[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 `premerge-monolithic-linux` running on `premerge-linux-1` while building `llvm` at step 7 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/153/builds/29438

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

```
Step 7 (test-build-unified-tree-check-all) failure: test (failure)
******************** TEST 'LLVM :: CodeGen/X86/bfloat.ll' FAILED ********************
Exit Code: 1

Command Output (stderr):
--
/build/buildbot/premerge-monolithic-linux/build/bin/llc < /build/buildbot/premerge-monolithic-linux/llvm-project/llvm/test/CodeGen/X86/bfloat.ll -mtriple=i686-linux-gnu -mattr=avx512bf16,avx512fp16,avx512vl | /build/buildbot/premerge-monolithic-linux/build/bin/FileCheck /build/buildbot/premerge-monolithic-linux/llvm-project/llvm/test/CodeGen/X86/bfloat.ll --check-prefixes=X86 # RUN: at line 2
+ /build/buildbot/premerge-monolithic-linux/build/bin/llc -mtriple=i686-linux-gnu -mattr=avx512bf16,avx512fp16,avx512vl
+ /build/buildbot/premerge-monolithic-linux/build/bin/FileCheck /build/buildbot/premerge-monolithic-linux/llvm-project/llvm/test/CodeGen/X86/bfloat.ll --check-prefixes=X86
/build/buildbot/premerge-monolithic-linux/build/bin/llc < /build/buildbot/premerge-monolithic-linux/llvm-project/llvm/test/CodeGen/X86/bfloat.ll -mtriple=x86_64-linux-gnu | /build/buildbot/premerge-monolithic-linux/build/bin/FileCheck /build/buildbot/premerge-monolithic-linux/llvm-project/llvm/test/CodeGen/X86/bfloat.ll --check-prefixes=CHECK,SSE2 # RUN: at line 3
+ /build/buildbot/premerge-monolithic-linux/build/bin/llc -mtriple=x86_64-linux-gnu
+ /build/buildbot/premerge-monolithic-linux/build/bin/FileCheck /build/buildbot/premerge-monolithic-linux/llvm-project/llvm/test/CodeGen/X86/bfloat.ll --check-prefixes=CHECK,SSE2
/build/buildbot/premerge-monolithic-linux/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: /build/buildbot/premerge-monolithic-linux/llvm-project/llvm/test/CodeGen/X86/bfloat.ll

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

Input was:
<<<<<<
            .
            .
            .
          399:  .text 
          400:  .globl pr63017_2 
          401:  .p2align 4 
          402:  .type pr63017_2, at function 
          403: pr63017_2: # @pr63017_2 
          404: # %bb.0: 
next:845'0             X error: no match found
          405:  testb %al, %al 
next:845'0     ~~~~~~~~~~~~~~~~
          406:  jne .LBB16_1 
next:845'0     ~~~~~~~~~~~~~~
          407: # %bb.2: # %cond.load 
next:845'0     ~~~~~~~~~~~~~~~~~~~~~~
          408:  movzwl (%rax), %eax 
next:845'0     ~~~~~~~~~~~~~~~~~~~~~
          409:  shll $16, %eax 
next:845'0     ~~~~~~~~~~~~~~~~
            .
            .
...

```

</details>

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