.1/lldb-x86_64-debian/build/lldb-test-build.noindex/module-cache-clang/lldb-api --executable /home/worker/2.0.1/lldb-x86_64-debian/build/./bin/lldb --compiler /home/worker/2.0.1/lldb-x86_64-debian/build/./bin/clang --dsymutil /home/worker/2.0.1/lldb-x86_64-debian/build/./bin/dsymutil --make /usr/bin/gmake --llvm-tools-dir /home/worker/2.0.1/lldb-x86_64-debian/build/./bin --lldb-obj-root /home/worker/2.0.1/lldb-x86_64-debian/build/tools/lldb --lldb-libs-dir /home/worker/2.0.1/lldb-x86_64-debian/build/./lib -t /home/worker/2.0.1/lldb-x86_64-debian/llvm-project/lldb/test/API/driver/batch_mode -p TestBatchMode.py
--
Exit Code: 1

Command Output (stdout):
--
lldb version 21.0.0git (https://github.com/llvm/llvm-project.git revision 2c0b888359c6c5976054bb423ba1d7b37bae9f1a)
  clang revision 2c0b888359c6c5976054bb423ba1d7b37bae9f1a
  llvm revision 2c0b888359c6c5976054bb423ba1d7b37bae9f1a
�7�[0;23r�8�[1A
(lldb) settings clear -all
�7
                                                                                �[0m�8(lldb) settings set symbols.enable-external-lookup false
(lldb) settings set target.inherit-tcc true
(lldb) settings set target.disable-aslr false
(lldb) settings set target.detach-on-error false
(lldb) settings set target.auto-apply-fixits false
(lldb) settings set plugin.process.gdb-remote.packet-timeout 60
(lldb) settings set symbols.clang-modules-cache-path "/home/worker/2.0.1/lldb-x86_64-debian/build/lldb-test-build.noindex/module-cache-lldb/lldb-api"
(lldb) settings set use-color false
(lldb) settings set show-statusline false
�7�[0;24r�8�[J(lldb) target create "/home/worker/2.0.1/lldb-x86_64-debian/build/lldb-test-build.noindex/driver/batch_mode/TestBatchMode.test_batch_mode_attach_exit/a.out"
Current executable set to '/home/worker/2.0.1/lldb-x86_64-debian/build/lldb-test-build.noindex/driver/batch_mode/TestBatchMode.test_batch_mode_attach_exit/a.out' (x86_64).
(lldb) process attach -p 546601
Process 546601 stopped
* thread #1, name = 'a.out', stop reason = signal SIGSTOP
    frame #0: 0x00007f06076ee443 libc.so.6`clock_nanosleep + 35
libc.so.6`clock_nanosleep:
->  0x7f06076ee443 <+35>: negl   %eax
    0x7f06076ee445 <+37>: retq   
    0x7f06076ee446 <+38>: nopw   %cs:(%rax,%rax)
    0x7f06076ee450 <+48>: subq   $0x28, %rsp
(lldb) breakpoint set --file 'main.c' -p 'Stop here to unset keep_waiting' -N keep_waiting
Breakpoint 1: where = a.out`main + 221 at main.c:29:13, address = 0x000055d8fb81b25d
(lldb) continue
Process 546601 resuming