[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-darwin` running on `doug-worker-3` while building `llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/23/builds/9584

<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/avx512-i1test.ll' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
/Volumes/RAMDisk/buildbot-root/x86_64-darwin/build/bin/llc < /Volumes/RAMDisk/buildbot-root/x86_64-darwin/llvm-project/llvm/test/CodeGen/X86/avx512-i1test.ll -mattr=+avx512f -disable-cgp-delete-phis | /Volumes/RAMDisk/buildbot-root/x86_64-darwin/build/bin/FileCheck /Volumes/RAMDisk/buildbot-root/x86_64-darwin/llvm-project/llvm/test/CodeGen/X86/avx512-i1test.ll # RUN: at line 2
+ /Volumes/RAMDisk/buildbot-root/x86_64-darwin/build/bin/llc -mattr=+avx512f -disable-cgp-delete-phis
+ /Volumes/RAMDisk/buildbot-root/x86_64-darwin/build/bin/FileCheck /Volumes/RAMDisk/buildbot-root/x86_64-darwin/llvm-project/llvm/test/CodeGen/X86/avx512-i1test.ll
/Volumes/RAMDisk/buildbot-root/x86_64-darwin/llvm-project/llvm/test/CodeGen/X86/avx512-i1test.ll:11:15: error: CHECK-NEXT: expected string not found in input
; CHECK-NEXT: xorl %eax, %eax
              ^
<stdin>:8:16: note: scanning from here
# %bb.0: # %bb1
               ^
<stdin>:9:3: note: possible intended match here
 testb %al, %al
  ^

Input file: <stdin>
Check file: /Volumes/RAMDisk/buildbot-root/x86_64-darwin/llvm-project/llvm/test/CodeGen/X86/avx512-i1test.ll

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

Input was:
<<<<<<
           1:  .file "<stdin>" 
           2:  .text 
           3:  .globl func # -- Begin function func 
           4:  .p2align 4 
           5:  .type func, at function 
           6: func: # @func 
           7:  .cfi_startproc 
           8: # %bb.0: # %bb1 
next:11'0                    X error: no match found
           9:  testb %al, %al 
next:11'0     ~~~~~~~~~~~~~~~~
next:11'1       ?              possible intended match
          10:  je .LBB0_1 
next:11'0     ~~~~~~~~~~~~
          11: # %bb.3: # %L_30 
next:11'0     ~~~~~~~~~~~~~~~~~
          12:  retq 
next:11'0     ~~~~~~
          13:  .p2align 4 
next:11'0     ~~~~~~~~~~~~
          14: .LBB0_1: # %bb33 
next:11'0     ~~~~~~~~~~~~~~~~~
           .
           .
           .
...

```

</details>

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