[llvm] [MemorySSA] Don't create phi nodes in fixupDefs() (PR #156021)

[LLVM Continuous Integration via llvm-commits]

llvm-ci wrote:

LLVM Buildbot has detected a new failure on builder `cross-project-tests-sie-ubuntu-dwarf5` running on `doug-worker-1b` while building `llvm` at step 6 "test-build-unified-tree-check-cross-project".

Full details are available at: https://lab.llvm.org/buildbot/#/builders/163/builds/25874

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

```
Step 6 (test-build-unified-tree-check-cross-project) failure: test (failure)
******************** TEST 'cross-project-tests :: debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_address/address_hit_count.cpp' FAILED ********************
Exit Code: 2

Command Output (stderr):
--
clang++ -O0 -glldb -std=gnu++11 /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/llvm-project/cross-project-tests/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_address/address_hit_count.cpp -o /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/build/projects/cross-project-tests/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_address/Output/address_hit_count.cpp.tmp # RUN: at line 7
+ clang++ -O0 -glldb -std=gnu++11 /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/llvm-project/cross-project-tests/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_address/address_hit_count.cpp -o /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/build/projects/cross-project-tests/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_address/Output/address_hit_count.cpp.tmp
/home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/llvm-project/cross-project-tests/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_address/address_hit_count.cpp:15:5: warning: 'delete' applied to a pointer that was allocated with 'new[]'; did you mean 'delete[]'? [-Wmismatched-new-delete]
   15 |     delete x;
      |     ^
      |           []
/home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/llvm-project/cross-project-tests/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_address/address_hit_count.cpp:12:14: note: allocated with 'new[]' here
   12 |     int *x = new int[3];
      |              ^
1 warning generated.
"/usr/bin/python3.10" "/home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/llvm-project/cross-project-tests/debuginfo-tests/dexter/dexter.py" test --fail-lt 1.0 -w --debugger lldb-dap --lldb-executable "/home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/build/bin/lldb-dap" --binary /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/build/projects/cross-project-tests/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_address/Output/address_hit_count.cpp.tmp -- /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/llvm-project/cross-project-tests/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_address/address_hit_count.cpp | /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/build/bin/FileCheck /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/llvm-project/cross-project-tests/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_address/address_hit_count.cpp # RUN: at line 8
+ /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/build/bin/FileCheck /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/llvm-project/cross-project-tests/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_address/address_hit_count.cpp
+ /usr/bin/python3.10 /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/llvm-project/cross-project-tests/debuginfo-tests/dexter/dexter.py test --fail-lt 1.0 -w --debugger lldb-dap --lldb-executable /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/build/bin/lldb-dap --binary /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/build/projects/cross-project-tests/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_address/Output/address_hit_count.cpp.tmp -- /home/buildbot/buildbot-root/cross-project-tests-sie-ubuntu-dwarf5/llvm-project/cross-project-tests/debuginfo-tests/dexter/feature_tests/commands/perfect/dex_declare_address/address_hit_count.cpp


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


```

</details>

https://github.com/llvm/llvm-project/pull/156021