[llvm] DAG: Use phi in alloca constant case to create virtual registers (PR #130254)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `lld-x86_64-ubuntu-fast` running on `as-builder-4` while building `llvm` at step 6 "test-build-unified-tree-check-all".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/33/builds/12642

<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-Unit :: Support/./SupportTests/48/88' FAILED ********************
Script(shard):
--
GTEST_OUTPUT=json:/home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/unittests/Support/./SupportTests-LLVM-Unit-2491294-48-88.json GTEST_SHUFFLE=0 GTEST_TOTAL_SHARDS=88 GTEST_SHARD_INDEX=48 /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/unittests/Support/./SupportTests
--

Script:
--
/home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/unittests/Support/./SupportTests --gtest_filter=Caching.NoCommit
--
/home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/unittests/Support/Caching.cpp:149: Failure
Value of: llvm::detail::TakeError(CFS->commit())
Expected: succeeded
  Actual: failed  (Failed to rename temporary file /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/lit-tmp-4n7ps5sw/llvm_test_cache/LLVMTest-c95492.tmp.o to /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/lit-tmp-4n7ps5sw/llvm_test_cache/llvmcache-foo: No such file or directory
)


/home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/llvm-project/llvm/unittests/Support/Caching.cpp:149
Value of: llvm::detail::TakeError(CFS->commit())
Expected: succeeded
  Actual: failed  (Failed to rename temporary file /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/lit-tmp-4n7ps5sw/llvm_test_cache/LLVMTest-c95492.tmp.o to /home/buildbot/worker/as-builder-4/ramdisk/lld-x86_64/build/lit-tmp-4n7ps5sw/llvm_test_cache/llvmcache-foo: No such file or directory
)



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


```

</details>

https://github.com/llvm/llvm-project/pull/130254