[llvm] [TableGen][GISel] Improve dead register handling (PR #120426)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-aarch64-darwin` running on `doug-worker-5` while building `llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/190/builds/11620

<details>
<summary>Here is the relevant piece of the build log for the reference</summary>

```
Step 6 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'LLVM :: ExecutionEngine/OrcLazy/multiple-compile-threads-basic.ll' FAILED ********************
Exit Code: 2

Command Output (stderr):
--
RUN: at line 1: /Users/buildbot/buildbot-root/aarch64-darwin/build/bin/lli -jit-kind=orc-lazy -compile-threads=2 -thread-entry hello /Users/buildbot/buildbot-root/aarch64-darwin/llvm-project/llvm/test/ExecutionEngine/OrcLazy/multiple-compile-threads-basic.ll | /Users/buildbot/buildbot-root/aarch64-darwin/build/bin/FileCheck /Users/buildbot/buildbot-root/aarch64-darwin/llvm-project/llvm/test/ExecutionEngine/OrcLazy/multiple-compile-threads-basic.ll
+ /Users/buildbot/buildbot-root/aarch64-darwin/build/bin/lli -jit-kind=orc-lazy -compile-threads=2 -thread-entry hello /Users/buildbot/buildbot-root/aarch64-darwin/llvm-project/llvm/test/ExecutionEngine/OrcLazy/multiple-compile-threads-basic.ll
+ /Users/buildbot/buildbot-root/aarch64-darwin/build/bin/FileCheck /Users/buildbot/buildbot-root/aarch64-darwin/llvm-project/llvm/test/ExecutionEngine/OrcLazy/multiple-compile-threads-basic.ll
PLEASE submit a bug report to https://github.com/llvm/llvm-project/issues/ and include the crash backtrace.
 #0 0x00000001054d1ee4 llvm::sys::PrintStackTrace(llvm::raw_ostream&, int) (/Users/buildbot/buildbot-root/aarch64-darwin/build/bin/lli+0x100e85ee4)
 #1 0x00000001054cff68 llvm::sys::RunSignalHandlers() (/Users/buildbot/buildbot-root/aarch64-darwin/build/bin/lli+0x100e83f68)
 #2 0x00000001054d25a0 SignalHandler(int) (/Users/buildbot/buildbot-root/aarch64-darwin/build/bin/lli+0x100e865a0)
 #3 0x0000000198f82584 (/usr/lib/system/libsystem_platform.dylib+0x18047a584)
 #4 0x0000000198f5121c (/usr/lib/system/libsystem_pthread.dylib+0x18044921c)
 #5 0x0000000198e77ad0 (/usr/lib/libc++.1.dylib+0x18036fad0)
 #6 0x00000001050888a4 void llvm::detail::UniqueFunctionBase<void, llvm::Expected<llvm::DenseMap<llvm::orc::SymbolStringPtr, llvm::orc::ExecutorSymbolDef, llvm::DenseMapInfo<llvm::orc::SymbolStringPtr, void>, llvm::detail::DenseMapPair<llvm::orc::SymbolStringPtr, llvm::orc::ExecutorSymbolDef>>>>::CallImpl<llvm::orc::Platform::lookupInitSymbols(llvm::orc::ExecutionSession&, llvm::DenseMap<llvm::orc::JITDylib*, llvm::orc::SymbolLookupSet, llvm::DenseMapInfo<llvm::orc::JITDylib*, void>, llvm::detail::DenseMapPair<llvm::orc::JITDylib*, llvm::orc::SymbolLookupSet>> const&)::$_45>(void*, llvm::Expected<llvm::DenseMap<llvm::orc::SymbolStringPtr, llvm::orc::ExecutorSymbolDef, llvm::DenseMapInfo<llvm::orc::SymbolStringPtr, void>, llvm::detail::DenseMapPair<llvm::orc::SymbolStringPtr, llvm::orc::ExecutorSymbolDef>>>&) (/Users/buildbot/buildbot-root/aarch64-darwin/build/bin/lli+0x100a3c8a4)
 #7 0x0000000105084614 llvm::orc::AsynchronousSymbolQuery::handleComplete(llvm::orc::ExecutionSession&)::RunQueryCompleteTask::run() (/Users/buildbot/buildbot-root/aarch64-darwin/build/bin/lli+0x100a38614)
 #8 0x000000010513d074 void* std::__1::__thread_proxy[abi:un170006]<std::__1::tuple<std::__1::unique_ptr<std::__1::__thread_struct, std::__1::default_delete<std::__1::__thread_struct>>, llvm::orc::DynamicThreadPoolTaskDispatcher::dispatch(std::__1::unique_ptr<llvm::orc::Task, std::__1::default_delete<llvm::orc::Task>>)::$_0>>(void*) (/Users/buildbot/buildbot-root/aarch64-darwin/build/bin/lli+0x100af1074)
 #9 0x0000000198f51f94 (/usr/lib/system/libsystem_pthread.dylib+0x180449f94)
#10 0x0000000198f4cd34 (/usr/lib/system/libsystem_pthread.dylib+0x180444d34)
FileCheck error: '<stdin>' is empty.
FileCheck command line:  /Users/buildbot/buildbot-root/aarch64-darwin/build/bin/FileCheck /Users/buildbot/buildbot-root/aarch64-darwin/llvm-project/llvm/test/ExecutionEngine/OrcLazy/multiple-compile-threads-basic.ll

--

********************


```

</details>

https://github.com/llvm/llvm-project/pull/120426