[llvm] [SelectionDAG] Folding ZERO-EXTEND/SIGN_EXTEND poison to Poison value in getNode (PR #122741)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `llvm-clang-x86_64-gcc-ubuntu-no-asserts` running on `doug-worker-6` while building `llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/202/builds/808

<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 :: CodeGen/X86/bfloat.ll' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
/home/buildbot/buildbot-root/gcc-no-asserts/build/bin/llc < /home/buildbot/buildbot-root/gcc-no-asserts/llvm-project/llvm/test/CodeGen/X86/bfloat.ll -mtriple=i686-linux-gnu -mattr=avx512bf16,avx512fp16,avx512vl | /home/buildbot/buildbot-root/gcc-no-asserts/build/bin/FileCheck /home/buildbot/buildbot-root/gcc-no-asserts/llvm-project/llvm/test/CodeGen/X86/bfloat.ll --check-prefixes=X86 # RUN: at line 2
+ /home/buildbot/buildbot-root/gcc-no-asserts/build/bin/llc -mtriple=i686-linux-gnu -mattr=avx512bf16,avx512fp16,avx512vl
+ /home/buildbot/buildbot-root/gcc-no-asserts/build/bin/FileCheck /home/buildbot/buildbot-root/gcc-no-asserts/llvm-project/llvm/test/CodeGen/X86/bfloat.ll --check-prefixes=X86
/home/buildbot/buildbot-root/gcc-no-asserts/build/bin/llc < /home/buildbot/buildbot-root/gcc-no-asserts/llvm-project/llvm/test/CodeGen/X86/bfloat.ll -mtriple=x86_64-linux-gnu | /home/buildbot/buildbot-root/gcc-no-asserts/build/bin/FileCheck /home/buildbot/buildbot-root/gcc-no-asserts/llvm-project/llvm/test/CodeGen/X86/bfloat.ll --check-prefixes=CHECK,SSE2 # RUN: at line 3
+ /home/buildbot/buildbot-root/gcc-no-asserts/build/bin/llc -mtriple=x86_64-linux-gnu
+ /home/buildbot/buildbot-root/gcc-no-asserts/build/bin/FileCheck /home/buildbot/buildbot-root/gcc-no-asserts/llvm-project/llvm/test/CodeGen/X86/bfloat.ll --check-prefixes=CHECK,SSE2
/home/buildbot/buildbot-root/gcc-no-asserts/llvm-project/llvm/test/CodeGen/X86/bfloat.ll:845:14: error: SSE2-NEXT: expected string not found in input
; SSE2-NEXT: xorl %eax, %eax
             ^
<stdin>:404:9: note: scanning from here
# %bb.0:
        ^
<stdin>:438:2: note: possible intended match here
 orl %ebx, %eax
 ^

Input file: <stdin>
Check file: /home/buildbot/buildbot-root/gcc-no-asserts/llvm-project/llvm/test/CodeGen/X86/bfloat.ll

-dump-input=help explains the following input dump.

Input was:
<<<<<<
              1:  .file "<stdin>" 
              2:  .text 
              3:  .globl add # -- Begin function add 
              4:  .p2align 4 
              5:  .type add, at function 
              6: add: # @add 
label:25'0       ^~~~
label:25'1       ^~~~
              7: # %bb.0: 
check:26         ^~~~~~~~
              8:  pushq %rbx 
next:27           ^~~~~~~~~~
              9:  movq %rdx, %rbx 
next:28           ^~~~~~~~~~~~~~~
             10:  movzwl (%rsi), %eax 
next:29           ^~~~~~~~~~~~~~~~~~~
             11:  shll $16, %eax 
next:30           ^~~~~~~~~~~~~~
             12:  movd %eax, %xmm1 
next:31           ^~~~~~~~~~~~~~~~
             13:  movzwl (%rdi), %eax 
next:32           ^~~~~~~~~~~~~~~~~~~
...

```

</details>

https://github.com/llvm/llvm-project/pull/122741